Geosynthetic Design Guidance
jor=
Hazardous Waste Landfill Cells
and Surface Impoundments
Hazardous Waste Engineering Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, OH 45268
by
Gregory N. Richardson
and
Robert M. Koemer
GEOMEMBRANES
GEOTEXTILES
GEONETS
GEOCOMPOSITES
GEOGRIDS
Geosynthetic Research Institute
Drexel University
West Wing—Rush Bid. (#10)
Philadelphia, Pa. 19104
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GEOSYNTHETIC DESIGN GUIDANCE
FOR
HAZARDOUS WASTE LANDFILL CELLS AND SURFACE IMPOUNDMENTS
"regory N. Richardaoa
Soil & Material Engineers, Inc.
Cary, North Carolina 27511
Robert M. Koerner
Geosynthethic Research Institute
Drexel University
Philadelphia, Penn. 19014
Contract No. 68-03-3338
Project Officer:
Robert Hartley
Land pollution Control Division
Hazardous Waste Engineering Research Laboratory
Cincinnati, OH 45268
HAZARDOUS WASTE ENGINEERING RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OH 45268
i
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Geosyrvthetic Design Guidance for
Hazardous Waste Landfill Cells and
Surface Impoundments
by
G. N. Richardson and R. M. Koerner
ERRATA SHEET
page III-32 CALCULATE NOT CALAULATE
Tmtg - 3E-05 NOT Tmtg ¦ 3E-06
page 111-33 i - 15/45 - 0,33 NOT i - 15/45 + 0.33
page III-34 CONSTANT GRADIENT NOT CONTANT GRADIENT
sigmaN - 1000 psf NOT sigmaN - 1000 psi
page III-35 PERMITTIVITY NOT PERMITIVITY
1.16E-07 sec*-l NOT 1.16E-06 sec*-l
mm* 3/sec NOT mmA3 sec
DR ¦ 34,684 NOT DR - 3,460
page 111-36 0.25 > 0.12 NOT 0.25 < 0.12
page 111-41 227,273 sec NOT 22,580 sec
65.6 hours NOT 7.8 hours
2.7 days NOT 0.3 days
page 111-43 PSEUDO PERMEABILITY NOT PSUEDO PERMEABILITY
a - 0.003 in* 2 NOT a = 0.003 m*3
WVT - 0.167 g/m*2-day NOT wvt - 0.167 g/m*3-day
Kpseudo » 6.24E-13 cm/sec NOT 0.62E13 cm/sec
page 111-44 qFML - 3.27E-13*12/.08 NOT .06 inches
1 gallon/acre/day - 4.26E-10 NOT 4.26E10
qFML - 6. 55E-11/4. 26E-10 NOT 4.26E-14
page 111-45 W - [0.941*62,4*.080/12]*[l*120/sin 30] NOT
[0.941*62.4*.060/123+[1*120/Sin 30]
page 111-48 T - (6-4+4/COS 26.5) NOT {6.4+4/C0S 26.5)
Concrete Anchor T ¦ 2074 lb/ft NOT 1990 lb/ft
Anchor Trench T - 735 lb/ft NOT 493 lb/ft
page 111-49 TENSION NOT TESION
Vc - ft* 3 NOT Vc - ft* 2
Fnb - 379 lbs NOT Fnb - 420 lbs
DR » 0.95 NOT DR - 1.01
F1 - 13000*cos 8*tan 12 - 2736 NOT
13000*COS 8*tan 12 - 2736
page IV-15 sigma'C ¦ 55 * [] NOT sigma'C ¦ 55 ¦ []
page IV-16 Qdrag - 680*PI*4*65 NOT Qdrag - 680*PI-4*65
page IV-17 [delta]nu/a«l.6 NOT [delta]nu/a-2.0
CLAY gamma=120 NOT CLAY ganma-12.0
page V-19 q - SURFACE WATER INFLOW RATE NOT
LEACHATE INFLOW RATE
page V-20 psf NOT pcf (3 times)
page V-21 psf NOT pcf
page V-22 STRAINrupture * 69% NOT Graph value of 7t%
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Abstract
Geosynthetic Design Guidance
For
Hazardous Waste Landfill Cells and Surface Impoundments
This report focuses on the development of guidance design procedures
for the evaluation of geosynthetic materials used in hazardous waste land
disposal cells and surface impoundments. These procedures are demonstrated
in typical applications. Primary geosynthetic components include flexible
membrane liners (FML) used to limit the flow of leachate, and leachate
collection/removal systems (LCR) that monitor for potential leakage of an
FML and provide for removal of the leachate from the system. Also
presented is design guidance for ancillary components including ramps,
interior berms, and standpipes. The*ancillary components are generally
controlled by operational and not statute criteria. Chemical compatibility
of the geosynthetic components and leachate is not considered in this
guidance document.
Potential failure modes for each geosynthetic component are
established. A design procedure is developed for evaluating each of the
potential failure modes. Each design procedure is based on calculation of
service conditions in the component under field conditions. A Design Ratio
(DR) is then calculated as the ratio of the limiting performance of the
component based on laboratory tests to the actual performance calculated
for field conditions. Minimum values for Design Ratio are recommended for
each design procedure.
Specific geosynthetic material properties are required to determine the
DR in each design procedure. A suggested range of values, based on
available data, is presented for each material property used.
Additionally, a summary of the test procedures used in evaluating each
specific material property is provided in the manual. Relevant standards
for each test are referenced when available.
Long-term performance of each component is dependent on the stability
of each material property over the design life of the facility. Time-
dependent factors that can influence components include material
rheological properties, material aging characteristics, growth of micro-
organisms within the system, and deformations due to settlement of the
contained waste. Guidelines for evaluating the long-term stability of each
component are presented.
The appendices of the report include a Glossary of terms and a
summary of the major design and index tests commonly used in Geosynthetic
applications.
ii
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TABLE of CONTENTS
Page
Forword i
Abstract ii
Tables v
Figures vi
Design Examples vii
Acknowledgments viii
Section I Introduction and Background
Scope of Document 1-1
Geomembranes 1-1
Geotextlles 1-3
Geogrids/Geonets 1-4
Goecomposites 1-4
Secure Landfills 1-5
Surface Impoundments 1-9
Long-term Considerations 1-10
Summary 1-10
Section II Summary
Design Priorities II-3
Research Needs II-4
Section III Design of Components Beneath Cell
Component Functions .... III-l
Leachate Collection/Removal(LCR) Systems. . . . III-2
Transmissivity Criteria III-2
Filter Criteria III-6
Strength Criteria III-9
Primary vs Secondary LCR Systems 111-10
Flexible Membrane Liners (FML) 111-10
FML Vapor Transmission III-ll
FML Stresses 111-12
FML Seaming 111-15
FML, Survivability 111-17
FML Anchorage 111-21
Surface Impoundment Considerations 111-25
FML Protection 111-25
Gas Venting 111-27
Section IV Design of Components Within Cell
Ramp and Traffic Considerations IV-1
Interior Berms . IV-4
Standpipe for Primary LCR IV-5
Down-Drag Forces IV-6
FML Strain Due to Down-Drag Forces IV-7
Monitor for Secondary LCR IV-8
Section V Design of Components Above Cell
Surface Water Collection/Removal (SWCR) .... V-5
SWCR Transmissivity V-5
iii
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SWCR Filtration V-6
SWCR Strength V-7
Flexible Membrane Cap (FMC) V-7
FMC Permeability V-8
FMC Stresses V-9
FMC Seaming V-10
FMC Survivability During Installation. . . . V-ll
Biotic Barrier V-12
Gas Collection and Venting V-12
Vapor Transmissivity V-15
Vent Pipe Details V-16
Section VI Construction/Fabrication Considerations
Flexible Membrane Liners/Caps VI-2
Specifications VI-2
Fabrication VI-6
Construction VI-8
Construction Quality Assurance VI-17
Drainage/Filtration Components VI-25
Specifications VI-25
Construction VI-28
Construction Quality Assurance VI-28
Subgrade VI-29
Specifications VI-30
Construction VI-30
Construction Quality Assurance VI-31
Section VII Long-term Service Considerations
Flexible Membrane Liners VII-1
Chemical Attack VII-1
Photochemical Attack VII-2
Ozone Attack VII-2
Biological (Micro-organisms) Attack .... VII-3
Thermal Effects VII-5
Environmental Stress Cracking VI1-6
Environmental Stress Rupture VII-7
Aging Effects from Soil Burial VII-8
Leachate Collection/Removal Systems VII-10
Creep/Stress Relaxation Effects VII-10
Chemical Attack VII-10
Biological (Micro-organisms) Attack . . . .VII-13
Thermal Effects VII-14
Aging Effects from Soil Burial VII-15
Cell Cap Performance VII-15
Hydrolysis Effects VII-15
Gas Venting and Interaction VII-17
Special Concerns VII-17
Section VIII Appendices
Conversion of Units A-l
Glossary B-l
Index Test Procedures C-l
Design Test Procedures D-l
INDEX E-l
iv
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List of Tables
Page
Table 1.1 Basic Composition of Polymeric Geomembranes .... 1-3
Table 2.1 Design Priorities - Liner System II-3
Table 2.2 Design Priorities - Cap System II-4
Table 3.1 Tear Resistance of FML 111-20
Table 6.1 Available NDT Methods for Evaluating Seams .... VI-6
Table 6.2 Wind Uplift Forces VI-14
Table 6.3 Overview of Nondestructive Geomembrane Seam Tests . . VI-22
Table 7.1 Micro-Biological Attack on Plastics VII-4
Table 7.2 Thermal Properties of FMLs VII-5
Table 7.3 Burning Characteristics of FML Polymeric Materials . VI1-6
Table 7.4 Soil Burial Tests on Polyester VII-9
Table 7.5 Chemical Resistance Properties of Fibers VII-12
Table 7.6 Alkalinity Study on Geotextiles VII-13
Table 7.7 Biological Effects on Geotextile Strength . . . .VII-14
Table 7.8 Effects of Heat on Fiber Properties VII-16
Table 7.9 Results of Soil Burial Tests VII-17
Table 7.10 Moisture Regain and Water Imbimition of Fibers . . .VII-19
v
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LIST OF FIGURES
Page
Figure 1.1 Synthetic/Clay Double Liner System 1-5
Figure 1.2 Synthetic/Composite Double Liner System 1-6
Figure 1.3 Composite/Composite Double Liner System 1-7
Figure 1.4 Proposed RCRA Cell Cap Profile . . . . . . . 1-9
Figure 2.1 Growth in American Geosynthetic Market II-2
Figure 3.1 Profile of MTG Double Liner System III-l
Figure 3.2 Leachate Head vs Collector Pipe Spacing III-3
Figure 3.3 Elastic Compression Curves-Transmissivity .... III-5
Figure 3.4 Settlement Trough Models 111-13
Figure 3.5 Compressive Stress Model 111-14
Figure 3.6 Configuration of Geomembrane Field Seams 111-15
Figure 3.7 Seam Strength Tests 111-17
Figure 3.8 Puncture and Impact Resistance 111-19
Figure 3.9 FML Anchors - Details 111-22
Figure 3.10 Forces and Variables - Anchor Analysis 111-24
Figure 3.11 Liner Cover Stability Analysis 111-27
Figure 3.12 Gas Vent - Details 111-29
Figure 4.1 Geometry of Typical Ramp IV-1
Figure 4.2 Cross-Section of Typical Access Ramp ...... IV-2
Figure 4.3 Interior Berm - Waste Separation IV-4
Figure 4.4 Interior Berm - Operations IV-5
Figure 4.5 Standpipe/Drain - Details IV-6
Figure 4.6 Isolated Standpipe - Details IV-7
Figure 4.7 Standpipe Induced Strain in FML IV-9
Figure 4.8 Sidewall Standpipe - Detail IV-10
Figure 4.9 Standpipes for Secondary LCR System IV-11
Figure 5.1 Geosynthetics in RCRA Double FML Cell Profile . . . V-4
Figure 5.2 Transmissivity Data for Geotextile V-6
Figure 5.3 FML Stress-Strain Performance V-10
Figure 5.4 Seaming Composite Membrane V-ll
Figure 5.5 Water Trap in Vapor Collector system V-14
Figure 5.6 Air and Water Transmissivity in Geotextile .... V-15
Figure 5.7 Gas Vent Pipes - Details V-16
Figure 6.1 Panel - Seam Identification Scheme VI-7
Figure 6.2 Design Maximum Wind Speed VI-14
Figure 6.3 FML Anchorage to Concrete - Details VI-16
Figure 6.4 Rigid/Flexible Penetrations - Details VI-18
Figure 6.5 Panel Placement Log VI-23
Figure 6.6 Geomembrane Seam Test Log VI-23
Figure 6.7 Geomembrane Repair Log VI-24
Figure 7.1 Laboratory Environmental Stress Cracking/Rupture . . VII-7
Figure 7.2 Influence of pH on Permittivity of Geotextile . . .VII-11
Figure 7.3 Strength Behavior of Nylon and Polyester in Water . .VII-18
Figure 7.4 Phases of Solid Waste Decomposition VII-18
Figure 7.5 "Sky Mound" Cap Planned for Hackensack Meadowland . .VII-21
vi
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LIST OF EXAMPLES
Example 3.1 LCR - Transmissivity:Waste Criteria 111-32
Example 3.2 LCR - Transmissivity:Surface Water Criteria . . . 111-33
Example 3.3 LCR - Transmissivity:Creep II1-34
Example 3.4 LCR - Permitivity 111-35
Example 3.5 LCR - FiltersRetention 111-36
Example 3.6 LCR - Filter:Clogging 111-37
Example 3.7 LCR - Strength:Sliding 111-38
Example 3.8 LCR - Settlement:Limit Analysis 111-39
Example 3.9 LCR - Settlement:Strain Compatibility II1-40
Example 3.10 LCR - Transmissivity:Response Time 111-41
Example 3.11 LCR - Strength:Composite Primary Liner 111-42
Example 3.12 FML - Permeability via WVT 111-43
Example 3.13 FML - De Minimis Psuedo Permeability 111-44
Example 3.14 FML- - Tensile Stress:Liner Weight 111-45
Example 3.15 FML - Tensile Stress:Down Drag at Filling. . . . 111-46
Example 3.17 FML - Localized Subsidence 111-47
Example 3.18 FML - Anchor Trench 111-48
Example 3.19 Soil Cover - Stability II1-49
Example 4.1 Ramp - Sliding Stability IV-13
Example 4.2 Ramp - Hydraulic Capacity IV-14
Example 4.3 Ramp - Wheel Loading on FML IV-15
Example 4.4 Standpipe - Down-Drag Forces IV-16
Example 4.5 Standpipe - Puncture Failure of FML IV-17
Example 5.1 SWCR - Transmissivity V-19
Example 5.2 Cover Soil - Stability / SWCR - Shear Strength . . V-20
Example 5.3 SWCR - Tensile Failure V-21
Example 5.4 FMC - Settlement V-22
Example 6.1 Wind Uplift - FML Placement VI-34
vii
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SECTION I
INTRODUCTION AND BACKGROUND
SCOPE OF DOCUMENT
This design guidance document was prepared to provide recommendations
for the design of synthetic components within hazardous waste land disposal
cells and surface Impoundments. The synthetic components Include flexible
membrane liners, textiles, nets, grids and composites. All these synthetic
components that are used within the ground are commonly called
geosynthetics. The 'geo' prefix Indicates the usage of the component on or
in the earth and is commonly applied to individual synthetic components.
Thus, synthetic flexible membrane liners used within the ground are called
geomembranes, etc. Both the application of geosynthetic materials to civil
engineering functions and the design of secure hazardous waste landfills
are emerging technologies with little cross-over expertise existing at
present. A majority of the references on geosynthetics are less than five
years old, and the current secure landfill configurations date from the
November 1984 Hazardous and Solid Waste Amendments (HSWA). While providing
guidance to facility designers and regulators, this document may spur
manufacturers of geosynthetic components into developing components
designed specifically for hazardous waste facilities. A Glossary of terms
generic to geosynthetics is provided in the appendix because.they are not
commonly available.
Geosynthetic components incorporated in the design of hazardous waste
facilities provide certain hydraulic functions as follows:
(1) Geomembranes limit the movement of leachate in the system,
(2) Geotextiles act as a filter to prevent the flow of soil fines
into drainage systems, or to provide planar flow for. drainage,
or as a cushion to protect geomembranes,and
(3) Geonets and nonwoven geotextiles allow planar flow of liquids and
serve as drainage systems.
Recently, composite materials have been developed to serve multiple
hydraulic functions. In addition to hydraulic functions, geosynthetic
composites can act as tensile elements to reinforce tensile-weak soils and
to bridge cracks caused by differential settlement of the waste fill
material.
GEOMEMBRANES
Geomembranes are impermeable synthetic liners used to control fluid
migration. Moisture moves through the membranes as a diffusion process
driven by concentration gradients (Flck's first Law) and not as a fluid
flow (Darcy's Law). These materials have an equivalent Darclan permeability
of typically 10"14 to 10~*3 cm/s. In general applications, geomembranes
are made of compounds having a base product of asphalt and/or polymer.
Only polymer-based geomembranes are reviewed in this document. Polymers
EPA I - 1
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used to make geomembranes are synthetic chemical compounds of high
molecular weight. The most common polymers used in making geomembranes are
linear or slightly branched molecular structures that are thermoplastic.
Thermoplastics undergo no chemical changes when repeatedly softened by
heating and solidified again by cooling.
The most common types of polymers used in the manufacture of
geomembranes are as follows (Giroud and Frobel, 1984):
Thermoplastics; Polyvinyl chloride (PVC), oil resistant PVC (PVC-OR),
thermoplastic nitrile-PVC (TN-PVC), ethylene interpolymer
alloy, polyethylene (PE), elastlcized polyolefin.
Crystalline Thermoplastics; Low density polyethylene (LDPE), linear-
low density polyethylene (LLDPE), high density polyethylene
(HDPE), high density polyethylene-alloy (HDPE-A), polypropy-
lene, elastlcized polyolefin.
Thermoplastic Elastomers; Chlorinated polyethylene (CPE), chlorinated
polyethylene -alloy (CPE-A), chlorosulfonated polyethylene
(CSPE), thermoplastic ethylene -propylene diene monomer (T-
EPDM).
Elastomers; Isoprene-isobutylene rubber (butyl rubber), ethylene-
propylene diene monomer (EPDM), polychloroprene (CR)
(neoprene), epichlorohydrin rubber (CV).
Note that the symbols in parentheses are those adopted by the National
Sanitation Foundation (NSF 54) and are common market abbreviations.
Currently the predominant geomembrane liner materials in industrial and
hazardous waste applications are HDPE, PVC, and CSPE (Waugh,1983,1984).
it should be noted that the common usage of the term High Density
polyethylene (HDPE) does not agree with its more formal definition under
ASTM D-1248 (Polyethylene Plastics Molding and Extrusion Materials). Under
this standard, polyethylenes are classified as follows:
Type Nominal Density, gm/cm3
I .910 to .925
II .926 to .940
III .941 to .959
IV .960 and higher
Type III is classified as high density polyethylene but reflects a higher
density than most commercial "HDPE" materials. The Type II materials are
classified as linear medium-density polyethylene but are commercially
referred to as "HDPE". This document uses the more common usage of "HDPE"
and thus will usually be referring to these Type II materials.
Additives are typically compounded with polymers to improve the
physical or long-term aging characteristics of the geomembrane. Processing
aids may be added to reinforce or soften the compound during the
manufacturing process. Plastlcizers are commonly used to impart
flexibility to a normally rigid polymer. Protection from ultraviolet light
EPA 1-2
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Table 1.1 Basic Composition of Polymeric Geomembranes
( after Haxo, 1986 )
Component
Composition of compound type
(parts by weight)
Crosslinked
Thermoplastic
Semicrystalline
Polymer or alloy
Oil or plasticizer
Fillers:
100
5-40
100
5-55
100
0-10
Antidegradants
Crosslinklng system:
Carbon Black
Inorganics
5-40
5-40
1-2
5-40
5-40
1-2
2-5
1
Inorganic system
Sulfur system
5-9
5-9
(UV) aging is provided by adding carbon black to the base polymer. In light
colored membranes, UV protection is achieved by the addition of titanium
dioxide. Additional aging protection may be provided by the use of
antioxidants to reduce the effect of surface oxidation and ozone, and
fungicides that prevent fungi and bacteria from attacking the polymer. The
percentage of a given membrane that is composed of such additives is
surprisingly high as shown in Table 1.1 (Haxo, 1986). The high percentage
of additives such as plasticlzers makes It Imperative that a 'fingerprint'
of the components of a given liner be known so that it can be verified that
the same polymer used to meet chemical compatibility requirements is
installed in the field.
Most geomembranes are manufactured using an extrusion, calendering, or
spread-coating process. The HDPE membranes gaining usage in hazardous
waste facilities are manufactured by extrusion of the polymer into a non-
reinforced sheet. Calendering forms a membrane by passing a heated
polymeric compound through a series of heated rollers. Spread coating
produces a reinforced membrane by coating a fabric with the polymer.
Reinforced membranes can also be produced using the extrusion or
calendering processes if the reinforcing fabric Is laminated to the
membrane while the polymer is still hot.
GEOTEXTILES
Geotextlles are fabrics constructed of fibers of synthetic materials
and Intended for engineering applications within soils. Each geotextile may
be classified as to the type of polymer, fiber, and fabric style used in
its construction. A majority of geotextlles in use today are manufactured
from polypropylene or polyester materials. The polypropylenes offer greater
chemical resistance while the polyesters exhibit less creep under constant
loads. Fiber types include continuous monofilament or monofilament yarns,
short lengths of fibers called staple, yarns made from staple fibers, and
fibers formed by slitting sheets of polymer. The fabric styles include
woven, nonwoven, and knit construction.
EPA 1-3
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Geotextlies are relatively high permeability materials developed to
allow the movement of liquid through the geotextile while at the same time
preventing the movement of adjacent soil particles. Additionally,
geotextiles can be used as a reinforcement to provide tensile strength to
soils and to bridge discontinuities that may develop in the subgrade.
Nonwoven fabrics are generally used to play a hydraulic role in a design
system, while woven and knit fabrics are used primarily in reinforcement
roles. Nonwoven fabrics play a large role in the design of hazardous waste
systems because the design emphasis is on control of leachate flow and
prevention of erosion.
Nonwoven geotextiles are generally manufactured in a four step
process: fiber preparation, web formation, web bonding, and post-
treatment. Fiber preparation Includes concurrent formation of continuous
filaments by extrusion of molten polymer through a spinneret nozzel, or
advanced formation of staples for later processing. Web formation produces
a uniform layer of unbonded fibers either by direct spraying of continous
filaments or the use of cards, garnetts, or air laying of staples on a
moving conveyor belt. Web bonding Interlocks the Individual fibers and is
commonly achieved using a melt-bonding, resin-bonding, or needle-punched
process. Post-treatment of the nonwoven geotextile may Include
impregnating it with (1) an acrylic resin to improve abrasion resistance,
or (2) a fungicide to limit growth of fungi and bacteria in the fabric.
Polymers generally used to make geotextiles include polypropylene,
polyester, and most recently polyethylene.
GEOGRIDS and GEONETS
Geogrids and geonets are relatively new products even for
geosynthetics. These materials are based on extruded polypropylene or
polyethylene. Grids are formed by first punching a regular pattern of
holes into sheeting and then drawing the sheeting uniaxially or biaxially.
The drawing process increases the modulus and strength of the sheeting.
Geogrids are principally used as reinforcement materials but can provide
limited planar flow capacity. Geonets are extruded nets formed by
extruding and bonding of up to three layers of polymer rods oriented at
acute angles to each other. While lacking the high strength of the
oriented geogrids, the geonets provide a significant capacity for planar
flow and are commonly used to form leachate or surface water collection/
removal systems.
GEOCOMPOSITES
Geocomposltes are high drainage polymeric systems made of a built-up
drainage core covered with a geotextile that acts as a filter. The cores
consist of columns, ribs, extruded nubs, etc.,¦ and vary widely in size,
shape, strength, and flow capacity. They are made from polystyrene, PE,
PVC, or other polymers. The geotextile Is usually attached to the core by
heat bonding, thermal glues, or with conventional adhesives. Care must be
taken to insure that the adhesive used does not contain sufficient volatile
organics that it contributes to the leachate. There are currently a large
number of geocomposltes commercially available with typical applications
Including being used as a substitute for lateral drains in roadways and as
back-of-wall drainage for retaining walls.
EPA 1-4
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SECURE LANDFILLS
On November 8, 1984, the Resource Conservation and Recovery Act (RCRA)
was amended by the Hazardous and Solid Waste Amendments (HSWA). Among the
provisions that went into effect were minimum technological requirements
for hazardous waste land disposal facilities, Section 3004(o). HSWA
requires that new units and lateral expansions of existing units at
hazardous waste landfills and surface Impoundments must have two or more
liners and a leachate collection system above (for landfills) and between
such liners. Additionally, HSWA required that new units and lateral
expansions of existing units at interim status waste piles (those in
existence on November 19, 1980) must meet the existing standards for liners
and leachate collection as contained in 40CFR264.251. A minimum "double"
liner composed of a single flexible membrane (FML) overlying a 3-foot thick
clay liner was allowed under HSWA pending issuance of EPA regulations or
guidance documents.
EPA draft Minimum Technology Guidance (MTG) Documents for liners and
leachate collection systems were made available on December 20, 1984 and on
May 24, 1985. Proposed codification of statutory provisions based on these
minimum technology guidance documents is outlined in the Federal Register,
Vol. 51, No. 60, March 28, 1986. In the draft guidance and proposed
codification, EPA defines performance requirements for two designs that it
feels meet minimum technological requirements for hazardous waste landfills
and surface Impoundments.
Filter Media
Primary FML
3FWWV
•» K { t « _•» iv* «% . .C
n u j
iaslil®
1« S & i>
msm
Drain Pipes
m
mm?.
mrnmrnw
Q Drain Pipes Q
mmim
ifeSisi
Thickness Based On
Break Through Time
Native Soil Foundation
(NOT TO SCALE)
Figure 1.1 Synthetic/Clay Double Liner System (EPA, 1985a)
The first "double-liner" system in the proposed codification is a
synthetic liner/clay liner design as shown in Figure 1.1. This design
includes a top synthetic liner designed and constructed of materials to
minimize the migration of any leachate constituents into the liner during
EPA I - 5
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the "active" life of the facility and the minimum 30 year "postclosure care
period." The lower clay liner is designed to limit the migration of any
constituent through the liner during this same period. The thickness of
the clay liner is a function of design, with a minimum thickness of 3 feet
specified. The actual thickness of the clay liner is controlled by the
calculated breakthrough time for a single constituent of the leachate to
pass through the clay liner. A conservative design assumes that the
interior FML will be penetrated the first year in service and will
therefore use a minimum 30-year breakthrough design.
Within the first system, the leachate collection and removal system
between the two liners must be able to rapidly detect and collect all
liquids leaking through the top liner, withstand chemical attack from the
leachate, and provide continuous service throughout the postclosure care
period.
Priimaiiy FML
Secondary FML \
7(1111/ X ./"¦¦¦¦¦¦¦
Filter Layer
Solid Waste
O Drain Pipes. Qj
O Drain Pipes Q
Native1 Soil Foundation
(NOT TO SCAIE)'
Figure 1.2 Synthetic/Composite Double Liner System (EPA, 1985a)
The second "double-liner" design is shown on Figure 1.2 and includes a
synthetic top liner and a composite bottom liner. At a minimum, the second
design consists of a primary leachate collection/removal system (LCR) (for
landfills), a primary flexible membrane liner (FML), a secondary LCR, and a
secondary composite FML/clay liner. The primary LCR system minimizes the
leachate head acting on the primary FML and allows for the removal of
liquids during the post-closure monitoring period. The primary FML serves
the same function as in the first system and must be designed and
constructed of materials to prevent the migration of leachate constituents
greater than de minimis quantities into the liner throughout the
EPA 1-6
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postclosure care period. The secondary LCR system between the two liners
should be designed and constructed to detect leaks in the primary liner,
and collect and remove liquids for treatment through the post-closure care
period. The secondary FML/clay liner is designed such that the two
components act as one system that is designed and constructed to prevent
greater than de minimis quantities of leachate through the composite liner
for a time of less than the post-closure monitoring period.
Recent minimum technology requirements in the Federal Register, Vol.
52, No. 74, April 17, 1987, indicates that a permeable soil liner with a
hydraulic conductivity of 10~7 cm/sec will have a minimum detectable
leakage rate of approximately 86 gallons per acre per day. A composite
liner consisting of an FML plus the soil layer will have a detectable
leakage rate of only .001 gallons per acre per day. These limits would be
appropriate for de minimis quantities. Unfortunately, no guidelines are
given for detectable leakage rates through a typical ML. Thus a rigorous
definition of de minimis is not available at present.
Acceptable double liner systems are not limited to the two designs
discussed in the guidance documents and presented above. Alternate double
liner designs will be acceptable if convincing performance equivalency can
be demonstrated with the specifications in the guidance documents. A
current alternative double liner design is shown in Figure 1.3 and
incorporates a composite FML/clay liner in place of the primary FML liner
in the guidance documents. The relative advantages and disadvantages of
this system are currently under review by EPA. The addition of the clay
liner increases the collection and removal efficiency of the primary FML,
but also significantly retards the ability of the secondary LCR to detect
leaks in the primary FML.
Primary FML
Secondary FML
filter Media
Solid Waste A o
t'i, 1*
•J"-'» A"" *•!?*""
P.
Composite
Pilmnry Liner
(NOT TO SCALE)
Drain Pipe Q
Composite
Secondary liner
Figure 1.3 Composite/Composite Double Liner System
EPA 1-7
-------
The EPA philosophy for minimizing the migration of hazardous
constituents into the environment is a two-pronged liquids management
program. One part of this management program is the use of technology to
maximize the containment and removal of liquids from the unit before they
can migrate into the environment. The two double-liner designs previously
detailed are meant to function in this manner. An additional aspect of
liquids management is the minimization of leachate generation through the
use of design control and operational practice to minimize the amount of
surface water entering the unit, particularly during the post-closure
monitoring period. The final cover system must therefore prevent Intrusion
of surface water Into the cell.
A proposed RCRA guidance (EPA, 1985c) final cover system for
uncontrolled waste sites is shown in Figure 1.4 and consists of an
optional gas collection layer or array, a low permeability layer consisting
of at least 2 ft. of clay and a 20 mil flexible membrane cap (FMC), a
surface water drainage layer, and a cover layer capable of supporting
vegetation. The gas collection or clay layer must provide a sound working
platform for placement of the overlying components. Specifications for soil
materials to be used In the foundation layer typically Include provisions
for a maximum grain size and a requirement that they are free of debris
that could damage the overlying FMC. The geometry of the gas collection
system is influenced by the subcell structure within the total cell. The
gas collection system functions to prevent the buildup of a signfleant
volume of gas vapors beneath the cover FMC. At facilities exposed to
significant surface water or potential subsidence, the designer may opt to
follow the design philosophy used in the liner system and use a double FMC
system with a leak detection system between them. Monitoring of the witness
drain would provide confirmation of the integrity of the upper FMC. The
current draft MTG does not require a double FMC on facilities using a
double FML.
The design considerations for the cover FMC differ significantly from
the liner FML's. During its projected lifetime, the cover FMC will not be
exposed to leachate but may experience significant environmental exposure
and potential straining due to settlement within the waste material.
Currently the cover FMC in many facilities Is of the same material and
gauge as the primary FML. This apparently was done to encapsulate the waste
material and based on the belief that the 'permeability' of the FMC must be
equal to or greater than the primary FML. Both practices may be
conservative but do not reflect EPA guidance (Landreth, 1987). While
greater discussion is given in Section V, it should be noted that current
RCRA guidance provides for only one FMC at least 20 mil thick and does not
require sealing of the FMC to the FML.
Atop the cover FMC, a surface water drainage layer Is placed to drain
liquid off of the FMC and away from the unit. This drainage layer may
Itself be composed of 3 subcomponents: (1) a bedding layer placed to
protect the cover FMC, (2) the actual drainage layer designed to remove
surface water, and (3) a filter layer that prevents movement of the
vegetative cover soil into the drainage component. The final vegetative
cover layer is required to support erosion resistant plant life and acts to
shield the cover components from sun and weather related adversities.
EPA 1-8
-------
Cover Soil mnrnnfflTTiiffflff
layer tilUll
,_ n "'"SS^"'Operational Cover
^^^N|jfcC|ay CoverlffiS^,
Figure 1.4 Proposed RCRA Cell Cap Profile
SURFACE IMPOUNDMENTS
Surface impoundments function similarly to secure landfills in that
waste materials are contained to prevent the contamination of ground water
at the site. The Surface Impoundment Assessment Report (EPA,1983) reported,
however, that most wastes placed in a surface Impoundment are waste waters
being contained as part of a treatment process. A surface impoundment is
not, therefore, necessarily the final resting place for the waste. Current
regulations exclude from surface impoundments those wastes that are
reactive or lgnltable. Also excluded are EPA hazardous wastes F020, F021,
F022, F023, F026, and F027 unless certain design, operating, and monitoring
procedures are approved by EPA and included in the facility management plan
(per 40 CFR Part 264.229).
Two options that influence design are given in the regulations for
closure of surface Impoundments. The first option is to remove or
decontaminate all waste residues at closure. Under this option the surface
impoundment can be constructed using a single liner (natural or synthetic)
if it is located more than 1/4 mile from any underground source of drinking
water. It must also comply with applicable ground water monitoring
requirements for a permitted RCRA facility (40 CFR 264 Subpart K). The
single liner must be designed to prevent breakthrough of the contained
waste during the life of the impoundment. At closure, all waste and liner
material contaminated by leakage must be removed. This option may be
desirable for surface impoundments that hold process waste liquids
temporarily.
EPA 1-9
-------
The second Impoundment design option Is for ln-place closure of
facilities containing waste piles that cannot be economically removed.
These impoundments must Incorporate a double-liner system with a leak
detection/collection system as previously described for a waste containment
facility. Waste contained In the Impoundment must have all free liquids
removed. The remaining waste must be solidified and stabilized to provide a
minimal bearing capacity. These facilities differ from secure landfills
only in the nature of the wastes contained during their operational life.
Current environmental laws (HSWA,1984) require that all surface
impoundments must conform to double liner standards by November 6, 1988.
LONG TERM CONSIDERATIONS
Section VII reviews long term performance considerations for
geosynthetics beyond the more obvious chemical compatibility
considerations. Most of these concerns are also shared by more conventional
•geo' 'synthetic' systems such as buried plastic pipe and electrical
cables. These considerations include microbiological degradation of the
synthetics resulting from the consumption of plasticlzers by the bacteria
or fungus, and stress cracking /rupturing of the synthetic resulting from
what should be allowable stress levels. The stress cracking/rupturing may
be the result of deficiencies within the synthetic or may be caused by the
applied stress and exposure to certain environmental conditions. Soil
exposure tests have also shown that potential oxidation-reduction processes
may occur in the synthetic as the result of burial. Obviously, when taken
either separately or collectively, the above mechanisms will have a
negative effect on the ability of a synthetic component to perform its
function.
Unfortunately the lack of available data does not allow Section VII to
provide much beyond pointing out such potential long-term considerations
and reviewing proposed accelerated test procedures. No laboratory data
currently exists to demonstrate the general impact of these long-term
problems and certainly no standard tests are available to evaluate each
concern in a given leachate.
SUMMARY
Geosynthetic components are now being used within all hazardous waste
landfill disposal cells and substitute for an increasing number of
natural materials within each cell. These geosynthetic components provide
the following roles within the cell:
(1) Liner - all FML's and FMC's are geomembranes,
(2) Drainage - LCR systems may be constructed using geotextlles,
geogrids, or composites to attain design transmisslvities,
(3) Filter - geotextlles are commonly used to allow leachate to
pass and yet prevent clogging of drain pipes within LCR
systems and to protect the surface water drainage components,
(4) Bedding layer - a geotextile can be used to protect the cover
geomembrane from damage related to placement of the surface
water drain.
EPA I - 10
-------
The design of these geosynthetlc components Is the primary focus of this
document. Construction and long-term considerations are also reviewed. It
should be noted, however, that chemical considerations have been excluded
from consideration under this contract and are described elsewhere
(Matrecon, 1987).
REFERENCES - SECTION I
EPA,(1983), Surface Impoundment. Assessment National Report, U.S.
Environmental Protection Agency,, EPA, 570/9.-84-002.
EPA, (19,85a)1, Minimum Technology Guidance on Double Liner Systems for
Landfill's* and Surface Impoundments - Design, Construction, and Operation,
2nd* Version,, U.S. Environmental Protection Agency, May 24.
EPA„(,1985b), Minimum Technology Guidance, on Slngl'e- Liner Systems for
Landfills, Surface Impoundments., and Waste Piles - Design, Construction,
and Operation;.,, Second Version, U.S. Environmental Protection Agency, May.
EPA,{1985c.), Covers for Uncontrolled Hazardous Waste Sites, U.S.
Environmental Protection Agency, EPA/540/2-85/002.
EPA,(1986), Minimum Technology Guidance on Closure Systems For Landfills
and Surface Impoundments - Design, Construction, and Operation, Draft, U.S.
Environmental Protection Agency.
Glroud, J.P.. and R.K. Frobel,(1984), "Geomembrane Products," Int. Water
Power and Dam Construction;,, Vol. 36, No.3, March.
Haxo, H.E.,(1986.), "Quality Assurance of Geomembranes Used as Linings for
Hazardous Waste Containment,"' Geotextiles and Geomembranes, Vol.3, No. 4.
Landreth, R.E.,(1987), Personal Communication, January 7.
Matrecon, 1987, "Lining of Waste Impoundment and Disposal Facilities
(Draft), Third Edition of Technical Resource Document, SW-870, U.S.
Environmental Protection Agency, Cincinnati, Ohio, 45268.
National Sanitation Foundation, (1983), "Standard Number 54 for Flexible
Membrane Liners," Ann Arbor, MI.
Waugh, S., (1983), "Geomembrane Market Weathers Hard Times During Early
80's," Geotechnical Fabrics Report, Vol. 1, No. 2.
Waugh, S., (1984), "Quantifying the Geomembrane Market In North America,
Past, Present, Future", 1st International Conference on Geomembranes, IFAI,
Denver, Colorado, June.
EPA I - 11
-------
SECTION II
SUMMARY
The design of hazardous waste containment cells and surface
impoundments Is currently a curious mixture of regulator-based minimum
requirements, performance based engineered design, and empirical rules-of-
thumb. This document emphasizes the analyses required to properly design a
synthetic component based on calculated field conditions and laboratory
measured component properties. Such synthetic components include the
flexible membrane liners (FML), and synthetic drainage layers (LCR) used to
replace layers of sand. The use of performance based design allows the
designer/regulator to properly evaluate the true degree of protection
against failure that regulatory minlmums or rules-of-thumb provide. It is
also apparent that our current level of knowlege regarding both long-term
and in-situ performance of the synthetic components justifies conservative
design practice and minimum criteria.
Each design consideration reviewed In this document is derived
beginning with the specific equilibrium equations and then Illustrated
using typical application scenarios. For stress related considerations, the
equations of equilibrium are based on 'free-body' diagrams that express
both the direction and magnitude of forces acting at a given point in the
component. The equations of equilibrium simply reflect the need for the sum
of the forces to be equal to zero in a given plane for equilibrium (at-
rest) conditions to exist. When a clear limit is known for the performance
of the geosynthetic, a Design Ratio is defined as the ratio of the
allowable material performance divided by the actual material service
conditions calculated. A minimum value for the Design Ratio of one would
then be required to prevent an undue amount of stress and/or strain of the
component. Unfortunately, our ability to accurately define both the
performance limits of the components and the service conditions requires
the use of minimum Design Ratios considerably larger than one to ensure
satisfactory performance. Suggestions are given for minimum values of
Design Ratios in each analysis consideration. The designer Is cautioned
however to verify that the limiting value of the Design Ratio reflects the
actual uncertainties associated with the particular design consideration.
Each design consideration is demonstrated using typical application data.
A Design Example sheet is provided for each consideration and includes a
concise review of required material properties, analysis procedure
development, and a typical application. It is unfortunately true that, at
this time, very few actual field data exist to verify the accuracy of the
solution provided for each consideration.
Beyond presenting the simple mathematics required to estimate the in-
situ performance of a geosynthetic, this document attempts to review the
current limitations in evaluating the actual performance of the synthetic
under realistic field conditions. The test procedures referenced in this
document are divided into index and performance tests. The index tests are
developed to provide a means of quality control for the manufacture and are
usually independent of actual field conditions. For membranes this includes
such tests as density and absorbed moisture. Performance based tests try to
simulate the true in-sltu environment faced by the component as an
essential part of the test process. Thus drainage components are tested for
EPA II - 1
-------
in-plane flow under normal stresses comparable to those generated by the
weight of overlying waste and with actual field soils or other components
adjacent to the component being tested. Performance tests are specific to
the given field conditions of a single project.
A significant limitation in performance-based design lies in the lack
of standardized test procedures that the designer can use. Many of the
tests presented in this document and reviewed in the appendices are not
formal standards and are currently in a state of change. In effect the
designer is caught between the owner's needs and current ongoing research.
The designer is cautioned to carefully review each laboratory test and
satisfy in their own mind that it accurately portrays the in-situ
conditions anticipated at the specific site.
The lack of recognized analysis and test procedures for the many
design considerations is due to the relatively short time that many of the
synthetic components have been available and to a similiar short time frame
that the design of any waste facility has come under scrutiny. Koerner
(1986) presented an estimated growth in the geosynthetic industry, Figure
2.1, that clearly shows the Infancy of geosynthetic use. Quite clearly, the
growth of the geosynthetic industry has occurred at essentially the same
time as the growth in regulatory concern over hazardous waste facilities.
Geotextiles
(Koerner, 1986)
•Geomembranes
.Geogrids
•Geocomposites
150
Year
Figure 2.1 Growth in American Geosynthetic Market
EPA II - 2
-------
DESIGN PRIORITIES
The design of a secure landfill requires a significant number of
design considerations. The tables presented in this section attempt to
weight design priorities for the components within the liner system. Design
priorities for the liner systems are given on Table 2.1 to gain an overall
perspective of the major geosynthetic design considerations. The priority
ratings are very subjective and reflect the design and research experience
of the authors for the "typical" application. The highest priority (1)
design considerations reflect modes of failure that would be catastropic to
the success of the facility. Thus for the FML any consideration that would
lead to penetration or tearing of the membrane would be rated 1. A similiar
rating of design considerations for the cap components is given in Table
2.2.
Table 2.1 Design Priorities - Liner System
Component
Consideration
Chemical Compatibility
FML
LCR
Filter
MTG Criteria
-thickness
-water vapor tran.
2
3
2
n/a
3
n/a
Mechanical Properties
-tensile/yield
-friction
-anchorage
-internal shear
1
1
2
2
2
1
2
2
2
2
3
3
Hydraulic Properties
-permittivity
-transmissivity
-clogging
n/a
n/a
n/a
n/a
1
2
1
n/a
1
Biological Properties
Construction Factors
-wind
-puncture
-impact
-tear
-seams
2
3
3
3
2
3
3
2
3
2
Long Term Factors
-Env. Stress Crack/Rupt 1
-durability/aging 1
-disturbances 2
3
1
2
3
1
2
* ( 1-high, 3-low, n/a-not applicable )
EPA II - 3
-------
Table 2.2 Design Priorities - Cap System*
Consideration
Chemical Compatibility
MTG Criteria
-thickness
-water vapor trans.
Mechanical Properties
-tensile/yield
-f riction
-anchorage
-internal shear
Hydraulic Properties
-permittivity
-transmissivity
-clogging
Biological Properties
Construction Factors
-wind
-puncture
-impact
-tear
-seams
GAS VENT
2
2
n/a
Component
FMC
2
2
n/a
3
2
1
3
n/a
3
3
3
3
3
2
2
1
1
3
3
n/a
n/a
n/a
SWCR
3
3
n/a
2
1
3
3
n/a
1
1
2
3
3
3
3
Filter
3
n/a
n/a
2
1
3
3
1
n/a
1
3
2
2
3
3
Long Term Factors
-Env. Stress Crack/Rupt 3
-durability/aging 2
-disturbances 2
2
2
1
3
2
1
3
2
1
( 1-high, 3-low, n/a-not applicable)
RESEARCH NEEDS
Close comparison of the highest priority design considerations given
in Tables 2.1 and 2.2 with the design examples in this document reveals
that many high priority design items are not currently well understood.
This is particularly true of biological and all long-term considerations
but is also true of such basics as the definition of the correct stress-
strain characteristics for FMLs. Immediate research needs resulting from
such a comparison include the following:
Better define the stress conditions in FMLs near penetrations,
sumps and in corners to determine if the designs should be based
on biaxial or confined tensile test data from the FML.
Verify that rates of biological growth on filter fabrics will not
prevent the flow of leachate into the collector system.
EPA II - 4
-------
Define operational procedures that will minimize the production
of waste generated gases and develop analytical methods for
predicting the rate at which gases will be generated.
Develop permittivity and clogging tests that better replicate the
ln-situ conditions experienced by the geosynthetic In the field.
Significant in its absence is verification of the long-term effect of low
concentrations of many hazardous wastes on the physical properties of the
components. This document does not, however, deal with chemical-related
considerations.
REFERENCES - SECTION II
Koerner, R.M.,(1986), Designing with Geosynthetlcs." Prentice-Hall,
Englewood Cliffs, New Jersey.
EPA II - 5
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SECTION III
DESIGN OF COMPONENTS BENEATH CELL
COMPONENT FUNCTIONS
Geosynthetic components beneath the hazardous waste materials within a
hazardous waste landfill cell provide the primary separation between
leachate generated within the cell and the surrounding hydrogeologic
environment. In the draft MTG (EPA,1985), this profile consists of two
subsystems, each with a flexible membrane liner (FML) and leachate
collection/removal (LCR) system. The draft MTG recommended cell liner
profile is shown on Figure 3.1. The FML and LCR nearest to the waste are
the primary system and function exclusively to contain leachate. The
primary LCR must be designed to allow no more than 1 foot of head to act on
the primary FML at any given time. The primary LCR also plays an important
role during operation of the cell when the primary LCR is used to drain
surface water collected within the cell and to protect the primary FML.
Solid Waste
filter Media
IS cm
Hydraulic Conductivity
} 1 X 10-2 cm/sec
Primary ICR
30 cm
— Primary FML
Secondary LCR
.076 cm
Hydraulic Conductivity
) IX 10—2 cm/sec
30 cm
— Secondary FML
Hydraulic Conductivity
4 1 X 10—7 cm/sec
Clay Liner
Unsaturated Zone
; Saturated Zone 2
. Native Soils
Figure 3,1 Profile of MTG Double Liner System
The additional FML and LCR systems are for the secondary containment
system. Leachate passing through defects in the primary FML is detected in
the secondary LCI and removed. The secondary LCR is commonly referred to as
a witness drain since it bears 'witness' to the integrity of the primary
FML. The secondary LCR system must also be designed to prevent more than
one foot of head to act on the secondary FML, while also providing a rapid
detection of leachate passing through the primary FML. As will be shown in
this section, the dual requirements of rapid detection and removal of
excess leachate can produce conflicting design criteria.
EPA III - 1
-------
LEACHATE COLLECTION/REMOVAL SYSTEMS
Leachate is defined as "any liquid, including any suspended components
in the liquid, that has percolated through or drained from hazardous waste"
(40CFR 260.10). Leachate is generated by the draining of liquids from
within the waste mass and from the infiltration of water from the surface
of the cell. Additionally, the LCR system is commonly used during operation
of the facility to remove surface water that has drained into the cell.
This water is assumed to be leachate. The quantity of leachate generated
depends on the types of waste, operational procedures, cover efficiency,
and water balance within the cell at a particular time. Liquid input to the
cell includes liquids in the deposited waste and surface liquids resulting
from precipitation or surface water. Liquid output includes evaporation,
transpiration, and seepage from the facility (Bass, 1986). Techniques for
estimating leachate volume are discussed by Schroeder, et al (1984).
Minimum Technology Guidance (MTG) provided by EPA (1985) provides
technical guidance on minimun design standards for LCR systems. Specific
guidance on leachate collection systems design includes the following:
o A granular drainage layer should be at least 30 cm (12 in.)
thick with a minimum hydraulic conductivity of 1 x 10~2 cm/
sec and a minimum bottom final slope of 2% after long term
settlement.
o Synthetic drainage layers may be used if they are equivalent
to the granular design, including chemical compatibility, flow
under load, clogging resistance, and protection of the FML.
o The drainage layer should include a pipe network which is
designed to efficiently collect leachate. The spacing of the
pipe network should be sufficient to ensure that no more than
1 foot of leachate will collect in the LCR. The pipe and
drainage layer materials should be chemically resistant to the
waste and leachate. The pipe should also be strong enough to
withstand expected loading.
o A filter layer (granular or synthetic) should be used above
the drainage layer to prevent clogging.
o The LCR system must cover the bottom and sidewalls of the unit.
Geosynthetic components within the LCR can, therefore, include a synthetic
drainage layer used to replace the granular layer or the pipe network
itself, and filter fabric designed to prevent clogging of the drain pipes
or synthetic drainage lines.
Transmissivity Criteria
A geosynthetic system used to replace the granular drainage layer must
provide either the minimum planar flow capacity defined by the Minimun
Technology Guidance or that required to maintain the liquid levels over the
liner at less than 30 cm (1 ft). The planar flow of liquids through the LCR
is defined by Darcy's equation as
EPA III - 2
-------
q - Kp i a
Eq(3.1)
q - Kp [dh/L] W t Eq(3.2)
where q is the flow rate, Kp is the permeability coefficient in the-plane
of the geosynthetic, dh is the head loss, L is the flow length, W Is the
width of the drainage layer, and t is the thickness of the drainage layer.
Because the thickness of most geosynthetic systems is difficult to
quantify, Equation 3.2 is commonly expressed as
q - [Kp t] [dh/L] W Eq(3.3)
q - § [dh/L] V Eq(3.4)
where 6 is defined as the transmissivity of the drainage layer.
Substituting minimum drainage layer properties as defined in the current
MTG guidance criteria (30 cm thickness and a minimum permeability of lxlO-2
cm/sec) results in a minimum required drainage layer transmissivity of 3 x
10-5 m2/a.
INFLOW
1111111111
DRAINAGE LAYER
MAX
CLAY LINER
L
Figure 3.2 Leachate Head vs Collector Pipe Spacing
The minimum transmissivity of an LCR may also be controlled by the
requirement to maintain no more than 30 cm ( 1 foot ) of leachate head
acting on the liner at all times. Conventional granular leachate control
systems are designed so that the maximum one foot head acting on the FML
remains within the drain layer. The head acting on the FML is controlled by
the rate at which leachate is being generated and collected within the
system, the hydraulic properties of the LCR, and the spacing of the
collector pipes within the LCR. These parameters are shown on Figure 3.2.
The maximum head acting on the FML for a uniform rate of leachate
generation is given by
EPA III - 3
-------
L Jc tan^cX tano*. / ~
Hmax " C + 1 /tan2c< + c ] Eq(3.5)
2 c c *
where c is defined as the inflow rate, q, divided by the hydraulic
conductivity of the LCR. The greatest uncertainty associated with this
calculation is accurately estimating the rate of leakage generated at the
LCR boundary. While beyond the scope of this document, methods for
estimating this quantity have been detailed by Wong(1977), Scharch(1981),
and Demetracopoulos(1984). This method has been supplemented by an
alternate procedure proposed by Moore (EPA,1983b) that is based on the
percolation velocity of the leachate. The maxlmim leachate head using this
method is given by
Hmax =
L
2n
/
- + tan2** -tano^
K
Eq(3.6)
where e is the percolation velocity based on conversion of the annual
percipitation rate into a uniform velocity (cm/sec) and K is the hydraulic
conductivity of the layer. The percolation velocity is equivalent to the
inflow rate but is based on the assumption of a given percentage
percolation of precipitation into the cell while the inflow rate is
influenced by soil permeability, waste characteristics, etc. In these
designs, the leachate phreatic surface remains within the LCR system.
Geosynthetic LCR systems are very thin when compared to equivalent-
flow granular LCR systems. Thus the one foot of head that may act on the
FML would not physically remain within the synthetic LCR layer. The one
foot head must be interpreted as a design-applied pressure that is assumed
to act at the interface between the synthetic LCR and the overlying soil.
The required transmissivity of a synthetic LCR is computed by equating the
rate of leachate inflow to the LCR with the flow capacity of the LCR. For a
of synthetic LCR, the volume of leachate entering the system is equal to
Qin - qm L w Eq( 3.7)
where qjn is the inflow rate of leakage generated at the waste LCR
boundary, L is the effective length of the LCR and W Is the width. The
quantity of leachate that can flow through the LCR system is given by
QLCR - 2 T [1 + Lsin( (1) )/2]/L Eq(3.8)
where <|> Is the slope of the LCR. Equating the leachate Inflow and flow
capacity of the LCR, an expression for the minimum value of transmissivity
of the LCR is obtained as
qL2
e - : Eq(3.9 )
4hmax + 2Lsin
The percolation velocity e can be substituted, for q. Example 3.1 details
the computation steps required to evaluate the mlmimum transmissivity based
on percolation velocity and leachate inflow criteria.
EPA III - 4
-------
An additional design criterion for the primary LCR may be a flow
criteria based on the need to remove surface water during operation. The
design will be influenced by both the details of the actual operation and
the design precipitation. The Inflow into the system is estimated using
runoff calculations of the form (EPA, 1986a)
Q - C I A Eq(3.10)
where Q is the surface water inflow, C is the runoff coefficient, I is the
average runoff intensity, and A is the surface area. The surface water
inflow is calculated and then the minimum transmisslvity of the LCR is
calculated using the analysis shown in Example 3.2.
100
Hydraway
Mtradratn I
Inkadrain
FHtram
12' Sand (K = 0.1 cm/sec)
12* Sand
-------
days of service if a soil is immediately adjacent to the LCR. As discussed
above, this reduction over time is caused by the intrusion of the adjacent
geosynthetic into the flow core and by creep related collapse of the core.
It is therefore very important that the laboratory test be performed under
boundary conditions that closely replicate the actual field conditions. In
particular, the test for the primary LCR should include soil adjacent to
the LCR and not use metal plates on both faces. The secondary LCR is
normally between two FMLs and therefore may be tested between sheets of
such material. The elimination of the soil boundary will eliminate creep
penetration of the soil and the geotextile. Because of this, the minimun
suggested Design Ratio for the primary LCR is greater than that for the
secondary LCR system. Details of the transmissivity test are given in
Appendix D.
Test data defining the time dependence of the transmissivity should be
determined. This laboratory data will reflect the combined influence of all
the creep mechanisms. Example 3.3 illustrates the technique used to
evaluate the ability of an LCR system to provide the minimum required
transmissivity over a design time period. The creep analysis technique used
in this example may not be appropriate for composite LCRs that use a formed
internal core. These systems may have multiple creep phenomena occurring
simultaneously with collapse limits associated with one or more of the
mechanisms. While the long-term transmissivity for such composite systems
obviously could be evaluated by running a conventional transmissivity test
for an extended duration, laboratory difficulties, > such as biological
growth, and test machine availability may preclude such testing. An
alternate solution is to analyze the service stress in each component and
predict the long term performance of each component. Procedures for such
calculations are based on measured long-term creep properties of each
generic component (Shestra and Bell, 1982). When possible, the designer
should compare the limited laboratory creep data with that predicted by
the analytical model developed by the manufacturer.
The design time period must extend over the projected monitoring
period for the facility. A minimum period of time would obviously be the
projected operational life plus the 30 year post-closure monitoring period.
In anticipation of potential extended monitoring, it is recommended that a
50-year minimum design life be used in projecting the service life of a
synthetic LCR system.
Filter Criteria
To ensure effective operation of the LCR over its design life, the
designer must ensure that leachate can freely flow into the system and that
the system does not become clogged due to the inflow of fines from the
surrounding waste and soil,layers. Specific attention must be given to the
horizontal boundaries between the LCR and adjacent soil or waste deposits
and around the collector pipe network within the LCR. Two types of soil
filter systems commonly used are graded granular filters and geotextile
filters. Granular filters rely on, a combination of soil layers having a
coarser gradation, in the direction of seepage to prevent movement of soil
particles. Geotextile filters were introduced only in the last 15 years and
rely on the fine and uniform porosity of the fabric to prevent the movement
of soil fines.
EPA III - 6
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The ability of leachate to freely flow through a geotextile filter is
influenced by the permittivity of the geotextile and the head acting on the
leachate. Permittivity Is defined here as K/t, where K is the permeability
of the geosynthetic and t is its thickness. It is reasonable to assume that
in fabrics having a significant thickness, nonwovens in particular, the
permittivity will decrease with increasing normal load. The only approved
permittivity test, ASTM D4491, does not provide for the application of
normal forces. Design Example 3.4 demonstrates the use of permittivity test
data in evaluating the flow characteristics of a geotextile. Be cautioned,
however, that large normal loads can reduce the permittivity value
significantly thus high Design Ratios are required.
Filter design criteria for geotextiles are still evolving. Current
analytical methods are based on an Apparent Opening Size (AOS) for the
geotextile. The AOS of the material is usually evaluated in the laboratory
using a test procedure developed by the Corps of Engineers (Calhoun,1972).
This test measures the percent of uniform glass beads retained on the
fabric for a range of bead sizes. The bead size having only S# retained is
defined as the 095 or AOS of the geotextile. There are a number of
techniques for evaluating the soil retention capabilities of a given
geotextile, all of which use soil particle size characteristics compared to
the AOS of the fabric. The simplest methods (Koerner, 1986) examines the
percentage of soil being retained on the #200 sieve (- 0.074 mm).
Accordingly (Task Force 25, 1983), the following recommendations are made:
1. Soil <50# passing the No. 200 sieve
AOS of fabric > No. 30 sieve (0.59 mm)
2. Soil >50# passing the No. 200 sieve
AOS of the fabric > No. 50 sieve (0.297 mm)
Slightly more restrictive criteria have been proposed (Carroll, 1983)
(Chen, 1981) based on the dgg of the soli sample, where dgg Is the particle
size of the soil at which 85# of the particles are finer. These criteria
are expressed as follows:
O95 of the geotextile
< 2 Eq(3.11)
dgs of the soil
and O95 of the geotextile
> 2 Eq(3.12)
d^g of the soil
The first criterion is intended to prevent particles of soil from flowing
through the geotextile while the second criterion is intended to prevent
the clogging of the geotextile.
A more conservative filtration design approach (Giroud,1982) includes
consideration of grading by including the coefficient of uniformity, CU,
for the soil in the criteria. The coefficient of uniformity is defined as
the ratio of the d^o to the d^o of the soil. The more uniform a soil in
particle size, the smaller is the CU. Note that gap-graded soils cannot be
EPA III - 7
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Identified using CU criteria. The relationships proposed to predict
excessive loss of fines during filtration are then given by
Relative Density,Dr
13
Loose(Dr<50£)
095<(CU)(d50)
095<(9d50)/cu
Intermediate
(50*80*)
Dense(Dr>80£)
095<1.5(CU)(d50) 095<(l3.5d5o)/CU
095<2(CU)(d5o) Og5<(18d5o)/CU
Where Dr is relative density, dso is the grain size corresponding to 50#
passing, O95 is still equal to the AOS of the geotextile, and CU is the
coefficient of uniformity!d^g/d^o) of the soil.
It should be noted that many designers argue that a filter layer is
not necessary when the quantity and loading rate of fines into the drainage
layer are small enough that the performance of the drainage layer is not
affected. Consideration of the anticipated particle size and flow
velocities of the leachate may indicate that fines will be effectively
flushed from the system without the need for a filtration layer. For
typical waste disposal cells it is reasonable to assume that flow
quantities and velocities will be low during post-closure monitoring, but
may be large during actual operation of the» facility. Additionally, the AOS
test, which serves as the basis for clogging criteria, does not accurately
portray the physical properties of a heavy nonwoven fabric. In these
fabrics, the glass beads used to conduct the test become entrapped due to
thickness and not porosity. Draft MTG (EPA,1985) recommends the use of a
granular or synthetic filter layer over the LCR to prevent clogging of the
LCR. Example 3.5 presents an evaluation of a geotextile for filtration
criteria.
The potential for clogging of the filter must be evaluated if the
long-term function of the filter is to be ensured. Acting as a filter, the
geotextile will trap soil particles within its pore space and could
eventually be blinded or clogged by these entrapped particles. Clogging
potential can be evaluated in the laboratory using the gradient ratio test.
This test evaluates a hydraulic gradient across the fabric. If the gradient
ratio predicted by this test exceeds 3, there is potential for clogging.
Additionally, the gradient ratio test device can be used to evaluate the
flow versus time relationship to evaluate the terminal or long-term flow
capability. Design Example 3.6 demonstrates the interpretation of gradient
ratio and long-term flow data for evaluating clogging potential.
Another approach to evaluating clogging potential is to avoid soils or
field conditions that have been shown to have a high likelihood of
producing clogging in a geotextile: 1) cohesionless sands and silts with
gap-graded particle size distributions and high hydraulic gradients,
2)permeating liquids having very high values of alkalinity, e.g. pH > 11,
and 3) situations where dynamic or pulsating fluid action occurs across the
plane of the geotextile filter. Of these three situations, the first two
are of most concern for waste facilities. Gap-graded soils can be readily
identified and should be avoided adjacent to any geotextile filter layer.
EPA III - 8
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The greatest danger of gap-grading occurs if unwashed sands or gravels are
used to form the LCR and a fabric wrap is placed around the collector pipe
network. For this reason, all sands or gravels used within a LCR must be
washed to remove the fines.
Strength Criteria
LCR systems must extend beneath the entire cell. As such, the LCR
system will be constructed on the sideslopes and be subjected to shear
stresses generated by the sliding potential of materials placed on top of
the LCR. These sliding stresses can place the synthetic LCR in tension and
produce in-plane strains. Additionally, the LCR may be subjected to
significant in-plane strains generated by the elongation of the LCR due to
settlement of the underlying subgrade. Both in-plane strains produce
tensile stresses that can disrupt or rupture the LCR. Geosynthetic LCR
systems are very thin when compared to a granular LCR system, and a greater
potential for disruption of flow exists in the synthetic LCR.
Sideslope stresses generated within the LCR by overlying materials are
calculated in Example 3.7. In general the friction between the LCR and the
FML will be very low and result in the LCR having to support the overlying
materials. The ultimate strength of the LCR material is determined in the
laboratory using a wide-width tensile test procedure. The friction between
the soil-LCR and LCR-FML is also determined in the laboratory using a large
direct shear test machine (Martin,1984). The Design Ratio calculated in
Example 3.7 relates only to complete failure of the LCR in tension. The
shear stresses acting on the LCR will also generate significant elongation
in the LCR and can produce undesirable deformation within the side-slopes.
The sliding evaluation is particularly critical if a composite soil/FML
primary liner is being used in the facility.
Settlement of the waste within the landfill will generate shear
stresses on the surface of the primary LCR in the same manner that
consolidation of soils produces down-drag forces on piling. The
consolidation of the waste mass within the facility is due to the weight of
overlying waste and the loss of liquids in the form of leachate. The waste
matter at the bottom is nearest the drainage face and under the largest
normal load. Thus, the waste will consolidate from the bottom first. This
consolidation will produce surface settlement of the waste and transfer
shear stresses to the LCR as the waste matter attempts to move downward.
Obviously the amount of shear stress generated will initially be controlled
by the amount of settlement that has occurred along the sldewalls of the
facility. For the shallow slopes (>3:1) used in most facilities very little
settlement should be evident at the sideslope. For steeper slopes(>2.5:1)
some settlement may occur at the sideslope. Example 3.8 shows the limiting
stress that would be produced in the LCR if it was designed to resist
settlements. These stress levels are clearly excessive. Fortunately,
however, the analysis of Example 3.8 neglects to examine the strain
compatibility between the LCR and the settling waste. The limit analysis in
Example 3.8 would be appropriate if the FML was very stiff or if the
settlement was very large. An analysis that is based on strain
compatibility between the LCR and the settling waste is given in Example
3.9. This analysis is more appropriate for the small edge settlements, and
flexible LCRs anticipated. The limitation of the strain compatibility
analysis Is our inability to analytically predict edge settlements.
EPA III - 9
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Primary Versus Secondary LCR Systems
The design of the secondary LCR system must consider that this system
will perform the same functions as the primary LCR with the following
exceptions:
1) The secondary LCR system does not normally handle the
volume of leachate and surface water runoff that the
primary LCR must drain during operation and post-closure.
2) The secondary LCR acts as a witness drain for the primary
FML and must provide a rapid collection/detection of
leachate.
3) The secondary LCR must support the overlying primary FML
and LCR systems and loads placed on them, see Example 3.10.
The first two factors indicate that the secondary LCR system must have the
minimum capacity required to remove leachate in case of failure of the
primary FML. An overly large capacity within the secondary LCR could delay
the detection of leachate. Estimating detection time of the secondary LCR
system is demonstrated in Example 3.10. Balancing the opposing needs of
rapid leak detection and flow volume may be based on management decisions.
Within the third exception above, the sliding evaluation is
particularly critical if a composite soil/FML primary liner is being used
in the facility. Example 3.11 evaluates the secondary FML for the composite
primary FML condition. Note that significant stresses are generated within
the LCR unless an increase in the FML/LCR friction angle can be realized.
Conventional FML materials, such as HDPE, provide a very low coefficient of
friction between the primary FML and the secondary LCR systems. Efforts to
increase this frictional bond have not been successful to date.
FLEXIBLE MEMBRANE LINERS (FML)
Flexible membrane liners are composed of membranes made primarily of
polymeric materials. These synthetic membranes are essentially impermeable
and are meant to control the flow of leachate out of the cell. In view of
their placement within the soil, these membranes are referred to as
geomembranes. The performance of the geomembrane is dependent upon the
following factors:
1) Sufficient thickness of membrane must be used to achieve de
minimis levels of leakage. Under draft MTG, a minimum
thickness of 30 mils is required for FMLs In secure
landfills and 45 mils for the FMLs in a surface impoundment
or when it will be exposed to weather for some time. Note
that the thickness of scrim or other reinforcement Is
included In computing thickness under MTG criteria.
2) Stresses that develop during installation and subsequent
use must not physically harm the membrane.
3) Seams that bind panels of geomembrane together must not
leak and must be physically strong in both shear and peel.
EPA III - 10
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Minimum seam strength requirements must be established.
4) Placement of the FML on the soli and cover on the FML must
not cause localized penetration of the membrane. Specific
minimum criteria for bedding materials as provided In MTG.
5) The FML must be securely anchored so that operational loads
do not dislodge the FML.
6) Construction practice must protect the FML from wind, Ice,
and other environmental factors that can damage the
membrane.
7) The polymeric material forming the FML must be chemically
stable when exposed to leachate.
8) Long-term considerations must be anticipated.
The first five factors will be discussed in this section, the sixth factor
is discussed In Section V, the seventh factor is beyond the scope of this
document but is discussed elsewhere (EPA,1983b), and the last factor is the
subject of Section VII.
FML Vapor Transmission
The permeability of most common polymeric membranes is sufficiently
low so that it cannot be evaluated using conventional permeability testing
procedures. The flow rates through conventional fixed or falling-head
permeameters would be so small that either evaporation would destroy the
leakage or extremely high gradients would be required to produce measurable
flows. Thus the FML is essentially impermeable to fluid flow based on
Darcy's law. The gas vapors from leachate can, however, diffuse across the
FML driven by vapor pressure gradients. This diffusion process is
quantified using Fick's first law (Lord and Koerner, 1984). The diffusion
constant can be measured using a water vapor transmission test (WVT), ASTM
E96. The diffusion rate is measured In the WVT test using water vapor as
the permeant. The test specimen is sealed over an aluminum cup having
either water or a deslccant in it, and a controlled relative humidity
difference is maintained on either side of the membrane. The weight gain or
loss of the aluminum cup and membrane is monitored for 3 to 30 days.
Further details of the test are presented in the appendix.
Both Darcy's Law and Fick's first law are both first order ordinary
differential equations. Thus the diffusion process measured in the WVT test
can be modeled as a psuedo-Darcian flow. Thus, while recognizing that the
test is based on diffusion and not flow, the WVT can be expressed in terms
common to Darcy's equation as follows:
Q m kpsuedo i A. t Eq(3.13)
or ^p sue do " C i Eq(3.14)
where [ Q/tA ] Is the WVT. The permeance or kpSue(}0 of the membrane is
defined as the WVT divided by the vapor pressure gradient, dh, that existed
EPA III - 11
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on the FML during testing. Further defining the gradient, 1, In Expression
3.10, the relationship of permeance to pseudo-permeablllty can be shown as
kpseudo - C Q/tA ] / [ dh/1] Eq(3.15)
kpseudo ¦ [ Q/tAdh ] x 1 Eq(3.16)
where [ Q/tAdh ] is the permeance and 1 is the thickness of the FML.
Results of a WVT test are presented in Example 3.12 and converted into a
conventional pseudo-permeability value of use to a designer.
While no membrane is totally impermeable, the designer must insure
that the FML allows no more that de minimis leakage under the maximum 1
foot head condition. De minimis is assumed in this document to equal 1
gallon/acre/day of leakage. Verification of this fundamental design
requirement is shown in Example 3.13. While it is assumed that
manufacturers of FML panels would supply the WVT test data required to
perform this check, it should be noted that the calculated Design Ratio is
typically large.
FML Stresses
Flexible membrane liners must support their own weight during
installation, resist down-drag forces generated as interior layers or cells
are built, and survive deformations from potential settlement of the
contained waste mass. Membrane tensile strengths for single ply,
unreinforced membranes can be determined using small 'dog bone' specimens
tested at a constant strain rate. These materials will show a linear
increase in yield force with thickness of the FML. Reinforced and multiple
ply membranes may be more sensitive to scale effects in testing and may
require the use of a wide-width test device. For reinforced and composite
membranes, the yield stress is not a linear function of thickness.
During construction of a cell, the FML is draped from the anchor
trench to the bottom of the cell. The tensile forces generated within the
FML due to self-weight are calculated in Example 3.14. This consideration
is normally critical only for unreinforced membranes that have an allowable
or yield stress of less than 1000 psi and on steep side slopes. A
relatively large Design Ratio in this mode does, however.minimize
elongation or stretch of the FML during installation.
Tensile stresses can be generated in the FML and LCR during placement
of waste against the cell sidewall. The waste can move downward as a block
as modeled in Example 3.15 or a deeper failure surface may develop. In both
modes, forces are transmitted to the FML through the LCR in response to the
downward movement of the waste. These forces transmitted to the FML can be
limited if there is a low coefficient of friction between the LCR and the
FML. When synthetic LCR systems are used, this friction is low enough that
only minimal force can be transferred to the FML. Example 3.15 uses a
granular LCR system to demonstrate the extreme case. It would appear that
down-drag forces both during operation and long term are best minimized by
using a synthetic LCR over the primary FML. The coefficient of friction
between membranes and either geonet or geotextile is very low so that
larger down-drag forces cannot be transferred to the primary membrane.
EPA III - 12
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The use of a composite primary liner (FML plus clay layer) can produce
extreme tensile stresses in the secondary FML. The clay portion of the
composite primary liner may produce significant shear imbalances in the
secondary FML resulting in high tensile forces within the primary FML.
Critical design conditions exist during construction if the clay portion Is
constructed much thicker than design and then trimmed. As shown earlier In
Example 3.11, the tensile forces generated by the weight of the composite
primary liner cannot reasonably be carried by currently available synthetic
LCRs and FMLs in tension. The forces must be carried by the surface
friction and adhesion forces that develop on the surface of the synthetic
components. Unfortunately, available FMLs have a very low adhesion and
coefficient of friction with both soils and synthetic LCR components.
Grcular Trough
Model
Triangular
2L
c aoaeeea.
VV>;.V-y;
JWXi:
C Kriipschield, 198 5 )
) 0.1 0.2 0.3
SETTLEMENT RATIO, S/2L
Figure 3.4 Settlement Trough Models
In addition to waste settlement, strains can be induced In the FML
from localized settlement beneath the FML. Such settlement may result from
improperly compacted fill around collection pipes or soft zones in the
underlying subgrade. The strains induced in the FML can be estimated using
a simple trough model that relates the depth and width of the settlement
feature to, the average strain in the membrane. This relationship is shown
on Figure 3.4. Knipshield(1985) has suggested that the strain given by the
trough model should be reduced to reflect the additional elongation that
occurs in the FML Immediately adjacent to the trough. This additional
deformable length is given by
x - E fy d ]/[ 2 A ft ] Eq(3.17)
where fy is the tensile yield or allowable strength of the FML, d is the
sheet thickness, A is the normal stress acting on the sheet, and ft Is a
force transmission factor defined by Knipshield to be 0.35. The ft factor
EPA III - 13
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is the friction coefficient of the soil to the FML and should be verified
for the particulars of a given field situation. The strain given by Figure
3.4 must be decreased to reflect the additional deformation. The corrected
strain is given by
strain - dl / [ L + 2x/2 ] Eq(3.18)
where dl is the increase in membrane length obtained using Figure 3.4, L is
the original width of the settlement feature, and x is the additional
deformable length. Example 3.17 demonstrates calculation of localized
settlement induced stresses in an FML. This analysis assumes that the FML
within the settlement area deforms uniformly. Knlpshleld indicates that
this condition is fulfilled for a FML having a high elastic modulus and a
minimum thickness. For HDPE the minimum thickness is given as 80 mil (2mm).
Load from Above
A A I i
(Knipschield, 1985)
Point Loads
With Hydrostatic
Protective Layer
LINER
Support Layer
Point toads
Without Hydrostatic
Figure 3.5 Compressive Stress Model
Pressure forces act on the FML due to the weight of the waste and soli
mass ...on top., of it.. This..pressure has been assumed to act as an even,
pressure in the previous calculations. In reality, however, the normal
stress acting on the FML will be Influenced by the particulate nature of
the soil above and below the FML. The particulate nature of the adjacent
soils produces concentrations of normal stresses as shown on Figure 3.5.
The very large stress peaks can lead to shear failure of the FML and
penetration of the soil particles into the FML. Support and protective
layers must be arranged to minimize the peak normal loads. Vest German
practice is to arrange the adjacent soils in normal grain, rough grain, and
fine grain structure adjacent to the FML. Evaluation of the impact of such
normal stresses must be performed in the laboratory using site specific
soils. If the FML cannot be protected by grading the soil, then protective
layers of geogrld or geonet must be used.
EPA III - 14
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FML Seaming
Methods used to seam polymeric membranes depend upon the composition
of the membrane and the environment the membrane is placed in. For
hazardous waste disposal facilities, general practice is to avoid any
bonding, method that will leave a residue of volatile organic solvents that
may eventually be confused with leachate. This consideration aside, the
common methods for seaming FMLs include adhesive or solvent bonding,
thermal bonding, extrusion or fusion welding, vulcanization, and mechanical
methods. Typical seam configurations used are shown on Figure 3.6.
LAP SEAM
LAP SEAM WITH GUM TAPE
- adhesive
s
gum tape
TONGUE and GROOVE SPIKE
factory 8"mUpe
vulcanized VfBgwagffr
EXTRUSION WELD LAP SEAM
FILLET WELD LAP SEAM
DOUBLE HOT AIR or WEDGE SEAM
JTTVff
Figure 3.6 Configurations of Field Geomembrane Seams
Solvent-bonded seams depend on the ability of a solvent to dissolve
the FML. The adhesive may be a bodied solvent adhesive, a solvent adhesive,
or a contact adhesive. The bodied solvent uses 8 to 12* of the FML polymer
dissolved in a volatile solvent. The solvent dissolves the surface of and
softens the two sheets to be bonded and, with the application of pressure,
enables a homogeneous bond. The solvent will evaporate with time leaving
only the parent FML polymer. Solvent adheslves function like a bodied
solvent but leave an adhesive that becomes an additional component in the
FML. Contact adhesives differ from solvent adhesives in that significant
pressure is not required to form a bond and the bond is instantaneous.
Bonding methods using solvents and adhesives are normally used with FMLs
composed of thermoplastics or thermoplastic elastomers.
Thermal methods can be used on most ML polymers except elastomers.
These methods are preferred in most waste facility projects because no
solvents are required. Thermal sealing uses forced air heated in excess of
EPA III - 15
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260° C (500° F) to melt the two surfaces to be joined. The two surfaces are
then rolled under pressure to force the two molten zones to flow together.
Alternately, the two surfaces can be melted using an electrically heated
wedge which is particularly good on thinner LLDPE and HDPE sheets. A third
thermal method is the dielectric method that uses a high frequency
electrical current to agitate the molecules within the FML to generate the
heat required for a melt. In this country this method is, however, limited
to use on thin liners and within a factory. Field dielectric seaming
techniques are used in Europe.
Thermal extrusion welds are specialized thermal methods limited in
application to thick HDPE liners. The specialized welders extrude a ribbon
of molten HDPE that melts and then bonds to the two HDPE surfaces. The
ribbon may be placed between the overlap and rolled to form a flat weld or
it may be placed between two mating edges to form a fillet weld. Currently
these are the most common seaming methods used in waste facility liners.
Vulcanized bonds are used on elastomers that will not go into solution
with solvents and have poor thermal bonding properties. These bonds use an
uncured tape formed of the polymer base with a cross-link agent. Under heat
and pressure, the crosslink connects both elastomer surfaces to the ribbon
to form a bond.
Recent work by Morrison (1986) on 37 combinations of supported and
unsupported polymeric sheet materials was directed at evaluation of seam
strengths over a 180-day period. Samples were exposed to 6 chemical
solutions, brine and water immersion, freeze-thaw cycles, wet/dry cycling,
heat aging, and accelerated outdoor aging. The results of the study
indicated that there is no direct correlation between the seam strengths
measured in shear and in peel. This study Indicated that the shear strength
is more indicative of the strength of the parent material, while the peel
test is a good Indicator of the strength of the seam. Both tests are
reviewed in the appendices. This study also indicates that the factory seam
requirements in NSF Standard No.54 aretoo low. The current requirement for
unsupported materials such as CPE requires a film tearing bond of 10 pounds
per inch. This is much less than can be easily obtained in the factory.
Currently there is no non-destructive field test for seam strength.
While field seam testing is discussed in greater detail in Section V, it is
helpful to review the two mechanical tests performed on samples cut from a
field seam. The actions of the shear and peel tests are shown on Figure
3.7. The shear test simulates inservlce stresses caused by thermal
contraction of the membrane or tensile stresses being applied across
adjacent sheets. Conventional acceptance criteria calls for the seam to be
as strong as the parent liner material. Peggs (1985) suggests that for HDPE
this may be Improved by requiring that the failure stress exceeds 80$ of
the tensile yield stress of the base material. Additionally, Peggs suggests
that the load elongation characteristics of the weld sample should be
closely compared to that of the base material. Premature strain failure of
the weld region may occur due to overheating of the seam during welding,
excessive surface roughening during preparation of the panels, or from
damage caused by accumulated dirt on the heated surfaces. Environmental
stress rupture may be caused by underheatlng of the seam during welding due
to stress cracking originating at the throat of the overlapped joint. The
peel test evaluates the quality of fusion in the weld and does not
EPA III - 16
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1
i
?3§s§ji
llll
IPs
i
SHEAR TEST
PEEL TEST
Figure 3.7 Seam Strength Tests
reproduce field loading conditions. Acceptance criteria for the peel test
include failure occurring through the membrane, failure occurring outside
the seam area, and if the peel strength exceeds 80?6 of the membrane yield
stress. The results of the peel test are influenced by the thickness of the
membrane, with the thicker membrane doing progressively poorer for a given
quality of weld. The degradation with thickness is due to the increasing
stiffness that introduces additional bending stresses to the seam.
A study of field construction and placement procedures by Shultz
(1982) found that problems in the installation of polymeric liners include
installation during marginal or adverse weather conditions, seaming around
penetrations, and the field or laboratory inspection of field seams. Dry
and warm field conditions are very important for proper seaming of
polymeric liners. Minimum recommended temperature for proper field seaming
is 15.5° C (60° F). While no maximum air humidity is specified for welding,
certain combinations of humidity and FML temperature can cause moisture to
condense on the surface of the FML. This moisture must be removed by
preheating the FML prior to seaming. Seaming around penetrations and field
inspection of FML seams is reviewed in Section V of this document.
FML Survivability
The ability of a flexible membrane liner to resist puncture and tear
during installation and operation is critical. Puncture of a liner can
occur due to falling objects, equipment moving on the liner, ice forces,
abrasion and movement against sharp objects. Tearing is typically the
result of a puncture being subjected to a tensile stress. In unreinforced
membranes, the resistance to puncture at low deformation speeds and tear
are a linear function of membrane thickness (Knlpschild,1985,and
Ainsworth,1984). Puncture of a membrane at high deformation rates, such as
generated by falling objects, was shown by Knlpschild (1985) to vary by the
square of the membrane thickness. Ainsworth, however, reports a linear
variation of puncture strength based on the Swiss Standard SIA 280/14. This
test measures the critical drop height at which a standard bolt will not
EPA III - 17
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produce penetration of the membrane. The general improvement of
performance with increased thickness is currently the basis for the use of
membranes substantially In excess of the 30 mil statutory minimum
thickness. Recalling Example 3.12, the FML thickness could be a fraction of
the statute requirement based on purely hydraulic considerations. The thin
membrane meeting hydraulic design guidelines would not, however, survive
the installation process.
Puncture damage to an FML at low deformation rates can occur due to
the presence of large rocks or sharp objects in the soil beneath or in the
cover placed on top of the FML. This puncture resistance of a membrane is
quantified using a simple laboratory test procedure that measures the
ultimate force required to drive a 5/16 inch metal rod through the
membrane, ASTM D3738. The puncture force Indicated by the test is generally
used as an index, with larger forces indicating a greater resistance to
penetration. Minimum puncture resistance requirements are not established.
However, the puncture resistance provided by the 30-mil statutory minimum
thickness of HDPE is approximately 80 pounds. This must serve as an interim
minimum design criteria.
Recent studies (Koerner,1986) have shown that the puncture resistance
of an unreinforced membrane at both low and high deformation rates can be
significantly increased by the addition of a geotextlle behind the
membrane, in front of it, or in both locations. The results of puncture
tests on four 30 mil FMLs with and without a 12 oz./sq.yard non-woven
geotextlle are shown in Figure 3.8a. Proportional improvements were also
measured using 6 and 18 ounce geotextlles. Current functional requirements
for gas collection and monitoring of FML leakage require that a layer of
sand or a synthetic drainage medium be placed beneath all FMLs. The
effective puncture resistance of the FML will be greater than that of the
FML alone. Puncture damage to an FML will be more likely to occur during
the placement of cover soil on top of the FML. Puncture damage resulting
from the placement of cover soils is caused by large rocks or sharp objects
in the cover soil being driven through the membrane by large normal
stresses from construction equipment during placement of the soil. Soil
gradation requirements are used to minimize the occurrence of rocks within
the cover soil. Typical cover soil gradation requirements are as follows:
U.S. Standard Sieve Percent Passing
Sieve No. Opening (Range)
#4 4.76mm 100-90
#10 2.00 95-70
020 0.84 80-50
#40 0.42 65-20
#100 0.149 40-10
#200 0.074 20- 5
In addition to gradation, a sufficient thickness of cover must be
maintained to protect the FML from damage due to equipment loading. A
complete discussion of construction criteria is given in Section V. The MTG
recommends that each FML must be protected from damage from above and below
by a minimum soil thickness of 30 centimeters (12 Inches) nominal, 25
centimeters (10 inches) minimum, bedding material. The bedding material is
to be no coarser than sand (USCS SP classification) with 100£ of the
EPA III - 18
-------
¦ somanm ¦anrnnim
~ananimtnB sammum
6 osy Geotextile
DM .IS *i 01.15 * IK .Km Dfl.fi*
Baomnunon
satmnuiKi
irn.fi*. at.is* nc.fi* wt.s*
¦«noMiuc
~agmtniNnniB
¦aomnuim
exkimiuih
12 osy Geotextile
IM.fi* Ol.fi* NC.fi* Dft
n ©rami row
smrcmuKa
tm .fi* 01 .fi* IK .fin Dfl .7m
Baoimiunw n
saoicaiiiMa n'
n
~aoimu mi tira
DM .fi * 01 .fi * NC.fi* DK .15 *
1 N = .225 (b.
18 osy Geotextile
BOOimiUfM
gGotcaiuna
-------
washed, rounded sand passing a 1/4-inch sieve. The material must be free of
rock, fractured stone, debris, cobbles, rubbish, and roots.
Impact-type tests, ASTM E23, provide an alternate index of FML
puncture resistance . The Impact test provides an index of the ability of
the FML to survive having cover material dropped directly on the FML. The
ASTM test was developed for metals and is capable of very large impact
energies. This test is currently tinder review by ASTM Committee D34 for use
with geosynthetics. As with puncture, Koerner(1986) showed that the impact
resistance of an FML increases almost linearly with thickness using the
proposed ASTM test. Knipschleld (1985), using the West German DIN 53 535
drop test observed an increase in puncture resistance, that is proportional
to the square of the thickness. Impact test; data from the proposed1 ASTM
test is shown on Figure 3.8b and generally indicates an Increase in impact
resistance with; the addition o£ a geotextlie. Note that there is no
consistent agreement between impact and puncture data for a given polymer.
In general, a polymer having good static puncture would also have good
dynamic impact resistance. Both puncture tests show that a thinner FML can
be used if it is protected by a geotextile. Current West German standards
require a minimum penetration drop height of 0.75m using the DIN test
procedure. While no correlation has been presented between the two tests,
the West German minimum corresponds to a 1.4cm (40 mil) thickness of HDPE.
Table 3.1 Tear Resistance of FML (Koerner, 1986)
Polymer Composition Reinforced Thickness Tear Resistance
HDPE
No
40
mil
25-30 lbs
(1)
No
80
60-70
(1)
No
100
75-85
(1)
PVC
No
20
mil
6 lbs
(1)
No
40
10
(1)
No
50
14
(1)
CSPE
Yes
45
mil
25 lbs
(1)
Yes
36
36
(2)
(1)
ASTM. D1004
(2) ASTM
D751
In addition to puncture, a FML can be damaged by large tensile
stresses that result in tearing. The tensile stresses during installation
can be generated by dragging the FML during placement, and by wind-induced
flapping of the FML. The tear resistance of a membrane is measured by
typically using a notched specimen subjected to tensile forces that open
the notch. Tear data for common unreinforced and reinforced polymers is
shown in Table 3.1. The tear resistance of an unreinforced membrane
increases with thickness of the membrane and is influenced by the polymer
type. Tearing of a membrane requires an initial penetration, an applied
tensile stress, and the ability to develop large strains. These conditions
are only met during initial Installation and can be minimized using the
field installation procedures presented in Section V. Current West German
standards require a minimum tear strength, DIN 53-455 , of 45 pounds.
EPA III - 20
-------
A membrane must have sufficient modulus In addition to penetration
and tear resistance. This ensures that excessive stretching of the FML will
not occur and that local sheet deformations due to settlement will be
resisted by a larger sheet area. West German standards require that the
membrane support 89.9 pounds (40N) per 1.97 Inches (50mm) width at less
than 556 deformation, i.e. approximate modulus of 900 lb/in. Additionally,
the West German standards require that the ultimate multi-axis strain
determined from a burst test should be at least 1056 at failure. Currently
such multi-axis data is available (EPA,1983) only in the form of Mullen-
burst test which is not suitable for membranes. A possible alternative is
the large scale hydrostatic test reviewed in Appendix D.
FML ANCHORAGE
The geotextiles-and geomembranes lining the sides of waste facilities
must be anchored at the top of these slopes to prevent movement of the
systems into the cell. An anchor must provide sufficient • restraint to
prevent this movement but should not be so rigid or strong that the
FML will tear before the anchor yields. The anchor should therefore be
designed to provide a reaction force that is greater than that required to
stabilize the synthetics and less than the- ultimate strength of the
attached components. Generally, the FML is anchored at the top of the berm
using a (a) friction method, (b) trench and backfill method or (c)
anchoring to a concrete structure, Figure 3.9. The trench and backfill
technique is most often recommended by manufacturers, probably due to its
simplicity and economy. Excavation of the anchor trench is accomplished by
a trenching machine or by using a bulldozer blade tilted at an angle.
FML panels should be anchored following the field seaming operation.
After the seaming crew has completed the seams for a particular panel, the
panel should be anchored by backfilling the trench with soil or by
anchoring the FML to the concrete structure. It is important that the
panel not be anchored until It has been completely seamed to allow
positioning as needed for optimum seaming. Anchoring the FML after seaming
avoids stress tears on or along the seam from thermal contraction and
expansion.
Anchor trench geometries include vertical walled trenchs, shallow "V"
trenches, and horizontal embedment. Each trench geometry requires a
different set of analysis assumptions. The vertical-walled trench requires
the least amount of space but creates construction problems due to the
vertical trench faces and greater difficulty in properly recompacting soil
within the trench. Horizontal embedment requires the most land surface but
makes the fewest analysis assumptions. Based on the accuracy of analysis
assumptions, the three geometries can be ranked best to worst as
horizontal, shallow "V", and vertical trench.
It should be noted that most anchor trenches are currently constructed
to meet general recommendations provided by the FML installer. These
recommendations are based on past experience and are purely empirical. No
definitive field testing on actual anchorage capacities was found in the
preparation of this study. In view of this lack of correlation between
design capacities and actual field capacities, the designer Is cautioned to
compare design geometries with that recommended by the FML Installer. When
significant differences in proposed geometries exist, a limited field
EPA III - 21
-------
,£u>
i£/M
1% Slope
1* Slope
V-2' Typ.
horizontal anchor
TRENCH ANCHOR
w
"0
>
M
CO
1% Slope-
Li2*-16' Typ.
Top of Slope—«j
Bolted Anchor System
1% Slope *-
Polymer Batten Strip
SHALLOW 'V* ANCHOR
CAST CONCRETE ANCHOR
Figure 3.9 FML ANCHORAGE DETAILS
-------
pullout test should be performed to establish the actual ultimate force
capacity of the anchor trench.
Both the shallow "V" and the horizontal embedment anchors rely
exclusively on the frictlonal bond developed between the sheeting and the
adjacent soil. Figure 3.10 shows the forces assumed and variables used in
the analysis of these anchors. The pullout capacity, T, of horizontal and
"V" anchors are given by
q L tanS
Thoriz = - Eq(3.19)
cos @ - sin£> tan S
[q(L-Lv+Lv/cosi) + (dvLv Xcs/2cosi)] tan$
T«yn = Eq(3.20)
cos p - sin ^ tan §
For deep waste cells, the runout length, L, required to develop sufficient
frictlonal resistance may become excessive. Both frictlonal anchor concepts
do, however, result in a significant simplification of analysis assumptions
and a corresponding increase in confidence of the resulting calculated
anchor capacity. Direct shear tests should be performed to establish the
soil-geosynthetic friction angle, % , used in these calculations.
The analysis assumptions used in the vertical wall anchor trench are
shown on Figure 3.10 for a trench anchor. The earth pressure assumptions
made in the analysis were first proposed by Koerner(1986) and do not
attempt to replicate the distribution of the actual field pressures but to
estimate the total horizontal force component provided by the soil. The
method sums forces In the horizontal plane to predict the anchor capacity.
The most glaring assumption needed in this analysis is whether the embedded
sheet will be stiff enough to produce a passive resistance force wedge.
While appropriate for concrete anchors .this assumption is poor for FML.
The 90 degree entrant angle of the FML sheet Into the trench produces a
very difficult design condition. The tension forces in the horizontal sheet
must be resisted by horizontal earth pressures from the soli adjacent to
the sheet. Actual horizontal earth pressures during this process are
largest at the surface and decrease to zero at some depth beneath the
surface. Vertical force components resulting from the earth pressures at
the ground surface and excess sheet tension may require pullout restraint
obtained from further embedment of the sheeting below the point at which
the horizontal earth pressure is zero. Unfortunately, no available analysis
procedure correctly models the anchoring of an FML in a trench. It is
reasonable to assume, however, that the earth pressure acting against the
FML on the inside of the trench will be bounded by the passive and at-rest
earth pressure assumptions. The anchorage capacity of the trench system can
therefore be bounded using the following expression
q L tan S + (K'+Ka)tan [0.5 VCsdat2 + -sin £> tanS
where K' is bounded by Kp and Kat-rest* For design it is recommended that
EPA III - 23
-------
Tcosfi
Cover Soil
horizontal anchor
Tcos
Tsin^
'V' ANCHOR
/- ^//6y/Av77 ? { to
Tcosp X G°Ver Soi' 1 ]
^y/AV/A1
t\*V
V»\
Z>
'II I II
nj_LLtJJLorE3=rx
*SB58r>
QO.'J
'AT
~
Tsin p
pa
CONCRETE ANCHOR
Figure 3.10 Forces and Variables - Anchor Analysis
EPA III - 24
-------
the FML be sized so that it will not fail in tension if the full Kp
pressure develops and T^re,^ calculated using Kat_rest should exceed the
pullout capacity to prevent failure in other modes.
The Design Ratio for the anchor should be low enough that the anchor
will slip and prevent the FML or geotextile from tearing. An overly
conservative design of the anchor may indeed lead to a needless tearing
failure of the FML. Since the function served by the anchor is short lived,
the designer can be justified! in using a. Design Ratio less than 2.0. An
anchor design, ia shown, on. Example 3.17 using a vertical trench, horizontal,
and a. shallow, "V"' anchor trench;.,
The FML can also be anchored to concrete structures along the top of
the berm by securing the geosynthetic with batten strips attached to anchor
bolts embedded in the concrete. This technique is also applicable for
bonding the FML to metal structures, such as pipes. A common approach
entails placing the anchor bolts on 15 to 30 centimeter centers. The liner
is placed over the bolts, an adhesive is generally applied to the FML, and
the batten strip is secured and bolted in place. The analysis
assumptions used in the vertical wall anchor trench are the same as shown
on Figure 3.10 for a trench anchor. The anchor capacity is calculated using
Eq(3.20) assuming K' is- equal to ' Kp. Compatibility of the
adhesive/sealant with the type of synthetic and liquid Impounded must be
verified to ensure the seal is maintained. Details of anchoring techniques
are discussed by EPA (1984) and Kays (1977).
SURFACE IMPOUNDMENT CONSIDERATIONS
FML Protection
The liner system, including soil and flexible membrane components,
plays a significant role in containing the wastes within the SI by
preventing the migration and escape of hazardous waste and its
constituents. To enhance the longevity of the liner, a protective covering
will usually be required over the uppermost component to prevent damage
from mechanical or environmental factors. The liner system will often have
an FML as the uppermost component, which is sensitive to many of the
following conditions (EPA, 1983):
1.
Ultraviolet degradation of some polymers;
2.
Infrared radiation;
3.
Mechanical damage during placement of waste;
4.
Wind;
5.
Wave action;
6.
Oxygen and ozone;
7.
Freeze/thaw;
8.
Hail/rain;
9.
Animals; and
10.
Vandalism.
A compacted soil liner is not as susceptible to these forces. However, a
soil covering will provide additional protection from weathering effects
which may change the properties or cause erosion of the liner. Weather
effects include freeze/thaw, wave action or wind.
EPA III - 25
-------
Protection of the FML is often provided by a soil cover of sufficient
thickness to prevent mechanical damage from normal facility operations and
maintenance equipment. In addition, the cover must withstand wind and wave
action, and other environmental effects while remaining stable on the
impoundment slope. EPA (1983) recommends a protective soil cover of at
least 45 centimeters (18 inches) in thickness and a maximum side slope of 3
horizontal to 1 vertical based upon field experience. It also recommends
the soil be placed at or near optimum moisture by light tracked vehicles to
provide slight compaction of the material. This cover soil will be exposed
to repeated wet-dry cycles and should therefore be primarily granular to
prevent the development of soil cracking.
A critical condition in the soil cover exists if the liquid within the
impoundment has saturated the cover soil and the liquid is then drained
from the impoundment. The liquid draining from the cover soil exerts a
seepage force that tends to push the soil cover downward. The design must
first establish the internal stability of the soil cover layer itself, and
then that of the soil layer on top of the FML. As the liquid within the
reservoir is drawn down, excess pore water pressures within the primarily
granular soil cover will dissipate and the liquid within the soil cover
will flow parallel to the sideslope. Assuming the liquid within the cover
is flowing parallel to the slope, the factor of safety, FS, against failure
within the soil is given as (Lamb and Whitman, 1979)
FS = ( 1 -Y„/ Ysat > (tan Is the effective internal angle of friction of the cover soil,
and «< is the slope of the cover soli. For typical values of "Jfw, ysat» ^ .
and o< , the resulting FS is always low and indicate potential failure by
sloughing of the cover soil on the slope of the sidewalls.
If the liquid within the impoundment is drawn down instantaneously,
then the initial flow of the fluid within the soli is horizontal. Excess
hydrostatic pressures within the cover soil dissipate quickly and then the
flow will be parallel to the slope. The Initial condition of horizontal
flow produces the larger flow forces (Giroud and Ah-Line,1984) but Is only
characteristic of a clayey soil cover or a catastrophic failure of the
impoundment.
The stability of the soil cover on the FML is verified by summing the
flow, gravitational, and anchorage forces parallel to the FML sideslope
surface. The general analysis method is shown on Figure 3.11. For a typical
granular cover, the soil-FML adhesion will be zero. If the cover soli
contains an appreciable amount of clay, then the seepage force will act
horizontal and be slightly larger than Indicated above, see Giroud and Ah-
Line, 1984. In addition to verifying stability, the calculations should be
continued on to calculate the tension in the FML due to the cover soil and
to verify the adequacy of the FML anchor and tensile strength. Design
Example 3.18 demonstrate this analysis assuming the cover soil Is a sand.
Work by Mitchell and Gates, 1986, indicates that eroslonal considerations
become significant if the sideslope Is steeper than 20 degrees, or
approximately a 3:1 slope.
EPA III - 26
-------
Neutral Block
wmr
| DRAW DOWN CONDITIOnT
Solve Neutral Block Force Polygon for F^g
cLV
Solve for Sliding Stability DR
_ Resisting Forces fnb fM
W|S|g=Effective Weight of Neutral Block
=Soil Cover-FML Friction and Adhesion
Driving Forces F$- + Wc sin (L
MB
Fm = Wc cos 0 tan S
Fs = Seedage = VS**' sin 0
Wc = Weight of.Cover V=Volume of Cover
Wc = Effective Weight of Cover
Figure 3.11 Liner Cover Stability Analysis
Gas Venting ......
Surface impoundments or waste piles constructed using FML's must
include provisions for removal of gases from beneath the membrane. These
gases may be produced by underlying organic soils, leachate induced
reactions, rising water table, or simply be air that is trapped in the
facility during construction. If these gases are riot removed, they may
build up beneath the FML and eventually lift the FML to the surface of the
contained fluid. These bubbles are commonly called 'whales' because of
their physical appearance. Excessive stresses can be generated within the
FML during formation of a whale and can lead to rupture of the FML. Gas
collection is also a design consideration for the cap that covers the cell
at closure and is discussed in Section V. The cap gas considerations are,
however, concerned with gases generated within the cell and not those
coming from the beneath the waste facility.
A recent study (EPA,1986a) indicates that no formal design procedures
are available for gas drainage systems. The air transmissivity of
geosynthetics has been studied and procedures are demonstrated in Section V
for calculating the air flow capacity of an LCR system. However, an obvious
problems in the design of such a system is the uncertainty associated in
estimating the rate of gas generation. For conventional sanitary landfills,
the rate of gas generation is estimated to range from 1.3 to 7.5 liters of
gas per kilogram of waste per year (Emcon,1980). For the cap gas system in
a hazardous waste landfill cell, even the lower value of this range is
conservative. The rate of gas generation from beneath a given surface
Impoundment is not as easily bounded.
EPA III - 27
-------
A number of guidelines have been developed for designing the gas
venting system beneath FMLs. Kays (1977) recommends that the bottom slope
of a facility that could experience gas generation from below the liner
should have a minimum slope of 3£. Geosynthetic materials suitable for use
as gas vents are as (Giroud and Bonaparte,1984) follows:
a. Needle-punched, nonwoven fabrics having a thickness from 80 to
200 mils
b. Mats ( 3/8 to 3/4 inch thick )
c. Nets or grids ( approximately 1/4 inch thick )
d. Corrugated, or waffled plates ( 3/8 to 3/4 inch thick ) covered
with fabric
These dimensions closely correspond to the geosynthetic materials that are
currently being used to fabricate LCR systems. Thus it is anticipated that
a properly designed LCR system will provide a good beginning for a gas
venting system. Operationally, it is not uncommon for passive gas collector
systems to be converted to active systems with the addition of fans. The
active system can move significantly larger volumes of gas.
The gas venting system will require additional design considerations
beyond that required for the LCR system. Beyond Increasing the bottom slope
from 2% to 3?6, the designer must provide sufficient gas vents high on the
side slopes Just below the top of the berm. The vent spacing may vary, but
a minimum vent spacing of 50 ft. is recommended. Typical gas vent details
are shown on Figure 3.12. These vents function just like those that vent
the plumbing system in a conventional house. Gas is allowed to leave the
system, yet rainfall and surface water is prevented from flowing into the
system.
Past problems with gas venting systems beneath surface impoundments
include failures caused by water collecting in the gas venting system and
either reducing the effectiveness of the vent or creating high water
pressures that eventually lifted the FML above the surface of the liquid
being contained. Under draft MTG (EPA,1985) an LCR would be under the FMLs
and would act as a gas venting system. Water entering this system due to a
failure of the gas vents would be removed as leachate and not allowed to
build up beneath the system. This additional water would add expense to the
operator to dispose of or treat, however.
EPA III - 28
-------
•liner
Air/Cm Vent
Two-Inch Minimum
_Ceote«lle or ~^®?3Ss? Cas flow
Drainage Composite
Openings In Vent to be Higher than
"Top of Berm or Overflow liquid level
Air/Cas Vent Assembly
liner
Geotextlle
Drainage Composite
««>— Cas flow
—Appro*. Six-Inches
Wind Cowl Detail
J
till
Geomembrane
Concrete
Bond Skirt of Vent-to liner
Figure 3.12 Typical Gas Vent Details
REFERENCES - SECTION 3
Ainsworth, J.B. and A.O. OJeshina, (1984), "Specify Containment Liners,"
Hydrocarbon Processing, Nov.
Bass, J., (1986), Avoiding Failure of Leachate Collection and Cap Drainage
Systems, Hazardous Waste Engineering Research Laboratory, U.S.
Environmental Protection Agency, Cincinnati, OH.
Calhoun, C.C., Jr., (1972), "Development of Design Criteria and Acceptance
Specifications for Plastic Filter Cloth," Technical Report F-72-7, U.S.
Army Engineer Waterways Experiment Station, Vlcksburg, Mississippi.
Carroll, R.G., Jr., (1983), "Geotextlle Filter Criteria," TRR 916,
Engineering Fabrics in Transportation Construction, Washington, D.C., pp.
46-53.
Chen, Y.H., D.B. Simons, and P.M. Demery, (1981), "Laboratory Testing of
Plastic Filters," Journal of the Irrigation and Drainage Division, ASCE,
Vol. 107, No. 1R3, September.
EPA III - 29
-------
Demetracopoulous, A. C., et. al., (1984), "Modeling for Design of Landfill
Bottom Liners," Journal of Environmental Engineering, ASCE, Vol. 110, No.
6, December.
Emcon Associates,(1980),Methane Generation and Recovery From Landfills, Ann
Arbor Science, Ann Arbor, Michigan.
EPA, (1983a), "Lining of Waste Impoundment and Disposal Facilities," Office
of Solid Waste and Emergency Response, Washington, DC, SW-870, March.
EPA, (1983b), "Landfill and Surface Impoundment Performance Evaluation,"
Office of Solid Waste and Emergency Response, Washington,DC, SW-869, April.
EPA, (1985), Minimum Technology Guidance in Double Liner Systems for
Landfills and Surface Impoundments - Design, Construction, and Operation,
U.S. Environmental Protection Agency, May 24.
EPA, (1986a), "Covers for Uncontrolled Hazardous Waste Sites," Hazardous
Waste Engineering Research Laboratory, Cincinnati, OH, U.S. Environmental
Protection Agency.
EPA, (1986b),"Geotextiles for Drainage, Gas Venting, and Erosion Control at
Hazardous Waste Sites," Hazardous Waste Engineering Research Laboratory,
Cincinnati, OH,EPA/600/2-86/085, U.S. Environmental Protection Agency.
Giroud, J.P.,(1982), "Filter Criteria for Geotextiles*," Proceedings of the
Second International Conference on Geotextiles, Las Vegas, Vol. 1.
Giroud, J.P. and C. Ah-Line,(1984), "Design of Earth and Concrete Covers
for Geomembranes," Proc. Intl. Conf. on Geomembranes, IFAI, Denver,
Colorado, June.
Giroud, J.P. and R. Bonaparte,(1984),"Waterproofing and Drainage:
Geomembrane and Synthetic Drainage Layers," Symposium on Plastic and Rubber
in Waterproofing, Leige, Belgium.
Kays, W.B.,(1977).Construction of Linings for Reservoirs, Tanks, and
Pollution Control Facilities. John Wiley & Sons.
Knlpshield, F.W.,(1985),"Material Selection and Dimensioning of
Geomembranes for Groundwater Protection," Waste and Refuse, Schmidt
Publisher, Vol.22.
Koerner, R.M., (1986a), Designing With Geosynthetics, Prentice-Hall.
Koerner, R.M., et al,(1986b),"Puncture and Impact Resistance of
Geotextiles," III Intl. Conf. on Geotextiles, Vienna, Auistria, April.
Lambe.T.W. and R.V.Whitman,(1979),Soil Mechanics, SI Version, John Wiley &
Sons,, New York.
Lord, A.E.,Jr. and R.M. Koerner,(1984),"Fundamental Aspects of Chemical
Degradation of Geomembranes," Proc. First International Conference
Geomembranes (IFAI), Denver, Colorado, June 20-24.
EPA III - 30
-------
Martin, J.P., R.M. Koerner, and J.E. Whitty, (1984), "Experimental Friction
Evaluation of Slippage Between Geomembranes, Geotextiles, and Soils," Proc.
First International Conference Geomembranes (IFAI), Denver, Colorado, June
Mitchell, D.H. and G.E. Spanner,(1984),"Field Performance of Synthetic
liners for Uranium Tailings Ponds: A Status Report," NRC FIN B2476, U.S.
Nuclear Regulatory Commission, March.
Mitchell, D.H. and T.E. Gates,(1986),"Interficial Stability of Soil Covers
on Lined Surface Impoundments," Proc. Twelfth Annual Research Symposium,
U.S. Environmental Protection Agency, EPA/600/9-86/022, Cincinnati, OH.
Morrison, W.R. and L.D. Parkhill,(1986),"Evaluation of Flexible Membrane
Liner Seams," U.S. Bureau of Reclamation under Interagency Agreement No. DW
14930547-01-2, Hazardous Waste Engineering Laboratory, U.S. Environmental
Protection Agency, Cincinnati, OH.
Peggs, I.D. and D. Little,(1985),"The Effectiveness of Peel and Shear Tests
in Evaluating HDPE Geomembrane Seams,"Second Canadian Symposium on
Geotextiles and Geomembranes, Sept., Edmonton, Alberta.
Scharch, J.F., (1981), "Improved Analytical Methods for the Design of
Leachate Collection Systems," Fourth Annual Madison Conference of Applied
Research and Practice on Municipal and Industrial Waste, September,
Madison, WI.
Schroeder, P.R., Gibson, A.C., and Smolen, M.D., (1984), The Hydrologic
Evaluation of Landfill Performance (HELP) Model; Vol. II, Documentation for
Version I. EPA/530-SW-84-010, Municipal Environmental Research Laboratory,
U.S. Environmental Protection Agency, Cincinnati, OH.
Schroeder, P.R., Morgan, J.M., Walski, T.M., and Gibson, A.C., (1984), The
Hydrologic Evaluation of Landfill Performance (HELP) Model; Vol. I, User's
Guide for Version I. EPA/530-SW-84-009, Municipal Environmental Research
Laboratory, U.S. Environmental Protection Agency, Cincinnati, OH.
Schultz, D.W.,(1983),"Field Studies of Liner Installation Methods at
Landfills and Surface Impoundments," Municipal Envlromental Research
Laboratory, U.S. Environmental Protection Agency, Cincinnati, OH.
Shrestha, S.C. and J.R. Bell, (1982), "A Wide Strip Tensile Test of
Geotextiles", 2nd International Conf. Geotextiles, IFAI, Las Vegas, August.
Task Force 25,(1983), Joint Committee Report of AASHTO-AGC-ARTBA, December.
Wong, J., (1977), "The Design of a System for Collecting Leachate from a
Lined Landfill Site," Water Resources Research, Vol. B, No. 2, pp; 404-410.
EPA III - 31
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Cell Component: L£^;hacte ^0U.e£TK>N/(?E.i
I
CO
to
Analysis Procedure:
(O PeplMC M.mMi)M~TgAM»MI-a»IViTY
• •$T>JUToRt » 3* I©"5 M1/®
• I - K»»t ^«AP
BUf
^~wa4 6sw <
(tt ^AL^UlaTC Maximum Kloxr-IAL ^rnE3"S
(3) OBUklM LA&a«AToa.Y T5*Jv)» m i»»ivi TY "P ATA
*
i
~
?
£
K
<^"'LSACHATE IMfVoW RArt.
k. » I 6**r of HfcAP
P^piijai. oepfh cap r® lcr
"J >Uuif l*JLIC,HT i6niT, L
«> -t« -5o -r« i-o
(4^ PfcF'tJfc Pfc»i- 60'
* Leachaje ikiFLow rate, cy » o-oirt/wr
* La®oRa1»*.Y T~qAwiMi-a-nviry C?».ta
(0 PeFujE MiuiMUm TnA**»Mi»>itfnY (V\jov~t ^mreauC)
(bo1, * {>•TA ^ ~ft^
<>...
: f
f
¦ -A A- A
NOftMAl STRESS ,Ht
O 200
• 2000
O S000
¦ toooo
A isooo
~ 20000
w "Tiie^ 7.4fc*lo
r** 18.0
DP
HTH
Tl«
Tut 4
. 000)4
3xiofar ^,6rt Maximal
Example No. 3.1
-------
Cell Component: levxate (?cmoual 5rifEM
fy>ngiHftratir>n;-fgAU»Mi**i>' iT"x <9PERAnoki5» , verify that Primab.v
LCK Ml U- HAMDLE ^UflFA't! MATec* «PEK<.ti«J
gf the Facility
Required Material Properties
Range
Test
Standard
Pla»ml PLoui Parity
Duft MT6 Minimum
lo'V/5*
T^^^^'vfTY
A«TM
Anaiysis Procedure:
(I*) C ALcJlaTE RlitJgFF VaLOME £PA^|18& £?/fr £nrep.iu<^ L£R
= »MijjiviTY
KtwRi-r**, ®«eJ^«n
• UAfea^neo Aae^,^* 2.5acb£«.
L£R PeaiME-rua t» WaTERX eo - l^»r
Ah-» 16*
AK.I^rr
( H^AJ^JlATE RJkjofF VoLUi~r£.
<2- 1*4 x 2.5 = loo rTy»ccxjo
^QM^Ea.T Q. T° 'RIpx E. kiT6RjMCt LCK
Io.of i£ « r5 * 1
^E*" PT*/*C
^&a" ^'"*4
(4)<^AL£.ULA"ffe r?g>4l^Kj gA-riO
^&T*VKJ A^fUAi. ^ w/ t* 4*>r.33 a.md <5^,* I 2&OT+P
see. £*3.i =*. •ood.M,*AecJ
. gOfc
.•°''7
u.<7.
ffa P££REa£E. MAjfeA^HEC? ARE.A.
Example No. 3.Z^
-------
Cell Component: ^»ut£TioN/^r«rE.M?
Consideration:*• DBTe»Miue u>N<5-Te«*M
£«£fcp IMPACT 0kJ fR#vW^MI**ivlTY 4XIJTHE7K-
Required Material Properties
Range
Test
Standard
Lmi<{-T6RM «a»«»AR PI.OWJ «"Af»A£iTT
fM.u)
A«WD46I7
*
Draft MIC MMnun
Analysis Procedure:
(.O Maximum MoHmal. ^Tg.ES5,<-? n
T£
—rvmspnw
u
fl
LA»P«TA| PhoJ Strfip
^•WTAk/r «f«Al>ISUT
¦ ."t".
--4
MlUlMUM Lift
T 5oy»k*.
CpO
£?¦> RtojEgr Lou^-Tt ».M "TbAm5MI*»iV|TY J
&f.X ®BTAlfcl From CjffAPMiCAl. PnojetfTIO«J
W ^AUJL^ffc Dt*<\u Rxr.o ,D^
S.r
PR »
<£>,
«fc<*
Design Ratio:
PRmiu'5-^ "UPU'fco £.*.!>. 1
4iu«e <:aLtf i-s uew
IU£U10||>.
References:
Example:
"Lamopiu. Mt. r •<<»'
• UwT WT. UJA5T6" So Ib/rf*
' Dt*4KI UffcTlMt " SOYIA*-" .^xlo^HouKS
• F"|KLD<^(tAOItKlTj C " ¦£>#£• (Zt* E«.?.|"^
^AlCUtAt£ Ma»iwum kJaRMAL "$TR66St g*k I
S'jj » d"xl2o ' 'Mroo Ib^ff*
(«-") OfcTAlKJ LgN^rffcaM ~Tbom-<>m)65'vitv PaTA
l3u>J£«r
4.4 *lo ~'•<1*4
($> Rttfiacr Lou^Tep^ "Tp.>»j^mi'»siviTy
From <^HA«.T ^LT* l.5*lo"S M^aec.
(¦4*) ^aUuIate t^e^igM Ratio
I.9«io 5
DR = 3xio6 = 5 ^
Example No. 3-3
-------
Cell Component: 3yME
EM
Consideration: ^>fep-M'T'v''TY , VERIFY THAT /k ^£<*T£xfil.e WILL ALLOW
LEACHAfe T« Flow -Through if.
Required Material Properties
Range
Test
Standard
FLtftO KJ»AMAL "(i ^fcoTtxTlLE.
To o-oo*}
C 4£c")
Pt KM iT'ViTY
A 6 ^Re<9
l<1 A.
AK
k
Ta V
T. Ta
£ pAB£T'« £ ^UaTiOki*)
M*<. I FT M£ ap
A • UmT A»,tA
^4 A-
^Z.") ^eoftxTiLt. Pei^Mir.viTf % l4/^e<
Re-WL-r* P£ c. A^fM P441I
L—TUReuLfckir Flow
:
«»*!
¦^lo K A
Rt'ftMf* ^o»>A£CTlowl
k - He ao
A - AREA oF YE1T
(3) ^al^uLat£ P&a^ki Rat»
Head
PR - ^
Design Ratio:
DR "> So
References:
Example:
4i\ze>o :
•LfcAcHAtt XwF'-oW P>AtE. ^ <^_= f-ol ft/a**
•MAsel»-lUrl j-lfi-AO * I FT ( DHAM*")
fl1>) ^aL^ulaTe. Required Pc-^Mi-fiv'Tr^
faE*1 I „ I \j6UM£ UW(f AAEA
5 Pay"' » M^xio'6 Sic."1
CO £7fefAi»i &^r£xTiLe. ^t.aMi-fivirr | i|><\e®
J
*| 1109-
» 4(55
® to 4o (to ®o too
HEAP, MM
£4g« I
V^E£>= 5^>* 4I&6 = 4
^aU.JlaT"6. C?C6i^M Ra-Tio
4 » _ ..
PR ¦ 7^3 *
Example No. 3.-^
-------
Cell Component: Coue^now/5>y4tgki
Consideration: ^r*L'TER" Petemtiom ^qmp*^£.^bajm *rre p^r»u6im<*j
of h£TViu£d ^oh. it> ofcuiMcj ^ize. op ^»
CWo£2(5
Peofboeo astm
Analysis Procedure:
(O^earMU 5i«e op ^ovet ^<>il ~n> ae Re.r*oKie.r? ^X^Tm D^2i')
Stcvt Opcai&K
(mfll)
CU»C.c,rwi» foa. whioj
5'/•<>*. uea pa*> th«ou^h the FA.0a.1t. h,°^>=- CluAm-vix)
(3) EvauVte. Filter ^biteria
Rtr. mr-ni-8
Design Ratio:
KJsr \WucAH-e.
References:
• ^IRoUP Cfl041
• £"ai».r»14. ^ h£ u C
• TASK. FofltS 4-6 0l®3")
Example:
^iv& si.:
• op ^to\£xr.001 r«i-k
C>,0 * * Oa\t, «\iveu mm (,-rbo)
(3) Evaluate Filter ^RifERia
"Ta4K. Fop,^e 2.5 : FVom &©% fA4wuZ.#^o ^5
CtA(u>u/<^heu t jx?B2 - .2-510.54 • o.4o ^ 2, OK
0,5/P,5 - .&lo.
-------
Cell Component: Leacha>TE e^tou/Removal- ^-farem~s
Consideration: Filter-Cu>qqiM^ ; evaluate -rue iwfuucm«. op
e.CT*.iioec> ^oil. pa«ticl6.^ okj the Permitivity a.
"' ^fcoTexTn-e.. • ' ¦
Required Material Properties
Range
Test
Standard
Pi AC <7* Mca^i1A£oF ^TEUHAl.
Ontl MTG Minimum
.1 -c> 30
^aAPt£ur RiT*®
Pro Rosed Afl.Hi
Analysis Procedure:
(1^ f^gFoKM CytAPifeMT gA.TW.~Te ST
Ahi*4CT /
L(mhu«-
^0lk ~~
c^fcjr&xpkE
HCT7*V7T
*~» >!
l*«T
P
_AV^"
_AW
AS" Thi£KU£4* ^ lW*H
(£) Evm_UATE ^RAP|6k-»T
^R> 3
t?PTu>KJM. LgKi^-TtRM Fl*ui _ZH*r
N|'C»UJI*W.
"T^ «Ta^m^iT>oki Tim£-
p*ih a.l
• K.O (n8£)
Example:
* Sell- 5 Tfc»T
AKt.-3.6"
A»VW* 5r
A ^ » 1.iEuT. ^a.tiq
CjK-I-Z4 < S-o
£y> optwwjaL Lotis-T^*-^ f*Low Tg-5=^9-5
1 1 li 1 1 1 1 1
III
1 1 > 1 1 11 >1 1 1 111111
10
Tim* (hr|
Mp • slight or Kje^ATr^e
.'. ^ttrtnTite. may -glrtta. ujiTV» tim£
Example No. 3.6>
-------
Cell Component: Leachntc Coti.ec.TioM/ Removal Sy-yrtM
Consideration ^-IPiKJQ Ev*,lU*.T£ «ritE'S6£» «AT£D
pocuu^ am or iKiTectiod ctu.* ^pja.££»jt T«
Sipcwalud OF FA^ILIT^.
Required Material Properties
Range
Test
Standard
paicnau
" LCR-T»-WA*rC } Su
* lcr-t.- Tml )4l
Ttu-iiut "5t«£u^tm o* LcR
Drill MTG Mninun
i©*-45*
\o -
Pmccy Shbab
•> «
Uift. Uipth
TemsuE
a*tm
A*Tri r
O 4S15
Analysis Procedure:
(l^ Evaluate im LCR
T- FL - FL
fv- Wca^feTAwS <-
# , ' * AXJCC£*»
w <#~£ tam 1
Wr^,(hJ^Y >U wiT ulT* m*4TE.
CO Q6TAIKI l-Afroa "Tfeu^liE 57g£u^Tri
£ - J^«5-
ii»iuq 4"-8" uilpe SAMPLE.
"*¦ "Tmax
(%) ^LcULA-re Pe^i^kj Ratio
1
%
<\
3
P
PRS
JG
Design Ratio:
PRm1U- 3. <9
References:
Example:
_^tiv£>-i 1
* Cen-THii>ojE4-» j l-»* 5'
• Uijit Uh ^'6ofcf
' 'St.opm A^ie, £ * io'
" FricTioM Ati^LE.5
* L^2"rt*WMr£ j " *io °
•» Lca-T.-FML , Sl'25*
(0 Ev*.lu1/>.t£ "Tbkj'&iom im LcR.
LJ ' Vx f KjT) ^ ($*(S/t*h3o'))&o - 1732 Ib/rr
F«- ITfl>Z « ie»5o*» Tau Ao' * I2.5& Ityrr
Fl» I7%z * -s3o*» TA.KJ 46° - <*11 Ifr/fr
"T ' 1258- 6" wipe sample T » 414o ib/r
LCfZ ¦5rwTH£T-c''
^^LgUtA,t£ P*£
-------
Cell Component: Le\chate £qile<=ti<»-i/Removal System
Consideration: ^rp*eK>e^JH-^e-ttiehemt ; Pete«?miwe ability or lcr
7 atlULTIM^ FgaM the
$ll&$iO£Nice. op THt >JTA.>U6.D WA.-ME.
Required Material Properties
Range
Test
Standard
Ft* ifriaM \ki^Lk LCt?-T«- l^W«re
L£R-T»- FML
"TeusiLE $T«e>g'
Pia.iuT'iueA,a
i-Jioc l~lic*n
AStm
Ct« WTfcTwO
ASTM
D-^516
Analysis Procedure:
(f) Evaluate Tkuaiou iki LCR
WHB«t ^ J
¦y.OKIir MT. WA4TS
H » P6PTM oF WAVT e
Slope a»-k;l£
S; L£R-To- w*.«TE FKKTiOU au<^lE.
Su'UR-T#-FMl- F"Ri«Ti«fcj A.MCjL£
( ^ O&TAiM LaSoRATOH Y ~T~E ui|L6 "^rgfeu^TH
^ee E>amPl£ 3*~t
(.3^ CklcJiMt. C7e.»iqKi Ra-Tio
.IW-K'
77TV77
PR -
1«TAL 5mEMI /ft
Design Ratio:
AUALY4)9 M £Thoo W*»T RE^<»Mi-i£kjPE£)
References:
Example:
^iveu".
• WIavts Weight, W«-120 ft
"Uuit Ur. UJam-c, t*&orcF
' 5u>ce ,^>--50°
• nri^TioM 2o*
Sl* >5°
0"i ^*>1-<;0LA.TE. IN L^R
"ToT^L Sue.Ate. / fooT
"T>>2. gaHio1 c»4V [T~»2o'--TAU*'j
x L 9®° J
T4= SZ)160 lb*/FT
LaboratoH'*' ~t6.N»n.e '$T<*eM<^Tn
set E-xamplC.
"T" - 49 60 lb./pr
(5>~) CT«^Ki I?atio
41 So
PK = " O-O'y
S2flto —
U
-------
Cell Component: / Ri>i.val System
Consideration : -"5&TTL£n6 MT ^ Evaluate P*oc>iJc»[
iu LCR by fe-rneMBKJT UIa«te.
Required Material Properties
Range
Test
Standard
L SAO - E. AT*okJ £ roa L<1R
Tevr
A^Tn
CM 515
Onll M1G Minmun
Analysis Procedure:
10 Evni^iatp SipgiMALi. ^fcrn&MBijT ~i> UUvre.
A**ume * Siu
M
13
>
I
rf*
o
5tntEM{uT05i»E5i«pi
MAX. W-tAM 6 >CTfL6MtJT
P * of 5iO£5Lof>e
(4) OgTAtM L*»»aWrtY 1«AP.El.>j^at,^j Paxa.
¦$ct £x/vMpie 3.7 , 6 t
V.tLO Y Ultimate e»^T«Al»J
E»rit~iA.T6 Mavh^Jim! im PJc To ~^£TrLfM6MT
"Assume L£{2 i^avfe.
L ^
'Al 5«£r.«.
&fn a *«me m t~T
(4) « P t»mu Oo-n,;
1l£lp"
PP.
U,-T <£.
Design Ratio:
P R KllO ^ 0'^>
t?R ULt * 1-5
References:
Example:
• ^loPb ^ • 2©*
• ^|-Ugl r IS
A
34* Ama**"-1^ IS * 4IW&00 - £.2 ,uc.we-»
fO #61Xim I ©A© - ElautE Ma*.
.6tbaiio iu L£C2 ("i£ To 5e nit MtuT
"MA*
L» 3»4)4« S\ ft : hb"
AL® A^ j5,r 6.Z I4\\jTx? ' 18-1 imcm
- 18.1
£m«-" 4.fc" ' 27.47.
(4^ <^ALf JlATE RaTi«»
P^TifcLo* J7.4" ©•4o Mq P^ult * 27-4'
Example No. 3.9
-------
Cell Component: Ieacnm-e Co\x^t^JRemoval System
Consideration: "T*^smis*i*sw»i"r* ^ n
LC E. P ftM u*e,£ &oTTo 1-1 Sa^o
H YMUitt.it COMDUefiviTT, K,^^,
Draft HIG MWnn
ia *?l*tc
A -.8
> I©"1 c
UOWE
PE.Ant*«tMl¥
A4TH 04417
ASTM D24W
Analysis Procedure:
SAfUg^TlEP L£R
(ft "T«ae' Fto»i Vfci«*if* in^urwttx lcb
t'lHif »f L£R UkiloM4e(WA.Trt£)
K l A, {daact'* Ej')
V, » velocity » |//^* K*
t'» hx»
\!| veu>«iTY» VVn
i« Ah/u 0 «L0f£ 0r «t»IWML
^•PokoSiTy, mSA^uae. *a <:*!.<
(*) c*.i£, '"IW Vetog.Tt I" *^r> Uvta
N * *.PPA«ti-ir vt locni' K L
•VU» «AM>
Ml*-?"4 **£"¦"< 'CvJ/n.^
#*» 1m »j*P*TiJuiT wi^m «f «*up Umit wE^nr,uAMD
I^ ^*uu»>t6 ToAvti. TT^e T
"tlMi - Ct~),
T* ^
-StOfcUJAkl
C
(M.
ar
Design Ratio:
kJ«T AfPlkA#Lt
References:
sju.ai
Example:
JJiyfiH ^^tT< ^iphviau. lxR
. Tr^su^Mfilivit* i®* ' * '®S 0 I.* <5.5
• "THifltMtM" 2- CM
¦ f«Ho4i"rv * f.S
Squirt feoTtoM Leg-
> Mvo*«iILIC. ^>UOUiTi«iT< , K » l*W
• Prv Jwrr we lijHT no f'f*
• ^rtaf'C «*v¦) <^»4,JkTe 'Tbue' flox Veto^i-ry im S^uthetic L£R
% • t 1*1 o* %Zc/i*»~] ! (r^)
- -oo\ m/scc,
Vt» .oo l/-5 • -Ooi. njtez « o.eoTb fr/itc.
(*¦} ^M.gLlu>,Tfc 'Taue' Tt«M VtUxaty m 6xuo L«-Vtft
[Vj] » I «io"1 f .no » .00 St cy+Ihc
no
^ * ZASx4t,» *
LVJ 5 .o»mJ."¥!> ' .02-7 <«/*!<:• »8xio PtAtc
9AUO 1 '
^ ^L^aLA.tit T»A.ViL. "T*h£.^"T
-rr 4 -^2_
1 ,cxn% .88 x1c"4
* 54 225SO * 7-& Moun-4
0*YS
Example No. %\o
-------
Cell Component: CtftLe^Tiou / 'Sy-»T6M®.
Consideration: ^T"£M'iPrimal u»^g •,*«¦>»ou ^LdC t»- 'Sf
SL^n T^-'S-.L,^
5pM L-td-SoiLjS^
Teu'Sii-g ^"beu^th or Leg
i o'T 5o*
Zo° -qS*
pi«e*rr Smsa*
V/iO£ W,dth
ASjm
(TbujtaTi VE~)
Astm
o4e^5
Orall MIG Minimum
M
>
I
to
Analysis Procedure: prm.
0} EvNlOAffc "T"fcU-<fU )KI Si-^c
C^uriMire ^.op£
itu^iow 9 "Cu ~ *"f u "TfciJ¦#U>U
UjHea E N
•tu' f«u "5U
Ul»ujgi^nr &on iiM&a, V«l
¦"fL' Wl^o»j3 TXf SL
ItMSION * * P/*"°^
^6Tmu LMoCAToay | ttgytt. 5t^Emqth ^ ^L^CZ.
^6£ t,A.r-iPLe 5.7 * TMt>
(V) <£AtciJl.VTt. Pfe5iE^Tio
T
' MH
m
WMW/T
PR *
fcj4«o*4
*L . «*T, -S.o MtumOf-i pePeMpiuc^du *wti*iPaT6c>
£#M4TBtJcT|0U LtfAPlM^
References:
Example:
£l^ey:
" Sufs j ^ » Z°"
"S«»LLluto UuiT Ut. ,"J{» |i©p<(*
^••L L luCn. TwicKUEwi ,d» 42.IUCH£<.
• Fa.«t»»j slch-t.-sfmu ( 13*
"bt^R-To- 5..(_ , Su » 2-a*
JTmL-To- io'L ^ Soj" I^°
' Ci\.\. OePTH ,C> » bo fx
(0 Ev*lua.T£ "Ttu^wgt-i m
4**1 So* 45S psf
Tj • U) <»sp tam £u » 4 S^> *cot> 1o x tajj 28®
» Zzn
f L* UJ £*¦* f> Ta*-j £L» 4S6x x TAwU ft*
- qa.T p-sp
Te.KJSn>wr[~r0-TL] * V>j$s [i la] * £oj$%jto • tiooo^ln
Cz^Oerri^iKi L»j3og.»Jo«.v Teu SiLE. "SrBeu^THj 'SLCR
¦S>£E, EfAMftt ~b.~l
XiJy 4C,5<3 lbAT
(.¦?>") ^UJlWE Pfc-sie^iu (?A~Po
KJ »TE : £ *T« tMt LoADiut^ OuDlTKM 3 r*«*i F
-------
Cell Component: FLEKiate Mem&b*.u£ Liueiz.
Consideration •(%"**»via K) V Ti auuixretmsB»an»-ct*Me4jiLm
or a HeMeii nue u-siKJCj uJvtur T6*t
PATA.
Required Material Properties
Range
Test
Standard
U<3c* VA«,tt "T« ,14 VT
la- o.I
yom Pre44u«6 @ twt Tsmp
R,» SELATi <* MJw.onY WiTMiw *iJP
Rj.* euixrwe humioiTy Jfa kno Leap (t<*04)
Example:
4
IV6U t
mil HPP£ mcmSKAmb
¦5*MPLi 4(?6A» 0.0a*> m*
' TEM«**niRfc* toS'f * S«aua*mo#-i f&e**J«£,5*5T„,m^.
• HOMioitY pippeaeuce i K,- Rl»^o%
(Q CfiMfUuvrt. IaJN/T foem E.yPtgtl*l6MTXl. C?CTA
UJVT'
^ * €ko\
"i " 224 x «****
S ^ ^r-i* -PKY
f J
S ^e»acAi€s
ta
¦
u
10 15
Tf-CCDAVS)
ft)
-------
Cell Component: flexible membkaue Liner
Consideration- DeMiuimis PEem£abi liTY j -rwe.
SA^S-rY BA*eo ou Actual. L£aKam*E. v/EMm
LEVSL C '^ALloU /aAV^*
pe M*u>m
Required Material Properties
Range
Test
Standard
R TffAK|«Mli4^U tfF FML
Pfcff Mfe
ASfH E.S
Draft MTG Minimum
Analysis Procedure:
(0 Calculate P^EHmbapili-r y of FmL F»sm PtEMt/ku«6
K*R»neo«fMHMiurr= PeRmewjce. * "t
t =» FmL. TmicK. M
( 2^) ^XlclIiAvTE \An3c DiFfJ*""-' ThpoO^k FML
3" K*..p.1AT
OfMI.
AH
i-HtAP t AH* 1 fr 5TAiJito*i-r
A, -AR£a
^AL^UL^TE Dem^u RaTio
pe » _
^TiiXr
Q 3
D*T*t
Design Ratio:
References:
2.o
&>£RU£R
aup Lord 0^64^
Example:
^iveu :
* 8<9miL WpPE.
• PmneK*>c& - 0.0048 metsi^ pesm £ 4ee Example 3.11^
(>"} ^Tal^UUTC R^UEPo PtBMEABlLiTY if FML
k* <3. oo4 8 x go ~ ^.384 METBi£ P£« m -mil
P*ue»«
an. K- S 32 X 10 % Cm /sc^. d
P«i/te»
3-2-~7 x 10 ^iM 55 x to iki* / ltd
*/*«*¦
E 1 £j»a.oH /A^ee/t7A-< »4-2fc» 10"
iu*/'tJ1 j¦ien
6.55» 10" _ ,
•• «T " Iftnn'4* °'155 ^/k"£/PAV
f ML
('•J) <^Au:L)LAj"e Pe.*i^Kj R at 10
•<»..!»» = ^5 ?Kl!
• .
Example No. 3.i?>
-------
Cell Component: Flexi&le Membrajje Lim^r
Consideration:"TT^«'ie - Li^er UJeic^ht ; evalume
ABILITY of FML to «uPP»bt it* okiu i*-iei^hT cu THE
5IB6
I
i*
VI
Analysis Procedure:
FmL "Ielhile foaee. (T
"TV U)«.m^-F
UHerc UJ-Liwee weight
*[^-1SJt-3 [• »d/*im^]
F - W ^ T»-w ^ 1_
(£) ^alcUL^je FMU. Teus'Le Stress ^ G*
G" s T/A, uncut »a* l'»
(9) o&tahj L»8oaAro«Y FmL "fiecp } - 5o°
( 0 £kL-gdi_ArE. FML *Te.Uf>
.. Iu
a. to *11"" "v'u
Z0
Pc.-H<;kJ gATto
pfc . 2««®/|& . IZZ
Example No. 5.1-1
-------
Cell Component: Flexible MeM&gAME Lim£k
Consideration ^tre-s^ - P onuP«>< M-FlLLItJCjj 4
FML /*CL)CDkf P D DJSllI/-. ^
I . r J ^Al^ilLATE
FML -»-rR£.*.$ ^EUERM'BD PJSIUC) «roij-ST&i'^Ti«w "ix>-i S,_ **
W= -Uuir wt. or UA-sre
(Q ^vlculvte FML Te kj5i>-E SreE.3^ .I4
f^^ALgJtKTE Pe-ilcjU g^Tio
PR 3 ^/c
Design Ratio:
Df2»|u * 5.'3o"
Fc-riou
+ PL£E -To- PFML^ %0 - 1^"
+ Pfm l—,<>-slcB^ -» 12."
• to mil WDPE
(0 d/^LiULATE PoIMM- Pl?A«i OKi FML.T
U - y% » 'Zz ( 5* (5/r 30-^80 =
1732 Ib/fr
Fu* H52 i CO-,iO° t TMJ - 5l^ IbjpT
Fl- 1132 xcos^o* * T^Mil"= 'itR Ib/fT
T- 514, -3iq - H7 ib/'T
Cz"^ ^Taic-ulatE Fm L "Tiu'SiiE ^TBE55 G"
G*e R~r/ C l^T") * 3S-AOO lb/FTZ »
2.74 |b/,ur
C2>} <9btviu LaBoc ktob-y FmL Yi£lb 'S>tbe55 .S'v
^££ EXAMPLE 3.1-4 GV^.2 ZZoo
1 *»/lM 1
(4} CALCULATE Pt'WciU EVti©
OK' ZZoo / 2"T4 ~ 8-0 qK
"2T
Example Mo. 3.is
-------
Cell Component: Flexible M£m&r^ue Lime.r
Consideration: ^o&^ipeMgE : E-vmukte ¦stra.iu-s luoueto
IN FML f 4U&5lC>£lU£E.
Required Material Properties
Range
Test
Standard
•TEn'SiLft ^trsm^tx <»r FmL
UJipc- kjic*x
Astvi-c>
•Thickue'»v pr FML
A>TH . "
* $oiL - FmL. rHicTiou KjuclE.
Dull MTG MMnuii '
PlRtcr5nE>kQ
A^TVl
£reur*.Tiv£~1
Analysis Procedure:
(0 £ »TMAJfc *$iig»Q6kl^£
• UlipfU of L* UliPtM OF i)iJ»CC.L.Yiu^ £/r £xcAv Q&1KIU UluifoRM 5tRMM flitM Fi«»">tfe3.4
- _ PtfTM «
OR-rrLeMtur Kxr.» t L
~ <£
(%") <^AUuLv>E Kp»i11»«JAL PefflHMA.9le Ltu^fVl
fvd
V «
* z\-ft
¦P^'UL-pKiJcre •nweiv f"»R Fml.
T "
tt"
(1^1 E»T*'MAT6 $U»»ip6ut£
•U-otM . 10"+ 2*l2" * 44" \ ^TTl£ME^T e
• pfe^tw* .2 r Ift-* 3
a,TTo • ^ Oj C»
(2"> Ce>TAo>J Um'^pUM i Fi«i. 3.4
^erriEMeur R^Tio«0.0&* ¦* £ » Z-O*/,
(*) £/u.^uiaJ£ AppiTi^mau PefaRMXgte Le.MqrH
x=
*
60 f?tvn.fc ^ra*m
£'•
16oo » .ofco
?t r6fl«oo1x.^?S
L i^J
3. "3 ikJ
•OI6-5
>s.t X»gu? * Zo /#
^^utr5+^^ *Io")
Example No. 3.1 ^
-------
Cell Component: Fl8».sl6 Mbhsraue [,M»uq
Consideration: Fml ^MmoaAtse -^AttoiATE mj-cho* * a parity f<,«
fmL Placed u-» author *<;e c»uF¦
ib
00
Analysis Procedure:
P£P""* &M*W^ji
=> ^=X^dcs-" 120 s oL-j£ Rg Kkicu^o. ^A.PAciTi6S
1.6 tot|8.4- S,u1«.4*1XuiS
Nt>c?lTourxl (m iMowu) ""^".TAU - 2.48 ">/fr
s4J-a->- 1 i.5'lMt*+J?s.) - 1 , .
1.^3^ «pr / '
•C^meaett A.MgMaw g^TWV/1*
-4'Z'-0' * ' 11 1Jat
4"36° *¦ Ka-.z-r
Motl«Kui»'»(5.T-.irt[>-S«tt*>g*'»g 3 _ laa Jh»
-1" I.3M JSP A1
1.331
-l^UlMog TSuqgH " "
- 4>-35'*Ko« .AtU
j- t40«4»r^P#4ft.74.£ft Ttoja'C-girltet^Z^t] m
HP, ' ^ =»
L -"Ko
Example No. 5J7
-------
Cell Component: F*Leyi»Le M&mbha.me '-iuiuh
rAMW«ratiA«- SrA,giLITV ^<»'l • VgRiFW -rw
Consideration. ^vea W|it MaT suoe ou FMu ^ v
iuoioB aPidTY Aud IM rML.
Required Material Properties
Range
Test
Standard
SoiLfio/es?-,FML P°
S -15°
\oco-Zzac>?tL
pi*e58
Analysis Procedure:
Refer cute Pi<;3.|C,
E x/kMPLE :
£pveu
I z.'-o"
VA' Void M E « loo Ft1
^ UI£i^Ht 7 loox !3©oa lb.
Erre^vt UIcic^mt
p'-fe" r|y = looxfcix ¦ VT4o lb.
d^oVttt Soil
7»Tr" i»o pep ~ Yb-» 6n.(»pci«
S.a/FML &omd
S' l6° c-"°
FML/lcR Bdud
§ - 12.* £=0
FML
tHI" —•
SoLv£ For "[6^*'°^
p^- \Z000* cos&°*- t*.u|2,- £.73^
T» 2H5-tT3(p ~-5k|
&ut "T «uu»r &£
-------
SECTION IV
DESIGN OF COMPONENTS WITHIN CELL
Components placed within the cell and on the primary FML Include
those required to meet minimum guidance criteria for the land disposal cell
and additional components required for operation of the facility. Statutory
related components within the cell include the standpipe system required to
both monitor and remove leachate from the primary LCR systems and a witness
system for monitoring the secondary LCR system. Operations-related
components within the cell include the ramp structure required for truck
access to below grade cells and interior berm walls used to segregate
wastes or operational functions. These operations components must be
designed to both perform under transient services loads and not fail the
statutory cell components during either the operation or post-closure
monitoring periods.
RAMP AND TRAFFIC CONSIDERATIONS
Heavily loaded vehicles must enter the cell during both the placement
of waste within the facility and during construction of cells. These
vehicles require a roadway that is wide enough for typical highway
transport vehicles or construction equipment and with a low enough grade
that these vehicles can routinely climb out of the cell. Typically this
will require a roadway 15 to 18 feet in width having a grade of no more
than 10-1256. This roadway profile will generally be constructed during the
initial excavation of the below grade cell and will define the profile of
the cell through placement of the primary LCR system. The geometry of a
typical ramp is shown on Figure 4.1. Above grade cells will not require
internal ramp structures, and cells only partially below grade will have a
greatly reduced ramp structure. The geometry of ramps is therefore very
site specific with no 'standard' ramp detail applicable to all sites.
Figure 4.1 Geometry of Typical Ramp
EPA IV - 1
-------
Design of this structure Is complicated by the low friction angle that
exists between typical FML materials and soil, the need to use the ramp
during the construction process, and the statutory requirement that the
double FML and LCR systems be continuous within the cell. The ramp is
normally used during construction of the cell and must support traffic that
includes off-road haulers, e.g. pans, that may produce significantly higher
loads than the eventual operational loadings. During this time, the ramp
will be exposed to seasonal effects that include freeze-thaw and
precipitation. A cross section of a typical ramp in a double FML cell is
shown1 on Figure 4.2 and raises significant design and construction
questions.
18' Typical
Roadway
bWm
Subbase
&>^.Compacted clay Line
sfpfll
Figure 4.2 Cross-Section of Typical Access Ramp
The design of the ramp must address the following loadings and
potential failure mechanisms:
1) Shear failure along the axis of the roadway caused by the
impact of breaking traffic and the weight of the roadway.
2) Shear failure along the axis of the roadway caused by
hydrostatic pressures from surface water draining through
the roadway.
3) Puncture of the primary FML caused by impacting; wheel loads
forcing the subbase stone into the membrane.
4) Ravelling of the roadway shoulder due to lack of
confinement.
5) Breakup of the roadway caused by freeze-thaw conditions.
EPA IV - 2
-------
Geosynthetic considerations are included in the first four mechanisms while
the freeze-thaw mechanism is typically eliminated by the use of granular
soils in the roadway base and subbase.
Shear failure of the roadway caused by the impact of breaking traffic
and the weight of the roadway is the classical sliding brick on an incline
problem. The static forces from the weight of the roadway combine with the
dynamic forces generated by the breaking of traffic on the roadway act to
move the roadway down the incline. The level of breaking force depends on
both the size and speed of vehicles and the number that are allowed on the
ramp at a given time. Many facilities have limits on vehicle traffic
allowed on the ramp at a given time. However, a conservative design is
ensured only by designing for a fully occupied ramp. Example 4.1 presents
the analysis used to verify the sliding stability of the roadway. The low
factor-of-safety allowed in this mode under full service load is a
reflection of the limited life of the ramp. As waste is added to the cell,
the ramp decreases in length and accumulated slippage Is buried. The
limiting frictional bond is typically between an FML and a synthetic LCR.
This bond can be significantly improved if a thin (3 inch) layer of sand is
placed between the LCR and the FML. This technique does not work with
geonets.
The ramp forms a catch basin that must be designed to handle the
surface water runoff coming from the cell sidewalls. The particulars of
this design will obviously be influenced by the anticipated peak rate of
rainfall. The roadway must incorporate a granular subbase or a drainage
system capable of handling this volume of runoff without allowing the build
up of pore water pressure beneath the roadway. A drainage system embedded
within the roadway will present operational difficulties since the outlet
of the drainage system will either be quickly buried In waste or will
require frequent excavation to maintain drainage. Example 4.2 shows the
general method used to calculate the total runoff and to verify the flow
capacity of the gravel within the roadway profile. Typically the roadway
section will not be able to handle the full surface water flow and a ditch
is required on the Inside of the roadway.
The same gravel required to allow drainage of surface water runoff
will present a significant threat of puncture to the underlying FML. The
roadway profile must be designed to both support the vehicle wheel loads
with a minimum amount of rutting and to minimize the puncture or tearing
forces applied to the FML.. Both design functions are good applications for
geosynthetics. A roadway surface can be reinforced through the addition of
a single layer of geotextile or geogrid. The load carrying capacity of such
a system can be estimated using a simple limit equilibrium technique first
developed by Barenburg(1975), and later modified by Giroud (1981). These
design procedures were developed for soils having a CBR ( California
Bearing Ratio ) less than 4. The heavily compacted clays forming half of
the lower liner will have CBR values considerably in excess of 4. The use
of a reinforced roadway will therefore produce little or no benefit.
Puncture resistance of the FML beneath the roadway can be improved by
using a thicker roadway section to reduce the stress level acting at the
elevation of the FML, or by providing a cushion layer of .^sand or
geosynthetic immediately above the FML. The use of an excessively thick
roadway section is detrimental in that both expensive air space Is wasted
EPA IV - 3
-------
and because the welgbt of the driving force acting to slide the roadway
down the ramp is increased. Therefore, the optimum design will use the
minimum roadway thickness required to prevent puncture of the FML. The
limiting contact pressure that the FML can tolerate is Influenced by the
cushion layer above and below it (see Figures 3.9-10, Koerner,1986).
Assuming that a sand or geosynthetlc cushion is used, the limiting contact
stress can be evaluated in the laboratory as the normal pressure at which
the cushion material begins to flow into the FML. Failure is typically
assumed when the penetration exceeds 1056 of the thickness of the FML. The
minimum roadway thickness can then be evaluated using the procedure given
in Example 4.3 using the most severe wheel loading. The use of a geotextlle
as the cushion layer for the FML is limited by the low coefficient of
friction between the two materials. This can be improved if a thin layer of
sand is placed between the geotextlle and the FML.
INTERIOR BERMS
WASTE
WASTE
Compacted Clay
_ _
2* Minimum
ICR
2% Minimum -
'•FML
Figure 4.3 Interior^ Berm - Waste Separation
Berms are constructed within a waste disposal cell to segregate
differing waste types or in some instances to provide a temporary boundary
for an above ground facility to be built in phases. Such berms must provide
an effective hydraulic barrier without requiring excessive air space or
disrupting the continuity of the underlying LCR and FML systems. It is
normal practice, however, to segregate the leachate that enters the primary
LCR from each of the cells. This.is accomplished to varying degrees by
adjusting the. contours of the LCR-FML system beneath the cells. The
simplest interior berm involves placing the berm lift by lift during
operation of the facility and minor contour changes to the LCR-FML systems.
This system Is shown on Figure 4.3. By constructing the berm In lifts as
the waste is placed, its cross section Is reduced to that required for
hydraulic considerations and not for stability. Materials used for
construction of the berm must have a permeability equivalent to that used
in the liner or less than lxl0~7 cm/sec (EPA, 1985).
EPA IV - 4
-------
y/Xw/Xvy//
•y/w
Storm Water
V
—//Wy/XNV
Operational Cover
jyr
WASTE
J/AsV*W
Compacted Clay
FML
FMl
//xvyxw/
Figure 4.4 Interior Berm - Operations
More elaborate berms have been constructed when a greater ¦ degree of
separation between the interior cells is desired or when operational needs
dictate. Figure 4.4 shows an interior berm designed to separate the active
landfill cell from a temporary storm water retention cell. To provide ample
capacity for the storm water retention cell, the interior berm must be
constructed to full section initially and not in lifts as the waste is
placed. As such, the internal stability of these berms must be verified
using conventional slope stability analyses. Complete segregation of the
wastes within the LCR system can be obtained using an FML seal placed
between the primary and secondary FMLs.
Large down-drag force can be generated on the berms as waste settles
within the cells. These down-drag forces can increase the normal forces
acting on synthetic systems underlying the berms and should be considered.
Additionally, the berms are less compressible than the waste materials
which may produce significant long term post-closure subsidence features.
Methods for evaluating the magnitude of such differential settlements are
reviewed by Murphy and Gilbert (1987). Such settlements are a major concern
in the design of the cap system placed over the completed cell. These
considerations are reviewed in Section V.
STANDPIPE for PRIMARY LCR
Single or multiple standpipes are usually provided as a means of
monitoring and draining leachate that accumulates within the primary LCR
system. Standpipes are therefore located at the low point of the collection
system or subsystem and create a sump. Each standpipe houses and provides
access to a pump used in removing the leachate that collects in the sump.
During operation of the facility, the standpipe may also serve as a drain
EPA IV - 5
-------
for surface runoff that occurs within the cell. The standpipe itself is
typically made of concrete or HDPE pipe that is placed as the cell fills up
with waste. A combined standpipe/drain detail is shown on Figure 4.5. This
standpipe has an outer zone of gravel that is retained during operations by
fencing.
Concrete Base
Gravel
%. . ¦ Sand
Steel Plate
FMl
Figure 4.8 Standpipe/Draln - Details
Down-Drag Forces
Design considerations for standpipes reflect the potential for large
down-drag forces in the standpipe due.to settlement of the waste and for
potential clogging of the standpipe by surface water runoff. Down-drag
forces acting on the standpipe are caused by the differential settlement
that occurs between the compressible waste fill and the rigid standpipe.
The level of force is influenced by the amount of settlement but is limited
by the bond between the soil.and the standpipe. Due to uncertainties in
estimating the amount of settlement the waste will experience, the limiting
bond force is used for design.
The limiting bond force can be estimated based on the shear strength
of the surrounding soil and the soil-standpipe friction angle. Note that
the 'surrounding soil* may be stone or gravel, waste materials, or
operational cover soil which has great variability. Procedures for
estimating down-drag forces are commonly used in the design of deep
foundations (e.g. piles) in underconsolidated soils. Knowing the friction
or adhesion between the soil and the standpipe, the down-drag force can be
calculated using the procedure demonstrated in Example 4.4, This procedure
neglects the time-dependent increase In the down-drag force and only
calculates the ultimate or limit down-drag force. Veslc (1977) indicates
that down-drag forces can be fully developed with settlements as low as 0.6
inch.
1PA IV - 6
-------
Reductions in the magnitude of the down drag force require that the
bond between the soil and the standplpe be reduced. This can be
accomplished by using a 'lubricant' between the two materials or by
Isolating the standplpe from the waste as shown on Figure 4.6. Lubricants
used to reduce down-drag forces may be actual grease, a bituminous coating,
or a synthetic membrane. While the low coefficient of friction between
soils and most membranes causes slope related stability problems, here this
poor bond can be used advantageously. The Influence of lubricants on down-
drag forces calculated is shown in Example 4.4. This example assume that
the use of a bituminous coating can lead to a six fold reduction in
downdrag forces. Vesic(1977) reported reduction factors ranging from 6 to
15 based on measured field data in clays and silts.
Standpipe
^Operational Cover
Wsss,,,,,,,.
2% Minimum.*.
mMS&SSS&Si®
Ami
mm
jZigsk
wmm
Figure 4.6 Isolated Standpipe - Details
FML Strains Due to Down-Drag Forces
Down-drag forces in the standpipe are transmitted to its base and can
generate high, , stress concentrations In the primary LCR and FML and
possibly bearing capacity failure of the underlying soils . The foundation
placed beneath the standplpe must distribute this force over the primary
LCR without causing a high stress concentration at the edge of the
foundation pad that could cause a puncture-type failure of the membrane.
The foundation system shown on Figure 4.5 incorporates a steel plate
beneath the concrete pad to allow a transition and avoid such stress
concentrations. Care must be taken to avoid making the plate overly rigid
and the FML must be protected from its edges.
EPA IV - 7
-------
The FML beneath the standplpe will have to conform to the vertical
displacements of the standpipe foundation. These displacements are
influenced by the relative stiffness of the foundation to the stiffness of
the underlying clay subgrade. Additionally, the displacements result from
both elastic deformations and consolidation of the underlying clay. The
amplitude of elastic displacements are given by
Pa
Delast - ( 1 - V2) K Eq(4.1)
E
where P is the average contact pressure of the foundation, a is the
foundation radius, E is the subgrade modulus, y is Poisson's ratio for the
subgrade, and K is a variable that depends upon the stiffness of the
foundation. Values of K for rigid and flexible foundations are shown on
Figure 4.7a. The consolidation Induced settlement of the foundation must be
added to the above elastic value. It is influenced by the distribution of
vertical contact stresses acting on the base of the foundation. This
distribution is Influenced by the stiffness of the foundation as shown on
Figure 4.7b. For the flexible foundation, the consolidation settlements
will be similiar in distribution to the elastic deformations of a flexible
foundation but typically larger in magnitude, A rigid foundation will have
consolidation settlements similiar to the elastic settlements but again
typically larger.
Two methods can be used for determining the maximum strain in the FML
due to the standpipe induced vertical settlements. The first method makes
the conservative assumption that no slippage occurs between the FML and the
bottom of the foundation, such that the maximum strain In the FML will
occur at the edge of the foundation. The strain in the FML is then
calculated from the change in length of the Interface surface. This is
appropriate for flexible foundations. The second method assumes that the
entire strain in the FML due to the vertical deflection of the foundation
occurs at the edge of the plate. This assumption produces an apparent
strain an order of magnitude larger than the first method and is
appropriate only for rigid foundations. Both methods for estimating strain
are shown on Figure 4.7c and are demonstrated in Example 4.5. Evaluating
foundation stiffness is left to the designer but guidelines for this
evaluation are available (Borowicka,1936).
Bearing capacity failure of the underlying soils can be verified using
conventional geotechnical procedures for a circular foundation, see NAVFAC
DM7.2.
Designs for smaller facilities and surface impoundments frequently run
the standpipes up the sideslopes. Both the primary and secondary standplpes
can be placed up the sideslopes as shown on Figure 4.8. The use of a
synthetic LCR forces the standpipes to disrupt the profile of the FML.
MONITOR for SECONDARY LCR
The secondary LCR acts as a witness drain to verify the integrity of
the primary FML. The monitoring system for the secondary LCR must allow
monitoring, sampling, and the removal of leachate if required. During
construction of the facility, the secondary LCR removes surface water from
within the cell. This water must be removed by the monitor system. Thus the
EPA IV - 8
-------
£
o
edge
1.0
1.0
c
o
u
2.0
t r
t r
l 22—
Rigid Foundation
A) ELASTIC SETTLEMENT CONSTANT
r/a
1—
Elastic Subgrade
Clay Subgrade
Sand Subgrade
. (after Terzaghi and Peck)
B) DISTRIBUTION OF CONTACT PRESSURES
€ - i
€ =
7Xt
Ae
-7^W7T
Method 1
Method 2
C) CALCULATION OF FML STRAIN
Figure 4.7 Standplpe Induced Strain in FML
EPA IV - 9
-------
Primary ICR
Side Slope Riser
geotextlle
geonet •
geotextlle
OPERATIONAL COVER
SAND
COMPACTED ClAYp
' Secondary ICR
Side Slope Riser
Figure 4.8 Sidewall Standpipe - Detail
monitor system for the secondary LGR must be capable of more than detection
of de minimis quantities of water. At the same time an overly large
capacity in this system could lead to a significant lag time in detecting
leaks within the primary FML. A vertical standpipe cannot be readily used
for this purpose since it would have to penetrate the primary FML. While It
is possible to design a secure penetration of the FML, see Section VI, good
design practice would require the penetration only as a last resort.
To avoid penetration of the primary FML, the monitor system for below-
grade cells must lay within the secondary LCR system and exit the cell by
following the slope of the side walls. The minimum pipe diameter is
controlled by that required for the monitoring pump and the flow required.
Typically a 8 to 10-inch HDPE pipe is used. Generally the secondary LCR
must be capable of removing fluids at the same rate as the primary LCR, but
the capacity will be obtained using many smaller monitor pipes to replace
the large standplpes. Cells using a synthetic secondary LCR will allow only
a minimum pipe diameter monitor to be used without providing trenches for
the pipe. A typical monitoring system for the secondary LCR system in a
below ground cell is shown In Figure 4.9a. The monitoring pipe must pass
through the primary FML at some point. In the system shown, the penetration
is made at the top of the cell to be above potential leachate. Failure of
the seal between the primary FML and the monitor tube at this location will
not allow leachate to enter the secondary LCR system. It should be noted
that a minimum side slope will make it difficult to place or remove pumps
in such monitor pipes.
Monitoring systems for the secondary LCR system in above-grade cells
can exit the system horizontally without penetrating the primary FML and
yet be accessable for monitoring. Such a system is shown on Figure 4.9b. In
most of these systems the pump may be placed within a sump that Is external
to the cell. Drainage of leachate into the sump Is by gravity flow which
provides a passive monitoring system for leachate generation. Anti-seep
EPA IV - 10
-------
^ WASTE
SECONDARY ICR STANDPIPE
A) SECONDARY LCR MONITOR - BELOW GRADE CELL
WASTE
//
SECONDARY LCR MONITOR
Anti-Seep Collars
B) SECONOARY LCR MONITOR - ABOVE GRADE CELL
Figure 4.9 Standpipes for Secondary LCR System
EPA IV - 11
-------
collars are typically used on such drainage pipes to prevent the piping of
liquid along the outer surface of the pipe. Such collars are typically
sized to add at least 10$ to the flow length required for such piping. The
use of anti-seep collars is currently the subject of concern in small dams
due to past problems in obtaining adequate soil compaction around such
collars. Many earth dams are currently being constructed without anti-seep
collars on embedded pipes. If anti-seep collars are used, then adequate
field CQA should be provided to ensure proper soil compaction adjacent to
the collar.
REFERENCES - SECTION IV
Barenberg, E.J., et al, (1975), "Evaluation of Soil-Aggregate Systems with
Mirafi Fabric," VIL-ENG-75-2020, University of Illinois, Urbana-Champaign.
Borowicka, H., (1936), "Influence of Rigidity of a Circular Foundation Slab
on the Distribution of Pressures Over the Contact Surface," Proc. First
International Conf. Soil Mechanics and Foundation Engineering, Cambridge,
Mass.
EPA, (1985), Minimum Technology Guidance on Double Liner Systems for
Landfills and Surface Impoundments - Design, Construction, and Operation,
2nd Version, U.S. Environmental Protection Agency, May 24.
Giroud, J.P. and L. Noiray, (1981), "Design of Geotextile Reinforced
Unpaved Road, " J.Geotech. Eng. Div., ASCE, Vol. 107, No. GT9, Sept.
Koerner, R.M., et al, (1986), "Puncture and Impact Resistance of
Geotextiles," III Int. Conf. of Geotextiles, Vienna, Austria, April.
Murphy, W.L. and P.A. Gilbert, (1987), Guidance Manual for Prediction and
Mitigation of Settlement Damage to Covers of Hazardous Waste Landfills
(DRAFT), Prepared for Hazardous Waste Engineering Research Laboratory, U.S.
Environmental Protection Agency, Cincinnati, OH.
NAVFAC, (1982;), Foundations and Earth Structures, Naval Facilities
Engineering Command, Department of the Navy, May.
Terzaghi, K. and R.B. Peck, (1967), Soil Mechanics in Engineering
Practice, John Wiley & Sons, New York.
Vesic, A.S., (1977), "Design of Pile Foundations," National Cooperative
Highway Research Program, Synthesis of Highway Practice, Synthesis 42,
Transportation Research Board, Washington, D.C.
EPA IV - 12
-------
Cell Component:
Consideration: -5UP|^ "VtHiFfTHAT RamP SJa-BAfE >¦»
5TA6L6 Jup£« LoaD.
Required Material Properties
Range
Test
Standard
S«<--LCR Au^lE. , S^
San. - PmL F*atcrww Au<^ic, 5 rni
Lit? - FViL pRi^Tia] \kj^L,£, ^
Zo-t$'
14 - 2t'
1 »~
5wEa£S
Astm f3«p»*£o
Dull M1G MMnm
Analysis Procedure:
(0E7fcrtu6 Paivuc^ Foncfj
ULs» wei^Mrof roapway „
LI** WtlCjHToP VffWiCLt ^
(^* M8MU16 WAKu<; PoRtfE. iC.-iVi,
(z) pe^iue. K e-ti^riMCj Fgg«;6t>
Fr I6TMU (9 er ^aduiav
« ( Uv4 UD * ^ * T^w SM1|J
Wm£«6 14-fBE miuimUm FlZ' LtM^TM
kl«£*6 £M1U r»THt MIUIMUM lurturMt MJHtjioM
(3") Pfcp-Itafc Pe.»^iu t?A,TiQ;D^
. $e.*i9Vug Fauces.
O^iviu^ foeiaE.4
r» + r.
DRr r& Co***.' -w/rO
Design Ratio:
W>Ttt ^Tfc.T>*
2.0 With PtUAMI^ l«*D»
References:
Example:
<^"ive.u'.
" E*r
Sofff
o *
-pAuilge. en iTtaiA
THitfUuew £4" |J« 8"
-' 5<*" Ifee «r
(i"> Pemue. pg'Vug
LleiY * iS««i8*At ""I30* Tot KiP
UlyViMi^ie Wci^Mr-' ^yrou r iig kip
Fg* HAkiU^ Fi|?KiP» ¦?'5KiP
(O ParmB ^e.-w«r>ut^
'2°
C,,M-
/^Pgfiue Pe.->ic;kJ [?£
i-ro
r-)l"7 ¦ .-1 Ilof\
P^Ticr*a ^mto-) 4
iTo.q
*46
• = l.n
^ESOMMtWP PlACuJcj -small LA.v£n Op Sa,uO ©ETWEElu
Let? au» TmL -n, lutq Fai^TiOkJ «KkJC,L£ SM1KJ
Example No. 4.
-------
Cell Component: pKMP
Consideration:£>5AiHM5S.•' v£*,fy that hamp^iu. u>4wty,
Required Material Properties
Range
Test
Standard
I M-PtMJt FLOUJ 4»P l-£P | ^
" pE*MCA6»Mr» ,K ,oP Sd06AS6
Ml NIC HMnn
* 1*
to cn/sec
-f -4 i
Id- id e»f*c
7«m<3M'MxiTt
(eUMEIJiUT Y
Asrvi oifi.17
A>tm oa^M
Analysis Procedure:
(A £«TiM».m PIoki l?x-n= q?
<5* c -T Au*. Cft* fee«)
M««i E»T1M>,T8 flttM ^ABaoTV of leg » g.APMAV Q
SvJRr^es
Water
act
'ID * as
act "W» witd
uMS«.e C?r.a0s' A A»a«£-A 1 v*^bapi6mt>iy«i»iT.r3t«»t
<5ura ' W kl»Mic>Tvt of lck
(«>) ^AUatATS. Pe-XM gAr.o|C>K
Fi-oto ^APitiTY
PR=
Flow f?AT£
Design Ratio:
'-5
References:
Example:
:
•Ramp *. Miotm * IS _F7» io"Sm*^£j: ' 3£&*ioS Ft"*/*&g
CO EsTivi*tTi. Fuxo ff/»cre. 1 MMlUe>: CAPACITY U.IITH >U SOAOkJAV I S
llrtu f riCIEUT % T*M6REF0R£ ProviDB
Fcovu cMAUhjC t.
Example No. 4.2.
-------
Cell Component
Consideration: MH££L LoA.Q,mq - vett'PV THAvT lOHt&L. LoA-DlUCj UIILL.
KJOT F~ML.
Required Material Properties
Range
Test
Standard
FML t-wive 'Str6w^TH C>
ia.x Sj eev->£ F*Ri^.T!«tJ ^Wic^le
2.S - 4o*
mPR EhIol
Asim Proposed
Oraft MIG Minimum
Analysis Procedure:
(O Perimb FiftLO
A«u HiHCj 2". | Pi-iTR'Si/Twu *3u>Pt
«• ~ v xr el i
c c Lc^dvJ
WH6R£ C^^OAOWAV -rviicc»*
Pcfu-iC Pfc^iqM RaTio PR
PR ?
f«MD 6rkEuj^
"55 T»NJ PKij ujJ 4 WH££L^> =~ 27-5 *lP 1Jm££l L«o
~ £jn»juc> i»UT^tr P(?64»J^6 ¦» 5 6 PVl
' RoAOkl^Y
* Tm"ic1oJ£66-> D»2'-o"
PEF'ME. F'&tP &KJTACT $rp£is , Cjc.
r / v*
trrEtT've R^oiu^* Soo^ Tf*55j w 12-k1
Q* TU«*-*U£v* a 2»' « 24"
g£.«. r,x. ¦]
L (|2.t»+24^
G^'. G>.5
Mfcvsuae FML <^>mP«e->5iv£ "$TH6m«,th , ^Peu
? D
pt?
G"c
So
US
"7.-7
Example No. 4.5
-------
Cell Component: St*udp,p6.
Consideration) ^oUJM ~ '• poieu-nAL r****•> «k*nw«;
«U STAMDPiPe A«C» tfoMPMt £o/k11U^ foB. REOjc-pioto of
THvje. Fogies
Required Material Properties
Range
Test
Standard
©F ^LAV Pi *-1-
Qraft WIG Minimum
A«J*M PlprostD
Analysis Procedure:
(0 StA.UDPiP6 PaUUpgA^ UIITWouT
H-
65
PAAq
D ¦£
ct
rr
i
i
;
L
t
>
\
i
(UAvFAtf DM7,2-)
00TA.IU dl FROM A»
D»rr)
CO StA-IUPPiPE PojJMPHAq UlTHoUT i^ToAvTIMq
d^/C'O.&b
.SSxSoo' 4So p,F
^DRAii* ^>8o* T * ^ * 6>5
- 5"^5ooo I b
- 555 IOP6
RATIO OF
C*/C
VERAGE CURVE FOR
CONCRETE Pll£S
AVERAGE
ALU PILES
VERY SOFT
rlEOIUM STIFF
y
VERY STIFF
500 1000 1500 2000 2300 3000
COHESION C.PSF
(2-) SrAMpPiPE Poj-Jij Dg«.q ki iTh ^ToAXlkiq
^o8AS- *55/6,
' ^Z.5 Kip»
Example No. 4.4
-------
Cell Component: Stumpp»pe
Consideration: PuMCTti"E °r Fhl
StrnEMtMT ar *TMJOPiPt klllt- MoT r*U*6 FAILURE
oFUwotttLviut; UR.
Required Material Properties
Range
Test
Standard
• ,c
* Pmct'u'i Ra1>0^
• C»|P*£»»U TmoEv , Cc
FML
* FML/S.
¦fMt
Otill MS Minimum
FmeTiou AmcjlE ,
STIMjw- AT-yifilO
,5-5 TiP
-.45
4o.1>
10 -%o°
[O-tOfo
TRiaxiai,
M
piflgcr
4«tm Pfe>ft>seo
ASTm2435
A-sTM fVofostO
Analysis Procedure:
(i)C*.ixuu.t£ £tA*ric 'Se.TrtfcMguT ^^mPquemt t Ael
P* *.yStt*.«s£ 4wTk't pREiUlAg
p <*.» Oykp.OS
"fh 6»v* ) K EQ(4i1
w
>
w
<
I
E.- sila<^nA.o& Mfaouim - Uooc.
BiCTlo
k- (Toy-i-tAUT -see p.<{- 4.1
£»u
* ("TT^n
M" TMl«KKI6SS OF LlkloeOMMC; CLAY lAVfcB
!?»» IKIiTi^U VaiD OATlo oP «A-f
4ft* A P
<-£« ^»»"F8E»4ieM IudCK
r .. , / - . , > £MA.mc£ iu UoRMki flUts*
(3> Estimate Stpa.im - Mlthoo I C Rq 4.7>/-» « I .6
• Sumu, £ * (S'-JO/A MMMe 9.' Zo-
fc")EynMnT6 SritAiu- He-rnao 2. CPi^4.1<")
S»we ftn trrectivt fML uw«;in, 9e (£„ 3.n)
StbaiUj £* / 2J?e
(5> <£"«U.*dlA-T6 Ps»iqu l?»TiaS
DR
Il
ti
te
£ "<1.0
c
~WW
[~_J-—»J
/a
%»W
Design Ratio
^^>2.0
References:
* Stl Ski HccUaux1! Tints
Example:
•StMjdPiPE. PtB ExAMPIE. 4.4
•Wtit^Te Ei-A'srie. Se-rrLeMeuT <2»mR»j£mT 4c i
A,
£u
3.2.7 fl-3Sl , , _ K
|o6o l^>— »OS ,UCT4
P'*M-s/ty*?>1*) «3,Owp
E» irOOt 1,8 KS|T » logo K«p
K* L& ©irnjrea
^>ut»LipAT,»u SE-m-t.HEt-iT gTotviPougufj ^
A^- 8*12
ft-
= O. 2 ^ n-iiTH
C^E»Tix«
Pf, f iwajl ^£A0MO£M
- ^6* &a 4 ito* rsF
Pc» iuiriA.1. (We«
* 4o*jfo- 4®ooP
-------
SECTION V
DESIGN OF COMPONENTS ABOVE CELL
An important aspect of the liquids management program strategy behind
EPA's statutory design is the minimization of leachate generation from the
infiltration of surface water into the cell. To prevent this infiltration,
the landfill must be sealedvor capped after the cell is filled. The
regulatory requirements (40 CFR 264.310) specify that final cover be
designed and constructed to:
(1) Provide long-term minimization of migration of liquids
through the closed , landf ill..
(2) Function with minimum maintenance.
(3) Promote drainage and minimize erosion or abrasion of the
cover.
(4) Accommodate settling and subsidence so that the cover's
integrity Is maintained.
(5) Have a permeability less than or equal to the permeability of
any bottom liner system or natural subsoils, present.
Recommended guidance has been developed for meeting these five regulatory
requirements (EPA, 1982). Although alternative designs could also meet the
five regulatory requirements, the ability of alternative designs would
have to be demonstrated with more detail than the recommended design.
RCRA guidance (EPA,1986) for covers at uncontrolled hazardous waste
sites specifies that the cover should consist of the following as minimum:
protective top cover, middle drainage layer, and low permeability bottom
layer consisting of an optional 20 mil synthetic upper component and a 2
ft. clay layer lower component. Some states have slightly different cell
cap profiles based on local conditions. For example, New York currently
requires a cover system that includes, from the waste outward, a final
operations cover (12 in minimum), three feet of compacted clay, a 40 mil
HDPE geomembrane, 18-lnches of vegetative cover, and 6-inches of topsoll.
The drainage layer is not included and is felt to pose a hazard to the
vegetative cover. Commentary In the Second MTG document on Double Liners
systems Indicates that EPA does not require that facilities using double
FMLs to also use two flexible membrane caps (FMC).
The design cross-section of the minimum RCRA cover Is shown on Figure
1.4. The upper layer of the cell cover system is a protective top cover
composed of vegetative and topsoil components. The protective top cover is
designed and constructed to prevent erosion and abrasion of the underlying
cover components, while functioning with minimum maintenance. A vegetative
layer forms the upper surface of the protective surface layer and functions
to reduce percolation into the cover system, shield the topsoil from
raindrop impact, stabilize the soil against the erosive and abrasive forces
of wind and water, bind and anchor the soil to form a stable mass, increase
EPA V - 1
-------
evaporation rates, and enhance the aesthetics of the site.
Selection of the vegetation species is an important consideration in
design of the cover and,is dependent upon factors-such as climate, site
characteristics, and soil properties. The vegetation must be both
persistent and not have roots that might penetrate beyond the upper
protective layer. References which provide discussions on available plants
and site selection criteria include EPA.(1979),. EPA (1983), and Lee, et al.
(1985). In some regions of the country, such as arid and semi-arid
climates, establishment of a vegetative cover is difficult or Impossible.
In these areas, a rock or gravel mulch layer of approximately 5 to 10
centimeters in thickness may be substituted for the vegetation
(Cline,1979).
The topsoil forming the protective top cover must be selected and
constructed to support the vegetation by allowing sufficient surface water
to infiltrate into the topsoil and by retaining enough plant-available
water to sustain plant growth through drought periods. Particle size
distribution, structure, and organic matter; content influence the quantity
of available water a given soil can supply and should be considered in
selecting the topsoil material. The mimlmum recommended topsoil thickness
is 60 centimeters (24 inches); however, some geographic regions may.require
a thicker layer to provide adequate plant available water. In general,
medium-textured soils, ^ such as loam soils, have the best overall
characteristics for seed germination and plant root system development.
The cell cover system Includes a drainage layer located below the
protective surface layer and immediately above the membrane component of
the hydraulic barrier. This drainage layer must intercept and drain
percolating water -to prevent it from standing on the hydraulic barrier.
The percolating water follows a downward migration path until the hydraulic
barrier layer is reached; i,t then flows horizontally under the force of
gravity , through the drainage medium to an outlet at.the perimeter of the
cover. A minimum drainage layer thickness of 30 cm (12 in) and a minimum
hydraulic conductivity of lxlO-2 cm/sec are recommended. The bottom slope
of the drainage media must be more than 2< iafter allowance for settlement.
The layer may be constructed of .granular drainage material classified by
the Unified Soil Classification System (USCS) as SP (poorly graded sand) or
synthetic drainage systems, such as geonets and geocomposltes.
The hydraulic barrier layer of the final cover system consists of two
components: 1) a compacted soil component haying a minimum field
hydraulic conductivity of lxl0~7 cm/sec; overlain by 2) a flexible membrane
cap (FMC). The FMC is placed in direct contact with the clay soil and a
compression seal is created by the overburden; thus the two components form
a composite barrier to the flow of percolating liquid. The recommended
minimum thicknesses of the two components are 60 centimeters (24 inches)
for the compacted soil and 20 mils (0.5 millimeters) for the FMC. The
actual thicknesses are based upon characteristics of the site, soil,
synthetic material, and expected external forces, such as settlement and
overburden pressures. Construction of the compacted soil component and
installation of the FMC are analogous to the practices used in liner
construction, discussed in Section III. Techniques similar to these, along
with appropriate CQA procedures,,should be employed In construction of the
hydraulic barrier. Additional recommendations on barrier design and
EPA V - 2
-------
construction are given in EPA (1986b), and information on development of a
CQA program is given by EPA (1986a).
The FMC component of the hydraulic barrier is placed directly above
the compacted soil component and immediately below the drainage layer. The
compacted soil will, therefore, act as a buffer and foundation for the FMC,
and the drainage layer will provide protection from overlying materials.
The drainage layer should be inspected for materials which may damage or
otherwise impair the synthetic FMC. Care must be taken to provide adequate
protection against damage to the FMC by equipment or personnel during
placement of the drainage layer. When possible, the FMC must be placed
wholly beneath the maxiumum frost depth at the facility site. Appropriate
CQA procedures, as discussed in Section VI, should also be maintained to
ensure the integrity of the FMC installation.
In a modern hazardous waste landfill, the compacted clay layer is
constructed upon a compacted layer of protective soil that provides a
uniform foundation or bench for construction of the cap. A gas collection
system is not typically needed in a hazardous waste landfill due to the
solidification of all waste and the absence of organic matter. However, if
required, the collection system is placed either above or beneath this
compacted clay layer. The gas collection system must be designed to both
handle the estimated volume of gas generated and to remain serviceable
under the projected long term settlement of the cap.
The design geometry of the cap is controlled by the need to move
surface waters away from the cell even after long term settlements have
occurred. Because the random bulk of the contained waste prevents good
compaction, significant settlements of the cap are possible. Poorly
compacted cells and those containing free sludge wastes require
stabilization of the waste prior to capping. Excessive settlements of the
waste can produce localized depressions that allow surface water to pond
and remain in contact with the FMC for a prolonged period of time.
Additionally, this settlement can produce significant strains within the
cap that threaten the physical integrity of the components that form the
cap. Initial design contours of the cap must therefore be sufficient to
ensure that positive drainage remains through the entire life of the cell,
but not so large that surface erosion is fostered on the initial profile.
The RCRA cap shown on Figure 1.4 is more frequently required to
interface with cell systems that use synthetic LCR systems on the
sidewalls.: A RCRA cap utilizing synthetic LCR-systems, is shown on Figure
5.1a. In both systems it is important that surface water be prevented from
entering either the waste or the LCR systems. This requires that the clay
component of the cap hydraulic barrier must form a compression seal with
the primary FML and that the LCR systems be Isolated from the cap. To
provide for this seal, the primary LCR will not be able to be anchored in
common with the primary FML or it may be necessary to remove that portion
of it that lies between the primary FML and the clay layer of the cap's
hydraulic barrier prior to placement of the clay layer. For the cell shown
on Figure 5.1a, the synthetic primary LCR was cut free at its anchorage
trench and folded over the protective soil cover. This would obviously
occur after the waste is in-place; at which time the anchor trench is not
serving a function. The clay layer, of the cap would then be in direct
contact with the primary FML. The FMC is placed in a trench at the
EPA V - 3
-------
ComPr«slon Seal
•# £
*
Cover Soil
swot
Compacted Clay
//Asy/#y/*- AWMT/.
Operational Cover
's&FMi
*»cZy,LTh°r T'*»c»
f"fusion We|
-------
perimeter of the cap to guard against erosional undercutting of the cap.
An alternative cap design is shown in Figure 5.1b which provides
welded sealing of the secondary LCR system and of the FMC to the primary
LCR. This 'total containment' design would be appropriate at sites having
high water tables or suffering from frequent flooding. Such sites are
obviously marginal but may be in existence under interim permit status. The
seaming of the FMC to the cap Is not deslreable If settlements within the
waste are anticipated. Such settlements could lead to failure of the seams
and tearing of the primary FML. For this reason, the alternate design is
not recommended.
A double drainage layer-FMC system may be appropriate for facilities
that are projected to experience significant settlements of the cap or be
exposed to severe environmental forces. The double drainage layer-FMC
profile would be the same as that shown on Figure 5.1a with two layers of
FMC and SWCR. The details for such a cap are very tedious to design and
even more so to construct. Yet, they are absolutely essential to the
proper, long-term performance of the waste facility.
SURFACE WATER COLLECTION/REMOVAL
The Surface Water Collection/Removal (SWCR) system is immediately
above the FMC and functions to drain surface waters away from the FMC and
to provide a protective bedding material for the FMC. Current MTG
recommendations provide for the use of a synthetic SWCR system if it can be
demonstrated that it will provide protection equivalent to that provided by
the conventional use of a 12-inch layer of sand. To demonstrate that the
synthetic SWCR can be used as a bedding material, it must be shown that the
SWCR will not exhibit brittle failure under the stresses from overburden
and equipment used for construction. The SWCR system must be designed so
that It has hydraulic properties sufficient to quickly remove collected
surface water, filtration characteristics that prevent clogging of the
drain due to infiltration of the soil, and adequate strength to prevent
damage to the system during installation or from service loads. On double
FMC caps the witness drain placed between the FMCs is designed in an
identical manner except filtration characteristics are not important.
SWCR Transmlssivlty
A geosynthetic system used to replace the granular bedding layer on
top of the FMC must provide sufficient planar flow capacity to prevent
surface water from accumulating and standing on the FMC. Unlike the LCR
systems, no maximum head is currently specified by statute or MTG criteria.
In that the FMC must have a permeability equal to or less than the thickest
FML, it would seem reasonable to design the FMC for a maximum tolerable
surface water head of 1 foot. The design amount of water entering the
system would therefore roughly equal the amount of leachate passing through
the liner system. Using properties suggested in the RCRA guidance, a 12
inch layer with a saturated hydraulic conductivity of not less than 10~3
cm/sec, the minimum transmlssivlty of the SWCR layer is 3 x 10"^ m2/s.
The transmlssivlty of a geosynthetic is influenced by the flow
gradient, the normal load on the system, and the long-term creep
EPA V - 5
-------
.001
.0001
.00001
— —-Q
.75 1.00 1.25
HYDRAULIC GRADIENT
NORMAL STRESS ,PSF
O 200
• 2000
a sooo
¦ 10000
A 15000
~ 20000
Figure 6.2 Transmissivity Data for a Needled Nonwoven Geotextlle
compressibility characteristics of the geosynthetic. These properties must
be evaluated in the laboratory. Typical laboratory curves for the short-
term performance of a geosynthetic drain are shown on Figure 5.2 for
hydraulic gradients less than 1.0. Example 5.1 presents the design
calculations used to evaluate the planar flow capacity of a given
geosynthetic drainage system. The design is based on a maximum head acting
on the SWCR of 1 foot. Because of the small normal stress, the long-term
creep of materials used for the surface water collection system rarely
influences the design. Long-term performance of the SWCR system is
evaluated using the same procedure as previously shown for LCR systems in
Example 3.3.
SWCR Filtration
The SWCR system must incorporate a properly designed filter fabric
into its surface that Is adjacent to the cover soil. This fabric must be
selected to allow the flow of water, yet prevent the movement of soil fines
into the core of the SWRC. Filter criteria are based on grain size
empirical relationships and the gradient-ratio test discussed in Section
III and are demonstrated in Examples 3.5 and 3.6. These criteria are also
applicable to the selection of a filter material for the SWCR system. An
alternate laboratory filtration test proposed by Koerner and Ko (1982) is
also shown in Example 3.5 for evaluating the clogging potential of the
SWCR. This test places a sample of the cover soil against the SWCR system
and monitors the flow of water through the system over time. Qualification
of the SWCR in this test is based on both the flow reaching a steady-state
condition and the flow rate being sufficient.
EPA V - 6
-------
SWCR Strength
The SWCR system must be analyzed to ensure that shear failures do not
occur at the surface or interior boundaries and that strains caused by
settlement or low shear capacity will not lead to rupture of the system.
The slope of the cover will range from the mlnlmlm of 2 degrees required
for the gas collection system to a maximum of 3:1 (18.4 degrees) that is
the limit for mechanized mowing of a slope. Typical cover slopes will be in
the range of 5 to 8 degrees. Cover soil placed on the SWCR system will want
to slide down the slope and Its stability must be verified. The friction
angle between the cover soil and the surface of the SWCR should be
evaluated in the laboratory under saturated conditions. This angle is
influenced by the physical properties of the cover soil and the surface
geotextile of the SWCR system. The extreme design condition will occur when
the cover soil is saturated and the SWCR system has the full design head
acting on it. Example 5.2 demonstrates the calculations used to establish
the stability of the cover soil.
The shear stresses transferred into the SWCR by the cover soil must
not exceed the shear strength of the SWCR itself. The shear calculations
presented in Example 5.2 model the transfer of shear forces to the surface
of the SWCR. Typically, the friction angle between the SWCR and the FMC is
significantly less than that between the cover soil and the SWCR. Thus it
is possible to transfer more shear stress Into the SWCR that can be
transferred from the SWCR to the FMC. The difference must be taken by the
SWCR in the form of tensile stresses. Example 5.3 demonstrates the
calculation of the magnitude of tensile force that can be transferred into
the SWCR. Note that the tensile strength of many SWCR systems has not been
formalized to date. These tension forces can be reduced by lowering the
slope, placing a thinner layer of cover soli, or by increasing the
frlctional bond between the FMC and the SWCR. This process of evaluating
shear stresses at each layer interface must be continued through the entire
profile of the cap.
Significant strains can be generated in the SWCR if settlement of the
waste occurs. However, the straining of the SWCR in a settlement depression
will not lead to a catastrophic failure of the cap. Water will continue to
flow around or through the settlement zone, albeit at smaller rates.
Evaluation of settlement-Induced strains Is more critical for the FMC
systems. This strain evaluation procedure is given on Figure 3.5 and is the
same for both FMC and the SWCR. The calculation of settlement-induced
strains Is demonstrated in Example 5.4.
FLEXIBLE MEMBRANE CAP
The FMC functions in the same manner as an FML, but under different
design conditions. The most significant design differences between the FMC
and a FML are as follows:
1) FMC systems will be exposed to surface water
infiltration so that chemical compatibility is not of
concern.
EPA V - 7
-------
2) FMC systems may lie within the frost zone in northern
regions and thus may be exposed to more significant
temperature ranges.
3) Surface settlement may lead to large strains in an FMC
during its service life.
4) FMCs typically experience their largest physical
strain during post-closure when the cap is in place
and not during construction or operation.
5) FMC systems must be designed to provide for venting of
gases generated within the cell and are therefore
subject to more designed penetrations.
6) The simplified geometry of the FMC results in an
easier installation than that required for FML systems.
7) Because of their shallow depth, FMC systems are more
prone to damage from burrowing rodents and roots and
other longrterm problems discussed in Section VII.
Thus while both the FMC and FML systems perform identical functions, the
design criteria for selection of the two membrane systems and details are
significantly different. The FMC is impacted by the FML design only by the
MTG requirement that the permeability of the FMC must be less than or equal
to that of the thicker FML or the underlying subgrade. In some states
having a authorized RCRA program, this has been interpreted to mean that
the FMC is the same material and thickness as the primary FML. This is not
the intent of the guidance and is not assumed in this document (Landreth,
1987).
The selection of minimum FML thickness and the design of LCR systems
in the liners were controlled by the statutory requirement to maintain less
than a 12-inch head of leachate acting on the FML with no more than de
minimis leakage through the FML. While no direct statutory or MTG
requirement exists for design of the cap, the 12-inch head is assumed to be
applicable to the design of cap membranes and drainage features. De Minimis
flow through the FMC is not applicable.
FMC Permeability
The permeability of most common polymeric membranes is sufficiently
low so that it cannot be evaluated using conventional permeability testing
procedures. The flow rates through conventional fixed or falling-head
permeameters would be so small that either evaporation would destroy the
leakage or extremely high gradients would be required to produce measurable
flows; A psuedo permeability of these materials can, however, be measured
using ,a water vapor transmission test (WVT), ASTM E96. The WVT test
requires the use of a controlled temperature and humidity test chamber.
Details of this test are presented in Section III and In the appendix.
Under draft MTG (EPA, 1986), the lower permeability layer of the cap
must provide a permeability less than that of either of the liners
underlying the cell. This document is developed assuming that the FMC is
EPA V - 8
-------
not necessarily of the same polymer as the FML. No attempt is made to
compare the psuedo permeabilities of the membranes based on WVT data.
Chemical compatibility requirements are assumed to be Inapplicable to the
selection of an FMC polymer. No data exists which shows that the FMC will
be exposed to vapors other than carbon dioxide or methane arising from the
underlying hazardous waste. Indeed, with a properly installed gas
collection system, the FMC should not be exposed to vapors from the waste.
FMC Stresses
Stresses introduced to the membrane during its service life are caused
by differential settlements of the waste below the cap. These differential
settlements are caused by non-uniform settlements of individual cells
within the facility. The amount of strain generated within the membrane is
influenced by the breadth and depth of the settlement feature. Figure 3.5
presents the average strain generated within the membrane using simple
plane strain circular and triangular settlement models. These simple models
were presented by Knlpschleld (1985) to represent settlement due to
Improperly backfilled pipe trenches or similar linear features. As the
width of the settlement feature becomes large, the average strain In the
FMC becomes quite small.
Settlement features in the cap are caused by settlement within the
underlying waste. These features will not necessarily be linear like that
generated by a pipeline trench. The average radial strain generated In a
spherical settlement feature Is the same as given in Figure 3.5 for the
plane strain mode. The transverse strains, those normal to the radial
strain, vary from zero at the surface to a strain equal to the radial
strain at the full settlement depth. The existence of significant biaxial
tensions in the FMC is important. Biaxial tension tests reported by Steffen
(1985) and Gluck (1985) show a dramatic reduction in the strain at failure
of HDPE subjected to biaxial tension. Stress-strain curves for HDPE, LDPE,
and PVC under uniaxial and biaxial tension are shown on Figure 5.3. The
uniaxial strain at rupture for HDPE is typically in excess of 600£. Under
biaxial tension, the strain at rupture has dropped to slightly more than
20£. Biaxial strain conditions and strains of 20$ are reasonable
expectations for FMCs experiencing significant settlement. The strain at
rupture for FMC components should be known and specified to avoid FMC
failure due to settlement. Design Example 5.4 demonstrates the calculations
required to verify the performance of the FMC given a known settlement
geometry. Estimating the amount of settlement for use in this procedure
remains the major uncertainty. Procedures for estimating settlement
geometry are reviewed by others (EPA, 1987).
That portion of the weight of the overlying soil carried by the FMC as
the settlement feature is generated can be shown to be quite small in
comparison to the total weight of the soil. The total vertical load being
carried by the FMC Is obtained by summing the vertical component of the FMC
stress acting at the edge of the settlement feature. Comparison of the
total vertical load on top of the FMC with that carried by the FMC clearly
show that the FMC Is not a major load carrying component. For circular
settlement features, the FMC will carry a greater, though still minor,
percentage of the overlying soil load. Thus, the most important load-
elongation feature for an FMC is not its modulus but rather its ability to
strain biaxially or under confinement without falling.
EPA V - 9
-------
4000
TO 3860 PSI AT 1180%
3000
KA
A.
X HOPE (Biaxial)
2000
rpf (Uniaxial)
PVOtBiaxial)
1000
(KEORNER.RICHARDSON—UNIAXIAL)
(STEFFEN—BIAXIAL)
CPE (Biaxial)
0
100
500
200
400
300
STRAIN, %
Figure 5.3 FML Stress-Strain Performance
In many facilities, it is common practice to weld the FMC to the
primary FML to provide total containment of the contained waste, recall
Figure 5.1b. This practice is not an MTG requirement and may lead to the
transfer of stress to the primary FML if excessive settlement of the waste
occurs near the edge of the cell. Such settlement would not be typical of a
controlled hazardous waste cell but could occur in cells containing
sanitary waste. Unless there is potential for the cell cap to be under
water during peak flooding, there is nothing gained, from seaming the FMC to
the primary FML.
FMC Seaming
Methods used to seam polymeric membranes depend upon the composition
of the membrane and the environment the membrane is placed in. For
hazardous waste disposal facilities, general practice is to avoid any
bonding method that will leave a residue of volitile organic solvents that
may eventually be confused with leachate. This consideration aside, the
common methods for seaming FMCs include adhesive or solvent bonding,
thermal bonding, extrusion or fusion.welding, vulcanization, and mechanical
methods. Typical seam configurations currently used are shown on Figure 3.6
and details of seaming techniques are presented in Section III of this
study. Some FMC seams have been developed that incorporate soil anchorage
into the seam. Figure 5.6 shows a seam of a reinforced membrane that
Incorporates both a sewn seam and soil anchorage (Phillips, 1986).
EPA V - 10
-------
FMC Survivability During Installation
The ability of an FMC to survive installation is dependent upon both
the physical properties of the FMC and the field conditions under which it
is placed. The sole design function of the FMC is to act as an impermeable
layer to prevent the migration of surface water Into the waste material. Of
greatest concern Is the accidental puncture or tearing of the FMC during
installation.. Construction related problems common during the Installation
of FMC systems include the following:
1) Subgrade preparation fails to remove large particles that
can penetrate the FMC or it leaves soft zones that lead to
large localized strains.
2) Placement of the surface water collection/removal system
atop the FMC leads to penetration of the FMC.
3) Field handling of excessively large field panels leads to
tears or excessive elongation of the FMC.
4) Installation practice leads to thermal or wind damage to the
The last installation problem relates more to fabrication practice and is
discussed in Section VI. Membrane survivability during construction can be
related to minimal membrane penetration and tear stress, and the use of
proper bedding material above and below. Detailed criteria for FML
survivability are discussed in Section III and are equally applicable to
FMC survivability.
Geomembrane
Geotextile
•(Sewn Seam
Anchor
(Phillips Fibers)
Figure 5.4 Seaming Composite Membrane
FMC
EPA V - 11
-------
Blotlc Barrier
In. some locations, a blotlc barrier may be advisable to reduce the
potential for Intrusion of animals (e.g., gophers, mice, etc.) or plant
roots which can disrupt the Integrity of the hydraulic barrier layer and
increase percolation of surface water through burrow tunnels or root
channels. Hakonson (1986) found a blotlc barrier of 60 centimeters (28
Inches) of 7.5 to 12-centlmeter cobblestone overlain by 30 centimeters (12
inches) of gravel was effective. The cobblestones were of sufficient mass
to deter burrowing animals and the large void spaces, which lacked water
and nutrients, acted as a barrier to plant root developments. Research is
not presently available on an optimum depth for a barrier layer; therefore,
the actual thickness of the biotic barrier should be based upon site
characteristics, including expected intruders, depth of plant roots, etc.
Cline (1979) also reported that the use of cobbles was effective in
limiting rodent penetration and also described the use of root toxins to
limit the penetration of plant roots.
Past research in West Germany, Rumberg (1985), Indicates that a
significant danger exists to membranes from burrowing below the facility.
Studies were performed with beavers and rodents to evaluate the
susceptibility of various membranes to damage from burrowing. Some
membranes such as soft PVC actually attracted the rodents and encouraged
damage. The best performance for an unprotected membrane was in the thicker
sheets of polyethylene. These rigid sheets are difficult for animals to
bite. This study led to the development of test procedures that use mice
(arvicola terrestrls) to predict the resistance of sheet to penetration.
Protective measures such as wire or glass mesh may offer a partial
solution.
GAS COLLECTION and VENTING
It is rarely necessary to design for control of gases when covering a
controlled hazardous waste site. Gases are evolved wherever decayable
(biodegradable) organic matter is buried; thus gas control is typically a
problem for sanitary but not hazardous waste landfills. Where municipal
and hazardous wastes are consigned at the same site, a gas problem is
likely. Where no decayable matter is buried, gas will probably not be a
problem. The following discussion of gas generation is intended to provide
a general review of the gas generation mechanism and not to imply that
dramatic quantities of gas are to be anticipated at controlled hazardous
waste facilities.
Within a few months of closure of a landfill containing organic
refuse, anaerobic decay conditions stabilize, and thereafter only two gases
are produced in appreciable quantity: methane (CH4, about 55 percent by
volume) and carbon dioxide (CO2. about 45 percent by volume). Trace
quantities of other gases may also be produced. The rate of waste gas
production decreases steadily, but some production may persist for many
years. In general, the methane gas being lighter than air Is the more
significant problem since it will Interface with the synthetic capping
system.
EPA V - 12
-------
The most serious problem from waste gases is the explosion hazard.
Methane (and some of the trace gases) Is combustible, and methane-air
mixtures are explosive over a certain range of composition (about 5 to 15
percent methane by volume). An explosion hazard develops when methane
migrates from a landfill and becomes mixed with air in a confined space.
Other actual or potential threats from waste gases include vegetation
distress, odor problems, property-value deterioration, physical disruption
of the cover, and toxic vapors. Vegetation kills are a demonstrated fact
at landfill covers. The exact damage mechanism maybe complex, Involving
oxygen starvation (asphyxiation), temperature Increase, plant toxicity,
etc.
Of more importance to the design of controlled hazardous waste
facilities, it appears that where toxic substances are buried in the
absence of decaying organic matter, the threat of their vapors reaching the
surface in dangerous quantities appears to be very small (EPA,1985). The
chief problem is the maintenance of the integrity of the cover. The rate
of migration of a vapor should be very much lower than that of a gas such
as methane or carbon dioxide because of the much higher equilibrium
pressure of the latter at any given* temperature. Therefore, it seems
logical to expect that migration of a vapor from beneath a soil cover would
rarely lead to a hazardous situation. The detection and measurement of
organic substances over waste sites has been a matter of recent research in
California (Karimi, 1983). Vapor diffusion through cover soils at
landfills is discussed in Farmer et al. (1980).
Gas-control systems make use of natural barriers when possible and of
constructed barriers such as trenches, membranes, wells, and vents.
Natural barriers to gas migration include moist, fine-grained soils and
saturated coarse-grained soils. Lateral methane migration is controlled at
a hazardous waste landfill boundary by the double FML side walls of the
cell. While the the quantity of gas generated within a hazardous waste fill
should be small, the presence of complete FML containment will maintain
anaerobic conditions throughout the waste and maximize the methane
production.
Gas withdrawn from a landfill is saturated with moisture which
condenses in the collection system. During collection, the gas undergoes an
expansion and temperature decline, and some water condenses. This moisture
must be removed from the header to prevent freezing or saturation of the
collector. The collected moisture fills the pore space of the venting
system and prevents the free passage of gases. Figure 5.5 details one
method of moisture drainage. The moisture is drained to a designed drainage
connection that allows for continual removal of the water. For a more
detailed discussion of gas control, the reader is referred to EPA (1982),
or Emcon (1980).
An additional factor that needs to be considered is the possible
fouling of gas drainage systems by the growth of a biomass of anaerobic
slimes (EPA 1986). This problem has occurred at gas drainage wells at
conventional municipal landfills. Such slimes will grow as coatings on
mineral particles. The larger the pore sizes in the gas drainage layer,
the longer it takes a buildup to block the pores completely. A discussion
of this and other biological growth considerations is given in Section VI.
EPA V - 13
-------
Water Overflow
Cas Flow
" Cas Well
CONDENSATE DRAIN TO COLLECTOR.
Cas Flow
Cas Well
CONDENSATE DRAIN TO WELL
MOISTURE CONTROL
Gas Flow
Water Flow
(after Rovers, et al)
Figure 5.5 Water Traps in Vapor Collector Systems
The gas collection system for a controlled hazardous waste facility
differs from that typically designed for a sanitary facility in that the
use of veils, pumps, etc. to accelerate the collection or generation of
gases is not advisable due to the possible presence of hazardous vapors and
EPA V - 14
-------
the possibility of surface water Intrusion through these collectors.
Additionally, very little data is available to aid the designer in
estimating the quantity of gas to be anticipated for a given waste
inventory within the cell. Mass-balance methods to estimate gas generation
rates have been proposed (EMCON, 1980); however, prior experience gained
from past cells at a given site remains the best source of data. In
addition to its collection function, the gas collection layer also provides
a stable working bench on which the closure cap can be constructed.
Vapor Transmisslvity
Gas and waste vapors rising from within the waste mass are Intercepted
by a gas collection layer placed between the clay component of the cap and
the waste itself. This gas collector layer must allow the gases to freely
flow to vent pipes that lead to the atmosphere and provide for drainage of
condensate that collects. A minimum slope of 2% is required to maintain the
gas flow, and slopes ranging from 2-556 are common. Kays (1977) recommends a
minimum 356 slope when gas collection is a major consideration. The minimum
2% slope must be maintained .even after the settlement of the waste that
will naturally accompany gas generation. Current MTG guidance (EPA, 1986)
recommends that the gas collection layer consist of a minimum of 30
centimeters (12-inch) of porous granular material simillar to that used In
the drainage layer. Drainage layers require a minimum hydraulic
conductivity of 2 x 10~2cm/sec or a transmisslvity of 3 x.10~®, m^/s. This
is the same criteria as for the synthetic LCR systems. Thus a synthetic
system that satisfies design criteria for the LCR could be used as a gas
collection layer.
100%
100*
WATER
80
'80
>-
h-
< 60
•AIR
UJ
<
5 *0
»-
<
UJ
u
20
(KOERNER, ET Al, 1984)
0.4
0.6
NORMALIZED PRESSURE RATIO
0.6
0
0.2
1.0
PRESSURE
Figure 6.6 Air and Water Transmisslvity in a Needled Nonwoven Geotextile
A synthetic gas venting layer can be constructed using nonwoven
geotextiles or geonet/geocomposite systems. The transmisslvity of the
design system must be verified in the laboratory under normal loads
exceeding that anticipated in the field. Both test procedures and design
considerations are presented in Section III for LCRs. The only additional
EPA V - 15
-------
laboratory check that should be made is to verify that air will freely pass
through the synthetic system after it has been saturated and allowed to
drain. Certain nonwoven materials retain a significant volume of water even
in apparent free drainage conditions due to capillary action. This retained
liquid fills the void space arid restricts the free movement of air or
gases. Research by Koerner,et al(1983) found that the movement of air
through a needled nonwoven geotextile.of 12 oz/sq.yd. was not influenced by
the presence of water in the voids. Data from these tests is shown on
Figure 5.6 and indicates that the presence of significant air movement can
reduce the water transmissivity of the geotextile. This same study found
that the air transmissivity of most nonwoven materials is several orders of
magnitude greater than the water transmissivity.
Vent Pipe Details
Gases passing into the gas collection layer must be vented to the
atmosphere or a collection system. The vent pipes required for this must
pass through the hydraulic barrier, drainage layer, and-protective cover
that form the cap. Basic design variables associated with vent pipes
Include vent pipe diameter, vent pipe spacing, and the detail related to
the vent pipe passing through the hydraulic barrier. Vent pipes are
typically made of schedule 80 PVC or HDPI pipe 2 to 6 Inches in diameter. A
typical vent pipe design is shown on Figure 5.7 for the MTG guidance cap
profile. A flexible boot must be bonded to the FMC to allow the vent pipe
to pass through the FMC. The vent pipe is inserted within the boot and
clamped to maintain a water-tight seal. Differential movement between the
gas collection layer and the top of the cap should be minimal so that no
telescopic couplings will be required for the vent pipe.
MASTIC
VENT to ATMOSPHERE
RISER
BOOT SEAL AT FMC
s- FILTER
FMC
Y, COMPACTED SOIL
CASKET
CAS VENT
OPERATIONAL COVE*
FIANCE SEAL AT fMC
Figure 6.7 Gas Vent Pipes - Details
EPA V - 16
-------
Vent pipe spacing is a function of the assumed rate of gas generation
and the size of vent pipe used. Typical rates of gas generation assumed for
sanitary landfills range from 0.5 to 7 liters per kilogram of waste per
year (L/kg/yr). Lacking better data, the designer of a hazardous waste cell
may assume that the level of gas generated within the cell will be a lower
limit to that associated with sanitary facilities, e.g. 0.5 L/kg/yr.
Designs may assume that the flow of the gas Is nonturbulent such that flow
is modeled by Darcy's law. This is true (Emcon, 1980) when the mean grain
size of the porous media is less than 0.2 cm. This condition should be true
for needled nonwoven geotextlles but may not be true for drainage nets.
References - Section V
Cline, J.F., (1979), Biobarrlers Used in Shallow-Burial Ground
Stabilization, PNL-2918, Battelle Pacific Northwest Laboratory,
Richland,WA.
Emcon Associates, (1980), Methane Generation and Recovery From Landfills,
Ann Arbor Science, Ann Arbor, MI.
EPA, (1979), Design and Construction of Covers for Solid Waste Landfills,
EPA-600/2-79-165, U.S. Environmental Protection Agency, Cincinnati, OH.
EPA, (1982), Handbook for Remedial Action at Waste Disposal Sites, EPA-
625/6-82-006, U.S. Environmental Protection Agency, Cincinnati, OH.
EPA, (1983a), Land Treatment of Hazardous Waste, SW874, U.S. Environmental
Protection Agency, Cincinnati, OH.
EPA, (1986), Construction Quality Assurance for Hazardous Waste Land
Disposal Facilities, EPA-530-SW-85-021, U.S. Environmental Protection
Agency, Cincinnati, OH.
EPA, (1986), Covers for Uncontrolled Hazardous Waste Sites, EPA/540/2-85/-
002, U.S. Environemental Protection Agency, Cincinnati, OH.
EPA, (1987), Guidance Manual for Prediction and Mitigation of Settlement
Damage to Covers of Hazardous Waste Landfills (Draft), U.S. Environmental
Protection Agency, Cincinnati, OH.
.Farmer, W.J., et al, (1980), .Land Disposal of Hexachlorobenzene Wastes,
EPA-600/2-80-119, U.S. Environmental Protection Agency, Cincinnati, OH.
Gluck, L. and J. Zohren, (1985), "Using Plastic Sheets as Sealants to
Protect Groundwater", Waste and Refuse, Schmidt Publishers, Vol. 22.
Hakonson, T.E., (1986), Evaluation of Geologic Materials to Limit
Biological Intrusion into Low-Level Radioactive Waste Disposal Sites, Los
Alamos National Laboratory Report No. LA-10286-MS.
Karimi, A.A.* (1983), Studies of the Emission and Control of Volatile
Organlcs in Hazardous Waste Landfills, Unpublished Ph.D Dissertation,
University of Southern California, Los Angeles.
EPA V - 17
-------
Kays, W.B., (1977), Construction of Linings for Reservoirs. Tanks and
Pollution Control Facilities, John Wiley & Sons, New York.
Knlpshleld, F.W.,(1985),"Material Selection and Dimensioning of
Geomembranes for Groundwater Protection," Waste and Refuse, Schmidt
Publisher, Vol.22.
Koerner, R.M. and F.K. Ko, (1982), "Laboratory Studies on Long-Term
Drainage Capabilities of Geotextiles," Proc. 2nd Int. Conf. Geotextiles,
Las Vegas, Nevada, IFAI.
Koerner, R.M.,et al, (1984), "Water and Air Transmissivity of Geotextiles,"
J. Geotextiles Geomembranes, Vol. 1.
Lee, C.R., et al, (1985), Restoration of Problem Soil Materils at Corps of
Engineers Construction Sites, Instruction Report EL-85-2, Waterways
Experiment Station, Vicksburg, MS.
Phillips Fibers Corporation, (1987), Personnal Communication.
Rovers, F.A., et al,(1977),"Procedures for Landfill Gas Monitoring and
Control," EPS 4-EC-77-4, Waste Management Branch, Environmental Canada.
Rumberg, E., (1985). "Investigation of Seal Sheet Behavior Against
Rodents," Waste and Refuse, Schmidt Publishers, Vol. 22.
Steffen, H., (1985), "Report on Two Dimensional Strain-Stress Behavior of
Geomembranes With and Without Friction," Proc. Int. Conf. in Geomembranes,
Denver, Co, IFAI.
EPA V - 18
-------
Cell Component: Sure^e UIa-tek £<>nEM j Removal Sv-yrg.m
Consideration:v itv , vegipr capactyqf swcr sy.tem
Tfl MMUPiHU l-FrUEAD With ^lYEU <\HT or Fill
1-o ^a*oiEnT, " /L- (6/e.,0")
(4") pepiMfc PesicjKj Ratio
PPv = "
Tie a
T,
ftiqUmao
Design Ratio:
DR *l<3.o
HIV
References:
wouq (nm
Example:
Qiv£.wj :
•Cover Soil Height, D=4'
• LIuiT UJh^HToF £»V£R Soil ^(» I SO PfF
"Slope A.uqL6 % »'&"
• Spaciu^of H f *Tf» A.USMI»»l\/|TY PaTA
• 5ljRFAe£ UaTEB. JuFiLTRA-nou RaTH., <^» . I Fi/ftVoav
(QPe-FiME MiuimUm TgAUSMrS&IViTY
—¦— 6o * I _ _ i I , . —S - j
T= , Z = 38.5 Ft /PA.YS 4-l*,IO m'Aec
I + 6>0 si u 8 '=.
(i\ ^"alclIlatE Maximum
6"^: I20* 4 * 4 So PSF
O&TViU SUCR TgAMsmtsiviTY from La& PatA ^ "QwcR
——-S- f-—
4-..
: a
ti
: t
^- --A-———A
,7j 1.00 1.25
HYDRAULIC CRADlENT
(4s) CAl^Jlatc Ps.*
-------
Cell Component: Surface 1-Jajeh Coiiec.t>ou/Removal System
Consideration: Shear Fumae : e^iuatc ¦SLlDlfcJq stability oF
CoVER Soil. A.UO DESiqu Ratio A^AHJST shear
fAiLuae. or 6UC.O,.
Required Material Properties
Range
Test
Standard
Fftic-ru&l
"' £&i£k£*tt. t» SWCR,^U
* Si-idfi % Fmcj 5l
*Sm6a« StSeH^th of SW^R
D'lM M1G Minimal)
3<9*-45*
\o'-Ao'
io- bo "yiu*
Piescr Shim*
UIipE U'PTH
ASIVi Rtoftsto
^•siVl D4S15
M
•0
>
<
I
to
o
Analysis Procedure:
(0 £ikLfc iRate Design Ratio For ^web
+A.M S>»
PR"
4*JU^>
^ - siope «r 1
'S'u ¦" 0» I h icKuE'SS o*
<^oVER «-lL
ffl^ALciltA-fis P»«au Ratio foa. SIaJ<^K ^meaq.
ALloiAi
PR
SmiM
Design Ratio:
»«-to'uS 0K> Z.o
•SWeR Sheas c?ft>5^o
References:
MarTiM >6tai. (1184)
KotQMta ,Et Ai-
Example:
• fttnrTi»\j A.ML -n» 5W«^R »
-S|J£R "T5» FMC »£5*
• Slope Awqie * 5.7*
"CovER Soil. DtprX ~ 4*
• CoyBA S..L DbusiTY * IZo Vojfl*
•Shear Sj-rbm^tm SucR= ISi^/iu'1
(¦"> ^~A.LguiA.Te. De.«c;ki Ra.tio f«>r Cover
PR- ^Ld°T , g.o > 2-o ok
w Tau ^.1® ^ t-
Shear. StsE»-> f Belquj Sulj5.7''* 4oIP« Suj^R ^H6AS
D«-
l^» x}44
27 3
' 9.6,>5.c?
Example No. 5.2.
-------
Cell Component: Surface Uater £oue• slope
^ ^*ALcUUA.ie ~i6M-«l»U IU Sl\JCR
"£« ' < -T L
(%) C- AlcUlajE Pesi e^u Ratio
DR-^—
1 I***/
T.xx'UcriMAIt TEWSlLE. STRE-U^TH ^SkJfTR
Design Ratio:
PR>5-o
References:
Example:
^iveu*.
• p(?i^T"»u ^uLB «f SkcR ® ib/m
* Si-oce = Zoo ft.
(0 ^*al i ate "Swear Stress Asovt ®. 5eu>^j
SU^R
®'n'* 4*I2o»4^o PcF
48P T*u4o°^»« 5.7* "¦ ^ol p5p
ft.-*e^PsF
^A.LcUl>vTE "TIlj-MoU ilj 5ki^R
XiA*3 ^4ol-2«3) 2ok- ' - o.lt> uq
Z°no
Example No. 5.3
-------
Cell Component: Fie«iaie Mimbrmje ^af>
Consideration: : »r fm^- r* *«v.v*
56TfLi-MiuT RfSULTiuq From lou^-TERM WA*re rsMnilMMM
r«Ktiip,fes M>>y ee biasiai or uuia.xiaa. .
Required Material Properties
Range
Test
Standard
Fifvi»it Mimmauc ^*p
- Yibu> -stbaim r»« Pmu ^WU)
Draft MTG Minimum
la - 2*7.
wioeutorfl
4S1W D4&IS
Analysis Procedure:
CO Estimate. ^uwttm1 af 'Sc.ttw&mbut PtwewuM
* Depth BK9€.OaU % •CITtC MiuT X UAire CEptH
(Stl^tVT miuimdm
* U'OJM JMiO'eU MiwimUm ££u. DiMKM*iom
OR PA.-ST ExPBRlEUCe
(*") (TaUUiate Si-rngt^CMT Ratio(sR
SR ~ DS»*TW /uiotN
C?"> Qt>T»*iM UmiForm Straim f*»* R "iA
SdqqtVT <;iR<:ULAft -fRoJ Qbtailj STR€a>»^SmAiU FoR fMC
^ ^dJ»T AT RUfTilBt)
^ PtE* £
RUFT / "gj,,.
20
OcuUf Trough Mo^d
IS
S
SETTLEMENT RATIO, S/2L
Design Ratio:
u">£o Rupture
References:
KmiP-^H I6.LD ^1105*^
Example:
<^lV6Mi
• MiuimiIm UltBtH of " 5a FT
' Depth «f U1a-»T6 '««ft
• Z*aMffe*iTE FMC *T,l« + ^BOM6m8»AU«J
° UwAXIAL
4«rf
So
|oe
STraiu.%
in E*»T'WlWe ,C OF S&TT1-6.M6MT FeA1VW6
' SettuEHEMT DEPtM* S%x3o a 2 A FT
(*¦> <^AtBTTI.£MEUT RaTi<9 , *5R
• SR» 2.5/50 » .OS
(5) OfeTAlM li U 1 Fog N1 StraiM , £ Ut-iir
See PicjORe =»• <£*UuiP» I %
(_41
-------
SECTION VI
CONSTRUCTION/FABRICATION CONSIDERATIONS
The successful application of geosynthetlcs to hazardous waste
landfills and surface Impoundments requires the interaction of the design
engineer, manufacturer, installer, contractor, and owner/operator. These
may be separate companies or may be under a single company. The individual
responsiblities are as follows:
1) engineer - design of components
2) engineer - prepare specifications
3) manufacturer/installer - fabrication of component
4) installer/contractor - installation of component
5) manufacturer/installer - quality control of component
6) owner/operator/third party engineer - quality assurance for component
The interaction of these groups will depend upon the particular component
and the management structure of the particular facility. Some components,
such as FMLs, may be installed by the company that actually manufactures
and fabricates the membrane. Other components, such as geotextiles, are
commonly installed by the general contractor for the overall facility
construction.
Minimum requirements for construction quality assurance for hazardous
waste land disposal units have been established by EPA in a recent
Technical Guidance Document,TGD (EPA, 1986a). Under this program,
construction quality control (CQG) activities are defined as those
performed by the. construction contractor, manufacturer, or fabricator to
control the quality of the constructed or installed component. These
activities include a planned system of inspections used to directly monitor
and control the quality of the construction. Construction quality assurance
(CQA) is defined as a planned system of activities that provide assurance
that the facility is constructed as specified in the design. Development
and implementation of a CQA program is the responsibility of the facility
owner/operator. Well planned and implemented quality CQC/CQA programs begin
during design and proceed through Installation and operation of a landfill
or surface impoundment. Frequently these services are provided by a third
party engineer.
The type and implementation of CQC/CQA programs have varied greatly
within the industry. Prior to the TGD there was no industry-wide standard
practice.. Recommendations from several designers and manufacturers
regarding CQC/CQA suggest that the following items be incorporated into
CQC/CQA programs:
o A checklist to assure all facility requirements have been
met.
EPA VI - 1
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o A specific plan to be used during construction for
observation, Inspection and testing of subgrade, liner
material, factory and field seam quality, installation
workmanship, and assurance that the design is followed.
Daily records must be maintained of all aspects of the
work, including tests performed on the subgrade and liner,
as for example, vacuum box seam testing with periodic
field seam tensile testing.
o Throughout construction, a qualified auditor responsible
to the operator/owner should review and monitor output.
This is an ongoing check on the contractor/installer. It
generates confidence that the work was indeed done as
planned. Changes to planned procedures must be justified
immediately and subsequently documented.
CQC/CQA programs can result in more effective Installations by assuring
planned review and tracking of all installation activities.
FLEXIBLE MEMBRANE LINERS/CAPS
The installation of flexible membrane liners requires proper planning
before construction. This planning Includes development by the engineer of
contract specifications for the components, development of fabrication
details by the manufacturer/installer, and performance of CQC/CQA
procedures by the owner/operator and Installer to verify material quality
and field procedures. Many of the important elements of Installation must
be reviewed and inspected by the component installer, the general
contractor, and the owner/ operator. These Important elements of
installation Include subgrade preparation, onsite storage of materials,
installation equipment, manpower requirements, procedures for liner
placement, field seaming procedures, sealing around structures or
penetrations, quality control/quality assurance procedures and soil cover
requirements. For many facilities, the design engineer serves as an agent
of the owner/operator for these Quality Assurance functions. Conversely, it
is not unusual for the owner/operator to use in-house engineering to
perform all of the engineering functions for the facility.
Specifications ,
A synthetic liner is covered by overlapping layers of specifications
that include those prepared by the membrane manufacturer, the installer,
and by the design engineer. Those specifications prepared by the engineer
are project specific and include performance specifications that reflect
the actual design. These specifications are the minimum standards for the
project but may be superseded in part by more rigid specifications of the
manufacturer or installer. With the exception of performance
specifications, the specification concerns presented here are commonly
found in manufacturer's, installer's and the design engineer's
specifications. The design engineer should indicate that the project
specifications can be superseded by more stringent specifications of the
manufacturer or installer. The project specifications prepared by the
engineer are, however, the minimum specifications for the FML.
EPA VI - 2
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While no two projects have identical specifications, those prepared by
the manufacturer, installer, and the engineer will typically cover the
following concerns: 1) Document Control, 2) Raw Material, 3) Manufactured
Sheet, 4) Delivery and Storage, 5) Installation, and 6) Sampling and
Testing. Since most liner projects are bid to the Installers, it is
important that any discrepancies in the specifications of the Involved
parties be resolved very soon after the FML contract is awarded. The
document control program is part of the CQC/CQA program discussed later in
this section. Very soon after award of the FML contract, a document control
program that satisfies the needs of the facility CQA officer must be
established.
Raw Material
Synthetic polymer resins are manufactured by . many large * chemical
companies and generally delivered to liner manufacturers in bulk rail cars.
These resins resemble granular or powdered sugar and must be tested to
ensure their quality before being fabricated into manufactured sheet. The
FML manufacturers will typically include the following tests of the resin
in their product specifications:
1) Density (ASTM D-1505), expressed as the weight per unit volume
at 23 degrees C.
2) Melt Index (ASTM D-1238), qualifying the molecular weight of
the material as demonstrated by the rate at which It flows
through a .0825-Inch diameter orifice.
3) Percent Moisture (ASTM D-570), expressed as a percent moisture.
These tests are the initial 'finger print' tests used to qualify resin
prior to its being formed into sheet. Typical limits for HDPE materials are
given in the Appendix on geosynthetic properties. An additional test used
by a limited number of sheet manufacturers is lnfared spectroscopy. This
test produces a curve that can be overlayed to a standard curve for
acceptance. It is important that the FML material delivered to the field be
the same as used in the chemical compatibility testing, e.g. EPA9090. Sheet
manufacturers will typically retain a bag sample of each lot of raw resin
used. These samples are retained for use In litigation should major failure
of a given lot of manufactured sheet occur.. The key finger printing tests
then become thermo-gravametric analysis (TGA) and differential scanning
calorimeter (DSC), reference Haxo, 1983.
Manufactured Sheet—
The resin is processed into manufactured sheet using an extrusion,
calendering or spread coating processes. Samples of the manufactured sheet
are taken during production and after a conditioning period. The frequency
of sampling may be based on a minimum number of samples per shift (or 24
hours), or resin batch, or roll. Unfortunately, there is no standard
requiring production sampling on the basis of square footage produced. Thus
the sampling rate can vary between manufacturers. The finished sheet
samples are then subjected to the minimum following tests: •
1) Thickness (ASTM D-1593)
2) Tensile Properties (ASTM D-638), defining the tensile
EPA VI - 3
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strength at yield and break, and the elongation at yield
and break.
3) Tear Resistance (ASTM D-1004), expressed in pounds.
4) Carbon Black Content (ASTM D-1603), expressed as a percent.
5) Carbon Black Dispersion (ASTM D-3015)
6) Dimensional Stability (ASTM D-1204)
7) Stress Crack Resistance (ASTM D-1693)
These tests provide a signature of the finished product and are not design
oriented. Specifications must ensure that the specific polymer material
tested for both physical and chemical properties is the same as delivered
to the job site. It is suggested that density and molecular weight
measurements be taken on a periodic basis. Additionally, any significant
variation in the values obtained from these tests indicates a production
quality control problem. Published values for these properties are given in
the appendices for many available geomembranes^ A brief description of each
test procedure is also presented in the appendices.
Delivery and Storage—
FML material is typically shipped to the job site in rolls or folded
on pallets depending on the polymer used to form the FML. For Instance,
polyethylene should never be folded under any conditions and will always be
delivered to the site in rolls. Project specifications must require that
each roll or pallet be stored off the ground and protected with a covering
that prevents physical damage, contamination by dust or water, and exposure
to direct sunlight. The specifications should also require that each roll
or pallet be identified with the following minimum information (Schmidt,
1983, EPA 1986b):
1) Name of manufacturer/fabricator,
2) product type,
3) product thickness,
4) manufacturing batch code,
5) date of manufacture,
6) physical dimensions (length and width),
7) panel number per design layout pattern, and
8) direction for unrolling panel.
The site CQA officer should: inspect each roll or pallet of FML to ensure
compliance with these specifications and maintain a record of all roll
identification tags.
Project specifications should require that all geomembranes delivered
to the job site be stored in a secure area that protects the panels from
vandalism by man or animal, contamination by dirt, dust or water, and from
extreme heat caused by direct sunlight. Typical specifications will limit
the extreme temperature of the membrane to less than 140° F to prevent
blocking (sticking) of the rolled or folded panel faces together. If the
climate is hot, then the geomembrane should be conditioned(e.g. by
EPA VI - 4
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powdering) to prevent blocking. The geomembrane should be stored In a air
conditioned room, if necessary, to prevent loss of plasticizers (PVC) or
curing (CSPE). Manufacturers quality control programs are typically
somewhat vague and simply require storage that 'prevents damage to any part
of the product'. Many such QC manuals do, however, limit the stacking
height of rolls (usually to two) and should be inclusive in the designers
specifications.
Installation—
Installation specifications for geomembranes are focused on a visual
inspection of the manufactured sheet and the quality of field seams. Field
weld specifications will require dally quality control testing of the
welding procedure and lnplace seams. Daily CQC testing of the welding
procedure should require that a field test weld section be tested several
times during a given shift. The length of the test weld will vary depending
upon the weld type. Typically test lengths for HDPE are 3 feet for
extrusion welds and approximately 1 foot for hot shoe (wedge) welds.
Manufacturers specifications will require testing ranging from manually
pulled 'peel' test that base acceptance on seam failure occurring in the
parent material, to the tests required under NSF 54 Standards. These tests
require 1 inch samples to be tested in both peel and shear. The designer
should review the field QC specifications of prospective
manufacturers/installers and require minimum NSF 54 testing in the general
project specifications. Details of in-place seam testing are discussed
below.
Sampling and Testing—
It is generally recognized that the geomembrane Industry can produce a
flawless sheet but experiences difficulty in maintaining this level of
quality in seaming two sheets together. Flawless field seams are difficult
to obtain for the following reasons (Koerner,1987):
- sloped preparation surface
- nonuniform (or yielding) preparation surface
- nonconforming sheets to the subsurface (air pockets)
- slippery liners made of low friction material
- wind-blown dirt in the areas to be seamed
- moisture and dampness in the areas to be seamed -
- penetrations, connections and appurtenances
- wind fluttering the sheets out of position
- ambient temperature variations during seaming
- uncomfortably high (and sometimes low) temperature for
careful working
- expansion and/or contraction of sheets during seaming
The sampling and testing program must be designed to detect such problems
said to adjust the frequency of testing when required by field conditions.
Project specifications must require that FML seams be 1009& tested
using a nondestructive technique such as vacuum box or ultrasonics. Lord
(1986) summarized NDT tests for typical polymers. Table 6.1. The
ultrasonic shadow method has only recently been added to this list of NDT
tests. Koerner(1987) presents a summary of this latest NDT test on HDPE
seams. The specific test procedures for such testing should be detailed In
the project specifications since applicable standards are not available at
EPA VI - 5
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Table 6.1 Available NDT Methods for Evaluating Seams
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sheet by the manufacturer prior to shipment to the installer. For other
sheeting, e.g. HDPE, the manufactured sheets are sufficiently wide that all
of the fabrication is performed by the installer. The design enginner
should review the methods and orientation of all factory or field seams to
ensure that design physical properties are not compromised.
The general panel layout for a given facility Is normally provided by
the installer. The design engineer should review the panel layout to check
that the following guidelines are met:
1) Field seams should run up-and-down the slope and not terminate
at the bottom of the slope but runout for a minimum distance
of 3 feet.
2) Overall field seam length should be minimized.
3) No penetration of the primary FML below the top-of-waste
elevation should occur.
The installer should submit the general panel layout for approval by the
design engineer and for use by the project CQA engineer in monitoring the
FML sheeting as it arrives on the job site. At this time, the two parties
should agree upon a numbering scheme for both the panels and the welds
between the panels. A typical numbering scheme is shown in Figure 6.1. This
numbering scheme plays an important role in assuring that prefabricated
panels are properly positioned during installation and that CQA records of
seam tests are clear regarding the location of seaming difficulties.
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EPA VI - 7
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Construction
Successful Installations of an FML system were found by Schultz
(1983,1985) and Bass (1984) to depend on the experience of the field
installation crew and their attention to significant construction details.
This Section reviews the field details that influence the quality of
installation. While the topics are slmlllar to that discussed in Section
11, the emphasis in this section is on construction procedures and not on
design of the FML which is covered in Section III.
On-site Storage of Material—
Membrane materials are normally shipped to a construction site, and
must be stored prior to placement. Most materials are rolled on tubes or
folded and shipped on wooden pallets. Provisions should be made for
equipment to unload and transfer the rolls or panels of synthetics. The
rolls are generally very heavy and may require special or modified
equipment to move them without damaging the material. Protection for the
liner materials from the effect of heat and from vandalism by man or damage
by animals is required. These are the most Important storage
considerations. All FML's, except HDPE, should be stored out of sunlight
to prevent their degradation and minimize blocking. Blocking occurs when
liner materials stick together, causing the material to rip when it is
unrolled onto the subgrade. Excessive heating can also degrade the surface
of the material, causing problems with field bonding. Covering the
material with white plastic or storage out of direct sunlight is
recommended for all materials.
Installation Equipment—
Equipment often required to install a membrane liner includes a fork
lift truck, backhoe, or front end loader for material placement and various
tools necessary for material positioning and field seaming. A fork lift
truck, with large rubber tires (not warehouse type), is most often
recommended for material placement, because some material is shipped to a
site on wooden pallets. All equipment should be limited to 6 psi or less
ground contact pressure.
The equipment needed to seam the material together Is basically
similar for all types of material, with the exception of high density
polyethylene. High density polyethylene is fused or welded together and
requires special equipment.
Manpower Requirement—
Manpower requirements for the installation of liner materials is a
function of the rate that the installer wants to place panels and
accomplish field seaming. Typically, installation contractors will
recommend five to ten people on site when placing and seaming one panel at
a time. Generally, a crew foreman will direct the activities of the field
crew. He may not directly participate in the unrolling and positioning of
panels or In field seaming. However, he must be experienced in the
installation of the specific liner material.
Crew size recommendations also depend on the complexity of the
installation and the experience of the field crew. If the majority of the
crew members are recruited locally, more members may be needed due to lack
of experience. At the present time, the trend is toward having installation
EPA VI - 8
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contractors retain field supervisors who travel from Job site to job site.
Large jobs where . crews perform specific tasks may involve many locally
recruited and inexperienced people.
Project specifications prepared by the designer commonly stipulate
minimum experience levels for the installers foreman and field supervisors.
While difficult to implement, such specifications do ensure a minimun
experience level for the installer. Such specifications typically require a
minimum of one year experience for the foreman and no less than 3 months
experience for the field supervisors. Alternately, specifications may
require experienced based of square footage of installed FML. Such
experience must be continous and with the same polymer membrane selected
for the project.
Liner Placement—
Important considerations that should be followed in placing a membrane
liner are as follows (Schultz,1985):
o Follow manufacturers' recommended procedures for adhesive
system, seam overlap, and sealing to concrete
o Use a qualified installation contractor having experience
with membrane liner installation, preferably the generic
type of liner being Installed
o Plan and implement a quality control program which will
help ensure that the liner meets specification and the Job
is installed per specifications
o Document inspection for review and recordkeeping
o Conduct Installation during dry, moderately warm weather
(above 45°-60°F depending on material)
o Subgrade should be firm, flat, and free of sharp stones,
gravel or debris.
Before moving a panel from the storage site to the installation location, a
number of tasks must be performed. The anchor trench around the perimeter
of the installation for the panel should be completed. The soil excavated
from the anchor trench should be raked smooth on the cell side of the
trench so that the panels can be unrolled . Other things that must be
accomplished prior to positioning a panel are: (1) the subgrade should be
raked smooth or compacted if necessary; (2) there should be no standing
water in the cell or impoundment; (3) any concrete structures that must be
seamed around should be prepared prior to unrolling the panel; (4) if
skirts are to be used around footings on concrete structures, these may be
in place prior to the beginning of panel placement; and (5) any outflow or
inflow structures or other appurtenances should be in place.
Placement often begins with the unfolding or rolling of the panel in a
lengthwise direction. If necessary, the panel is then unfolded in the width
direction, either down the side slope or across the floor. The panels are
normally unrolled on the inside of the anchor trench, eliminating the need
to move the liner across the trench. The field crew then begins to
EPA VI - 9
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position or "spot" the panel into its proper location according to the
installation plan. As panels are spotted, sand bags are placed along the
edges to prevent uplift and subsequent wind damage. Sand bags are typically
required at a minimum spacing of 2-foot centers on the windward edge of the
panel. If the windward side cannot be identified, then the sandbags must be
placed around the entire panel. These sandbags may be left in place until
the completed liner is stabilized by placement of overlying components. A
method for calculating the number of sandbags required at a give site is
discussed later in this section. Note that old rubber tires are not
recommended in place of sandbags because they lack enough weight to be
effective and hold water that can spill onto work areas. Wind induced
lifting of the membrane is strongest near the top of the berms and nearest
the corners. In surface Impoundments, the wind lift problem may continue to
exist during operation of the SI. In these cases, vents simillar to gas
vents are installed to allow the wind to suck the air out from under the
liner. A vent simlliar to that used for gas venting, see Section V, is used
for such applications.
The instructions on the boxes containing the liner must be followed to
ensure that the panels are unrolled in the proper direction with the
correct side exposed for seaming. The panels should be pulled relatively
smooth over the subgrade. If the subgrade is smooth and compacted.then the
liner should be relatively flat on the.subgrade. However, sufficient slack
must be left in the material to accommodate any possible shrinkage due to
temperature changes. The amount of slack required depends on the material
being installed.
The FML panels should be spotted in such a way that sufficient seam
overlap of the adjacent panel is maintained. Recommended overlap varies
from 3 to 6 inches. The installation contractor should, however, follow
the manufacturer's recommendations in terms of overlap and bonding system.
The integrity of field seams depends on the following factors:
1. Manufacturer's guidelines for adhesives should be followed.
The seaming system must be compatible with the FML and be
applied under the correct ambient condition;
2. Cold temperatures can prevent successful bonding of panels.
Some manufacturers recommend that adhesive bonding take place
only when temperatures are above 60°F (15°C);
3. The seam surface must be clean and dry. The presence of
moisture interferes with the curing and bonding
characteristics of the adhesive, while the presence of dust
creates voids which provide a path for fluid migration through
the seam. Either soli particles or moisture embedded in the
seam can result in crack initiation points which expand with
stress and aging.
4. The liner should rest on a dry, hard and flat surface to
facilitate the application of pressure rollers; and
5. Panels should be installed and seamed on the same day to
minimize the risk of FML damage by wind and erosion of soil
under the FML by rain.
EPA VI - 10
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The finished seams should be free of wrinkles and the surface should
be flat and rolled. Some manufacturers recommend that field seaming begin
at the center of the panel and continue to each end of the seam. This
procedure minimizes large wrinkles or 'fishmouths' which may potentially
occur if seaming begins at the ends.
As in compaction of a soli liner, placement of the FML on the facility
sideslope is a critical aspect of liner construction. Generally the panels
should be of sufficient length to be placed so that field seams will run
perpendicular to the toe of the slope (i.e., seams should run vertically
rather than horizontally along side slopes). This method reduces stress on
field seams. Corner patterns should be cut for fit in a tailored fashion.
Field Seaming—
The panels should be unfolded and spotted so that a sufficient seam
overlap of the adjacent panel is maintained. Some materials, such as HDPE,
must be allowed time to relax and temperature adjust prior to seaming.
Seam overlap recommendations vary with liner manufacturer and liner type.
Recommended overlaps vary from 3 to 6 inches.
Field seaming is a critical factor in flexible membrane liner
placement and is discussed in greater detail In Section III. Liner
manufacturers publish recommended procedures for achieving successful field
seams with one of four methods generally recommended to seam materials in
the field. These are as follows;
o Solvents: bodied adhesive, solvent adhesive, or contact adhesive,
o Thermal : hot wedge, hot air, and dielectric,
o Introduction of hot base: extrusion or fusion, and
o Vulcanization with uncured gum tape or adhesive.
The installation contractor should use the manufacturer's recommended
procedure. In some instances, an installer may have worked with a
manufacturer to develop an improved technique for that installer. In such
a case, the method should be allowed if it meets peel/shear testing
requirements and chemical compatibility restrictions.
The integrity of the field seam is determined by many factors. The
most Important factor is that the seaming system used must be compatible
with the liner material and suitable for use under actual field conditions.
Generally, manufacturers recommend seaming at temperatures above 45°-60°F
depending on the material. If ambient temperatures are below this range,
some manufacturers suggest installation activity cease. Many HDPE
manufacturers allow seaming at temperatures significantly below this level.
Such cold weather seaming requires more destructive seam tests to ensure
bonding for seam integrity. Another important factor in field seam
integrity is that the surfaces to be seamed are clean and dry when the
field seams are made. The presence of any moisture can interfere with the
curing and bonding characteristics of the adhesive used. The presence of
any dirt or foreign material can Jeopardize seam strength and provide a
path for fluid to migrate through the seam or as stress crack Initiators.
An upper temperature limit for thermal and extrusion weld field
seaming is commonly related to the installer and not the Installation
EPA VI - 11
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procedure. With welds occurring at 500°F (260 °C), the human installer
becomes the limiting factor with Increased temperature. High ambient
temperatures may quickly evaporate the active agent in solvent cements and
require a significant reduction in length of seam prepared at a given time.
The consistency of the solvent cement should be checked frequently to
verify that excessive amounts of the solvent have not evaporated.
With the exception of extrusion welding, pressure must be applied to a
seam after the solvent, adhesive, or heat has been applied. Therefore it is
recommended that the liner ideally should rest on a dry, hard flat surface
for rolling. Installers recommend that a board or other suitable hard
surface be placed underneath the overlap of the liner material. Overlaps
can be anywhere from 3 to 6 Inches wide, depending on the type of material
and the conditions under which seaming takes place. Once the board is
placed underneath the liner and the overlap is sufficient, then the top
liner material should be peeled back and the surface prepared for the
adhesive.
The specifics of the particular seaming technique must be fully under-
stood by the Installer and CQA staff. In the case of some liner materials,
e.g., EPDM and CSPE, a surface cure must be removed with a solvent wash
prior to seaming. Field crews should have suitable gloves to prevent skin
reactions from the solvents. Respirators and eye protection are also
recommended. On HDPE membranes, the surface must be physically roughened to
remove the surface oxidation layer. Once the surface cure has been
removed, the adhesive can be applied to the liner material. With a bodied-
solvent adhesive, it is recommended that the two surfaces be placed
together immediately and rolled with a steel or plastic roller
perpendicular to the edge of the panel. Conversely, contact adhesive
systems require that a certain tackiness be achieved before the two
surfaces are placed together. Safety and seaming considerations must be
carefully reviewed for the particular seaming method used.
The crew should be careful not to allow any wrinkles to occur in the
seam. All surfaces should be flat and rolled. It is important, whatever
adhesive system is used, that the adhesive be applied uniformly. Some
Installers recommend that field seaming normally begin at the center of a
panel and continue to each end of the seam. This minimizes large wrinkles
which could occur if seaming began at one end or the other. In all cases,
the adhesive system to be used by the field seaming crew should be that
recommended by the manufacturer or a suitable substitute approved for a
specific job.
Generally, panels are placed so that field seams will run
perpendicular to the toe of the slopes; that is, the seams will run.up and
down rather than along the side slopes. Perpendicular seams are
recommended when side slopes are 4 to 1 or greater in slope. The
reinforced materials can be placed so that seams run horizontally on side
slopes less than 4 to 1. However, perpendicular seams on side slopes are
most often recommended for all cases. This practice minimizes stress on
field seams. Corner panels are cut to fit as required, usually pie-shaped
from berm to the bottom of the facility.
Installation of liner materials and field seaming during adverse
weather conditions require special considerations with respect to
EPA VI - 12
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temperature limitations. This is particularly true with the thermoplastic
materials, since their properties change with temperature. Temperature
also affects the rate that solvents will evaporate and the rate that seams
become strong. Most manufacturers suggest that their adhesive systems work
best when the temperature of the liner material itself is above 60° F.
When ambient temperatures are below 60° F and a solvent adhesive system is
being used, heat guns can provide an effective means to help bring the
temperature of the liner material up to ideal conditions. Extreme caution
must be exercised when using heat guns around flammable solvents, which may
ignite, and cholorinated solvents which may generate toxic gas.
Cold weather seaming requires that the field crew exercise caution
when making seams to assure that the temperature of the liner material
reaches minimum acceptable conditions. A cold weather contact adhesive is
sometimes used. Field seaming during precipitation must be avoided.
Depending upon the location and the weather conditions, the number of
panels placed In one day should not exceed the number which can be seamed
in one day. This assures that, should bad weather conditions occur
overnight, unseamed panels will not be left on the subgrade, subject to
damage, especially from wind.
Wind Uplift Forces—
Wind blowing over a geomembrane exerts varying amounts of uplift force
depending on the velocity of the wind and the roughness of the surrounding
land. When not adequately resisted by sandbags, the membrane will lift off
the ground and exert tear stresses on the sheet and seams. Such wind
induced stresses have been responsible for numerous failures. Using methods
developed by the flat roof industry, some insight into the problem can be
gained.
In the absence of site specific data, design wind speeds for the USA
are given in Figure 6.2. These values are annual extremes based on a 100-
year mean recurrence intervals and represent worst case situations. These
contour values are used directly with Table 6.2 to determine the wind
uplift value based on elevation above ground and surface roughness. Thus
the method is applicable for FMLs placed at the ground level and on
elevated caps. For FMLs below grade we recommend a linear extrapolation as
demonstrated in Design Example 6.1. It should be noted that the roofing
industry recognizes that the perimeter and corners of sheets are the
initiating points for uplift and compensate accordingly. For example, they
multiply the perimeter uplift forces by 2 and the corner values by 3 for
added safety. ' The temporary nature of a liner installation may-not Justify
such conservatism.
Anchoring—
Proper anchoring of the liner around the facility perimeter, as well
as conscientious tailoring and sealing of the liner around penetrating
structures, are essential to satisfactory liner performance. Generally, in
cut-and-fill type facilities, it is recommended that the liner material be
anchored at the top of the dike or ben one of two ways: (1) using the
trench-and-backfill method, or (2) anchoring to a concrete structure. The
trench-and-backfill method seems to be recommended most often by liner
manufacturers, probably due to its simplicity and economy. Excavation of
the anchor trench in preparation for laying the liner is usually
accomplished with a trenching machine or by using the blade of a motor
EPA VI - 13
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Table 6*2 Wind Uplift Forces, PSF (Factory Mutual System)
Wind Isotach, mph
(Figure 6.2)
Height Above
Ground, (ft)
City.Suburban Areas
and Wooded Areas
70 80 90 100
.Towns
110
Flat,Open Country,
Coastal Belt>1500ft
70 80 90 100
or Open
from Coast
110 120
0-15
10*
11
14
17
20
14
18
23 29
35
41
30
10
13
17
21
25
16
21
27 33
40
48
50
12
15
19
24
29
18
24
30 37
44
53
75
14
18
22
27
33
20
26
33 40
49
58
* Uplift Pressures in PSF
90
90
100.
120
•70
120
SYSTEM) |
(FACTORY MUTUAL
Figure 6.2 Design Maximum Wind Speeds
EPA,VI - 14
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grader tilted at an angle. Soil from the excavation should he spread away
from the anchor pit and smoothed to facilitate unrolling and spotting of
panels.
Before opening and spotting the panels, provisions should be made for
temporarily, e.g. with sandbags, securing the edges of the liner panels in
the anchor trench while the seaming takes place. After the seaming crew
has completed the seams for a particular panel, the trench is backfilled
with earth that was excavated from the trench. The trench should not be
backfilled until after the panels have been seamed so that panels can be
positioned for optimum seaming. If the trench (and the edge of the liner)
is to be capped with concrete curbing, it is recommended that reinforcing
rods be positioned vertically in the trench prior to backfilling. These
reinforcing rods can serve to 'nail' the liner to the bottom of the trench
while the seaming Is done. Care must be taken to prevent puncture of the
FML outside of the trench.
The perimeter of the liner may also be anchored to a concrete
structure along the top of the berm or dike. This is usually accomplished
with anchor bolts drilled or embedded into the concrete and batten strips
composed of a material resistant to attack by the chemlcal(s) to be stored
in the facility. Concrete that is to come Into contact with the liner
should have rounded edges and be smooth and free of all foreign materials
to minimize abrasion and chemical Interaction with the liner material.
Anchor bolts should be positioned not more than 12 Inches apart on centers.
Concrete adhesive is applied in a strip (minimum width 3-6 inches,
depending on the liner material) between the liner and the concrete where
the batten strips will compress the liner to the concrete. A strip of
lining material (chamfer strip) may be sandwiched between the liner and the
concrete wherever the liner material contacts an angle in the concrete
structure to prevent abrasion. The batten strips are positioned over the
liner material and secured with washers and nuts to the anchor bolts.
Mastic should be used to effect a seal around the edge of the liner
material. Several alternative methods for anchoring to concrete structures
are shown in Figure 6.3 (Koerner, 1986).
Sealing Around Structures/Penetrations—
Depending on the design and purpose of the facility, one or more types
of structures may penetrate the liner. These penetrations could include
inlet, outlet, overflow or mud drain pipes; gas vents; level indicating
devices; emergency spill systems; pipe supports; or aeration systems.
Penetrations may occur in the bottom or through one of the sidewalls,
depending upon their function. Because tailoring and sealing the liner
around structures can be difficult and offers a possibility for failure of
the liner, several manufacturers recommend that over-the-liner pipe
placement be used wherever possible. This design facilitates future
repairs or "maintenance to the piping system and eliminates penetrations.
Penetrations through the liner must be designed so that the object
penetrating the liner is either rigidly fixed in its location relative to
the liner or so that a flexibility is designed Into the connection that
allows relative movement of the liner and the penetration without failing
the liner. These two types of penetration details are shown on Figure 6.4.
The rigid penetration relies on an underlying concrete foundation to fix
the location of the-penetration. The flexible details in turn rely on slip
EPA VI - 15
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Corrosion Resistant. Attachment
Bolt and Socket /
Timber Batten
i : »
Figure 6.3 FML Anchorage to Concrete - Details
connections fabricated into the boot to prevent tension in the liner. Both
details attempt to control the strains generated in the liner from waste
settlement induced movements within the liner.
When penetrations through the liner are necessary, most lining
manufacturers recommend specific materials and procedures to be used to
establish an effective seal around the various types of penetrations.
Proper design of the penetrations and selection of an adhesive material
that is compatible with the liner are important factors to be considered
relative to expected liner performance. For instance, some liner materials
are not easily sealed to concrete. Selection of alternative materials may
be required. Other materials, on the other hand, may offer optimal
conditions for obtaining a good seal; for example, PVC liner can be
effectively sealed to PVC pipe using the appropriate solvent to bond the
materials together.
Most manufacturers offer standardized engineering designs for: (1)
seals made in the plane of the liner, and (2) boots to be used around
penetrations. If inlet or outlet pipes are introduced into the facility
through a concrete structure, the seal can be made in the plane of the
liner. A special liner-to-concrete adhesive system is suggested that is
designed for each liner material. Anchor bolts embedded in the concrete
and batten strips of stainless steel should be used to secure the liner to
the concrete. Mastic should be used around the edges of the liner material
to effect a complete seal.
Typically, specialized features such as pipe boots or shrouds are
fabricated at the manufacturing facility to design specifications, although
EPA VI - 16
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they can sometimes be prepared in the field by experienced personnel. Where
reinforced membrane liners are being Installed, manufacturers sometimes
recommend that boots be constructed of unrelnforced liner of the same type
as that being Installed. This allows the slightly undersized boot to be
stretched over the appurtenance to assure good physical contact and allows
some expandability in case the adjacent liner stretches due to settling.
The boot is slipped over the pipe after the main piece of the liner has
been cut and fitted around the base of the pipe. The proper adhesive is
applied between the pipe and boot and a stainless steel band is placed
around the boot where the adhesive has been applied. The base of the boot
is seamed to the main part of the liner using the same adhesive system and
methods used to make the field seams. Boots should be checked prior to
installation to ensure that the angle of intersection with the base is
consistent with the angle created between the pipe and subgrade.
Construction Quality Control/Qual1ty Assurance - FML
Competent CQC/CQA inspection is Imperative if installation of the FML
is to result in a barrier which is effective in controlling migration of
leachate to the underlying soils. Placement and surfacing of the subgrade,
FML placement and seaming, and sealing of penetrations through the liner
require a considerable degree of quality control which should be part of
the CQA program assigned to a representative of the facility
owner/operator. The representative is required to assure that contractual
obligations of the installing contractor and installation specifications
are fully met.
Construction Quality Control—
There are three specific areas of quality control concern for the
installer in a polymer membrane lined facility. These are the subgrade,
FML seams, and sealing of penetrations through the liner. Relative to FMLs,
the important subgrade considerations Include proper preparation of
adjacent soil layers and assuring that no "bridging" occurs in the liner
material where angles are formed by the subgrade. Bridging is the
condition that exists when the liner extends from one side of an angle to
the other, leaving a void beneath the liner at the apex of the angle.
Bridging occurs most often at penetrations and where steep sidewalls meet
the bottom of the cell. Installers recommend that particular attention
should be directed to keeping the liner in contact with the subgrade at
these locations and that it be in a relaxed condition. It is also
important to be sure that compaction of the subgrade in these areas meets
design specifications to avoid localized stressing of the liner material or
seams.
Construction Quality Assurance—
The owner/operator is responsible for establishing a Quality Assurance
program to monitor all phases of the FML Installation. A knowledgeable
representative of the primary facility operator, or representative of the
ultimate owner of a lined facility, should be assigned as the quality
control agent or engineer on liner Installations., The agent will be
required to assure that the contractual obligations of the Installing
contractors) are met and that the Installation specifications are fully
met. Personnel reviewing the design or performing quality control
EPA VI - 17
-------
Geotextile
Weld
tSmmIP
awwfry//
sleeve
<8
'MV/
W
T)
H»
RIGID PENETRATIONS
FLEXIBLE PENETRATIONS
OS
pipe sleeve
/
Geotextile
is?03£sS§3
steel clamp
FML
Pipe
Primary FML
m&
Secondary FML
Figure 6.4 Rigid-Flexible Penetrations - Details
-------
functions for a liner installation should be familiar with the liner
manufacturer's recommendations regarding all facets of the materials' use
and installation. This includes everything from the liner's compatibility
with the material being stored, to recommendations regarding specific
adhesive systems and special seaming instructions around penetrations.
Sampling Strategies - General Discussion—
The CQC/CQA programs established to monitor the quality of FML
installation must establish reasonable sampling strategies for tests to be
conducted on the geomembrane. For the most part, the sampling performed
during the manufacture and fabrication is controlled by the CQC programs of
the manufacturer and installer. It is not until the FML components reach
the jobsite that the owner/operator's CQA program begins to sample the FML.
Various strategies exist for determining the frequency of sampling and the
acceptance criteria for these tests. These sampling strategies typically
fall into one of the following categories:
1) 100-Percent Inspection,
2) Judgmental Sampling, and
3) Statistical Sampling.
It is expected that the CQC/CQA programs for FMLs will involve tests based
on all of the sampling strategies. Greater details regarding these
strategies are given in the TGD (EPA, 1986a).
The use of 100# inspection must be limited to observations and
nondestructive tests. Such inspection may be based on purely subjective
evaluation, such as visual inspection, or on actual nondestructive testing,
such as the use of a vacuum box to inspect for seam leaks. Examples of 100#
inspection include those tests used for FML seams and anchors, collector
system pipe joints, pump function, and electrical connections.
Judgmental sampling refers to any sampling strategy where the
decisions concerning sampling size, selection scheme, and/or locations are
based on nonstatistlcal methods. The objective may be to select typical
sample elements to represent the whole, or to identify zones of suspected
poor quality. The frequency of sampling will frequently reflect the
confidence that the designer has in the CQA personnel. Judgmental sampling
strategies must try and reflect accurately the as-built condition of the
facility and yet locate samples in questionable regions. Since the sampling
is done on a purely Judgment basis, statistical analysis of the data Is not
practical due to probable bias in the data.
Statistical sampling methods are based on probability theory and are
used to estimate specific statistical characteristics, e.g. the mean value,
that are used to define acceptance of the construction. The sample
selection is based on an objective random process. Selection of this random
process is, however, based on experienced judgment. In statistical
sampling, a sample unit refers to the smallest unit into which the
component in question is divided. For example, the FML could be overlain
with a grid with each grid section being a sample unit. The underlying
requirement for statistical sampling is that each sample unit must have the
same known probability of selection. .
EPA VI - 19
-------
There are many variations in sampling strategies possible. A review of
those commonly used in facility CQA is given by EPA (1986a). The most
common methods Include the following:
1) Stratified Sampling -The sampling is based on a weighing
scheme that is dependent upon some property of the sample
unit.
2) Two-Stage Sampling - Multiple samples are taken from each
selected sample unit.
3) Systematic Sampling - Typically involves sampling every
n**1 sample after an initial random start.
4) Simple Random Sampling - Each sample unit has em equal
probability of being tested.
Probably the most satisfactory method to the engineer concerned about
sampling all parts of the block is a combination of (a) stratified random
sampling and (b) systematic sampling with a random start.
Selection of Sample Size - General Discussion—
A statistically rational and valid method of selecting sample size is
given in ASTM (Annual) Designation E-122, "Standard Recommended Practice
for Choice of Sample Size to Estimate the Average Quality of a Lot or
Process." The equation for the number of units (sample size, n) to include
in a sample in order to estimate, with a prescribed precision, the average
of some characteristic of a lot is:
n - ( ts/E )2 Eq(6-1)
or, in terms of the coefficient of variation
n - ( tV'/e)2 Eq(6-2)
where
n = number of units in the sample
t «= a probability factor from the Student-t Tables
s = the known or estimated true vaiue of the universe,
or lot, standard deviation
E = the maximum allowable error between the estimate to
be made from the sample and the result of measuring
(by the same methods) all the units in the lot
V'= coefficient of variation = s/X , the known or
estimated true value of the universe or lot e =
E/X, the allowable sampling error expressed as a
percent (or fraction) of X
X - the expected (mean) value of the characteristic
being measured.
The probability factor, t, corresponds to the level of confidence that the
sample expected value will not differ from the actual value by more than
the allowable difference, E. A sample size needed to estimate the
reliability of the overall material will not be small enough to be used to
assess the quality of a subsection.
EPA VI - 20
-------
Typical FML CQC/CQA Programs—
Field quality control/assurance testing of FMLs is focused on the
quality of seams produced in the field. Installers will usually base their
field CQC program on periodic destructive testing of sample velds made on
FML sheeting slmiliar to that being installed, and on 10056 nondestructive
seam testing using a vacuum box. The destructive testing is not on seams
that are part of the actual facility, but are prepared on a periodic basis
specifically for testing. The frequency that destructive samples are
prepared varies from the beginning, and end of an 8-hour shift to as
frequently as every 3 hours. The Installers quality control test program is
designed to verify the continuity of the seams using 100% testing and the
strength of the seams using a statistical periodic sampling program. The
major objection to the program is that the seam strength samples are
prepared specifically for testing and may not be representative of the FML
seams. Destructive testing of actual FML seams occurs every 500 to 1000
feet of seam and on a judgmental basis if soil or water are suspected of
contaminating a seam.
The Construction Quality Assurance (CQA) program of the owner/operator
is typically built on a statistical program of both destructive and
nondestructive testing. These programs are normally based on statistical
methods of sampling that base the number of tests on the performance of
previous tests. For example, the minimum number of tests of a given lot
using Equation 6.1 is based on the standard deviation of the actual lot.
While this number must be initially estimated, the estimate can be revised
on a regular basis using the data obtained from previous destructive
samples from all lots. This can be demonstrated by examining a typical
sampling program for destructive testing of FML seams. Initially the
sampling program could be based on Equation 6.1 with the following
assumptions:
- t = 1.97 (95% confidence level)
s = estimated standard deviation.
= 10% of mean
E = allowable error set at 10% of mean
Substituting these values into Equation 6.1 indicates that four tests per
lot are required. Here a lot may be defined as the welds performed during a
given shift. During the course of the installation, the destructive tests
performed can serve as a basis for a revised estimate of the standard
deviation. Thus if the seam quality is poor, the standard deviation will
increase and the number of destructive CQA tests required will increase.
For seams that fail, the MTG recommends that the seam be reconstructed
between the failed and any previously passed seam location. If this is an
excessive length, then the installer can go 10 feet on either side of the
failed test, take another sample, and if it passes reconstruct the seam
between the two locations. In all cases. the reconstructed seam must be
bounded by two passed test locations.
While the installer has performed a 100% nondestructive test of the
seams, it is not unusual for the CQA program to require a percentage
retesting of all seams using a longer dwell time for the vacuum box test.
Typical dwell times used by installers in performing the vacuum box test
EPA VI - 21
-------
are 10-15 seconds at a vacuum of 2.5 psl. CQA vacuum tests may require
dwell times exceeding 90 seconds. These longer dwell times must be used
with caution because they can put excessive strains on thin liners. As with
destructive testing, the CQA program should provide a systematic method for
increasing the percentage of nondestructive testing based on the percentage
of failures found in the CQA testing. Some of the NDT tests previously
shown on Table 6.1 can provide 100# testing of the seams to supplement the
standard vacuum tests.
Maintaining clear records of Installation and testing is an important
part of the CQA program. The record systems typically utilize the seam and
panel numbering systems previously shown on Figure 6.1. These records will
typically include the following forms:
1) Panel Placement Log
2) Geomembrane Seam Test and Inspection Log
3) Geomembrane Repair Log
The panel placement log, Figure 6.5, documents the condition of the
subgrade, weather, and panels during the installation of a given panel.
This log may enable the CQA officer to find a common cause of panel seam
problems, e.g. cold temperatures. The next form chronologically Is the
geomembrane seam test and inspection report shown on Figure 6.6. This log
records the results of the seam tests and notes any defective seams
requiring repair and further testing. The final log is shown on Figure 6.7
and records the repairs made to the defective seams. Each CQA officer must
establish a system of logs to document the correct Installation of the
liner. The logs presented here are intended only for guidance in
development of such logs. A particularly attractive aspect of ultrasonic
testing methods is their ability to record continuous, hard-copy of the
results of the inspection, see Table 6.2.
Table 6.3 Overview of Nondestructive Geomembrane Seam Tests
after Koerner and Kichardson(1987)
Pr
Lmarv Use
r
Ceneral Comments
Nondestructive
Tesc Method
Contractor
Design
Engr.
Insp.
Third
Party
Inspector
Cost of
Equipment
Speed
of
Tests
Cost
of
Tests
Type of
Result
Recording
Method
Operator
Dependency
1. ait lance
yes
-
-
$200
fast
nil
yes-no
tnanua 1
v. ImkIi
2. mechanical
po int
(pick)
stress
yes
nil
fast
ni 1
yes-no
ItUlllU J 1
v. Ui^\i
3. vacuum
chamber
(negat ive
pressure)
yes
yes
$1000
slow
v. high
yes in*
111.411(1.« 1
4. dual seam
(posit ive
pressure)
yes
yes
$200
fast
mod.
yes-114
nunutrl
low
5. ultrasonic
pulse echo
•
yes
yes
$5000
mod.
high
yes-no
auloiiKit-ic
UMdet'Jli-
6. ultrasonic
impedance
-
yes
yes
$7000
mod.
high
qua Iitat ive
autoaut ic
unknown
7.. ultrasonic
shadow
"
yes
yes
$5000
nod.
high
qualitdiive
autonuit ie
low
EPA VI - 22
-------
PANEL PLACEMENT LOG
Panel Number
Owner:
Project: _
Date/T ime:
Line & Grade
Surface Compaction:
Protrusions:
Ponded Water: Dessication:
Panel" Conditions
Transport Equipment:
Visual Panel Inspection:
Temporary Loading:
Temp. Welds/Bonds:
Temperature :
Damages:
Seam Details
Seam Nos.: • '
Seaming Crews:
Seam Crew Testing:
Notes:
Figure 6.5 Panel Placement Log
EPA VI - 23
Weather:
Temperature:
Wind:
Subgrade Conditions
-------
GEOMEMBRANE SEAM TEST LOG
CONTINUOUS TESTING DESTRUCTIVE TEST
SEAM
No.
SEAM
LENGTH
VISUAL
INSPECT
AIR
TEMP.
TEST
METHOD
PRESSURE
INIT/F1NAL
PEEL
TEST
SHEAR
TEST
LOCATION
OATE
TESTED
8Y
Figure 6.6 Geomembrane Seam Test Log
GEOMEMBRANE REPAIR LOG
DATE
SEAM
PANELS
LOCATION
MATERIAL
TYPE
DESCRIPTION.of DAMAGE
TYPE OF
REPAIR
REPAIR TEST
TYPE
TESTED
BY
Figure 6.7 Geomembrane Seam Repair Log
EPA VI - 24
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DRAINAGE/FILTRATION COMPONENTS
The leak collection and removal system is designed to drain liquids
accumulating in the liner system. Conventional leak collection systems
consist of a 1-foot-thick granular media immediately overlying the
hydraulic barrier. The ability of this system to drain away moisture is
enhanced by constructing the system at a minimum slope of 256, and by using
permeable sands or gravels that are free'of fines. Geosynthetic components
within a conventional LCR system are usually limited to the possible use of
a geotextile bedding layer over the underlying FML, and the use of a filter
fabric to separate the drainage media from the overlying clays. Totally
synthetic LCR systems replace the layer of gravel or sand with a layer of
geonet or a heavy nonwoven geotextile having equivalent planar flow
properties.
Several key differences exist between the procedures used for
placement of the FML and those used for synthetic components within the
LCR. Unlike the FML, the LCR components are typically placed by the general
contractor responsible for the overall construction of the facility. This
contractor may not show the same expertise in the placement of LCR
components that the specialized manufacturer/installer has in the placement
of the FML. Thus it is important that the CQA officer play a greater role
in monitoring the quality of LCR components. The geonets.geocomposites, and
geotextiles used in the LCR are also normally frequently fabricated in the
field during installation. A given roll of drainage net may therefore not
have a unique location in the facility. The CQA officer will therefore have
a greater responsibility to monitor and record the placement of these
components by roll or mianufacturer's lot number.
Specifications
The project specifications must clearly' indicate the required design
performance criteria for the potential drainage and filtration components.
While the variations in synthetic materials to be used is considerable, the
basic requirements are very simple. These requirements include:
1) All synthetic compounds must be inert and unaffected by
long-term exposure to potential leachate or design loads.
2) Drainage materials- must satisfy minimum TGD criteria
under the normal loads predicted for the specific facility.
3) Filtration materials must not clog or blind due to the
fines contained in adjacent soils.
4) Adhesives or hot glues used to adhere the various synthetic
components together must not contribute constituents to
the leachate.
5) All connections must be made using the same polymer system
as Is used for the geomembrane seams themselves.
These criteria are design-oriented and not readily field tested or
evaluated. The project specifications may therefore define criteria that
EPA VI - 25
-------
are not readily verified by the CQA procedures. It is usually necessary for
the CQA officer to establish index tests for each component to ensure that
installed materials are the same as those prequallfied in actual laboratory
tests.
Component Qualification—
The prequalification of a given synthetic product is normally the
responsibility of the manufacturer. Appropriate laboratory tests must be
performed on each component using actual site-specific soil samples
provided by the design engineer. The results of such testing and a sample
of the synthetic material are normally submitted to the design engineer for
approval prior to bidding the project. Confirmation tests are performed at
the discretion of the design engineer. Design-oriented testing performed on
LCR components includes the following:
1) Drainage materials must have a minimum transmissivity~pf.
0.02 ft^/minute. at gradients less than 1 and under normal
loads anticipated in actual service. Consideration of
long-term compressive creep should be addressed in this-
testing.
2) The clogging or blinding potential of geotextiles used in
filtration must be evaluated using the gradient ratio
method or an approved test.
3) The frictional strength between a geosynthetlc component
and its adjacent soil or synthetic component is evaluated
using a large size direct shear test. A minimum shear box
size of 12"xl2" is recommended.
4) Tensile strengths should be evaluated using wide-width
test procedures for geotextiles or geonets.
These tests are not suited for field CQA needs. Once a geosynthetlc
material is qualified based on its design properties, then index test
properties for that material must be established to ensure that it Is not
replaced by an inferior product during construction. These properties
include unit weight, thickness, tensile strength, trapezoidal tear,
puncture and color. Sueh index properties serve as.a fingerprint, of the
qualified material and enable the CQA officer to monitor field
installation.
Delivery and Storage—
Geotextiles, geocomposites, and geonets are typically shipped to the
Job site in rolls. Project specifications must require that each roll be
protected with a covering that prevents physical damage, contamination by
dust or water, and exposure to direct sunlight. The specifications should
also require that each roll be identified with the following mimimum
information:
1) Name of manufacturer/fabricator,
2) product type,
3) product unit weight,
4) manufacturing lot number,
EPA VI - 26
-------
5) date of manufacture,
6) physical dimensions (length and width),and
7) panel number per design layout pattern if applicable.
The site CQA officer should inspect each roll to ensure compliance with
these specifications and maintain a record of all roll identification tags.
Project specifications should require that all geotextiles delivered
to the Job site be stored in a secure area that protects the rolls from
vandalism by man or animal, contamination by soil, dust or water, and from
extreme heat caused by direct sunlight. An example of such a problem is
when a heavy geotextile drainage material becomes saturated by rainwater.
The unit weight of the material can triple causing considerable difficulty
is placing the material without damaging it or underlying components.
Installation—
Installation specifications for geosynthetic components in the LCR
system must ensure that the completed LCR drains properly and that it will
remain free-flowing for the design life of the cell. The drainage of a
synthetic LCR is influenced by both vertical and horizontal alignment and
folds or wrinkles in the imderlying FML. The drainage characteristic of a
conventional 1-foot-thick drainage layer is not significantly influenced by
the presence of folds or wrinkles in the FML. Synthetic drainage layers,
however, are less than an inch in thickness. Thus significant folds or
wrinkles in the underlying FML can actually lead to a reverse flow in the
as-built system. Project specifications must clearly indicate the accuracy
to which the alignment must be maintained and the amount of wrinkles or
folds allowed in the FML. Excessive wrinkles or folds are usually corrected
by cutting the FML, overlaping the edges of the cut, and then seaming the
exposed edge of the cut.
Project specifications should also clearly indicate the Joining
details for both drainage and filter components. Drainage media may simply
require butting adjacent panels together whereas a material overlap is
normally required for filtration layers. Geonets are typically Joined using
polyethelene ties to bind butted panels together. If a composite drainage-
filtration component is used, then the filter fabric may be heat bonded to
Join adjacent panels. Horizontal seams in the drainage media should be
avoided on sideslopes because of the reduced tensile strength of such
Joints. A minimum overlap of a filter fabric \Z to 18 Inches is commonly
used to prevent movement of- fines into the drainage core.
Sampling and Testing—
Synthetic components for the LCR systems are normally Installed by the
general contractor responsible for construction of the facility and not a
specialized manufacturer/installer. The general specifications should not
require the general contractor to perform index tests on the material. The
specifications should require the general contractor to maintain a record
of the manufacturer's data that accompanied each roll and to perform a
visual inspection of the material to check for obvious damage or variation
in material.
The responsibility to perform index tests and obtain samples of the
LCR materials should be maintained by the CQA officer for the facility.
This is discussed in greater detail within this section.
EPA VI - 27
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Construction
Construction of a leak collection/detection layer should extend up
the sldewalls. The advent of synthetic drainage nets has resulted in many
facilities being constructed with the synthetic systems on the sldewalls
and having bottom drainage layers of granular material and drain pipes.
Synthetic drainage net material is often used on the sldewalls in place of
the granular system because it is easy to install on steeply sloped
sldewalls. Steep sldewalls cause the granular drainage material to slump
down, whereas the synthetic drainage material tends to remain in place. An
obvious fabrication rule is to avoid horizontal seams in the synthetic LCR
systems on the sideslopes. All seams are**c|apable of only a portion of the
tensile strength of the parent sheeting and should be avoided when the
synthetic will experienced prolonged tensile forces.
A conventional leachate collection/removal system is Installed in the
following manner: A layer of granular material (about 5 cm thick) is
spread over the underlying layer (e.g., an FML). The protective soil
covering should be comprised of material which is free of clods, stones or
other sharp objects that can puncture the FML. If the underlying layer is
an FML, the granular material will provide protection for the FML as well
as bedding for the drain pipes. The perforated pipes are then laid on this
layer according to the drainage layout in the design specification. In
most cases, perforated pipes of four to six inches in diameter are used.
The perforations in the pipe should be faced downward to, prevent clogging
from the drainage material. After placing the pipes, the' remaining
granular material is spread over the area in a single loose lift to the
required thickness and compacted with a vibratory roller into a firm base
for the primary FML.
If synthetic drain panels are used, they should be unrolled and
spotted as in FML Installation, however, the panels are not overlapped and,
seamed. They should be placed end to end and connected according to the
manufacturer's suggested procedures, with the lower portion of the panel
extending into the granular or other bottom layer to enhance continuity
between the drain layers. A geotextile filter should be placed on top of
the drain panels to prevent clogging due to infiltration of fine materials
from above. The synthetic drain system should be secured in the anchor
trench as in the FML installation.
Construction Quality Assurance
As discussed earlier, the CQA program plays the role of monitoring the
installation of geosynthetic components within.the LCR. Each filter or
drainage component is usually accepted based on design tests that are not
reasonable for use in field CQA applications. The design engineer must
therefore provide the CQA officer with a 'fingerprint* of the accepted
material that uses simple index, tests as a basis for acceptance.
Additionally, since these components are typically fabricated In the field,
the CQA officer must establish a record keeping system that records the
final location within the facility of all inventoried rolls.
As a practical consideration, It is important that the CQA officer be
provided samples of each of the components that are known to satisfy the
EPA VI - 28
-------
design criteria. With these reference 'standards* the CQA officer has a
basis for evaluating general field observations. It is also recommended
that the CQA officer inventory and obtain a sample of each roll of
geosynthetic that is received at the jobsite. These samples should be
marked to identify the machine direction and tagged with the manufacturers
roll information. An alternative to sampling every roll is the geotextile
sampling strategy given by ASTM D4354. This strategy samples a limited
number of rolls within a given lot designation. The number of rolls sampled
is a function of the total number of rolls in the lot.
Filtration Fabric Index Tests—
Filtration fabrics function to allow leachate to pass into the
drainage materials and to minimize the movement of soil particles through
the plane of the fabric. As such the size of the pore spaces ( or Apparent
Opening Size ) and permittivity of the fabric are key physical properties.
The problem is that the AOS and permittivity of a geotextile are not ready
field Indexes. Assuming that the correct polymer, fabric construction (e.g.
nonwoven), and surface finish are used, the use of unit weight should
provide a reasonable control for filtration fabrics. Care must be taken to
properly precondition the fabrics before measuring unit .weights to
eliminate descrepancies due to variations in water content. Oven drying the
fabric samples in the same manner that soils are dried (ASTM D-2216) is
recommended.
Geosynthetic Drainage Material Index Tests—
Geosynthetic drainage components Include geonets, geocomposites, and
thick geotextiles. The physical structure of the geonets and composites is
large enough that a visual comparison with the 'standard' maintained by the
CQA officer and a comparison of unit weights and/or thickness . should
provide adequate quality assurance for these components. As with
geotextiles, care should be taken to precondition the samples prior to
obtaining unit weights to eliminate variations in moisture content. The
thick nonwovens used as drainage layers pose a more difficult problem to
properly 'fingerprint' using index tests. These materials will normally be
a composite that includes the filtration layer and the drainage layer.
Field testing of such nonwovens will typically be limited to unit weight as
recommended for filtration fabrics.
SUBGRADE
General industry suggestions are very similar regarding subgrade
characteristics. For an earthen structure, the subgrade must be firm and
dry, free of all rocks, roots, debris, or other objects that might tear or
puncture the liner. Excavation and backfilling are recommended if necessary
to meet these conditions. Where vegetation has been cleared to prepare the
site, or soil has been brought in to provide a bed for the liner, soil
sterilization may be specified to prevent grasses from growing through the
liner. This is especially true in areas where prior growths of nut or quack
grasses have existed. Areas where excavated soil is deposited to create
subgrade may also require sterilization. Care must be taken in soil
sterilization since most sprays used for such applications are highly toxic
and are hazardous by themselves. Compatibility of any synthetic component
that will contact the sterilized soil should be verified. A survey, of
EPA VI - 29
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current methods of constructing compacted soil liners by Elsbury (1985)
Identifies processing, placement, and compaction required to construct a
suitable soil liner.
Specifications
With regards1 to geosynthetlcs within hazardous waste facilities, the
major concerns regarding soils are that they provide adequate support to
the synthetic component and that they are free of rocks or other objects
that could damage adjacent geosynthetlcs. The support characteristics of
the subgrade are normally covered in the project specifications by
requiring a given percentage compaction of the soil beneath secondary FML
and the drainage media below the primary FML.
Construction
Compaction of the subgrade is normally specified to provide a firm
support for all membrane lining materials. Generally, a fill subgrade is
compacted only at the surface. Usually, the minimum compaction of the
subgrade material will be specified. Most liner Installations specify that
the density of the subgrade be at least a specified percentage of that
obtainable by the Standard Proctor Test, ASTM D698, with 90 percent of
Proctor being the most frequently specified relative compaction. Some
contracts will specify the compaction equipment which is to be utilized,
number of equipment passes per layer, layer thickness, permissible water
content range at placement, and method and location of water addition.
The regularity and texture of the surface of the uppermost layer is
critical to a successful liner installation. A plane surface after
compaction is the most desirable one for liner placement but is not always
achievable or specified in the contract. In many installations, soil clods
or local surface irregularities will be flattened (further compacted) by
the overlying weight of the stored material after the facility is filled.
Further, it Is thought that the polymeric membrance liners will adjust
their- shape over any clods so that no detrimental effects will result.
Nevertheless, rocks or Irregularities with sharp edges must be eliminated
from the finished subgrade during the compaction/construction process even
when not specified in the contract if liner integrity is to be maintained.
Within the polymeric membrane liner industry, there is a difference of
opinion as to how smooth surfaces must be to maximize liner Integrity. The
opinions vary with the liner material. It is generally agreed, however,
that the smoother the finished surface, the chance of liner failure due to
subgrade inadequacies is reduced.
Fine Finishing of Surface—
If compaction has been accomplished with a sheepsfoot compactor, it is
normal to fine-finish the surface. 'Fine-finishing is an intensive aspect
of subgrade preparation.. Depending on the design specifications, various
techniques are irecommended. A smooth surface on the bottom and sidewalls
can be accomplished with various drags which aid In the formation of a
regular, flat working surface. Fine-finishing with vibrating rollers and
drags Is recommended on a slightly.wet surface; thus, water tank trucks may
be required during the .fine finishing activities. Occasionally, soil
EPA VI - 30
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additions are required to bridge surface irregularities if the
irregularities cannot otherwise be removed. Sand is useful for this
purpose as it is easily compacted.
The fine-finishing process is critically dependent on the proper care
and control of water. If rain occurs during or immediately after >the fine
finishing work on a slope, small brooks, ruts, ravines, etc., may be eroded
into the surface. Thus,the expenditure of effort to fine-finish slopes and
bottoms for subsequent membrane liner placement is not recommended when
rainfall is imminent; conversely, the placement of liner material on fine
finished slopes is recommended as soon after completion of "finishing" as
possible to ensure that no surface soils are "lost" to the erosive effects
of surface runoff. During the fine-finishing stage, any grasses and other
vegetation must be removed from the subgrade layer to prevent their
penetration into the FML layer. Timing,between activities Is critical in
maintaining proper moisture content of the subgrade; therefore, the FML
should be placed on the finished subgrade as soon as possible after
completion of the finishing process.
Construction Quality Assurance
The construction quality assurance program for the placement of the
soil liner under MTG (EPA,1985) begins with the construction of a test fill
to establish the relationship between the index properties used to monitor
construction and the physical soil properties used in the design. EPA
guidance provides the following guidance for test fills:
1. Construction of the test fill should use the same
materials, equipment, procedures, and CQA to be used In
the actual facility;
2. The test fill should be at least four times wider than *
the widest piece of equipment to be used in construction;
3. The test fill should be long enough to allow construction
equipment to reach normal operating speeds before
entering the test fill;
4. Construction data should be used to determine the
relationship of field test results (moisture
content/density/hydraulic conductivity) to the compaction
method, equipment speed, and loose and compacted lift
thickness; and
5. A set of index properties should be selected for
monitoring and documenting the quality of construction
obtained in the test fill.
During placement of the subgrade, a documented program of measuring and
logging the index tests in the subgrade must be implemented. Details of
such a program are presented elswhere (EPA, 1986a).
EPA VI - 31
-------
Between the time that the subgrade is placed and the FML is installed,
the condition of the subgrade can deteriorate. The panel placement log
requires the installer to approve the subgrade prior to placement of the
liner. This approval is typically based on a visual inspection of the
subgrade for surface quality and the use of proof rolling to establish the
strength of the subgrade. Proof rolling may simply be monitoring the rut
depth produced by construction related equipment passing over the site.
Excessive rutting indicates that subgrade soils have been disturbed and
require replacement before the liner is installed.
REFERENCES - SECTION VI
Bass, J.M., et al, (1984), Assessment of Synthetic Membrane Successes and
Failures at Waste Storage and Disposal Sites, U.S. Environmental Protection
Agency, Cincinnati, OH.
Elsbury, B.R., et al, (1985), Optimizing Construction Criteria for
Hazardous Waste Soil Liner, Phase I Interim Report, U.S. Environmental
Protection Agency, Cincinnati, OH.
EPA, (1985), Covers for Uncontrolled Hazardous Waste Sites, EPA/540/2-
85/002, Environmental Protection Agency; Cincinnati, OH.
EPA, (1986a), Construction Quality Assurance for Hazardous Waste Land
Disposal Facilities, U.S. Environmental Protection Agency, Cincinnati, OH.
EPA,(1986b), Hazardous Waste Surface Impoundments (Draft), Prepared by K.W.
Brown and Associates for U.S. Environmental Protection Agency, Cincinnati,
OH.
Frobel, R.K., (1984), "Methods of Constructing and Evaluating Geomembrane
Seams,? Int. Conf. on Geomembranes, IFAI, Denver, Co.
Gagle Company, Inc., (1986), Construciton Quality Assurance Quality Control
Manual, Tulsa, OK.
Gundle Lining Systems, Inc., (1986), Quality Control Manual, Houston, TX.
Haxo, H.E., (1983), "Analysis and Fingerprinting of Unexposed and Exposed
Polymeric Membrane Liners," Proc. 9th Annual Research Symposium, Land
Disposal of Hazardous Waste, EPA-600/9-83-018^
Kays, W.B., (1977), Construction of Linings for Reservoirs, Tanks, and
Pollution Control Facilities. John Willey & Sons, New York.
Koerner,R.M., et al., (1987), "Geomembrane Seam Inspection Using the
Ultrasonic Shadow Method," Proc. Geosynthetics '87, New Orleans, IFAI.
Koerner,R.M. and G.N. Richardson, (1987), "Design of Geosynthetic Systems
for Waste Disposal," Proc. ASCE-GT Conf. on Geotechnical Practice in Waste
Disposal, Ann Arbor, MI, June.
EPA VI - 32
-------
Lord, A.E. Jr., (1986), "NDT Techniques to Assess Geomembrane Seam
Quality," Proc. Mgmt. Uncont. Haz. Waste, Washington, D.C., HMRCI.
National Sanitation Foundation, (1983), "Standard Number 54 for Flexible
Membrane Liners, Ann Arbor, MI.
Poly-America, Inc., (1986), Reference Manual-An Engineering Approach to
Groundwater Protection, Grand Prairie, TX.
Schlegel Lining Technology, Inc., (1984), Quality Assurance Program,
Houston, TX.
Schultz, D.W., (1983), Field Studies of Liner Installation Methods at
Landfills and Surface Impoundments, U.S. Environmental Protection Agency,
Cincinnati, OH.
Schultz, D.W., (1985), "Field Studies of Geomembranes Installation
Techniques," Int. Conf. on Geomembranes, Denver, CO, IRAI.
Schmidt, R.K. , (1983), Specification and Construction Methods for Flexible
Membrane Liners in Hazardous-Waste Containment, Technical Report No. 102,
Gundle Lining Systems, Inc., , Houston, TX.
EPA VI - 33
-------
Cell Component: FU^eie. Membraus.
Consideration: JdiMeJ=j£x •* BAq
SPK*feo. rML/FMd. PAm£l^ dJriu^ Pia^CmCmT.
Required Material Properties
Range
Test
Standard
Fl£x'»L£ MiMftlAue
• liM>T HEIGHT
3-20ovr
BEWSJTr
asTm one
Dull MIG KWmun
Analysis Procedure:
PfcTegMiue pesi<;ij MakimJm Uimp Speed VMIUO
•UsS «|T6 SPEOF'C DATA REF6REV6 Fi .#• puiiJO
KJott : Perform Uweab. inter p»i-atk»u f«r peptms ^"<»ft
(^ JlaTE Samp Sao
• Us* WEi^wt op sAue>0Aq
• -mi&UrARY A*6A= Puluo/us-- TA
^AlgJl.Mfc C>t*lqM RaTiO
OK -
TA/
Ca- fieldtribitTA*.y area]
Design Ratio: References:
Example:
• PmiLA06LPHiA,PA
-AuuJal Extreme. Uiud^peeo CF"iq£,2*)
^wiuo "SOwpK
• Uiiuo » |O0 Y* E«TB,EmE. j OpEMiToiluTRY
• FML DEPTH "~2 O FX
• 5*.tJOBA.q 3 0O lb. @ | PEO. IO S<». Ft.
• Height t® Fm • - Zofr oft ^ 4 2a Fr
(D DETERMINE Desi^h Max'mJm Uimp Speed %V UIUP
'UMfcjp
- so MPH ^TRef
I1-) PtTSBMixe U*©0 MPH
Limeab
TMTtHPlA-P'U
C R£f. TAjBLL ^ALCJlAT& SauO Bfcq SPAIi-JC^
-*o Fr Soib/,, psF s ¦s^f x-
^TaL^iKaTE PEtie;i_i Ratio^
-to FT. =»• l.t>l\o.o- o.T} wq
O F-r =*• 5-t/io.o = 0.57 fiq
2.l
-------
SECTION VII
LONG TERM SERVICE CONSIDERATIONS
This section of the report brings into focus the fact that solid waste
disposal facilities must be designed with long-term service considerations
in mind. Up to this point in the report, the focus has been on Immediate,
or short-term, events and phenomena. Now, time frames of 30 to 50 years
(some people suggest much longer) must be envisioned. Hence, chemical,
biological, thermal and general aging deterioration of the liners and their
leachate collection/removal systems must be considered. Unfortunately,
quantifiable design methods for long-term concerns are usually not
available. Thus this Section is written on a qualitative basis. Whenever
possible, specific data and Information will be offered. The section Is
divided into three parts: the FML's, LCR's, and the cap/ closure system.
FLEXIBLE MEMBRANE LINERS
Of foremost Importance with the liner themselves is the long-term
effects of leachate on polymeric materials from the leachate within the
containment cells. This includes both the primary and secondary FMLs on
both bottom and sides of the facility. Schnabel (1981) defines polymer
degradation as changes in physical properties caused by reactions Involving
bond scission. Bond scission may be initiated by chemical, photochemical,
biological, thermal, mechanical, and radiation stimuli.
Chemical Attack
As noted in the Introduction, chemical degradation and its testing
protocol is beyond the report scope. It is, however, foremost in
importance and, as such, covered elsewhere in various EPA documents, e.g.,
see Matrecoh(1987). It should be brought to mind, however, that the current
testing protocol via EPA 9090 Method is focused on highly concentrated
leachate exposure at elevated temperatures for very short periods of time,
e.g., for 120 days. It begs the question as to the influence of low-
concentration, ambient temperature, and long-exposure effects on the liner,
where a sparsity of information is available. Clearly, research is needed
in this regard.
The main mechanisms involved in chemically Induced bond scission insofar
as thermoplastic materials like PVC, CPE, HDPE, etc, are concerned as
follows:
o Metathese - breaking of carbon-to-carbon bonds
o Solvolysis - breaking of carbon-to-noncarbon bonds in
the amphorous (liquid phase)
o Oxidation - liquid reaction with molecular oxygen
o Dissolution - separation into component molecules by solution.
Obviously, when taken either separately or collectively, the above
mechanisms will have a negative effect on the FML's ability to function
properly.
EPA VII - 1
-------
One approach which has been taken to evaluate chemical mechanisms Is
that of accelerated aging at elevated temperatures. By obtaining a
reaction energy between two test specimens at different temperatures and
using an analytical model, e.g., Arrhenlus modeling, It Is possible to
obtain a long-term projection of the equivalent time exposure. The
Arrhenlus model.assumes that the the rate of chemical reactions is given by
K* - Rt/C Eq(7.1)
where JC* is the rate constant at temperature (t), R"1- is the measured rate
of change of a chemical component, and C is a constant. The rate constant
is a. function of temperature according to the, Arrhenlus equation
v .: K - Ae"E/RT Eq(7.2)
where A is a constant, E is the reaction activation energy, T is
temperature (°F), and R is the gas constant. See Koerner and Richardson
(1987) for a numeric example of this procedure.
This procedure is however, not without its limitations and challenges
and must be further assessed for its validity and usefulness. Studies by
Mitchell and Cuello (1986) indicate that immersion tests such as EPA 9090
give slmillar results and are much less expensive. They felt that the added
cost and complexity of the accelerated aging test did not appear to be
warranted.
Photochemical Attack
Photochemical attack of polymers is caused by ultraviolet (UV) light
that foster oxidation of the polymer. UV resistance in polymers is normally
achieved by adding a low (<5#) percentage of carbon black to the polymer to
make the membrane opaque. Accelerated testing of photochemical aging is
performed by focusing mirrors on the test specimens to concentrate the
sunlight. As this also generates significant heat, it is normally necessary
that the specimens be sprayed with water to cool them. This test is
referred to as EMMAQUA, equitorial mount with mirrors plus water spray. The
method normally accelerates the solar exposure by a factor of 8.
EMMAQUA test results reported by Morrison and Parkhill (1986) Indicate
that thermal degradation of samples typically occurred after 6 months of
exposure. HDPE samples actually melted during this exposure; Indicating
that the degradation may have been more thermal than photochemical. This
work also suggests that the current NSF Standard 54 EMMAQUA requirement for
certifying new FML's may also be too severe. The NSF standard requires the
equivalent of eight months of EMMAQUA exposure.
Ozone Attack
Ozone, a powerfully oxidizing form of oxygen (O3), attack of FML's has
been .recognized as a potential problem as evidenced by the number of ASTM
test standards directed towards its evaluation. All currents tests,
however, seem to focus on thermoset membranes. Such tests Include ASTM D518
(general rubber deterioration), ASTM D1171 (surface ozone cracking
outdoors), and ASTM D1149 (surface ozone cracking in a chamber). In this
EPA VII - 2
-------
latter test, the specimens are placed under a tensile stress or strain In a
chamber containing an ozone-air atmosphere at a controlled and prescribed
temperature. The ozone concentration can be varied and Is measured by a
spray-jet device or a single column absorption device. The test specimens
are examined at given time Intervals and their condition recorded. Failure
is caused by surface cracking In the high stress or strain region as
observed under a slight magnification. Test method ASTM D 1171 recommends a
2X magnification, while ASTM D1149 recommends a 7X magnification. When
comparisons are being made to a given reference material, they are usually
made at fixed time Intervals with the comparison based on the degree of
cracking.
Biological (Micro-organism) Attack
The microbiological degradation of FML's by micro-organisms such as
fungi and bacteria has received very little attention. Clearly, solid
waste has a great abundance of micro-organisms, some of which are
detrimental to certain plastic products. It Is likely that the more
organic the waste, the more active will be those micro-organisms. The focus
of biological problems with FML's is that once the bacteria or fungi has
attached themselves to the synthetic or natural material adjacent to the
liner they will eventually use it for a food source. This would be
disastrous to the integrity of the FML. Current research is directed
towards developing synthetic systems that resist the growth of such micro-
organisms. Microbes may be placed In four categories;
o Bacteria (weight may exceed 1,000 pounds per acre for soil)
o Fungi (One gram of soil commonly containing 10 to 100 meters of mould
filament)
o Actinomyces (one gram of soil containing 0.1 to 36 million)
o Algae (a number of varieties exist).
The premier reference in this area is an in-house research report by Khan
of ICI, as reported by Rankilor in 1981. The summary table is reported
below (See Table 7.1) in which It can be seen that all plastics suffer some
deterioration. It also must be remembered that these results are for soil
microbes which might well be less numerous and less harmful than those
resulting from solid waste in a landfill.
Research has been conducted by the electric transmission line industry
for buried plastic conduits. Rankilor (1981) reports on some of this data
where severe degradation has not occurred at least by micro-organisms.
EPA VII - 3
-------
Table 7.1
Material
- Micro-biological Attack on Plastics, after Rankllor (1981)
Observations on susceptibility
1.Nylon The material contains polypeptide linkages, and it might be
supposed that microbiological attack is highly probable.
According to Russian work, nylon suffered from a change of color
and a weakening of the film due to microbiological attack,
particularly by Penicillium and Aspergillus.
2.Polyester
Microbial degradation of the material was reported by several
investigators. Potts, et al (1973) found blodegradation of
polyesters of varying structure and molecular weight (a group of
fungi and bacteria used as test organisms). They found that an
epsilon caprolactone polyester of about 40,000 molecular weight,
which had no branch, was readily utilized by fungi and bacteria.
3.Poly-
ethlylene
The material shows a good resistance to microbiological attack,
especially when pigmented with carbon black. The US Navy
Department observed that the material of lower molecular weight
supported microbial growth, this being In agreement with the
work of Jen-Hao and Schwartz. Potts, et al, found that some of
the LDPE having molecular weight between 10,000 to 14,000 was
appreciably blodegraded. They attributed this effect to the
presence of low molecular weight species (<500 mol wt.).
4.Poly-
propylene
The material shows good resistance- to microbiological attack.
Potts, et al, (1973) observed biodegradability of a large number
of commerical plastics including polyprolylene (a group of fungi
and bacteria were used as test organisms). The microbial growth
was thought to be due to the presence of a biodegradable
additive in the sample.
5.Polyvinyl The overall conclusion from several experiments is that the
material, rather than the polymer itself, is directly attacked
by microbes, particularly fungi. Hueck (1973) reported
discoloration of the PVC materials and precipitation of FeS by
sulphate reducing bacterial. Schwartz investigated a range of
chlorinated lower paraffins of Increasing chlorine content, and
showed that bacteria could use these easily as a source of
carbon up to chlorine content of 30#, above which growth rate
slowed down and became non-existent at 5056 (PVC and vinyl
chloride monomer have <50# of chlorine).
6.Poly- The material shows a fair amount of resistance to microbial
styrene attack. Potts, et al (1973) found hardly any microbial growth
on polystyrenes of molecular weight from 600 to 214,000 and on
copolymers of styrene (comonomers included were: acrylic acid,
sodium acrylate, dimethyl ltaconate, acrylonitrile, ethyl
acetate and methacrylonitrile). The chemical structure of
polystyrene is basically similar to that of polyethylene
(hydrogen atoms on alternate carbon atoms replaced by phenyl
groups). The introduction of the phenyl groups does not render
the polymer more bio-Inert since aromatic rings themselves are
biodegradable.
EPA VII - 4
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Thermal Effects
Short-term thermal changes can be particularly troublesome. During
cold cycles, FML's are stretched tight in many locations in a lined
facility. These same locations become very loose during warm cycles and
(when uncovered) often lift off of the ground where a wavy surface is
commonly seen to occur. Such variations even occur when cloud cover
shields the sun from striking the FML surface. Table 7.2 gives the
coefficient of thermal expansion of some common polymers aj^j calculates the
amount of deformation that occurs in section i', 10* and 100' in length due
to a temperature change from 100°F down to 50°F. Also shown is the
equivalent tensile strain that is mobilized in these sections due to this
contraction. While these equivalent strains appear low, they are calculated
assuming that the strain will be uniform over the entire length of the FML.
In the field this rarely occurs. Instead the strains tend to be very
localized and can lead to significant fabrication problems and possible
failure of seams.
Table 7.2 Thermal Properties of FML's and Illustration Showing the
Influence of a Temperature Change of 50°F
Material Average Coefficient of Change in Length Corresponding Tensile
Thermal Expansion
(x 10~5 per lOp)
(Deformation) for
10'
100'
Strain
in FML {*>)
Polyethylene
low density
10
.0050
.0500
.500 ft.
.50
med. density
12.5
.0062
.0625
.6250
.62
high density
12.5
.0062
.0625
.6250
.62
Polypropylene
6.2
.0031
.0310
.3100
.31
Polyester, cast
alloy type 4.2
styrene type,
rigid 4.8
.0021 .0210
.0024 .0240
.2100
.2400
.21
.24
Polystyrene
general purpose 4.0
heat, chemical
resistance 3.7
Polyamide
Nylon 6,6 5.5
Nylon 6 5.0
Nylon 11 5.5
.0020 .0200 .2000
.0018 .0185 .1850
.0028 .0275 .2750
.0025 .0250 .2500
.0028 .0275 .2750
.20
.18
.28
.25
.28
Temperature under natural conditions never reach the softening or
melting point of the polymers. For example:
o Nylon 66: sticks at 445°F (229°C); melts at 500°F (260°C)
o Polypropylene: melts at 325°F (163°C) to 335°F (168°C),and
o Polyester: melts at 325°F (249°C to 550°F (288°C),
EPA VII - 5
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These temperatures cannot be reached unless some unnatural event occurs.
Unfortunately, landfill fires are not at all uncommon and In such cases
these high temperatures can be reached. They would be disastrous to the
Integrity of the FML.
The actual temperatures reached at the bottom and sides of a solid
waste landfill have been measured and values as high as 160 ° F have been
reached. As shown in Table 7.3, Wolfgang (1959) gives a very comprehensive
list of the burning characteristics of fibers. While not of direct concern
to the FML Itself, such elevated temperatures will actively promote
biological growth which was discussed previously.
Table 7.3 Burning Characteristics of FML Polymeric Materials,
after Wolfgang (1959)
Fiber Polyethylene Polypropylene Polystyrene
Before touching
flame
flame
After leaving
Odor
Ash
Melts, shrinks
and curls from
flame
Melts and
burns
Burns rapidly
Burning
paraffin
Soft, round
same color as
fiber
Shrinks rapidly
from flame,
curls and melts
Melts, ignites
with difficulty
Burns slowly
Faintly like
burning asphalt
Hard, round
light tan
Melts, shrinks,
and curls from
flame
Melts and burns
Burns rapidly with
production of great
deal of soot
Benzene
hyacinth
Soft, round,
same color as
fiber
Environmental Stress Cracking
Stress cracking of polyethylene has been reported as early as 1950 by
Carey (ASTM Bull, ASTBA, No. 167, July 1950), and its significance has been
recognized via ASTM Standard D1693 entitled "Environmental Stress-Cracking
of Ethylene Plastics". Under certain conditions of stress and in the
presence of environments such as soaps, wetting agents, oils, detergents,
or organic substances, ethylene plastics may exhibit mechanical failure by
cracking. Figure 7.1a shows the existence of such cracking which occurred
on laboratory test specimens but has also been similarly seen in field
applications.
By definition, stress-crack is an external or internal rupture in a
plastic caused by a tensile stress lower than the short term mechanical
strength of the material. Failure is usually interpreted by visable
EPA VII - 6
-------
DENDRITIC CRAO
A
Holder
Tension
THROAT RUPTURE
O
-\ s
J
V
o
Wel
-------
deformation
o brittle failure or fracture In a direction perpendicular to the
direction of loading.
The distinction between the first two cases is the magnitude of the stress
level verses the yield stress of the FML at 50°C. Stress levels less than
yield will produce minor deformations while stress levels above yield leads
to large deformations. The third case is of greatest concern and leads to
cracking which is usually very' dramatic and problematical. ,
All candidate FML polymers should be evaluated in this manner before
final acceptance for use in a landfill or surface Impoundment. Such tests
should be carried out in both the FML sheet and the seams used to join
sheeting. This latter case of seam cracking is quite possibly related to
poor workmanship practices, see Figure 7.1b.
Aging Effects from Soil Burial
FML degradation due to burial in soil involves numerous chemical
Interactive processes. While very complex to assess, all involve the
potential oxidation-reduction breaking of bonds, previously referred to as
bond scission. Research involving soil burial Is relatively scarce and
certainly very fragmented. Some of the findings will be described here,
but it should be noted that solid waste burial represents a much more
aggressive environment than the reported work to date. As such, these
findings should be considered "lower-bound" observations.
The ICI report cited earlier and reported in Rankilor (1981) presents
numerous situations.
o On Polyamides: Soli tests on 26 specimens were reported
Strength changes were the most noticeable for Nylon 6,
following occurred:
1 year burial - 9056 of strength retained
2 year burial - 90-88# of strength retained
4 year burial - 80# of strength retained
8 year burial - 75# of strength retained
The loss of strength was attributed to polylmer degradation by
hydrolysis due to soil moisture. Water is absorbed by the polymer and
diffuses in It, thereby causing bond scission. These diffusion routes
and their rates are quite important to assess and then to compare to
the local environment (particularly when under elevated temperatures)
and the level of mechanical stress.
o On Polyester: Potts, et al report on caprolactone polyester exposed up
to 12 months in an unidentified soil. The results were dlsasterous as
seen in Table 7.4. While only conjecture, it is possible that the soil
was highly alkaline, in which the above effects could have been
anticipated. More complete details are given on this topic in the
discussion of leachate collection/removal systems in this section.
by Miner,
where the
EPA VII - 8
-------
Table 7.4 Soil Burial Tests on Polyester
after Potts,et al (1973)
Burial Time
(months)
Tensile Strength
(lb/sq.in.)
Elongation
(*)
Veight Loss
(*)
0
2
4
6
12
2610 + 103
1610 + 180
520 + 220
100
negligible
2.6 + 1.1
negligible
negligible
369 + 59
7 + 2.0
0
8
16
25
42
o On Polyolefins: For polyethylene and polypropylene buried up to 8
years, Miner (1973) found insignificant changes in strength. De Coste,
however, found that high density polyethylene suffered major loss In
elongation, even to the point of embrittlement, and a slight decrease
in strength. This may not have been from the soil, however, since the
air-aged specimens had similar results. Thus the results are not very
conclusive.
o On Polyvinyl Chloride: The premier body of information on PVC liners
is held by the U.S. Bureau of Reclamation. They have used PVC liners
for water conveyance canals for over 20 years. Numerous reports have
been issued on the subject of aging, see Morrison and - Starbuck. In
general, loss of plasticlzer by leaching occurs over time resulting In
black tacky surface deposits on the liner. This usually is accompanied
by a slightly lower elongation at failure, higher tensile strength and
higher modulus. There appears to be no direct evidence that the PVC
resin itself has been degraded.
o On Polystyrene: Eight year soil exposure test were conducted by Miner
(1972) who found a "mild effect" on these compounds. Details of the
soil environment and the particular type of polystyrene were not
included.
In all of the foregoing discussion, it must be remembered that this report
deals with solid waste and "generic" families of plastic FML's. This latter
point is worthwhile emphasizing since one type of polymeric liner material
might (will) be very different than another. Haxo, et al (1984) gives a
indication of the variations that a particular liner material can contain,
Table 1.1. Notwithstanding the polymer variations, there are particularly
hostile soils where care must be exercised.
o Acid sulphate soils occur in flat, swampy or marshy, organic areas and
generate dilute surphuric acid . Solid waste is expected to produce
similar conditions. The net effect is a very low pH where it is known,
for example, that polyaramids deteriorate rapidly.
o Organic soils are troublesome in that three conditions usually result;
organic acids and solvents are generated, water saturation occurs and
. microbial activity is high. Each situation is somewhat site-specific.
EPA VII - 9
-------
o Chemically active soils should obviously be dealt with cautiously.
Usually grouped by pH and then followed by details such as the
predominantly soluble' salts or ferrous (ferric) oxide, the appropriate
liner polymer is essentially handled via the chemical compatability
testing protocol, e.g. EPA Method 9090.
o Volume-change soils such as result from expansive clays or frost heave
are geotechnical engineering related phenomena and must be treated as
such.
Echoing Rankilor's closing statement, "there is a clear indication of an
increasing need for soil burial tests". We add, that when solid waste
burial is involved the need Is even greater.
LEACHATE COLLECTION/REMOVAL SYSTEMS
While some of this subsection has overlapped with the previous one, the
emphasis here is on flow capability and clogging of drainage geosynthetlcs.
Only those strength and elongation considerations which may affect the
filtration and drainage functions will be considered, e.g. creep and stress
relaxation. Discussion here centers on the geotextile filter placed under
the solid waste and the geonet or geocomposlte drains placed above the
primary FML and between the primary and secondary FMLs.
Creep/Stress Relaxation Effects
Both of these long-term influences have impact on the filtration and
drainage capability of the geosynthetic systems involved. Creep is
particularly important in both primary and secondary leachate collection
and removal. At the extreme, of course, this flow capability can be
completely cut off causing the system to fall. Creep designs were Included
in each of the designs of Section 3 where appropriate. The primary point
to re-emphasize here is that a sufficiently high factor of safety on
breakdown stress of the drainage core and strength of the geotextile is
necessary. What this value Is numerically, however, is a difficult
decision unless specific experimental data is available. Some work has
recently become available in this regard, e.g. see Slocumb, et al (1986).
Stress relaxation is relevant for the geotextile filter covering the
primary leachate collection and removal system and for both primary and
secondary FMLs on both sides of the secondary leachate collection and
removal system. In both situations, large deformations can be anticipated
(hence reduced drainage capability) unless high factors of safety on
ultimate strength are used. Again conservatism is warranted In light of
Insufficient experimental data.
Chemical Attack
The chemical compatibility testing protocol for geotextiles, geonets
and geocomposltes is very poorly defined in contrast to FMLs. Standards
organizations like ASTM are just beginning to become Involved. While some
form of strength is the usual focus for incubated FMLs (i.e. tensile, tear,
EPA VII - 10
-------
puncture, etc.), one Is at a loss to target a comparable property for
geosynthetics used for a means other than a reinforcement function, I.e.
for drainage. At this point in time It Is probably best to use published
values of polymeric chemical compatibility of which a sizeable list is
available. Hoarz (1986) has recently published a large list from Amoco
Chemicals Corp., Phillips Fibers Corp. and Hoechst Fibers Industries for
both polypropylene and polyester. In such lists one sees trends, e.g.,
highly alkaline liquids degrade polyester geotextiles. However, to what
degree and precisely when the pH is a factor is not mentioned. Table 7.5
by Kaswell (1963) gives some generalized comments. Needed is work which
precisely defines the situation.
FLOW
TIME
(SEC)
200
180
160 •
140 •
Fabric
120 -
broka
100 ¦¦
to 494 sac
o at 122 days
~
PH « 12
(R-0.88)
o
PH « 10
(R-0.96)
¦
PH - 7
20 40 60 80 100 120
AGE (DAYS)
140
(Halse, et al)
Figure 7.2 Influence of pH on Permittivity of Geotextile
Figure 7.2 shows the time required for a constant quantity of alkaline
water (of indicated pH) to flow through a 3 oz/sq. yd. polyester
geotextile. Seen is that the time for a liquid of pH 7 liquid to flow was
constant, however at pH 10 flow increased dramatically and at pH 12 the
geotextile actually disintegrated. This response suggests that this type
of polyester geotextile should simply not be used with any highly alkaline
liquid. This information is currently under development for six
commercially available geotextiles indicated in Table 7.6.
It should be noted that there is no known data set for geonet or
geocomposlte drainage systems currently available. It is of major concern
and should be a high priority item.
EPA VII - 11
-------
Table 7.5 Chemical Resistance Properties of Fibers (Kasvell,l963)
EFFECT OF ACIDS
EFFECTS OK ALKALIES
EFFECTS OF OTHER CHEMICALS
EFFECTS OF ORGANIC SOLVENTS
Nylon fa Oxidising agents and Mineral acids
eucti as hydrocloric and sulfuric
cause degradation. Others euch as
bensolc and oxalic will cause loss
In tenacity and elongation depending
upon tlae and concentration. '
Substantially inert.
Generally good resiatance
Generally insoluble. Soluble
In cose phenolic compounds
and In concentrated foraic
acid.
Nylon 6b Boiling In ft* hydrochloric acid
ultiaately causes disintegration.
Dissolves with at least partial
decomposition In cold concentrated
solutions of hydrocloric. sulfuric,
end nitric acids.
Substantially inert.
Generally good resiatance
Generally insoluble. Soluble
in sose phenoic coapounds
and in concentrated foraic
acid.
Darvan
nytrll
Little effect even at high concen-
trations.
Fair to good resistance
to weak alkalies.
Generally good resistance
Generally insoluble
Polyethylene Very resistant
Polypropylene Very resistant „
Dacron
polyester
Fortrel
polyester
Kodel
polyester
Good resistance to aoat mineral acids.
Dissolves with at least partial
decoaposltion by concentrated solutions
of sulfuric acids.
Good resiatance to aoat mineral acids.
Dissolves with at least partial
decoaposltion by concentrated solutions
of sulfuric acids.
Good resistance to aott mineral
acids, and fair resistance to
concentrated sulfuric acid.
Very resistant with the
.exception of oxidative
agents.
Very resistant with the
exception of oxidative
agents.
Good resiatance to weak alkalies
and moderate resistance to strong
alkaliea at room teaperatures.
Disintegrated by strong alkalies
at boiling temperatures.
Good resistance to weak alkalies
and aoderate resistance to strong
alkaliea at rooa temperatures.
Disintegrated by strong alkalies
at boiling teaperatures.
Good resistance to aost alkali
concentrations at rooa
temperature. Disintegrated by
strong alkalies at the bell.
Generally good resistance
Generally good resistance
Generally good resistance.
Excellent resistance to
bleaches and other oxidising
agents.
Generally good resistance.
Excellent resistance to
bleaches and other oxidising
agents.
Not affected by aoat coaaon
cheaic&ls. Good resistance
to bleaches and other
oxidising agents.
Swollen at rooa temperature by
chlorinated hydrocarbona, soluble
at 16Q
-------
Table 7.6 Akallnlty Study on Geotextiles of the Type Shown in Fig. 7.4
No
Polymer
Fabric Construction Mass/Unit Area
1
2
3
4
5
6
Polypropylene (PP)
Polyvinylchloride (PVC)
Polyester (PET)
Woven monofilament
Woven monofilament
Needle non-woven
2.8
14.7
19.5
3.0
3.0
2.9 oz/sq.yd
Polypropylene (PP)
Polyester (PET)
Needle non-woven
Heat set non-woven
Heat set non-woven
Polypropylene (PP)
Biological (Micro-organism) Attack
It is almost certain that micro-organism growth of bacteria and fungi
will affect the filtration capability of geotextiles and the drainage
capability of geonets and geocomposites. The initial phenomenon is clearly
one of blocking and/or clogging rather than degradation as was the case
with FMLs. It is also possible that the attachment of the micro-organisms
onto the geosynthetlc will cause long-term degradation, but this has not
been documented. What work is available in the literature concerns
geotextiles. Ionescu, et al. (1982) tested six types of geotextiles
consisting of different mechanical and hydraulic properties. They
were as follows;
o needled nonwoven polypropylene (fine, short staple fibers)
o needled nonwoven polypropylene (coarse, long staple fibers)
o needled and resin bonded nonwoven polyester (fine, short staple
fibers
o needled and resin bonded mixed polymer (various fine, short
staple fibers
o woven polypropylene, from fribrillated yarns
o woven polypropylene, fibrlllated in warp
The incubation media Included the following:
o distilled water (control medium)
o iron bacteria of pH = 6.5
o desulfovibrlos medium of pH = 7.0
o levan-synthesizing bacteria of pH = 7.0
o liquid mineral medium of pH - 7.0
o water collected from the Black Sea.
o compost from plant residues
o fertile alluvial soil
They found some micro-organism growth in the iron bacteria, desulfovibrlous
and leva-synthesizing bacteria, but in insufficient amounts to affect
the filtration capability of the geotextiles. Tensile strength of the
geotextiles remained unchanged and Infrared spectrograms showed that no
fiber degradation had occurred. Thus the biological growth problem in
geotextiles was not a major issue according to Ionescu, et al (at least
within the limits of their study).
EPA VII - 13
-------
More recently, however, Troost and den Hoedt (1985) found otherwise.
For the following cultures, under under 13 months of exposure, severe
strength reductions did Indeed occur;
o Alternaria alternata
o Aspergillus versicolor en niger
o Chaetomium globosum
o Cladosporium herbarum en species
o Fusarium species
o Paecilomyces variotti
o Penicillium expansum
o Stachybotrys atra
o Ulocladium chartarum
The resulting data shown on Table 7.7 is for six commercially available
geotextiles. As micrographs clearly indicated, both rapid growth on the
fibers and weakening of them did indeed occur.
This contrasting set of data (Ionescu, et.al. vs. Troost/den Hoedt) is
indicative of the lack of a adequate data base from which any degree of
confidence can be gained. Furthermore, it should be understood that the
drainage situation in geonets and geocomposltes has not been addressed at
all, nor have elevated temperatures acting over long time periods.
Table 7.7 Biological Effects on Geotextile Strength,
after Troost and den Hoedt (1985)
No. Polymer Initial Strength Weight % Residual Strength After
kN/m g/m2 3 mos. 13 mos.
A PP 30 220 75 75
B PE 45 180 91 90
C PA 75 230 99 99
D PES 65 230 98 97
E PES 200 450 100 99
F PP 200 730 76 75
Thermal Effects
Two subjects must clearly be separated in tabulating the influence of
heat upon fiber properties: (1) tensile properties of fibers tested at
elevated temperatures; and (2) tensile properties of fibers tested at room
temperature after exposure to elevated temperatures for selected time
periods. The former indicates the capability of the fiber to perform at
the required elevated temperature. The latter is often used as a criterion
of heat degradation resistance. Both effects for various fibers from which
geotextiles are made are listed in Table 7.8. Completely lacking in the
literature are thermal effects on the performance of geonets and
geocomposltes.
EPA VII - 14
-------
Aging Effects from Soil Burial
General aging effects on the performance geotextiles, geogrids and
geocomposites buried in solid waste is completely unknown. While obviously
a combination of chemical, biological and thermal mechanisms can occur
there are a host of open ended questions. Indeed the potential synergism
between these different phenomena while the material is in service and
under stress is a further complication.
Some insight can be gained, however, by assessing the effects of soil
burial where a few long-term studies with geotextiles have been reported.
Sotton, et al. (1982) examined samples which were in place for up to 12
years. Both mechanical and hydraulic properties were examined and compared
to original properties. Losses were generally nonimal with maximum losses
of 30*.
The National Research Council of Canada (Koerner, 1986) is testing the
effects of burial on fabrics. Recognizing that soil is very variable
material, their test soils range from 99* organic to 100* Inorganic, have
a wide range of pH values, and vary greatly in elemental composition and
microorganism content. The tests involve 12 cm x 12 cm fabric samples of
polyethylene terephthalate, polypropylene, and nylon-polypropylene
biocomponent fabrics. The test method is designated CGSB 4-GP-2 Method
28.3 and is similar to AATCC Test Method 30-1974 and Federal Standard No.
191, Method 5762. Samples are removed at 3-month intervals and are tested
according to the diaphragm pressure (Mullen burst) test found in ASTM
Method D774. Future testing will involve other fabrics and a wider range of
soil conditions.
The Proceedings of the 3rd International Conference on Geotextiles in
Vienna (1986) produced several papers of interest in this regard. For
example, Metei, et al (1986) show results for geotextiles in place up to 5
years with minor change in properties, see Table 7.9. By far, the most
important development to date in this area of soil degradation of
geotextiles has been the November 4-6, 1986 Seminar by RILEM entitled "Long
Term Behavior of Geotextiles" in France. The Proceedings of this Seminar
are unavailable at the time of this writing.
CELL CAP PERFORMANCE
Concern for the FMC's along with their associated surface water
collection and removal systems have many long-term features in common with
the FML's and leachate collection and removal systems beneath the waste.
Thus the sections on biological, thermal, stress cracking and aging effects
are completely applicable here as well as in Sections 7.1 and 7.2. There
are, however, a few differences which warrant this special section.
Hydrolysis Effects
While undoubtedly more subtle than chemical effects due to leachate
exposure, polymeric materials exposed to water (rainfall and snowmelt) will
react over long time periods. Moisture adsorption and Imbibition are well
known phenomena and average values are well documented, see Table 7.10.
EPA VII - 15
-------
Table 7.8 Effect of Heat on Fiber Properties,
after Kasvell, 1963
Fiber
Nylon 6
(regular)
Nylon 11
Nylon 66
(regular)
Effect of Heat
Exposure on Properties
Sticking temperature - 400°F
Melts at 420°-430°F. Slight
discoloration at 300°F for
5 hours. Decomposes at 600°F.
Melting point 365°F.
Sticking temperature 455°F
Melts at 482°F.; turns
slightly yellow when heated
in air at 300°F. for 5 hours.
Physical Properties
at Elevated Temperature
Tenacity decreases with
temperature Increase.
Shrinks when heated.
70°F 5.0 gm/den
200°F 4.7 gm/den
300°F 3.3 gm/den
28?6 elong
27# elong
32# elong
Polyethylene Softens at 225-235°F; melts at
low density 230-250°F. Thermally sensitive
with respect to shrinkage;
Polyethylene Softens at 240-250°F; melts at
high density 255-280°F.
Polypropylene Softens at 300-310°F.; melts at
325-335°F.
Polyvinyl Yellows slightly at 428°F.;
alcohol melts above 430°F.
Dacron Sticking temperature 455°F; no
polyester color change 7 days at 302°F.
Melts at 480°F; safe ironing
temperatures up to 360°F. if
fabric has been stabilized.
70°F 5.0 gm.den \Tf> elong
176°F 4.2 gm/den 3056 elong
348°F 3^6 gm/den 38£ elong
320°F 3.0gm.den 45# elong
Fortrel
polyester
Kodel
polyester
Vycron
polyester
Melts at 482°F.
Melts at 555°F.; safe ironing
temperature below 425°F.
Melts at 450°F.
70°F. 2.5-3.0 gm/den
These values, however, do not indicate the extent of the interactions. One
needs the actual behavior, as shown in Figure 7.3 for nylon 66 and dacron
polyester, in order to get a clear perspective of the influence under load.
Needed, of course, is the long-term behavior for assessment of the cell cap
perf ormance.
EPA VII - 16
-------
Table 7.9 Results of Soil Burial Tests,
after Matel, et al (1986)
Geotextlle Time In
operation
Coefficient
of normal
permeability
K(m/s)
Madril M 400
0
2
0.68
0.43
88
69
0.60x10-3
0.58x10-3
Terram 1000
0
3
5
0.47
0.36
0.45
44
34
33
0.30x10-3
0.13x10-3
Drenadex
0
5
0.95
0.97
44
45
3.00x10-3
1.80x10-3
Gas Venting and Interaction
As described in detail in Section 4, gases are indeed generated in
solid waste facilities in varying amounts and over varying periods of time.
Figure 7.4 gives a qualitative indication of the situation. Here it is
seen that both methane and carbon dioxide are produced in the greatest
amount but also many other gases are generated in lesser quantities. The
major polymeric materials in the cell cap that these gases Interact with
are the gas collection geotextlle and the underside of the secondary FMC.
There are no known test methods nor references on this topic although the
literature on filtration of industrial and stack gases is very abundant.
Technology transfer from this area is warranted.
Special Concerns
There are a series of special concerns for cell cap performance over
long periods of time which almost defy a quantitative analysis. Instead
they require sound judgment and a realistic (and futuristic) assessment of
possible harmful events. The group which has had some experience in such
an assessment is various Deparment of Energy contractors who have a mandate
to cover low-level radioactive waste sites. Here time frames are every bit
as long as with hazardous materials, and perhaps even longer. This section
is written with long-term concerns in mind.
Root Penetration —
Plant and tree roots cam penetrate very deep into the subsoil. The
depth is obviously dependent upon the type of plant, type of soil,
geographic location, etc, but depths of many feet are not uncommon. To be
sure, the depth of soil cover over a geosynthetic cap ( 4.0 ft) is within
reach of many plants under a wide variety of conditions. At the minimum,
EPA VII - 17
-------
NYbONCa 640-140-300 BRIGHT
MCRON POUTESTEH FBER, 22D-SO-5I BRIGHT
S
R
3
R
-
I III
/// /^'
\U A>
if//
W ^\7or
V"
t
~ «*
III'
III1
Itl
//#' '
us' i
/IFI'
//i'l'
' ~
~
~
~
/
/
¦ —ffttl''
////'
///'''
///'''
/if" /
///'//
'//
-
Ail AT 70*r.
AT KSICMJCO
MLfllVC HUMOmO.
— M WATCH AT
COWNATCB
TCMPCflOTMCt.
SO
60
S
B
o
.
s
r^x
ll
Hf
ID /
Ic '
If '
K%
^-«aoT
I'"''
1
Mu '
ma *
MB 1
if/I 1
ffA f
Hh9
Jitt*
s
¥>'
' *
/
»
—-IM AM AT TO*f,
AT MSMNtfCO •
RELATIVE HUM0TTO.
—— IN WATCH «r
OCSMMATCO
TtMKJUnjRCft
10
20 30
% ELONGATION
40
90
60
•A ELONGATION
Figure 7.3 Strength Behavior of Nylon and Polyester in Water
GAS
COMPOSITION
<%>
PH
conductivity
Ujmhovcmi
SECONO STAGE
AEROBIC FIRST
PHASE I STAGE
ANAEROBIC phase
TIME
Figure 7.4 Phases of Solid Waste Decomposition
EPA VII - 18
-------
Table 7.10 Moisture Regain and Water Imbibition of Fibers,
after Kasvell, 1963
Percent Moisture Regain at
70°F., 65# R.H. 70°F., 95* R.H.
Percent Water
Imbibition(Q)
Nylon 6, regular
Nylon 6, high tenacity
Nylon 66, regular
Nylon 66, high tenacity
Nylon 11
Polyethylene, low density
Polyethylene,
high density
Polypropylene
Polyvinyl alcohol
Dacron polyester,
regular
Dacron polyester,
high tenacity
Fortrel polyester
Kodel polyester
Vycron polyester
4-5
4-5
4.5
4.5
1.18
0
0
0
4.5
0.45-0.8
0.4-0.8
0.4
0.4
0.6
6.5-8.5
6.5^8.5
8.0
8.0
less than 0.1
less than 0.1
0
0.5
0.5
0.8
10
0.01
0.01
25-35
0.9
2.0
2.0
one could anticipate the roots to penetrate the geotextile filter, work
themselves into the geocomposite drainage core space and eventually
partially, or completely, block the surface water collection and removal
system. The ways to stop such a situation would be to design a very deep
soil cover layer or to select vegetative growth which does not contain deep
root systems. While this second alternate is the obvious choice, one can
easily visualize many years after closure where vegetation develops from
natural circumstances and create severe damage. The situation is one,
however, where remedial action can be taken without disturbing the FMC.
Burrowing Animals —>
Rodents and other burrowing animals present a severe challenge to the
long-term life of a cell cap closure. While going for a food source they
will penetrate through almost anything, certainly through a synthetic liner
system. The. muskrat problem in Dutch river dikes is a notorious and well
known situation. The key here seems to be lack of moisture. If the
primary surface water collection system properly drains its water (rapidly
and completely), there should be no compelling reason for animals to burrow
through the closure into the encapsulated solid waste. Thus localized
depressions, i.e., bathtubs, must be avoided. Other concepts, such as
layer of heavy gravel or cobbles within the soil cover have been considered
for low level radioactive cover systems and may be applicable to hazardous
waste landfills as well.
Wind Erosion —
Wind erosion is a well known and definable process which should be
within the design state-of-the-art. It is very much a site specific
situation, .but one in which reasonable design assurity should be
EPA VII - 19
-------
attainable. For high above-ground landfills the shape and general
configuration of the surrounding area must be considered. For situations
of particular concern, wind tunnel studies to evaluate the aerodynamics of
the final configurations are not beyond reason.
Water Erosion —
As with the previously discussed wind erosion, the problem of water
erosion is also site-specific. This subject, too, has been evaluated and
designs are available. Geosynthetics play an important role in this area
for many erosion-control systems are available which use mats, webbings,
nets, lattices, threads, etc., made from polymeric materials. The
mechanisms that they function under are to allow for growth to establish
itself and simultaneously retard erosion, see Koerner (1986) for a number
of these systems. Their lifetimes are not of critical concern for their
main mission is to promote natural vegetative growth to resist potential
erosion. If this growth should subsequently die, then the lifetime of the
synthetic erosion control system would be an issue.
Man-Made Intrusion —
Here is perhaps the most dangerous of these special concerns; Love
Canal bears testimony to this statement. Proper signs, fences, warnings,
etc., seem destined to short-term lives. Focus for the long term must be
on the closed solid waste facility itself. Its size, shape and presence
must Itself engender caution or danger to a potential intruder. Further
note that this intrusion may be accidental or intentional. The intentional
situation is of maximum concern. Considerable care and concern are
certainly warranted on this issue, as are all of the Issues in this section
on Special Concerns.
Asthetics —
To date, completed landfill caps are ominous zones buffered from the
public by fencing. The effect to the region is much like that obtained by
munitions dumps; vast open areas that appear to be permanently lost for
public use. Recently some public landfill owners have begun to explore
alternatives for such cultural dead zones. An example of this is the recent
commissioning of artist Nancy Holt by the Hackensack Meadows Development
Commission to transform a municipal waste landfill cap Into an
environmental art form. The 57 acre cap will be transformed into a "Sky
Mound" that includes earth mounds up to 100 feet in height. These mounds
will frame sunrises and sunsets when viewed from the center of the cptj. The
astronomy theme is carried on to an interior lunar zone that is surrounded
by a circular moat that serves as part of the surface water collection
system and looping arches of the methane recovery system. Pipe tunnels
through selected mounds are aligned with stellar helical settings of the
stars Sirius and Vega. These extrordlnary features are shown on Figure 7.5.
Land surrounding the cap will be converted to a wild bird refuge.
While not endorsing the specifics of the Hackensack project, it is
clear that the cultural impact of a landfill cap can be minimized. However
it should be cautioned that features such as earth mounds or surface
Impoundments within the cap must be carefully engineered to prevent damage
to the underlying cap system. Differential settlements that are the result
of surcharges generated by mounds or other 'art' features could easily lead
to failure of the FMC. The longterm performance of the cap must not be
compromised by surface structures regardless of their function or Intent.
EPA VII - 20
-------
Figure 7.5 HSky Mound" Cap Planned for Hackensack Meadowland
REFERENCES - SECTION VII
DeCost, J.B., (1972), "Effect of Soil Burial Exposure on the Properties of
Plastics for Wire and Cable, "The Bell System Technical Journal, Vol. 51.
Halse Y., Koerner,R.M., and A.E. Lord, (1987), "Effect of High Levels of
Alkalinity on Geotextiles," Accepted for publication in Geotextiles and
Geomembranes, London.
Haxo, H.E., et al, (1984), "Permeability of Polymeric Membrane Lining
Materials," Proc. Int. Conf. on Geomembranes, Denver, CO, IFIA.
Hueck, H.J., (1973), "The nature of the Biodegradation of Materials Wi,th
Special Reference to Polymers," Proc. Conf. Degradability of Polymers and
Plastics, Institute of Electrical Engineers, London.
Hoarz, Ray, (1986), Geotextiles for Drainage, Gas Venting, and Erosion
Control at Hazardous Waste Sites, EPA/600/2-86/085 U.S. Environmental
Protection Agency, Cincinnati, OH.
Ionescu, I., et al, (1982), "Methods Used for Testing the Bio-Colmation and
Degradation of Geotextiles", 2nd Int. Conf. Geotextiles, Las Vegas, NV.
Kaswell, E.R., (1963).Handbook of Industrial Textiles, Wellington Sears
Co., New York, NY.
EPA VII - 21
-------
Koerner, R.M., (1982), Designing With Geosynthetlcs. Prentice-Hall, NJ.
Koerner, R.M., and G.N. Richardson, (1987), Design of Geosynthetic Systems
for Waste Disposal," ASCE-GT Specialty Conference, Geotechnlcal Pratice for
Waste Disposal, Ann Arbor, Michigan.
Matrecon, Inc., (1987), "Lining of Waste Impoundment and Disposal
Facilities, " (DRAFT), Third Edition SW-870, U.S. Environmental Protection
Agency, Cincinnati, OH.
McGill, D.C., (1986),"Jersey Landfill to Become an Artwork," N.Y. Times,
Sept 3.
Metei, et al, (1986), "Data Regarding the Long-Term Behavior of Some
Geotextile Filters," Illrd Int. Conf. Geotextiles, Vienna, Austria.
Miner, R.J., (1972), "Effect of Soil Burial Exposure on Properties of
Molded Plastics," The Bell System Technical Journal, Vol. 51.
Mitchell, D.H., and R. Cuello, (1986), "Geomembrane Selection Criteria for
Uranium Tailings Ponds," NRC FIN B2476, Pacific Northwest Laboratory,
Prepared for Division of Waste Management, U.S. Nuclear Regulatory
Commission.
Morrison, W.R. and L.D. Parkhill, (1987), "Evaluation of Flexible Membrane
Liner Systems," U.S. Bureau of Reclamation for U.S. Enviromental Protection
Agency, Cincinnati, Oh.
Morrison, W.R. and J.G. Starbuck, (1984), "Performance of Plastic Canal
Linings," U.S. Bureau of Reclamation, REC-ERC-84-1.
Potts, J.E., et al, (1973), "The Effect of Chemical Structure on the
Biodegradability of Plastics," Proc. Conf. Degradebility of Polymers and
Plastics, Inst. Electr. Engineers, London.
Rankilor^ P.R., (1959), Membranes in Ground Engineering, John Wiley & Sons,
New York.
Schnabel, W.,(1981).Polymer Degradation, McMillian Publishing, New York.
Slocumb, R.C., Demeny, D.D, and B.R. Christopher, (1986), "Creep
Characteristics of Drainage Nets," Proc. 9th Conf. on Mgmt. of Uncontrolled
Hazardous Waste Sites," HMCRI, Silver Springs, Md.
Sotton.M., et al, (1982),"Contribution to the Study of the Clogging of
Geotextiles Considering Long-Term Conditions," Proc. Second International
Conf. on Geotextiles, Las Vegas.
Troost, G.H. and G. den Hoedt, (1985), "Resistance of Geotextiles to
Physical, Chemical and Microbiological Attacks," (in Dutch), Enka Research
Institute, Arnhem, Holland.
Wolfgang, W.G., (1959), "The Burning Characteristics of Fibers," In Man-
Made Textiles Encyclopedia, J.J. Press, Textile Book Publ. Inc., New York.
EPA VII - 22
-------
Appendix A Conversion of Units
LENGTH
AREA
1 mm = 0.0394 in.
1 cm = 10 mm = 0.394 in.
1 m = 100 cm = 39.4 in.
1 km = 1000 m = 3280 ft.
1 in. = 2.54 cm
1 ft. = 0.305 m
1 yd. = 0.914 m
1 mile = 1.609 km
3.28 ft.
= 0.621 mile
1 cm2 = 0.155 in.2
1 m2 = 10.8 ft2 = 1.20 yd2
1 ha = 2.47 acres
1 in.2 = 6.45 cm2
1 ft2 = 0.0929 cm2
1 yd2 = 0.835 m2
1 acre = 0.405 ha
= 43,560 ft2
CAPACITY
VOLUME
1 liter = 1000 cm3
1 liter = 61.0 in.3
1 liter = 0.264 U.S. gallon
1 U.S. gallon = 3785 cm3
gallon = 231 in.3
gallon = 3.78 liters
= 0.001 liter
= 2.64 x 10-^ U.S. gallon
ft5 = 7.48 U.S. gallon =28.3 liters
1 U.S
1 U.S
1 cm3
UNIT WEIGHT
1 N/m-
1.02 x 10 ^ g/cm3
= 6.37 x 10~3 lb/ft3
1 g/cm3 = 9.81 x 103 N/m3
=62.4 lb/ft3
1 lb/ft3 = 1.57 x 102 N/m3
= 1.60 x 10-2 g/cm3
cm
i3 = 0.0610 in.3
1 m3 = 35.3 ft3 = 1.31 yd3
1 in.3 = 16.4 cm3
1 ft3 = 0.0283 m3
1 yd3 = 0.764 m3
TEMPERATURE
1°C = 1°K = 1.8°F
1°F = 0.555°C = 0.555 K
0 K = -273°C = -460°F
Tc = (5/9)(Tf - 32°)
= Tk - 2730
Tk = Tc + 273°
= (Tf + 460 )/1 .8
Tf = (9/5)TC + 32°
= 1.8Tk - 460°
STRESS
1 N/m2 = 1 Pa
= 1.02 x 10
= 2.08 x 10
"5 kg/cm2
2 lb/ft2
1.45 x 10-^ lb/in2
1.04 x 10-5 ton/ft
1 kg/cm2 = 9.81 x 10^ N/m2 = 14.2 lb/in2 = 2.05 x103 lb/ft2
= 1.02 tons/ft2
1 lb/in.2 = 6.89 x 103 N/m2 = 7.03 x 10~2 kg/cm2 = 144 lb/ft2
= 7.2 x 10-2 ton/ft2
1 lb/ft2 = 4.79 x 10 N/m2 = 4.88 x 10"^ kg/cm2
= 6.94 x 10-3 lb/in.2 = 5.00 x 10"^ ton/ft2
1 ton/ft2 = 9.58 x 10^ N/m2 = 9.76 x 10"1 kg/cm2
= 13.9 lb/in.2 = 2000 lb/ft2
FORCE
1 N = 102.0 g = 0.225 lb = 1.124 x 10_<* ton
1 g = 9.81 x 10"3 N = 2.20 x 10-3 lb = 1.102 x 10-6 ton
1 lb = 4.45 N = 453.6 g = 5.00 x 10"^ ton
1 ton = 8.89 x 103 N = 9.07 x 105 g = 2000 lb
-------
Appendix B
GLOSSARY
References:
Scott, J.D., and E.A. Richards (198*0, Geotextile and Geomembrane
International Information Source. The Canadian Geotechnical Society,
Rexdale, Ontario.
Koerner, Robert M. (1986), Designing with Geosynthetics. Prentice-Hall,
Englewood Cliffs, NJ.
FHWA (1985), Geotextile Engineering Manual, update by Barry Christopher
and Robert Holtz of previous FHWA workshop manual titled "Use of
Engineering Fabrics in Transportation-Related Applications."
EPA B-l
-------
abrasion,
the ability of a fabric to resist wear caused by rubbing against another
surface.
abrasion resistance,
the ability of fabric surface to resist wear by friction,
absorption,
for geotextiles. the process of a fluid being assimilated or incorporated
Into a fabric.
, actinic degradation,
strength loss of fibers and fabrics due to exposure to sunlight or
accelerated weathering light source.
adhesion,
tho state In which two surfaces are Held together by lnterfaclal forces
which may consist of molecular forces or interlocking action or both.
Measured in shear and peel modes.
air lanes,
a device used to test, In the field, the integrity of field seams in
plastic sheeting. It consists of a wand or tube through which compressed
air is blown.
alloys, polymeric,
a blend of two or more polymers (e.g.. a rubber and a plastic) to improve
M a given property {e.g., Impact strength).
"0
r anchor trench,
o long, narrow ditch on which the edges of a plastic sheet are buried to
tp hold it In place or to anchor the sheet.
^ apparent opening size (AOS),
see equivalent opening sl2e (EOS)
arching,
the formation of soli " particles upstream of a geotextlle where the
particles arch (or bridge) over the fabrics' voids.
area change,
increase or decrease in the area of fabric specimen subjected to o
specified condition,
aspect ratio,
the width to length ratio of a fabric test specimen prior to uniaxial
tensile testing.
atmosphere for testing geotextiles,
for geotextiles, air maintained at a rolatlve humidity of 65 ond o
temperature of 21 »2°C.
basis weight,
deprecated term (do not use in the sense of mass per unit orea).
berm.
the upper edge of a pit or pond where a membrane liner is anchored. The
berm may be wide and solid enough for vehicular traffic.
biaxial tensile test,
a tensile test In which a fabric specimen Is subjected to tensile farces
In two directions 90° to one another, usually the machine and
cross-machine directions.
biological stability,
ability to resist degradation from exposure to microorganisms,
blinding,
the condition where soil particles block openings on the surface of o
geotextlle, thereby reducing hydraulic conductivity of the geotextlle.
blacking,
a synonymous term for blinding or also when sheets of am FMl. stick together
due to excessive heat and pressure.
blocking,
a synonymous term for blinding,
bodied solvent adhesive,
an adhesive consisting of a solution of the liner compound used In the
seaming of liner membranes.
bonding,
the process of combining fibers, filaments, or films Into sheets, webs or
bats by means of mechanical, thermal, or chemical binding.
boot,
a bellows-type covering to exclude dust, dirt, moisture, etc., from a
flfxibl# Joint.
breaking factor,
tensile at break in force per unit of width: units. SI. newtons per meter;
customary, pounds per inch.
burst strength,
the resistance of a fabric to rupture from pressure applied at right
angles to the plane of the fabric under specified conditions, usually
expressed as the pressure causing failure. Burst result from tensile
failure of the fabric.
butyl rubber,
a 'synthetic rubber based on isobutylene and a minor amount of isoprene.
It is vulcanlzoble ond features low permeability to gases and water vapor
and good resistance to aging, chemicals, and weathering.
calender,
a precision machine equipped with three or more heavy internally heated or
cooled rolls, revolving in opposite directions. Used for preparation of
highly accurate continuous sheeting or plying up of rubber compounds and
frlctioning or coating of fabric with rubber or plastic compounds.
chemical bonding,
a bonding process in which the individual flbners in the fabric web ore
cemented together by chenmical interaction.
chemical stability,
obllity to resist chemicals, such as ocids, bases, solvents, oils and
oxidation agents; ond chemical reactions, Including those catalyzed by
light.
-------
chlorlnoted polyethylene (CPE),
fomlly of polymers produced by chemlcol reaction of chlorine on the linear
backbone chain of polyethylene. The resultant rubbery thermoplastic
elastomers presently contain 25 to 45* chlorine by weight ond 0 to 25*
crystollinity. CPE con be vulconised but is usually used In a
nonvulcanized ftrm.
ehlorosulfonated polyethelene (CSPE)
family of polymers that ore produced by polyethelene reacting with
chlorine ond sulfur dioxide. Present polymers contain 25 to 43* chlorine
ond 1.0 ro 1.4* sulfur. They ore used In both vulcanized ond
nonvulcanlzed forms. Most membranes bosed on CSPE are nonvulcanlzed (ASTM
designation for this polymer is CSM).
clogging,
movement by mechanical oction or hydraulic flow of soil particles into the
voids of fobric and retention therein, thereby reducing the hydraulic
conductivity of the geotextile.
coated fabric,
fobric which hos been Impregnated and/or coated with a rubbery or plastic
material in the form of a solution, dispersion, hot melt, or powder. The
term also applies to materials resulting from the application of a
preformed film to a fabric by means of calendering.
composite,
See Fabric, composite.
tt
compressibility,
™ property of a fabric describing the ease with which it can be compressed
normal to the plone of the fobric.
W
^ constant-rate-of-extension tensile testing machine (CRE),
a testing machine in which the rate of increase of specimen length is
uniform with time.
constant-rate~of-load tensile testing machine (CRL),
a testing machine In which the rate of increase of the load being applied
to the specimen is uniform with time.
constant-rate-of-traverse tensile testing machine (CRT),
o testing machine in which the pulling clamp moves ot a uniform rate ond
the load is applied through the other clomp which moves appreciably to
actuate a weighing mechanism, so thot the rate of Increase of loads or
elongation is dependent upon the extension characteristics of the
specimen.
creep,
the slow change in length or thickness of a material under prolonged
stress.
ereep (static),
increasing strain at constant stress,
cross-linking,
o general term referring to the formation of chemical bonds between
polymeric chains to yield on insoluble, three-dlmensionol polymeric
structure. Cross-linking of rubbers is vulconlzation. See also
Vuncanlzatlon.
cross-machine direction,
the oxls within the plane of o fabric perpendlculor to the machine
direction.
cross plane,
the direction of a geosynthetlc which is perpendicular to its long,
manufactured, or machine direction. Referred to in hydraulic conductivity
of a geotextile.
curing,
See Vulcanization.
cutting resistance,
the resistance of the fabric or fiber to cutting when struck between two
hard objects.
deformation,
the lengthening of 6 geosynthetlc under load from its orlglnol
manufactured dimensions.
denier,
the weight In grams of 9000 m of yarn,
density,p,
mas$'per unit volume.
dielectric seaming.
See Heot seaming.
dimensional change,
a generic term for changes in length or width of o fabric specimen
subjected to a specified condition.
direction, cross machine,
In textiles, the direction
direction of movement the
(syn. wldthwise).
direction, machine,
in textiles, the direction in a
direction of movement the fabric
(syn• lengthwise).
downstream,
the direction on the opposite side of a geotextile from which woter is
moving.
elasticity,
the ' property of motter by virtue of which it tends to return to its
orlglnol size ond shape after removal of the stress which caused the
deformation.
elastomer.
See Rubber.
elongation,
the increase in length produced in the gage length of the test specimen by
o tensile load.
in a machine-made fabric perpendicular to a
fobric followed in the manufacturing machine
mochine-made fabric parallel to the
followed in the manufacturing machine
-------
elongation at break, Eg,
the percent elongation corresponding to the breaking strength, that Is,
the maximum load.
elongation, percent, E,
for geotext.lies, the Increase In length of o specimen expressed os o
percentage of the nominal gage length,
erm,
a synthetic elastomer honed on ethylene, propylono, and a small amount of
o nonconjugated dlene to provide sites for vulcanization. EPOM features
excellent hear, ozone, and weathering resistance ond low-temperature
flexibility.
•plchlorohydrin rubber,
this synthetic rubber includes two epichlorohydrln-based elastomers which
are saturated, high-molecular-weight, aliphatic polyethers with
chloromethyl side chains. The two types Include a homopolymer (CO) and o
co-polymer of eplchlorohydrln and ethylene oxide (ECO). These rubbers are
vulcanized with a variety of reagents that react dlfunctlonally with tho
chloromethyl group, including diamines, urea, thioureas,
2-mereaptolmldazollne, and ammonium salts.
•poxy binding,
a bonding process in which the fabric web is impregnated with epoxy which
serves to coot and cement the fibers together.
equivalent opening size (EOS),
number of the U.S. Bureau of Standard sieve (or Its opening size in
millimeters or inches) having openings closest In size to the diameter of
uniform particles which will allow 5* by weight to pass through the fabric
when shaken In a prescribed manner.
EVA,
family of co-polymers of ethylene ond vinyl acetate used for adheslves and
thermoplastics modifiers. They possess a wide range of melt indexes.
extruder,
o machine with a driven screw for continuous forming of rubber by forcing
through a die; can be used to manufacture films and sheeting.
fabric, composite,
a textile structure produced by combining non-woven, woven, or both
manufacturing methods.
fabric, knitted,
a textile structure produced by lnterlooplng one or more ends of yarn or
comparable material.
fabric, non-woven,
for geotextlles, o planar textile structure produced by bonding.
Interlocking of fibers, or both, accomplished by mechanical, chemical,
thermal, or solvent means, ond combinations thereof. NOTE; The term does
not include paper or fabrics which are woven, knitted, or tufted,
fabric, woven,
a planor textile structure produced by Interlacing two or more sets of
elements such os yarns, fibers, rovings or filaments where the elements
pass each other usually at right ongles and one set of elements ore
parallel to the fobrlc oxls. NOTE: Excluded ore knotted fabrics.
>•
W
I
fabric reinforcement,
o fabric, scrim, and so onj used to add structural strength to a two- or
more ply polymeric sheet. Such sheeting Is referred to os "supported."
fatigue resistance,
the ability to withstand stress repetitions without suffering a loss in
strength.
felt,
o sheet of matted fibers mode by a combination of mechanical and chemical
action, pressure, moisture, and heat.
fiber,
basic element of fabrics and other textile structures, characterized by
having a length at least 100 times its diameter or width which can be spun
Into a yarn or otherwise mode into a fabric.
filament,
a fiber of extreme length,
filament yarn,
the yarn made from continuous filament fibers,
fill.
fibers or yarns placed ot right angles to the warp or machine direction,
filling,
yarn running from seivoge to selvage ot right angles to the warp In a
woven fabric,
filling direction,
see direction, cross machine. NOTE; For use with woven fabrics only,
film,
sheeting having nominal thickness not greater than IB mils,
filter cake,
a thin layer of fine soil particles accumulated in the sail adjacent to
the fabric as a result of smaller soil particles being washed through the
soli pores.
filter cloth,
the depracoted term for geotextlle,
filtration,
the process of allowing water to easily escape from soli while retaining
soil in place,
flexural rigidity.
general: resistance tb bending or flexural rigidity is called flex
stiffness in Federal Specification CCC-T-19 lb., Textile Test Methods No.
2506.2.
specific: , the couple on either end of a strip of unit width
bent into curvature In the absence of tension. The method measures the
bending length. Flexural rigidity is calculated directly by multiplying
the cube of the bending length by the weight per unit area.
freez-thaw resistance,
ability to resist degradation caused by freeze-thow cycles.
-------
friction angle,
on angle, the tangent of which is equal to the ratio or the friction force
per unit areo to the normal stress between two materials.
geocell,
a three-dimensional structure filled with soli, thereby forming a mattress
far increased bearing capacity and maneuverability on loose or
compressible subsoils.
geocompoeite,
a manufactured material using geotextlles, geogrlds. and/or geomembronos
in laminated or composite form.
geogrid,
a deformed or nondeformed not like polymeric material used with
foundation, soil, rock, earth, or any other geotechnlcal
engineering-related material as an integral part of human-mode project,
structure, or system,
geomemtorone,
an essentially Impermeable membrane used with foundation, soil, rock,
earth or any other geotechnlcal engineering related material as an
Integral part of a man-made project, structure, or system.
geosynthetlcs,
the generic classification of all synthetic materials used In geotechnlcal
engineering applications; it includes geotextlles, geocells, geogrlds,
geomombranos, and geocomposltes.
W
2 geotechnieal engineering,
** the engineering application of geotechnlcs.
BJ geotechnlcs,
I. the generic classification of all synthetic materials used in geotechnlcal
engineering application; it includes geotextlles, geocells, geogrlds,
geomembrones, and geocomposltes,
geotechnology,
the application of science and engineering techniques to the exploitation
and use of natural resources such as mineral resources.
geotextlle,
any permeable textile used with foundation, soil, rock, earth, or any
other geotechnlcal engineering related material os on integral part of a
man-made project, structure, or system.
geotextlle tensile modulus, J,
the ratio of the change In tensile force per unit width of the geotextlle
to the change in corresponding strain. The geotextlle modulus is usually
expressed In H/m Clbf/ln).
geotextlle tensile modulus, Initial, J,,
for geotextlles, the slope of the Initial portion of a force per unit
width curve. Discussion: The initial modulus is the ratio of the Chang©
In force to the change in elongation. The elongation being expressed as o
fraction of the original length.
geotextlle tensile modulus, secant, Jsec,
the ratio of change m force per unit width to a change in elongation
between two points on a force per unit width curve, particularly the
point* of zero force and o specified percent elongation. Discussion: The
secant is expressed os a fraction of the original length.
grob tensile strength,
a modified tensile strength of o fabric. The strength of a specific width
of fabric together with the additional strength contributed By adjacent
oreas. Typically, grab strength Is determined on a 12-ln.-wlde strip of
fobric, with the tensile lood applied at the midpoint of the fobrlc width
through 1-in.-wide jow faces.
gradient ratio,
the ratio of the average hydraulic gradient across the fabric ond the 1
in. of soil immediately next to the fabric to the average hydraulic
gradient across the 2 In. of soli between 1 ond J in. ottave the fabric, as
measured In a constant head permeab111 ty test.
heat bonding,
a process by which fabric filaments are welded together at their contact
points by subjection to a relatively high temperature.
heat seaming,
the process of Joining two or more thermoplastic films of sheets by
heating areas in contact with each other to the temperature ot which
fusion occurs. The process is usually aided by a controlled pressure. In
dielectric seaming the heat is induced with in films by means of
radlo-fregency waves.
hydrophilllc,
a material's attraction to water,
hydrophobic,
a material's repulsion of water.
Impact resistance,
resistance to fracture under shock force,
in-plane,
the direction of a geosynthetlc which Is parallel to its long,
manufactured, or machine direction. Referred to In hydraulic situations.
knit,
See Fobrlc, knit,
knitted fobric,
a textile made up of loops of fibers connected by straight segments,
lapped joint,
a Joint made by placing one surface to be joined partly over another
surface and bonding the overtopping portions.
lateral restraint reinforcement,
the action of increasing the ultimate bearing capacity ond
load-deformation modulus of soli placed over fabric through the mechanism
of fobrlc resistance to .cover material horizontal movement, thereby
Increasing the modular rotlo of the system.
length, bending,
general; a measure of the Interaction between geotextlle weight and
fabric stiffness as shown by the way in which a geotextlle blends under
its own weight. It reflects the stiffness of a geotextlle when bent in
one plane under the force of gravity and Is one component of drope. NOTE:
bending length is colled drape stiffness in Federal Specification CCC-T-19
lb. Textile Test Methods,Ho, 5286,2.
specific: the cube root of the rotlo of the flexurol rigidity to
~.he weight per unit areo.
-------
leno fabric,
on open fabric in which two warp yarns wrap around each fill yarn to
prevent the warp or fill yarns from sliding over each other.
machine direction,
the axis within the plane of the fabric parallel to the direction in which
a fabric Is processed onto rolls as the final step of production.
mass per unit area,
the proper term to represented and compare to amount of material per unit
area (units ore oz/yd2 or g/m2).
melt bending,
see heat bonding.
membrane,
In this book the term applies to a continuous sheet of material, whether
prefabricated as o flexible polymeric sheeting or sprayed or coated in the
field, such as a sprayed-on asphalt.
membrane-type fabric support,
additional roadway support capacity gained from the vertical resultant of
fabric tensile stresses developed.as the result of subgrade rutting.
modular ratio,
the ratio of the deformation modulus of a layer of material to the
deformation modulus of an underlying material,
modular ratio effects,
the decrease in stresses transmitted to a road subgrade, corresponding to
increase modular ratio and vice versa.
modulus,
the stress on stretching a material to different elongations (e.g.. E^gg
and E200>-
modulus of elasticity,
the . ratio of stress to strain within the elastic range, also known as
Young's modulus.
monofilament,
a single filament of a man-made fiber, usually of a denier higher than 15.
multllaxial tensil test,
a tensile test in which o fabric specimen is subjected to tensile forces
in more than two directions.
multifilament,
a yarn consisting of many continuous filaments or strands,
needle punched,
mechanically bonded by needling with barbed needles,
needle punching,
subjecting a web of fibers to repeated entry of barbed needles that
compact and entangle individual fibers to form o fabric,
neoprene (polyettlaroprene), .
generic name for a synthetic rubber, based primarily on chlaroprene ( . ..
chlorobutadiene). Vulcanized generally with metal oxide. Resistant
ozone and aging and to some oils.
nitrile rubber,
a .family of copolymers of butadiene and acrylonltrlle that can be
vulcanized into tough oil-resistant compounds. Blends with PVC are used
where ozone and weathering ore Important requirements in addition to its
inherent oil and fuel resistance.
nonwoven fabric,
a textile structure produced by bonding or interlocking of fibers, or
both, accomplished by mechanical, chemical, or solvent means.
normal direction,
for geotextiles, the direction perpendicular to the plane of a geotextlle,
nylon*
generic name for a family of polyamlde polymers characterized by the
presence of the amide group - CONHj. Used as ascrlm in
fabric-reinforced sheeting.
offset tangent modulus,
a tensile stress-strain modulus obtained using a straight line to
represent the stress-strain curve drown parallel to and offset by a
prescribed distance from a line tangent to the initlol portion of the
actual stress-strain curve.
op«n area,
that portion of the plane of the fabric in which there are no filaments,
fibers, or films between the upper and lower surfaces of the fabric. This
is expressed as a percentage of the total area.
optimum depth,
the thickness of engineering fabric cover material, in a rood system,
which will result In development of maximum reinforcement potential of the
cover material.
penetration resistance,
the fabric property determined by the force required to penetrate a fabric
with a sharp pointed object. Initial pentration is by separating the
fibers. Further penetration is essentially a tearing process.
percent open area,
the net area of a fabric that is not occupied by fabric filaments,
normally determinable only for woven and non-woven fabrics having distinct
visblle and measureoble openings that continue directly through the
fabric..
permeability,
(1) a generic term for the property that reflects the ability of a
material to conduct a fluid. (2) the capacity of a porous medium to
conduct or transmit fluids. (3> the amount of liquid moving through a
barrier in a unit time, unit area, and unit pressure gradient not
normalized for but directly related to thickness.
permeability (longitudinal or in plane),
the fabric property which permits water to be transmitted in the plane of
the fabric.
permeability (transverse),
the fabric property which allows water to pass through perpendicular to
the plane of the fabric.
-------
permittivity,
for o geotextlle, the volumetric flow rote of woter per unit cross section
oreo, per unit head, under laminar flow conditions. In the normol
direction through a materlol.
piping*
the process by which soli particles are washed In or through pore spaces
In drains and filters.
plastic,
o material that contains as an essential ingredient one or more organic
polymeric substances of large molecular weight, is solid in its finished
state, and at some stoge in its manufacture or processing into finished
articles, can be shaped by flow.
plastlclzer,
o plastlclzer is a material, frequently "solventlike," Incorporated In a
plastic or a rubber to Increase Its ease of workability, its flexibility,
or dlstenslbllity. Adding the plastlclzer may lower the .melt viscosity,
the temperature of the second-order transition, or the elastic modulus of
the polymers (EVA). The most important use of plostlclzers Is with PVC.
where the choice of plastlclzer will dictate under what conditions the
liner may be used.
polyester fiber,
generic nome for a manufactured fiber in which the fiber-formlng substance
is any long-choln synthetic polymer composed of an ester of a dlhydrlc
alcohol and terephthallc acid. Scrims made of polyester fibers are used
for fabric reinforcement.
polymer,
o macromolecular material formed by the chemical combination of monomers
having either the same or different chemlcol composition. Plastics,
rubbers, and textile fibers are all hlgh-molecular-welght polymers.
polymeric liner,
plastic or rubber sheeting used to line disposal sites, pits, ponds,
lagoons, canals, and so on.
polyvinyl chloride (PVC),
o synthetic thermoplastic polymer prepared from vlnylchlorlde. PVC con be
compounded into flexible ond rigid forms through the use of plstlclzers,
stabilizers, fillers, and other modifiers; rigid forms used In pipes odn
well screens; flexible forms used in manufacture of sheeting.
por# size,
the size of an opening between fobrlc filaments because of the variability
of opening sizes; equivalent opening size (EOS) Is used to quantify this
fobric property.
porosity,
the ratio of the volume of void spoce to the total volume. NOTE: Usually
expressed as a percentage of the volume.
puncture,
the rupture of a fobrlc by a force normal to the fabric plane while the
fabric is constrained in all directions in that plane, applied by a small
diameter object.
puncture resistance,
extent to which a material is able to withstand the octlon of a sharp
object without perforation. Examples of test of this proporty are Federal
Test Methods stnadard No. 1018, Methods 2011 or 2065.
reinforcement,
strengthening of a soil-fabric system by contributions of the fabric
inclusion.
resin bonded,
the Joining of fibers at their intersection points by resin In the
formation of a nonwoven geotextlle or geocomposlte.
resin bonding,
the fabric web is Impregnated with a resin which serves to coot ond cement
the fibers together.
roll goods,
a general term applied to rubber ond plastic sheeting, whether fabric
reinforced or not. It Is usually furnished in rolls.
rubber,
a polymeric moteriol which, at room temperotur, is capable of recovering
substantially in shape ond size after removal of a deforming force. Refers
to both synthetic and noturol rubber, also called an elastomer.
scrim,
a woven, open-mesh reinforcing fabric made from continuous-flloment yarn.
Used in the reinforcement of polymeric sheeting.
seam strength,
strength of a seam of liner material measured either in shear or peel
modes. Strength of the seams is reported either in absolute units (e.g.,
pounds per inch of width) or as o percent of the strength of the sheeting.
seeant modulus,
a tensile stress-strain modulus obtained using a straight line (to
represent the stress-6traln curve) drawn from the origin through a
coordinate representing a stress measured at o specified strain.
separation,
function of fabric as a partition between two adjacent materials to
prevent mixing of the two materials.
sheeting,
a form of plastic or rubber in which the thickness is very smoll in
proportion to length and width and in which the polymer compound is
present os a continuous phase throughtout, with staple,
short fibers in the ronge 0.5 to 3.0 in.
soil-fabric friction,
the resistance to sliding between engineering fabric and soil, excluding
the resistance from soil cohesion. Soll-fobrlc friction is usually
quantified ift terms of a friction angle.
specific gravity,
the rotlo of the density of a fabric to the density of woter obtained by
weighting both Items in air. A specific grovlty less thon one Implies
that the fabric will float.
spun-bonded fabrics,
fabrics formed by continuous filaments which have been extruded ond
drawn.
staple yarn,
yarn mode from staple fibers.
-------
stiffness,
the ability of o fabric to resist bending when flexurol stross Is applied,
•train,
the change in length per unit of length in a direction,
strength, bursting,
a measure of the oblllty of a fabric to resist rupture by a force normol
to the fabric plane when applied over an area of 6.0 cm? while the
fabric Is constrained In all directions in that plane.
strength, tearing, F, (F),
the force required either 1) to stort or 2) to continue or propagote a
tear in a fabric under specified conditions.
stiffness,
resistance to bending,
strlkethrough,
a term used In the manufacture of fabric-reinforced polymeric sheeting to
Indicate thot two layers of polymer hove made bonding contact through the
scrim.
•trip tensile test,
a unloxlal tensile test In which the total width of a fabric of prescribed
dimensions is gripped prior to subjecting to tensile forces.
subgrade intrusion,
localized aggregate penetration of a soft cohesive subgrade and resulting
displacement of the subgrade into the coheslonless material.
subgrade pumping,
the displacement of cohesive or low-cohesion fines from a sotureated
subgrad into overlying aggregate, as the result of hydraulic forces
created by transmittal of wheel-lood stresses to the subgrade.
supported sheeting,
See Fabric reinforcement.
surface euro,
curing or vulcanization which occurs in a thin layer on the surface of a
manufactured polymeric sheet or other items.
survivability,
the ability of a fabric to be placed and to perform Its intended function
without undergoing degradation.
syphoning,
the transferring of a liquid to a lower level over an intermediate higher
elevotlon than both of the endpolnts, which con be achieved by saturated
geotextlles in planar flow.
tangent modulus,
o tensile stress-stroln modulus obtolned using a strolghtline (to
represent the stress-stroln curve) drawn tangent to a specified portion of
the stress-strain curve.
tear strength,
the maximum force required to tear a specified specimen, the force acting
substantially parallel to the mojor axis of the test specimen. Measured
in both initiated ond uninitiated modes. Obtained value is dependent on
specimen geometry, rote of extension, ond type of fabric reinforcement.
Values are reported In force (e.g., pounds) or force per unit of thickness
(e.g., pounds per inch).
tenacity,
the fiber strength on a grams per denier basis,
tensile modulus,
see tensile stress-strained modulus,
tensile strength,
the strength shown by a fabric subjected to tension as distinct from
torsion, compression, or shear.
tensile strength-strain modulus,
o measure of the resistance to elongation under stress. The rotlo of the
change In tensile stress to the corresponding change In strain.
test, tensile,
in textiles, a test in which a textile material Is stretched to determine
the force-elongation characteristics, the breaking force, or the breaking
elongation.
tests, wide-width strip tensile,
for geotextlles, a uniaxial tensile test In which the entire width of a
specimen Is gripped in the clamps and is greater than the gage length.
tex,
denier divided by 9.
textile,
orglnally a woven fabric, now generally applied to:
1) staple fibers ond filaments suitable for conversion to or use os
yarns, or for, the preparation of non-woven fabrics.
2) yarns made from natural or manmode fibers.
3) fabrics ond other manufactured products mode from fibers os defined
above and from yarns.
thermal shrinkage,
for a geotextlle decrease in length, in width, or both as measure in the
atmosphere for testing geotetlles or an unrestrained specimen that has.,
been subjected to o specified temperature for a specified length of time.
thermal stability,
the ability of fibers and yarns to resist degradation at extreme
temperatures.
thermoplastic,
copable of being repoeatedly softened by Increase of temperature and
hardened by decrease In temperoture. Most polymeric liners ore supplied
In thermoplostic form because the thermoplastic form ollows for easier
seaming both in the factory and on the field.
thermoplastic elastomers,
now materials which ore being developed and which are probably related to
olostlcized polyoleflns. Polymers of this type behave similarly to
cross-linked rubber. They hove a limited upper-temperature service range
which, however, is substantially above the temperoture encountered In
waste disposal sites (200°F may be too high for some TP£s).
thickness,
the normal distance between two surfoces of o fabric. NOTE: Thickness is
usually determined as the distance between an onvll, or bose, and a
pressure foot used to apply a specified compressive stress.
thickness,
thickness under o specified stress applied normal to the material.
-------
thickness nominal, t0, (L),
of a geotextile, thickness under a compressive stress of 2.0 kPA applied
normal to the material.
thread count*
the number of threads per inch in each direction with the worp mentioned
first and the fill second (e.g., a thread count of 20 x 10 means 20
threads per inch in the warp and 10 threads per inch in the fill
direction),
toughness, breaking, T, (E/m),
for geotextiles, the actual work per unit surface area of material that is
required to rupture the material, it is proportional to the areo under
the load-elongation curve from the origin to the breaking point (see also
work-to-break). Olscussion: for geotextiles, breaking toughness is
calculated from work-to-break, gage length, and width of a specimen or
specific work-to-break divided by the width,
transmisslvity,
for a geotextile. the volumetric flow rate per unit thickness under
laminar flow conditions, in the in-plane direction of the fabric.
transverse direction,
deprecated term (see direction, cross machine),
ultraviolet (UV) radiation stability,
the ability of fabric to resist deterioration from exposure to sunlight,
ultrimote elongation,
the elongation of a stretched specimen at the time of breok. Usually
*d reported as percent of the original length. Also colled elongation at
P* break.
ultraviolet degradation,
the breakdown of polymeric structure when exposed to light.
nO
uniaxial tensile test,
a tensile test in which a fabric specimen is subjected to tensile forces
In one direction.
unsupported sheeting,
a polymeric sheeting consisting of one or more plies without o
reinforcing-fnbric layer or scrim.
upstream,
the direction on the near side of a geotextile from which woter is moving,
vacuus) box,
a device used to assess the integrity of field seams in membrane liners,
void ratio, e»
the rotlo of the volume of void space to the volume of solids. NOTE: In
a geotextile, the solids ore assumed incompressible and include fibers,
yarns, binders ond combinations thereof, if present.
voids,
the open spaces in a geosynthetic material through which flow con occur.
vulcanize,
used to demote the product of the vulcanization of a rubber compound
without reference to shape or form.
warp,
fibers or yarns parallel to the fabric machine direction.
warp direction,
see direction, machine, NOTE: this term is commonly used for woven
fabrics only.
water vapor transmission (WVT),
water vapor flow normal to two parallel surfaces of a material, through a
unit area, under the conditions of a specified test such as ASTM E96.
web,
the sheet or mat of fibers or filaments before bonding or needle punching
to form a nonwoven fabric.
weft,
deprecated term (see direction, cross machine).
width, w, (L),
for o geotextile, the cross direction edge-to-edge measurement of a fabric
in a relaxed condition on o flot surface.
woof,
deprecated term (see direction, cross machine),
workability,
the abllityof a fabric to be easily handled, layed, and sewn, ond further
simplify construction procedures.
work-to-break, W, (LF)»
in tensile testing, the totol energy required to rupture a specimen.
Discussion: For geotextiles, work-to-break is proportional to the areo
under the load-elongation curve from the origin to the breaking point,
woven fabric,
a textile structure comprising two or more sets of filaments of yarns
interlaced in such a way that the elements pass each other essentially at
right angles and one set of elements Is parallel to the fobrtc axis.
woven, monofilament,
woven fabric produced with monofilament yarns,
woven, multifilament,
the woven fabric produced with multifilament yarns,
woven, slit film,
the woven fabric produced with yarns produced from slit film,
woven, split film,
woven fabric produced with yarns produced from split film,
yarn,
a generic term for cintinuous strands of textile fibers or filaments in o
form suitable for knitting, weaving, or otherwise intertwining, to form o
textile fabric. It may comprise (1) a number of fibers twisted together,
(2) a number of filaments loid together without twist (a zero-twist yarn),
(3) a number of filaments laid together with more or less twist, or £%)
-------
APPENDIX C - INDEX PROPERTIES
I GEOMEMBRANES PAGE
Water Absorption/Moisture Content, ASTM D570 CI-1
Flow Rate of Thermoplastics, ASTM D1238 CI-2
Density/Specific Gravity, ASTM D792 CI-3
Carbon Black Content and Concentration, ASTM 1603 CI-4
Pigment Dispersion in Plastics, ASTM D3015 CI-5
Nominal Thickness, ATSM D751 CI-6
Durometer Hardness, ASTM D2240 CI-7
Dimensional Stability, ASTM D1204 CI-8
Heat Deterioration of Rubber, ASTM D573 CI-9
Thermal Expansion, ASTM D696 CI-10
Volatile Loss from Plastics, D1203 CI-11
Brittleness Temperature, ASTM D746 CI-12
Ozone Resistance, ASTM D1149 CI-13
Puncture Strength, Proposed ASTM CI-14
Impact Resistance, Proposed ASTM CI-15
Tearing Resistance, ASTM D1004 CI-16
Breaking Load and Extension, ASTM D638 CI-17
Water Vapor Transmission, ASTM E96 CI-18
Burial Degradation, ASTM D3083 CI-19
Environmental Stress Cracking, ASTM D1693 CI-20
Environmental Stress Rupture, ASTM D2552 CI-21
Peel Adhesion of Geomembrane Seams, ASTM D413 CI-22
II GEOTEXTILES
Grab Tensile Strength, ASTM D4632 CII-23
Strip Tensile Strength,ASTM D1682 CII-24
Hydrostatic Bursting Strength, ASTM D751 CII-25
Tearing Strength (Trapezoidal), ASTM D4533 CII-26
Abrasion Resistance, Proposed ASTM CII-27
Pore (Opening) Size, Proposed ASTM CII-28
Degradation From Exposure to Ultraviolet Light
ASTM D4355 CII-29
Temperature Stability, ASTM D4594 CII-30
Water Permeability (Permittity), ASTM D4491 CII-31
Compression Behavior/Crush Strength, Proposed ASTM CII-32
-------
IHDSX PROPERTY! WATER ABSORPTION/MOISTURE CONTENT
OF PLASTICS
usrauwcts TB8T MBTHODt ASTM D570
MOTHS**!*! METHODSI
SCOWBI GEOMEMBRANBS OR RAW MATERIALS
FOR GEOMEMBRANES AND GEONETS
TARGE* VKLUBt PERCENT OF WATER ABSORBED
UNITS: Percent
summary or jcsthodi
This test method is used as
an index test to determine
the water absorption of
finished geomembranes or to
determine the moisture
content of resins used in the
manufacture of geomembranes
and geonets. The moisture
content and the water
absorption may be an
indicator of mechanical
properties of the finished
product. The procedure may
not be suitable for
scrim-reinforced
geomembranes.
Specimens say consist of
pellets, bars, tubes or
sheets. For water absorption
tests, the specimens are
first dried in an oven at a
temperature ranging from 50
to 100 C (depending on
temperature stability of the
specimen) for a period of 24
hours. After this drying
period, the specimens are
weighed. The specimens are
then immersed in distilled
water for a specific period
of time <2-hour, 24-hour, or
long-term) at a temperature
specified in the test method.
After the immersion period,
the specimen is removed and
again weighed. The water
absorption is the increase in
weight, expressed as a
precent of dry specimen
weight.
For moisture content
determination, the "as
received" specimen surface is
dried and then the specimen
is weighed. The specimen is
then dried in an oven for
24 hours, removed and
weighed. The moisture
content is the change in
specimen weight, expressed as
a percent of the "as
received" weight.
TMST BQ0IFMKHTI
Scale (±0.001 gm) and oven
(50-110 C).
Cl-i
XHDSX PROPERTY t
RZrSRZHCZD TB8T KBTHODI
AIiTBSHATZVX METHODS!
SCOPE 1
Txmst value»
UNITS J
SUMMARY OF KBTHODs
The Melt Flow Index is an
empirical Indicator of the
uniformity of polymer resins
such as polyethylene and
polypropylene or finished
goods made from these polymer
resins. The test is
essentially a quality control
test for thermoplastics but
may be indicative of the
uniformity of other
mechanical properties of the
specimen or other specimen
types produced using
identical processes.
The specimens consist of
powered, film strips or
pellets of resin. The test
conditions, including test
temperature,- load or
pressure, are selected from
appropriate material
specifications. Two or more
conditions are generally
required. The test cylinder
and plastometer are preheated
to the specified temperature,
which ranges from 125 to
315 C (257 to 600 F). The
piston is removed from the
cylinder and a prescribed
weight of specimen (depending
on the expected flow rate) is
placed into the cylinder.
The weighted piston is
replaced into the cylinder
and the entire apparatus is
preheated from 6 to
S minutes. The specimen is
purged from the cylinder and
is extruded from the base.
FLOW RATE OF THERMOPLASTICS
ASTM D1238 (Method A - Manual
Method)
THERMOPLASTIC RESINS FOR GEOMEM-
BRANES, GEONETS AND GEOGRIDS
MELT FLOW INDEX
gm/10 min.
The amount or rate of purge
is regulated to ensure scribe
marks on the piston are at
the proper reference start
position as outlined in the
test method. When the start
position requirements are
met, timed extrudates are
collected (between 6 and
8 minutes from charging) at
prescribed time intervals.
Each extrudate is weighed.
The extrudate weight is
multiplied by the factor
listed in the test method to
obtain the flow rate in grams
per 10 minutes. Clean the
apparatus and repeat the
procedure under other test
conditions if required,
TEST XQ0XSMB8X!
Plastometer, cylinder and
piston materials and details
are shown in test method for
manual and automatic
equipment.
INSULATION ORIFICE
CI-2
-------
INDEX PROPERTYt
REFERENCED TB8T KETHODI
USimim KBTEODSI
SCOPEt
TJUtSB* V*LUB«
CHITS I
DENSITY/SPECIFIC GRAVITY
ASTH D792 (Method Al)
GEOSYNTHETICS RAW MATERIAL
RESINS OR GEOMEMBRANE SHEET
DENSITY OR SPECIFIC GRAVITY
ga/cc or dimensionless
suwosy or xbthodi
The above teat method covers
the determination of density
and specific gravity of solid
plastic sheets, rods,
pellets, etc. The test can
be performed on raw polymer
material (such as a polyester
for geomembranes) or finished
products such as
geomembranes. Specimens are
removed in a random fashion
from homogeneous laboratory
samples. All specimens are
conditioned at a specific
constant temperature and
relative humidity for not
less than 40 hours prior to
testing. The tests are
performed at'a temperature of
2 3-2 C (73 F) and 50*% rela-
tive humidity.
Specimens mass can be
anywhere from 1 to 50 g. The
immersion media is normally
water unless the specimen is
prone to physical changes
upon contact with water. The
specimen is first weighed in
air to the nearest 0.1 mg.
The method involves
suspending the plastic
specimen from a scale and
completely immersing the
specimen in deaired distilled
or demineralized water. A
sinker may be attached to the
specimen if it is lighter
than water. All air bubbles
are carefully removed, and
the immersed specimen and
sinker {if used) are weighed
while immersed. The specific
gravity is the ratio of the
apparent weight of the
specimen in air to the
difference of the specimen
dry and wet weights at a
temperature of 23 C. The
density (gm/cc) is calculated
by multiplying the specific
gravity by a conversion
factor of 0.9975.
TEST EQUIPMENTS
Analytical Balance with
precision within 0.1 og,
corrosion resistant wire,
sinker and immersion (usually
glass) vessel.
CI-3
XHDBX PROPERTYI
REFKIUEWCED TEST XXTHODf
ALTERNATIVE METHODS!
SCOPEI
rasstz VAL0B!
UNITS!
CARBON BLACK CONTENT AND
CONCENTRATION
ASTH 01803
POLYETHYLENE GEOMEMBRANES,
GE0NETS OR CE0GRIDS
CARBON BLACK CONTENT AND
CONCENTRATION
% and g/cc
SUXXMtY or XSTHODl
The referenced method covers
the determination of carbon
black content and density for
quality control testing of
polyethylene, polypropylene,
and some other plastics. The
assembly of the apparatus is
illustrated in the test
method. A small porcelain
boat is heated using a bunsen
burner, placed in a dessicant
(such as calcium chloride)
and allowed to cool for at
least 30 minutes. The boat
is then weighed.
Approximately one gram of
plastic specimen is placed
into the boat and weighed to
determine the* original
specimen weight to the
nearest 0.0001 g. The
specimen and boat are heated
for 15 minutes in a furnace
up to 600 C under a constant
flow of nitrogen. The
specimen is allowed to cool
for 5 minutes under the
nitrogen flow and is then
removed from the furnace and
cooled in the dessicant for
at least 30 minutes. The
boat and specimen are again
weighed to the nearest
0.0001 g to determine the
residue mass. All tests are
performed with duplicate
specimens. The carbon black
content is the residue mass
divided by the initial
specimen mass, expressed as
percent. The carbon black
concentration (g/cc) is the
product of the residual mass
and the specimen density
divided by the initial
specimen mass.
TBS? SQUXPHBMTt
Furnace, combustion boat,
drying tube and glass tubing
gas flow meter and reagents
including dry ice, calcium
chloride, nitrogen and
trichloroethylene. Detailed
descriptions of all reagents
materials and apparatus, are
contained in the test method
Cl-i
-------
INDEX PROPERTYI
REFERENCED STANDARD PRACTICEI
ALTERNATIVE METHODSI
RCOVKt
TARdET VAltfBl
0HIT8!
PIGMENT DISPERSION IN PLASTICS
ASTM D3015
THERMO PLASTIC GEOMEMBRANES
CARBON BLACK DISPERSION
Visual Comparison to Standard
summary or kbseooi
The referenced Standard
Practice covers the procedure
for examining and grading
plastic compounds to check
quality of pigment
(specifically carbon black)
dispersion. Grading or
classification of thin
section specimens is
performed by comparison
against grade standards.
Carbon black dispersion and
quality, the presence of
foreign matter or unpigmanted
resin, etc., can be an
Indicator of overall utility
of the material in field
applications. Only compounds
that are translucent in thin
sections (such as
polyethylene), can be
accurately examined. The
observational standards for
grading of the specimens are
generally agreed upon between
purchaser and seller, and are
not included in the Standard
Practice.
Six specimens, approximately
1.6 mm (0.063") In diameter,
are removed from six separate
compound samples. Thin
sections are placed on a
microscope slide at 10 mm
(0.375") intervals, and a
second slide is placed over
the specimens. The assembly
is placed on a hot plate which
is controlled to a
temperature suitable to
press out the specimens to a
uniform thickness and
diameter. The slides are
removed form the hot plate
and allowed to cool. The
specimen assembly is placed
beneath a microscope and
examined at a magnification
of 10OX. Each specimen is
rated against the
observational standard.
Standards are numbered in
ascending order from the
best quality (one) to the
worst quality. A minimum
point of acceptability is
usually set in a
specification. Flaws,
unpigmented areas, etc., are
noted for each specimen.
TOST EQUIPMENT!
Microscope, slides, hot plate
with pyrometer, and
sectioning equipment.
CI-5
INDEX PROPERTY I
REFERENCED TEST METHOD!
ALTERNATIVE METHODS1
SCOPE:
TARGET VALUE!
QUITS!'
GEOSYNTHETIC NOMINAL THICKNESS
ASTM D751
ASTM D1593 (Indirect Method)
GEOKEMBRANES, GEONETS
NOMINAL THICKNESS
mm (inches or mils)
SUMMARY Of METHOD!
The referenced test method
covers the determination of
the nominal thickness of
geosynthetic sheet of low
compressibility such as
geonets and most geomembranes
The procedure is not
recommended for highly
compressible geosynthetics,
such as nonwoven geotextiles
or very open or thick
geogrids or geocomposites.
Geotextile thickness is
proposed to be measured under
a compressive stress of 2 kPa
(0.29 psi).
The thickness is measured
using a dead weight type
thickness gage with a dial
graduated to 0,025 mm
(0.001"). The pressor foot
is circular having a diameter
of 9.5 mm (0.375"). The
thickness is measured under a
normal compressive stress of
23.5 kPa (3.4 psi) after a
seating period of 10 seconds.
Similar measurements are made
at least at five uniformly
distributed locations
throughout the sample. The
reported thickness is the
average of the five
measurements.
TSST EQUIPMENT!
Thickness gage as described
above.
CI-6
-------
INDEX PROPBRTYS
BBraUBMCZD TBST MBTHODJ
JLLTBRHMIVB METHODSI
SC07BS
TMtOB* fM.DE I
oiriT«t
SUHOJtY 07 M1TE0DS
Th« reference test method
outlines the procedure to
obtain the Shore type
duroaeter hardness for
geomeabranes. Two types of
duroaeters are described!
Type A tor softer materials
(such as rubber) and Type D
for harder materials, such as
thermoplastics. The
duroaeter hardness is an
empirical test for quality
control purposes. There nay
be no correlation between
duroaeter hardness obtained
from this method and values
obtained using other methods,
such as the Rockwell
Hardness, ASTK D785.
The test specimen consists Cf
a square measuring at least
25 mm (1") for single
hardness determination. The
specimen thickness is at
least 6 mm (0,25"), which may
ba attained by stacking
pieces of identical material
providing that the surfaces
between the plies are in
complete contact. The test
apparatus consists of a 2.5
to 3.2 ma (0.10 to 0.13")
diameter pressor foot, a
steel indentor (for Type A or
Type D) and an indicating
device. The indicating
device is graduated from
zero, for full extension, to
DUR0KETER HARDNESS
*crmi FI99AA
NOTCHED (Charpy i IZOD)
ASTM 0785 (Hard Plastics),
ASTM D1415 (Rubber)
ALL GEOMEMBRANES
HARDNESS
Dimansionless
100 for zero extension. A
calibrated spring is attached
to the indentor so that the
force applied to the specimen
is a known function of the
hardness. Tests are run at
23° (73 F). The specimen is
placed on a firm surface, and
the durometer is held
vertically so that the
presser foot is parallel to
the surface of the specimen.
The scale on the indicator is
read after the foot has been
in contact with the specimen
for 1 second unless a longer
loading period is specified.
The penetration is read
directly from the gage. The
hardness is determined from
the calibration of the device
for a known loading and
penetration. The applicable
force equations appear in the
test method.
TJtBT BQOZFKBBTt
Pressor foot, indentor (Type
ASD), indicating device and
spring calibrating device. A
sketch of the durometer
spring calibrating device as
well as details of the
indentors are presented in
the test method.
CI-7
XXDBX PROPERTYI
REFERENCED TEST METHOD I
WTBSHMXVZ METHODS!
SCOPE;
TASSET VALUBl
tJHITSl
DIMENSIONAL STABILITY
ASTM D1204
THERMOPLASTIC SEOMEMBRANES
CHANGE IN SPECIMEN DIMENSIONS
t
SUMMARY O* KBTHODS
The referenced test method is
intended as an index test to
determine the dimensional
stability of nonrigid plastic
geomembrane specimens at
specified elevated
temperature and exposure
tine.
Two 250x250 am (10"xl0")
specimens are removed from
the laboratory sample by
means of a cutting template
or die. Each specimen is
marked to show the direction
of extrusion or callendering.
The midpoint of each edge of
the specimen is marked as a
reference point for
measuring. The specimens are
conditioned and then placed
on heavy flat paper dusted
with talc to prevent
restriction of the specimen
expansion, a second layer of
paper is placed over the
specimen. The specimen is
then placed in an oven. The
temperature and exposure time
are selected by the user or
from an applicable material
specification.
After removal from the ovens
and reconditioning, the
specimens are again measured
to the nearest 0.25 mm
(0.01*). The percent change
(expansion) of the exposed
specimen is recorded.
ZB8S EQUIPMENT!
Oven, scale, thermometer,
specimen cutting die or
teaplate, heavy paper sheets
and talc.
a.b.x.y MARK MIDPOINTS OF SPECIMEN
CI-8
-------
XXDBX PBOPEHTY;
BEZBBBKCBn TEST MBTEODl
ALTERNATIVE KBTHOD81
SCOV8I
TAJUJB* rXLVBt
UNITS:
HEAT DETERIORATION OF RUBBER
ASTM D573
RUBBER GEOMEMBRANES
CHANGE IN BREAKING STRENGTH
%
smoaxx or kbteooi
The referenced method is a
comparison test to determine
the influence of elevated
temperatures on the physical
properties of vulcanized
rubber. The dumbbell-shaped
specimens are exposed to
specified elevated
temperatures in an air
environment inside an oven.
After a particular exposure
time, the physical properties
are determined and compared
to control data. Tensile
properties for the rubber
specimens are determined as
directed in ASTH D412. Three
or more specimens' are tested
for each exposure period.
Testing Intervals are
dependent on the type of
rubber and the test
temperature. Typical
intervals are 2, 4, 7 and
14 days. At the end of the
aging interval, the specimens
are removed from the oven and
allowed to cool at room
temperature for at least 16
hours before properties tests
are performed. The changes
in tensile properties
(breaking strength and
elongation) are plotted
against time or compared to
the applicable material
specifications.
TBS* BQOZPXBHTl
Constant-Rate-of-Extension
(CRE) tensile testing device,
specimen cutter, oven,
temperature monitoring and
control devices, and specimen
rack.
Cl-9
IHDEX PROPERTY!
RBFEREIICBD TEST METHODI
ALTBKKATXVE XBTHODSI
SCOPE I
TARGET VALUBt
OHZTSI
THERMAL EXPANSION
ASTM 0696
CRYSTALLINE AND THERMOPLASTIC
GEOMEHBRANES
COEFFICIENT OF THERMAL EXPANSION
Expansion per unit length per
degree Celsius
The referenced test method
covers the determination of
the coefficient of linear
thermal expansion of plastics
over a specific range of
temperatures. Thermal
expansion is an elastic
(recoverable) component of
elongation of plastics.
Other components include
deformation caused by changes
in moisture, phase changes,
curing and stress relaxation.
This test is conducted under
conditions that reduce all
other components except for
thermal expansion or
contraction. For this
reason, the test yields only
an approximation of true
behavior.
Tests are conducted at
temperatures of -30°C (-22 F)
and 30 C (86 F). Conditioned
specimens measuring 50x125 mm
(2"x5") are placed within a
fused-quartz-tube dilatometer
which consists of two
cylinder dilatometers. The
net pressure on the specimen
between the dilatometers is
70 kPa (10 psi). The
apparatus is placed into a
*30 C (-22 F) bath.
Deformation of the specimen
is measured using an LVDT or
dial gage under constant
temperature until there is no
change in deformation after
about 5 to 10 minutes. The
procedure is repeated in a
constant temperature of 30 C
(86 F) and deformation is
again recorded. The
coefficient of thermal
expansion is the change in
length recorded due to
heating or cooling divided by
the product of the original
specimen length and the
temperature difference.
TBST SQ0XPKBNTI
Fused-quartz-tube dilatometer
"(details included in Test
Method) LVDT or dial gage,
constant temperature liquid
bath and thermometer or
thermocouple,
LVOT
VITREOUS
SILICA ROD
VITREOUS
SILICA TUBE
SPECIMEN
10 QUARTZ-TUBE DIL^^pTER
-------
INDEX PROPERTYI
REFERENCED TE8T XBTHOD:
ALTBRHATIVS METHODS:
8COPBI
TARGET VALUE:
UNIT8:
VOLATILE LOSS FROM PLASTICS
ASTM D1203
REFER TO ASTM E197
THERMOPLASTIC OR CRYSTALLINE
GEOMEMBRANES
WEIGHT LOSS
%
summary or methods
This empirical method covers
the determination of the
volatile loss from a plastic
material under specific
temperature and time
conditions using activated
carbon as the immersion
medium. Relative comparison
of geomembrane specimens of
the same nominal thickness
can be conducted. Tvo
methods are described.
Method A is the direct
contact method and Method B
is the wire cage method,
vhich may yield a more
precise result.
Geomembrane specimens are
50 mm (2") diameter disks.
After a conditioning period
of at least 20 hours at 23 C
(73 F) and 50* relative
humidity, the specimen
thickness and weight are
measured. Three test
specimens are used for each
test. A specified volume of
activated carbon is placed in
the bottom of a 1-pint
container. For Method A,
layers of activated carbon
are placed between each of
the three specimens. For
Method B, the wire cages are
separated by layers of
activated carbon. The
container is sealed and
placed in an oven at a
temperature of 79 C (158 F)
for a period of 24 hours. At
the end of the heating
period, the specimens are
removed, brushed free of
activated carbon,
reconditioned for 20 hours,
and reweighed. The volatile
loss is expressed as the
percent of weight loss before
and after the heating period.
TEST EQUIPMENTS
Oven (or bath), containers
(1-pint paint cans or screw
top jars) balance,
micrometer, metal cages
(Method B), and activated
carbon as specified in the
test method.
CI-ll
INDEX PROPERTY J
REFERENCED TEST MEXBOD:
ALTERNATIVE METHODS!
SCOPE:
TARGET VALUE:
UNITS:
BRITTLENESS TEMPERATURE
ASTM D746 (Plastics)
ASTM 02137 (rubber and
reinforced)
GEOMEMBRANES
gRITJLENESS TEMPERATURE
8UXXARY 07 KETHOD!
The referenced test method
covers the determination of a
temperature at which
geomembrane specimens exhibit
an impact failure under
specified conditions. The
method is essentially an
index test but may be used to
predict the behavior of
specimens at low temperatures
under similar loading and
deformation conditions.
The test specimens are
clamped at one end and held
horizontally similar to a
cantilever beam. The
vertical striking member is
released downward to impact
the specimen with a striking
edge having a radius of
1.57 mm (0.062"). A sketch
of the striking member, clamp
and specimen appear below.
The specimen consists of a
6.4 mm (0.25") wide rectangle
that is long enough to
facilitate clamping plus
allowing a 25 mm (1")
extension. A minimum of ten
specimens are tested at each
test temperature. The
specimens and clamp assembly
are placed in a constant
temperature bath for three
minutes. The initial test
temperature is selected at a
temperature where a 50%
failure rate is expected.
Each specimen receives a
single impact by the striking
member. Each specimen is
examined to determine if
failure has occurred. The
temperature is varied by 2 to
10 C increments until all 10
specimens fail at the lowest
temperature and none of the
ten specimens fail at the
highest temperature.* All
test data (i.e., % failures
vs. test temperature) is
plotted and the brittleness
temperature is defined as the
temperature at which 50% of
the specimens have failed.
This Is determined
graphically.
TEST EQUIPMENT:
Constant temperature bath,
temperature conducting,
monitoring and controlling
equipment, specimen clamp
(drawing available from ASTM)
and striking member.
STRIKING EDGE RADIUS
1.67+0.13mm
SPECIMEN
CLAMP
2.5±0.6cm
CI-12
-------
XHDKX PROPERTY:
SB7BSSKCBD TEST METHOD:
ALTERNATIVE METHODS:
SCOPEI
TARGET VALUE I
UNITS:
OZONE RESISTANCE
ASTM D1149 (Lab Method)
ASTM D1171 (Outdoor Method for
Soft Rubber)
RUBBER GEOMEMBRANES
TIME TO CRACK FORMATION
hours
SUMMARY 07 METHOD:
The laboratory test method
referenced is limited in
scope to vulcanized rubber,
although the applicability to
other materials, such as
plastics, is not addressed.
The test method may not
provide results consistent
with real-time outdoor
exposure. It provides a
means of estimating the
resistance of a rubber
specimen to cracking when
exposed to ozone under
certain conditions in an
enclosed chamber. Since
ozone attack is related to -
termperature, ozone
concentration, stress
relaxation of the specimens,
etc., this test method is
recommended only as a
comparison between candidate
materials tested under
identical conditions. The
test chamber has a minimum
volume of 0.11 to 0.14 m (4
to 5 ft. ) and is capable of
generating and maintaining an
air-ozone stream of constant
rate and ozone concentration.
The air-ozone mix is
circulated over the test
specimens at a temperature of
40 C(104 F) or any
temperature selected by the
user. The standard ozone
partial pressures are 25, 50,
100 and 200oPa, or as
selected by the user. Test
specimens can consist of a
rectangular strip, a bent
loop, or a tapered strip.
The specimens are placed into
grips at prescribed
elongations ranging from 10
to 20% for the rectangular
and tapered strip specimens.
The specimens are inspected
daily (more often for special
tests) under a recommended
magnification of 7x to detect
the appearance of ozone
cracking. The time to first
observed cracking and the
specific test conditions are
reported.
TB8T EQUIPMENT:
Ozone chamber as described in
the test method. Ozone
Generator, such as a mercury
vapor lamp, and all
associated circulation and
monitoring equipment.
Commercial equipment is
available, but a source is
not listed in the test
method.
LOOPED
SPECIMEN
HOLDING
~ BLOCK
CI-13
INDEX PROPERTYI
REFERENCED TEST METHOD:
ALTERNATIVE MBTHODS:
8COPB:
TARGET VALUE I
UHIT8:
PUNCTURE STRENGTH
PROPOSED ASTM
CBR PLUNGER (DIN 54307)
GEOTEXTILES, GEOMEMBRANES,
GEOCOMPOSITES
PUNCTURE STRENGTH
N (lbf)
SUMMARY 07 METHOD:
TEST EQUIPMENTS
The test specimen is placed
between horizontal ring
clamps without pretensioning.
The attachment is placed
within a constant-rate-of
extension tensile testing
device. The exposed area of
the specimen is 45 mm
(1.75") in diameter. A solid
steel 8 mm (5/16") diameter
rod with a 4 5 camfered edge
is used to puncture the
specimen. The test is
performed at a rate of rod
travel of 305 mm (12") per
minute. The ultimate load
(or double peak loads for
geocomposites) is recorded as
the specimen puncture
strength. The number of
specimens is determined by
selecting the 95% probability
level, but 15 specimens per
test is considered to be the
upper bound number.
Drawings of rod and ring
clamp attachments will be
available through ASTM. CRE
tensile testing device
required.
I
6 6/32*
39/92* \ /
SPECIMEN
HOLDER
8PECIMEN
CI-U
-------
XMDKX PBDIBHTYt IMPACT RESISTANCE
BX72BXHCBD TXBt METHOD! ASTH PROPOSED
AiTKIOttTIVS KSXS0D8I NOTCHED (Charpy & IZOD)
ASTM D256, DROP CONE METHODS
SCOSSt GEOTEXTILES, GEOMEMBRANES, SOME
GEOCOMFOS XTES
TMSOMt VU
-------
XHDSX PROPERTY* BREAKING LOAD AND EXTENSION
RXrERKHCSD TBST MBTHODJ ASTM D638
JtLTSRM*TrVB METHODS: ASTM D882 (Thill Plastics)
ASTM D4I2 (Rubber)
SCOPE > THERMOPLASTIC OR CRYSTALLINE
GEOMEMBRAHES
MUUJB* VALDBJ TENSILE strength and elongation
mrzTSi kPa (psi) and %
SUMMARY or METHOD*
The referenced test method
covers the determination of
the tensile properties of
plastic dumbbell-shaped
specimens as thick as 14 mm
(0.55"). For geomeabranes
less than 1 ma (40 mil)
thick, ASTM D882 is the
preferred method. The test
is essentially an index test,
although under certain
testing conditions, it may
yield design oriented data.
The specimen sizes are
selected based on the type of
material tested and its
thickness. Five dumbbell
type specimens ranging in
narrow section width from 6
to 19 ma (0.25 to 0.75") are
presented in the test method.
Preparation of test specimens
using a die cutter is
recommended. All specimens
are conditioned for a period
of at least 40 hours prior to
testing in a Constant-Rate
of-Extension (CRE) tensile
testing device. For
isotropic materials, 5
specimens are tested for each
sample. For anisotropic
samples, 5 specimens are
removed in each of the
principal directions of
anisotropy. Specimens are
loaded to failure at rates
specified in the test method
In order to cause failure
between 0.5 to 5 minutes
testing time. Specimens that
break at the jaws or along an
obvious flaw are discarded.
The average tensile strength
at yield and break is the
yield or breaking load
divided by the original
minimum specimen cross
sectional area. The modulus
of elasticity can also be
calculated as directed in the
test method.
TEST EQUIPMENTS
CRE Tensile Testing Device,
grips, extension indicator,
and specimen die cutter.
TYPE n SPECIMEN
18mm
'
1
T
60mm
183mm
CI-17
XHDBX PROPERTY!
RBPEREHCBD TEST METHOD I
JLLTBJUttTrVK METHODS I
SCOPEi
TARGET VXiOTl
TOUTS J
WATER VAPOR TRANSMISSION
ASTM E96
ALL GEOKEMBRANES
PERMEANCE
metric perm
SUMMARY OP METHOD I
The referenced test method
covers the determination of
the rate of water vapor
transmission (WVT) of sheet
geomembranes under specified
test conditions. The water
vapor permeance of a specimen
is the rate of WVT to the
vapor pressure difference
between the two outer
surfaces of the specimen in
units of a metric perm. The
water vapor permeability for
a homogenous material is the
product of the permeance and
the specimen thickness, and
is expressed in units of
metric perm-centimeter.
The test consists of several
methods, each performed under
specific temperature and
relative humidities. In one
procedure a dessleant
(generally anhydrous calcium
chloride) is placed within a
dish which is completely
covered by the specimen and
sealed to prevent movement of
water vapor except through
the specimen. The
environment outside the
specimen is maintained at a
temperature of 23 C (73 F)
and a relative humidity of
50*. The change in relative
humidity across the specimen
(0% Inside dish, 50% outside
dish) is the driving force of
water vapor transmission
through the specimen. An
WVT DISH —
alternate method involves
filling the dish with water
(relative humidity 100%) and
covering the dish with the
specimen. The environment
outside the specimen is
maintained at a relative
humidity of 50% to again
generate WVT. The WVT is
measured by successive
weighings of the specimen and
dish over time (under the
controlled test conditions).
The results of the weighing
of three specimens for each
test method performed is
plotted. When a straight
line fits (within weighing
error) four properly spaced
points (i.e., a steady state
exists), the slope of this
line is the rate of WVT. The
required conversion factors
and calculations for
determining permeance and
permeability are provided in
the test method.
TEST BQOIPMBHTt
Environmental test chamber as
described in the test
procedure with capability to
continuously record and
adjust temperature and
relative humidity. Test
dishes, sealant and
dessicant. Details of test
dishes and sealing methods
are provided in the Appendix
of ASTM E96.
WAX
SEAL
SPECIMEN
EFFLUENT
CI-18
-------
nrozz novnoYs
aBFBRBXCBS TEST METHOD I
UXUOasrV* KBTH0D8!
SCOPS!
TJUMBT TOKFSs
UNITS:
BURIAL DEGRADATION
ASTH D3083
GEOMEMBRANES
TENSILE STRENGTH RETAINED
%
8UJOOJK 07 XBTHODt
The referenced test method Is
included in a general
specification for PVC
sheeting. Because of the
relatively short burial
period (30 days) and limited
soil conditions examined, the
referenced test method is not
suitable as a design aid.
Three 25 x 150 an (1x6")
specimens are prepared in the
machine and cross machine
direction. The specimens are
buried to a depth of 5" in
soil "that is rich in
cellulose-destroying
microorganisms" for a period
of 30 days. At the end of
30 days, the specimens are
removed and tested in
accordance with ASTM D882 and
compared to the tensile
strength of control
(unburied) specimens.
The test may also be
performed in a soil compost
(pH of 6.5 to 7.5, moisture
content between 25 and 30%
and constant temperature
between 32 and 38C), The
specimens are removed and
percent of tensile strength
retained is calculated.
TEST EQUIPMENT!
Greenhouse type apparatus
capable of maintaining the
test conditions listed above
and Constant-Rate-of-
Extension (CRE) Tensile
Testing Device.
CI-19
PROPERTY:
TUT METHODS
JLLSSBXkTrVX HBTHOSSt
SCOPSI
TARGBT VALUEI
UVXTS!
ENVIRONMENTAL STRESS CRACKING
ASTM D1693
THERMOPLASTIC GEOMEMBRAHES
PROPORTION OF FAILED SPECIMENS
%
SUlOCAttY OF METHODS
The referenced test method
was developed to cover the
determination of the
susceptibility of ethylene
plastics to environmental
stress cracking under
specified conditions.
Environmental stress cracking
of a geomembrane is highly
dependent on the stress
history and conditions of the
specimen and on the nature of
the reagent used. Under
certain conditions, an
indication of the performance
of the specimen can be
obtained. Generally, the
method is used as an index
test.
Test conditions such as
specimen thickness, notch
depth and test temperature
are selected by the user from
the three standard conditions
listed in the test method.
Rectangular specimens
measuring 30x13 mm (1.5x0,5")
are removed from the sample
usincr a cutting die. Each
conditioned specimen receives
a notch on one surface using
a special nicking jig. Ten
specimens are placed in a
bending clamp (see Figure)
with the notch facing upward.
The specimens are placed
inside a test tube containing
the reagent to be used during
testing. The reagent may be
a surface-active soap, such
as Igepal CO-630, or any
liquid organic that is not
absorbed by the specimen.
For special testing, the end
use waste fluid can be used
as the test reagent if the
concentration can be
controlled during testing at
elevated temperature. The
specimens are inspected at
the end of the immersion
period which is set at
48 hours in the absence of
any other material
specifications. The number
of failures (any crack
visible to the naked eye) is
recorded and expressed as the
percent of total number of
specimens tested.
TEST EQUIPMENTI
Specimen cutting die,
nicking Jig, specimen
holders, test tubes, reagent
and constant temperature
bath. Detail drawings of
test apparatus are available
from ASTM, or it may be
obtained commercially.
SPECIMEN
CI-20
TEST ASSEMBLY
-------
ezaioaaitcs bbdsistyi environmental stress rupture
RSra&SVCXO ZEST MBSSODl ASTH D25S2
xtassxjam kbthodsi —
SCOPEI POLYETHYLENE GEOMEMBRAHES
¦aKSBT VUDSI TIME to specimen rupture
UKIT8! hours
amaaxx or hsthod
Th« referenced test method
covers tits determination of
the susceptibility of
polyethylene to stress
rupture under specified
conditons. The test is
generally used to rank the
Performace of polyethlyenes
under a constant tensile load
in the presence of a surface
agent at a specified test
temperature. Like
environmental stress
cracking, environaental
stress rupture is dependent
on test environment, loading
and speciment stress history.
Results obtained do not
necessarily relate to the
field performance of the
geomembrane,
Twenty specimens are cut to
the shape shown below. The
thickness is measured and the
minimus cross-sectional area
of each specimen is
calculated. The test load
for each specimen is selected
based on the constant test
stress selected by the user.
The test bath is filled with
a surface active agent, e.g.,
Igepal €0-630 and the
temperature of the bath is
set to 50 C. Specimens are
attached to the test frame,
and immersed in the test
bath. Each specimen is then
loaded and the elapsed time
to failure is recorded. The
type of failure (brittle or
ductile) is recorded -
brittle failures are
preferred. The failure time
for each specimen is plotted
on semi-log paper versus the
specimen plotting position.
The best fit straight line
through the data points is
used to determine the F.0
value, that is the probiole
time required for 50% of the
speciments to fail in a
brittle mode. The F_- value
is reported. The tests can
be run on the parent material
or on the seams.
TOST EQUIPMENT
Specimen cutting die, stress
rupture apparatus, surface
agent, and constant
temperature bath are
commercially available.
MS
>0 POSITION!
SPECiMtN trr«
CI-21
IHDKX TOOFBSTX:
SBF8KSMCED IKS* KSTSODI
UTSSKLTXYI METHODSJ
SCOPBl
TUQST VM.UBS
OMITS:
PEEL ADHESION OF GEOMEMBRANE
SEAMS
ASTM 0413 (modified)
ASTM D816 Method C (Rubber)
ASTM D751 (Reinforced Geomem-
brane)
GEOMEMBRANE SEAKS
PEEL STRENGTH
N/m (Ibf/in)
suxhary or mstbod*
The "peel" test is performed
on test specimens removed
from a sample of factory or
field geomembrane seams or
"welds" for quality control
purposes. In addition, the
ply adhesion of composite
materials can be tested using
this method. The test can be
performed in the field or the
lab.
A rectangular specimen,
usually 25 to 50 mm (1-2")
wide is carefully cut from
the test sample. Opposing
edges of the seam specimen
are placed into grips of a
Constant-Rate-of-Extension
(CRE) tensile testing device
(see figure). A 90 or ISO
peel test can be performed,
with the latter most suited
for very flexible parent
sheet material. The specimen
is tested to failure at a
rate of 50 to 150 mm/min (2"
to 6"/min). The maximum
force is recorded. The
specimen is carefully
observed, to identify the mode
of failure (peel failure of
weld, tearing of sheet
material, etc.). Tradition-
ally, the geomembrane
industry has interpreted the
results of this test in a
qualitative manner using the
film tear bond (FT8)
criteria. The test is used
as an indicator that the
apparent strength of the bond
is greater than the strength
of the parent material. This
is a visual determination
often used as a basis of
qualifying field welds. The
recorded adhesion force can
be used as a check on
specimen variability.
TEST EQUIPMENT»
CRE Tensile Testing Device.
Specimen cutting die.
SPECIMEN
WCID
I
S0° PEEL TEST
W® PEEL TEST
CI-22
-------
INDEX PROPERTYI
REFERENCED TEST METHOD:
ALTBKMATIVB MBTHODSJ
SCOPE!
TARGET VALUB:
GRAB TENSILE STRENGTH
ASTM D4632
ASTM D1682 (modified),
ISO 5032-1982(E)
GEOTEXTILES (except for knitted)
BREAKING LOAD
UNITSJ N (lbf)
SOTGtARY OF KBTHOD S
The Grab Tensile Strength
test described is suitable
for quality control testing
during manufacture or for
commercial acceptance test-
ing. There is no known
correlation between grab
tensile strength and strength
values obtained using strip
methods.
The grab tensile test is a
uniaxial test where the
specimen is wider than the
test clamps. The tensile
strength added by the
undamped portion of the
specimen is influenced
primarily by geotextile
construction. Testing of
knitted geotextiles using
this method is not recom-
mended. Because of the geo-
metry of the test and con-
tribution of undamped areas
a simple relationship between
load and elongation cannot be
expressed, so the term
"apparent elongation: is
used.
parallel to the direction of
loading. A pretension of
0.5% of the breaking load is
applied if apparent
elongation is to be measured.
Apparent elongation is
measured at the cross-head.
A CRE tensile testing device
is operated at a rate of
300 mm/min (12"/rain) until
rupture of the specimen. Ten
specimens are tested in each
of the principal directions
and results in each direction
are averaged and presented
separately. The breaking
load is the maximum load
applied to the specimen. The
grab strength has units of
force, although the unit of
force per unit width of the
aws is implied. It is
mportant to note the jaw
width (25 mm or 1") when
considering grab tensile
strength data.
A 100x200 mm (4x8") specimen
is placed centrally in a set
of parallel 25x50 mm (l"x2")
clamps such that the clamps
are spaced 75 mm (3") apart.
Care should be exercised to
insure that the long
dimension of the clamps are
TEST EQUIPMENT I
Constant-Rate-of-Extension
(CRE) tensile testing device,
flat clamps as described
above.
CI-23
INDEX PROPERTY!
REFERENCED TEST KBTHOD:
ALTERNATIVE METHODS»
SCOPE:
TARGET VALUE:
UNIT8:
STRIP TENSILE STRENGTH
ASTM D1682
GEOTEXTILES
BREAKING LOAD
N/m (lbf/in)
SUXKARY 07 METHODS
The strip tensile test is a
uniaxial test where a 25 mm
(1") or 50 mm (2") wide strip
of geotextile is extended
between two clamps moving in
a direction parallel to the
direction of loading until
failure of the specimen
occurs. The test generates a
load-elongation curve and is
suitable for quality control
or comparison testing of
geotextiles. Due to the high
transverse strains
("necking") which accompany
testing of some types of
?eotextiles, this test method
s not recommended for use as
a design aid.
The 75 mm (3-in. long)
specimen may be tested in the
wet or dry condition. A
pretension of up to 0.5% of
the maximum load can be
applied to the specimen. The
ultimate force required to
rupture the specimen is the
tensile strength of the
specimen.
TE8T BQUIPKENT:
Constant-Rate-of-Extension
(CRE) Tensile Testing Device.
SPECIMEN
76mm
26mm or
60mm
CII-24
-------
INDEX PROPERTY:
REFERENCED TEST METHOD:
ALTERNATIVE METHODS:
SCOPE!
TARGET VALUE:
HYDROSTATIC BURSTING STRENGTH
ASTM D751 (Diaphragm)
ASTM D3786
DIN 53861
GEOTEXTILES, SOME GEOMEMBRANES
BURSTING STRENGTH
UHIT8? kPa (pal)
sxnoaxY 07 method:
The referenced test method
was developed for testing
coated fabrics which have a
relatively low elongation at
failure. Geomembranes having
relatively low elongations at
failure, such as reinforced
membranes, may also be tested
using this method. Testing
of high elongation rubber or
thermoplastic specimens is
not be limited for use in the
diaphragm burst testing
device described.
The diaphragm bursting tester
can be operated either
hydraulically or
pneumatically. Two circular
steel disks with a 75 mm (3")
outer diameter and openings
of 31 mm (1.25") clamp the
specimen horizontally over a
membrane. The membrane is
expanded under a constantly
increasing pressure until
rupture of the specimen
occurs. The bursting
strength is the corrected
?ross pressure recorded, and
s reported as an average of
ten specimens.
TB8T 2QUXPX2HTI
Diaphragm Burst Tester (as
described in test method).
CII-25
INDEX PROPERTY:
REFERENCED TEST METHOD:
ALTERNATIVE METHODS:
8COP81
TARGET VALT7B:
UNITS:
TEARING STRENGTH
ASTM D4533 (TRAPEZOID TEAR)
DIN 53859/2 (TONGUE TEAR)
GEOTEXTILES
TEARING STRENGTH
N (lbf)
SUMMARY Or METHOD:
The trapezoid-type tear test
described measures the force
required to propagate a tear
in the test specimen. This
tear resistance is a function
of yarn or fiber type and
geotextile construction.
Tear strength is measured and
reported for each of the
principal geotextile
directions.
10 specimens are tested
in each principal direction
unless the coefficient of
variation of the geotextile
tested is known.
TEST EQUIPMENT!
CRE tensile testing device,
flat clamps.
On a rectangular specimen
measuring 76 mm by 200 mm
(V'xB"), a trapezoid is
marked, as shown below. A
15 mm (5/8") cut is made
perpendicular to the specimen
edge in the center of the
short (25 mm or 1") side of
the trapezoid. The specimen
is gripped in flat clamps
extending the entire width
of the nonparallel edges of
the trapezoid. The clamps
are placed in a Constant-
Rate-of-Extension (CRE)
tensile testing device, which
operates at a rate of
300 mm/min (l2"/min). The
total force is measured as a
function of jaw extension,
and the tearing strength is
the maximum force recorded.
If multiple peaks are
observed' on the force vs.
elongation plot, the tearing
strength is the value 'of the
highest peak. A total of
76mm (3*)
TEMPLATE
25mm
200mm
(8*)
15mm
: (5/8")
100mm
(4*)
1
SPECIMEN
CII-26
-------
XHDBX 7B0PBBTY:
KSTBStEVCKD TSSS KBTBOD:
jyWBBJELTXTX METHODS:
SCOPSI
TXUOBT T71I.DB I
ranxsi
ABRASION RESISTANCE
PROPOSED ASTM
ASTM D1175
GEOHEMBRAHES, GEOTEXTILES
TENSILE STRENGTH LOSS
%
SOJOOBY OJ KBTBOD J
The referenced test method
covers the abrasion
resistance of a specimen
using the sand paper sliding
block method. Like other
abrasion tests, such as test
methods using rotating wheels
or drums, this is an index
test method suitable for
comparison, within some
limitations, of candidate
geomembranes or geotextiles.
Because the ultimate utility
of this procedure in
geosynthetics has not been
determined, and because the
relationship between
laboratory tests and field
performance is not Known, the
abrasion test is not
recommended for use in
design.
The sand paper-sliding block
method involves a specimen
being abraded using a
reciprocal action under some
combination of normal
pressure, abrading cycles and
abrading surfaces.
Rectangular specimens
measuring 75 x 200 am (3"x8")
are clamped onto a stationary
upper plate in the test
device. The abrading medium
is placed on the lower
reciprocating plate. The
upper plate is released so
that the specimen and
abrading medium are in
uniform contact. The top
plate is loaded with a
specific weight, and the
specimen is abraded using a
stroke of 25 ma (1") at a
specific spaed and number of
cycles. Zn the absence of
other material
specifications, the abrading
medium is 100 grit Emory
cloth. The normal load is
1 kg, the speed is 30
cycles/minute and the test
duration is 250 cycles, or
rupture of the specimen. The
percentage of strength loss
is determined by testing a
set of control and abraded
specimens using the 2-in.
raveled strip or cut strip
method (ASTM 1682 modified).
Five specimens tested each in
the machine and cross machine
direction are tested, and the
average loss of breaking
strength is reported. The
test may also be run to
rupture of the specimens. In
this case, the average number
of cycles to failure for five
specimens is reported.
TB8T SQDXPK8NTI
Balanced head and block
assembly, cycle counter,
weights, abrading medium and
Constant-Rate-of-Extension
(CRE) Tensile Testing Device.
Details on the head and block
assembly are not yet
available.
CIl-27
PROPERTYI
8B7BRBXCBS TS8T METHODI
AlTEJUaTIV! XSTSODSi
SCOPEI
TAHGET WLUB:
UKIT8:
MAXIMUM PORE (OPENING) SIZE
PROPOSED ASTM
USA CORPS OF ENGINEERS CW02215
GEOTEXTILES
APPARENT OPENING SIZE (AOS)
mm
scmnxY or method«
The test method referenced is
one of the sieving-type
methods to determine the
apparent (equivalent) opening
size of a geotextile
specimen. This type of
procedure generates data that
is misleading for some
nonwoven geotextiles, and is
often difficult to interpret.
Although the test is Intended
as an index test, the opening
size data is being used as a
part of geotextile design in
filtration or separation
applications because there is
no widespread accepted
alternative at this time.
Caution in interpretation of
the results is advised since
the precision and interlab
bias of the method has not
been established.
The method involves placing a
geotextile specimen without
tension into a sieve frame
between two sieves. Uniform
spherical glass beads,
starting with the smallest
diameter beads, are placed on
the geotextile specimen, and
the frame is shaken for ten
minutes. The beads that fall
through the specimen are
weighed and expressed as the
percent of the glass beads
passing through the specimen.
The procedure is repeated for
the same specimen using
successively larger beads.
Trials are repeated until the
percent of beads passing
through the specimen is St or
less. Five specimens are
tested in this manner. The
apparent opening size (AOS or
095) is defined as the bead
diameter value, in mm, that
intersects the 5% passing
mark. The AOS can also be
expressed as a US standard
sieve number for the next
larger size sieve or mesh.
XBST EQOIPKBHTI
Sieve shaker, 200 ma (8")
diameter sieves, pan and
cover. Commercially
available glass beads and
anti-static devices. Sources
of beads and anti-static
devices will be published
with the test method.
CII-28
-------
XHDBX PROPERTY:
SBrESBKCBO TEST METHOD I
XLTBSHX1ZVS W5THOD8:
SCOPE:
TARGET VXLUB:
CHITS I
DEGRADATION FROM EXPOSURE TO
ULTRAVIOLET LIGHT
ASTM D4355
GEOTEXTILES
PERCENT OF TENSILE STRENGTH
RETAINED
% or N/m (lbf/in)
sunou or method:
The behavior of a geosyn-
thetic specimen exposed to
ultraviolet radiation is
compared to that of a control
specimen. Exposure consists
of 120-minute cycles consist-
ing of 102 minutes of light
followed by 18 minutes of
water spray and light within
a Xenon-Arc Apparatus. Five
specimens are tested for each
exposure time (150,300 and
500 hr UV exposure) for eac!=
of the principal directions,
and are compared to five
unexposed control specimens.
The specimens are compared by
testing for tensile strength
using a 2-in. wide strip
specimen (ASTM D1682
Method D). The percent loss
of strength of the exposed
specimens is calculated for
each exposure time. Results
can be expressed as a plot of
percent of breaking strength
lost (or retained) versus
exposure time.
The Xenon-Arc type exposure
cannot simulate all the
variables of ultraviolet
radiation contained in
sunlight. Test results may
have no direct correlation
to actual sunlight exposure.
TEST equipment:
Xenon-Arc Apparatus Type BH
or Type C, as described in
ASTM G-26, CRE tensile
testing device outlined in
ASTM D1682.
CII-29
TJIDBX PROPERTY:
REFERENCED TEST METHOD:
ALTERNATIVE KETHODS:
SCOPEt
TARGET VALUE:
UNITS:
TEMPERATURE STABILITY
ASTM D4594
GEOTEXTILES (except knitted)
CHANGE IN BREAKING STRENGTH AND
ELONGATION
%
BUXXARY 07 METHOD:
The referenced test method is
used as an index test to
compare the change in
breaking strength and
elongation of different
geotextile specimens under
controlled chnages in
temperature. Freeze-thaw,
elevated or low temperature
conditions can be examined,
and the relative effects of
these conditions on different
geotextiles compared. The 2"
cut or ravel strip tensile
test (ASTM D1682 modified)
is used as the referee method
for determining breaking
strength and elongation. The
test is performed using a
Constant-Rate-of-Extension
(CRE) device inside an
environmental chamber capable
of maintaining temperature
froo 040 C to 100°C (-4 0 F to
212 F). Five geotextile
specimens in the machine and
cross machine directions are
prepared as control specimens
and for testing within the
environmental chamber. After
the specimen is inserted into
the jaws of the CRE device,
the temperature of the
chamber is set. If desired,
a specified number of
freeze-thaw cycles may be
applied to the specimen prior
to testing. The tensile test
is performed at the specified
test temperature and the
specimen is tested to failure
as directed in ASTM D1682.
The average specimen breaking
load and elongation at
failure is compared to those
of the control specimens.
Results are reported as the
average percent change in
breaking load and elongation
under the specific conditions
tested.
TEST EQUIPMENT:
CRE tensile testing device,
environmental chamber with
temperature regulation and
measurement equipment.
CII-30
-------
XVDBX »ROP8RTX« WATER PERMEABILITY (PERMITTIVITY)
REFERENCED TEST METHOD! ASTM D4491
ALTERNATIVE METHODSJ France! CFGG NF G38-016
Other European
SCOPE! GEOTEXTILES
TARGET VALUE! WATER PERMITTIVITY
UNITS! sec
SUMMARY OF MBTHODSl
This standard describes test
methods for both constant
head and falling head
techniques.
Constant Head Test - A
constant head of 50 am (2")
is maintained over the 73 ma
(2.87") diameter specimen.
Flow quantity versus time is
recorded, Desired water
(dissolved oxygen content -
6 ppm) is recommended for use
in this test. The
permittivity is determined
from the average of
5 flow rate readings per
specimen. The permittivity
value for the specimen is
considered valid only within
the laminar flow regime. The
test method includes
provision for determining the
limits of the laminar flow
regime by running the test at
various heads. All values
are corrected for
temperature.
fa111na Mad last - % failing
head over a range from 80 mm
(3.25") to 20 mm (0.75")
is used to determine
permittivity of geotextile
specimens using the same
device and conditions as the
constant head technique. The
time for the water level to
drop the required distance is
recorded and averaged for at
least 5 trials per specimen.
All values are corrected for
temperature.
TEST EQUIPMENTI
Detailed drawings and
materials list available from
ASTM.
OUAQE FOR
FALUN Q HEAD TEST
STANOPIPE
OUTLET
ROTATINO
DISCHARGE
SPECIMEN
WATER
RESERVOIR
eii-3i
PERFORMANCE PROPERTYt COMPRESSIBILITY/CRUSH STRENGTH
REFERENCED TEST XETEOD:
ALTERNATIVE METHODSJ
SCOPE!
TARGET VALUE1
UNITS!
PROPOSED ASTM
Mi GEOSYHTHETICS
DEFORMATION UNDER LOAD
OR CRUSH STRENGTH
kPa (psf)
SUMMARY or METHOD I
The referenced draft method
covers the determination of
the compressive stress-strain
characteristics of
geosynthetics. The crush
strength can be evaluated for
some geosynthetics. The test
is intended as an index test,
but some data generated can
be used for design purposes,
for instance, the selection
of compressive stress levels
for use in compressive creep
testing. Since the
compressibility of a
geosynthetic specimen may be
highly time-dependent, the
use of this method alone to
predict long term behavior of
geosynthetics is not
recommended.
The specimens are at least
100 mm (4 in) square.
Geocomposite or geonet
specimens are trimmed to
preserve structural capacity.
The specimen is placed
between 2 flat rigid platens,
and a seating load of 2 kPa
(42 psf) is applied.
compressive loads are then
applied at a constant rate of
deformation of 1 mm/min.
Deformation and load are
recorded simultaneously for
at least 20 distinct data
points and the data is
plotted on a stress-strain
curve similar to the one
shown below. The test is
repeated on another specimen
at a deformation rate of 10
mm/min. The crush strength
and the compressive modulus
may be determined from the
¦tress-strain plot.
TEST EQUIPMENT«
Constant-Rate-of-Extension
(CRE) Testing Device, load
platens and load and
deformation monitoring
devices.
COuratOive strain, £ (ft)
CII-32
-------
APPENDIX D - PERFORMANCE PROPERTIES
I GEOMEMBRANES
PAGE
Chemical Resistance, EPA 90/90
Bonded Shear Strength (Shear), ASTM D751
Bonded Shear Strength (Shear), ASTM D816
Bonded Shear Strength (Shear), ASTM D882
Hydrostatic Bursting Resistance,
Nondestructive Seam Evaluation - Ultrasonic
Shadow Method - GRI# GM1-86
Nondestructive Seam Evaluation - Ultrasonic
Pulse Echo Technique - ASTM D4437
Nondestructive Seam Evaluation - Vacuum
Box Technique - ASTM D4437
Nondestructive Seam Evaluation - Pressure
Testing Technique
Nondestructive Seam Evaluation - Air Lance
Technique, ASTM D4437
Embedment Depth for Anchorage Mobilization
GRI# GM2 - 87
DI-1
DI-2
DI-3
DI-4
DI-5
DI-6
DI-7
DI-8
DI-9
DI-10
DI-11
II GEOTEXTILES
Breaking Strength - Wide Width Strip Method,
ASTM D4595
Sewn Seam Strength - Proposed ASTM
Coefficient of Soil/Geosynthetic Friction,
Proposed ASTM
Puncture Strength (CBR), DIN 54307
In-Plane Flow (Transmissivity), ASTM D4617
Water Permeability Under Stress, Proposed ASTM
Clogging Potential (Gradient Ratio Method),
Proposed ASTM
Long Term Flow Rate (Clogging), GRI# GT 1-86
DII-12
DII-13
DII-14
DII-15
DII-16
DII-17
DII-18
DII-19
III GEONETS/GEOCOMPOSITES
Tensile Creep, Proposed ASTM DIII-20
Compressive Creep, GRI# GS 4-37 DIII-21
Flow Channel Intrusion, GRI# GC 3-87 DIII-22
Bond Strength/Adhesion, ASTM F904 DIII-23
-------
72XT08X1JICB PROPERTY t
SSrotEJlCBD TEST KSTBOD;
ALTBKHATXVB METHODSJ
SCOPBl
tarqbt mrai
UHIT8:
CHEMICAL RESISTANCE
EPA 90/90 (Draft)
ASTM PROPOSED (Geotextiles)
ASTM D543 (Geomembranes)
GEOSYHTHETICS
CHANGE IN PHYSICAL AND
MECHANICAL PROPERTIES
%
amoaa.? or method*
The draft EPA method
referenced is the most
commonly used chemical
resistance or compatibility
test at this time. It is
intended as a means of
comparing different types of
geomembranes (to identify
incompatible ones) or to
provide the user with an
indication of geomembrane
behavior when.exposed to
certain chemicals or
leachates. Extrapolation of
such behavior over the design
life of the application
(often 50 years or longer) is
required.
This accelerated test
involves complete immersion
of the specimens in a
"representative" sample of
leachate or other chemical
expected to be present in the
geomembrane field
environment. The testing
period is currently 120 days,
although this period may be
extended to 180 days or more
in the final draft. Tests
are conducted at temperatures
of 23 and 50 C (73 and
122 F). A series of control
(unexposed) tests are run,
and duplicate tests are run
after exposure times of 30,
60, 90 and 120 days, althoguh
more frequest testing may be
performed. The tests
performed include: specimen
mass per unit area and
dimensional stability,
thickness, environmental
stress cracking (crystalline
or semicrystal1ine
specimens), tear, puncture,
tensile strength and
elongation, hydrostatic
resistance (except for
rubbers), volatiles,
extractables (except for
scrim reinforced) and ply
adhesion (for scrim
reinforced specimens or
seams). Creep-type
properties and other
performance properties are
not currently addressed. The
percent change in the
physical and mechanical
properties as compared to
control specimens is plotted
against immersion time. The
trend of the data provides an
indication of the
compatibility of the
geomembrane specimen and
waste fluid.
TBS* EQUIPMENTI
Suitable waste containers,
temperature monitoring and
control device, oven, waste
fluid monitoring and
circulating equipment,
analytical balance and all
apparatus required for
performing desired physical,
chemical and mechanical
properties tests.
DI-l
PBXrOJUOXCS PROPERTY I
RRTKBEWCTn TBSt METHODS
ALTERNATIVE KBTS0D8I
SCOPEI
TARG8T VALUB!
TOUTS I
BONDED SEAM STRENGTH (Shear)
ASTM D751
SCRIM REINFORCED GEOMEMBRANES
BONDED SEAM BREAKING LOAD
kN/ra (Ibf/in)
SOXXARY OF METHODI
The scope of the referenced
test method is limited to
bonded seam strength of
scrim-reinforced geomembranes
and some composites. The
method is a modified grab
method (ASTM D1S82). Jaws
for this method measure
25x75 mm (l»x3«). The
specimen is 50x200 ma (2"x8")
with the bonded seam in the
center of the long dimension
of the specimen. The free
ends of the specimen
extend parallel in opposite
directions to allow clamping.
The specimen is loaded in
tension in a direction
perpendicular to the seam at
a rates of either 5 mm/a
(12"/min) or 0.85 ma/sec
(2"/ain). The maximum load
(kN/m or lbf/in) before
rupture of the
specimen is the bonded shear
strength. The location of
the observed rupture for each
specimen is recorded. A
minimum of three specimens
are tested.
TBST BQUIPXBSTl
Constant-Rate-of-Extension
(ORE) Tensile Testing Device,
flat clamps.
t
.CLAMP
WELD
SPECIMEN
\
DI-2
-------
PIBVOBIOXCS PROPERTY:
isratSMoro *bs* method:
iLTwaaixra methodsj
800781
XUOSS VALUEI
0HXT8S
BONDED SEAM STRENGTH (SHEAR)
ASTM D816 Method B
RUBBER GEOMEHBRANES
BONDED SEAM BREAKING LOAD
kN/m (lbf/in)
flmOOBY OT HBSBOSl
The referenced test method
was developed for testing
rubber adhesives. Method B
is used to measure the
adhesion in shear of a bonded
seam strip specimen measuring
25 db (1H) in the absence of
any seam specification. A
lap seas in the central
portion of the specimen is .
tested with the free ends of
the specimen parallel to and
on opposite sides of the seam
for clamping. The entire
specimen width is clamped.
The bonded area is kept
parallel to the direction of
testing bv using shims at the
jaw locations. This is to
reduce the peel component in
the failure of the specimen.
The test is conducted at a
strain rate of 0.8 ms/s
(2"/min) and the maximum load
applied to the specimen is
recorded. The shear adhesion
is reported as the average
load per unit width (kN/m or
lbf/in) for six specimens.
test BQOinmm
Constant-Rate-of-Extension
(CRE) Tensile Testing Device,
suitable clamps, specimen
cutting dye (optional).
t
CLAMP
SPECIMEN
\
01-3
psavoBiaiics profbrtxi
REFEREMCED TEST METHODS
lATEHl»TT9Ti METHODS*
8C0PBI
TARGET VALUE:
UNITS:
BONDED SEAM STRENGTH (SHEAR)
ASTM D882 (modified)
ASTM D638 (Dumbbell-shaped
specimens)
GEOMEMBRANES (except scrim
reinforced)
BONDED SEAM BREAKING LOAD
KN/b (lbf/in)
smoout* or mbtsodj
The referenced test method is
the preferred method for
testing for tensile or seam
strength properties of thin
(less than 1 am, or 40 mil in
thickness) plastic
nonreinforced geomembranes.
ASTM D638 is the preferred
method for testing plastics
greater than l mm (40 ail) in
thickness. For quality
control testing of seams,
modifications of ASTM D882
are generally used. The
specimen is 25 am (1") wide
and the length of the
specimen is 100 mm (4") plus
the width of the seam. As in
all tensile tests on
plastics, the specimen must
be cut out carefully to avoid
stress concentrations.
Cutting dies are required
to make all specimens as
uniform as possible.
The test specimen is gripped
along its entire width and
tested to failure at a
uniform rate of 8 mm/s
(20"/min), The ultimate load
per unit width of the
specimen is the bonded seam
breaking load in kN/m
(lbf/in). Each specimen is
carefully observed and the
mode and location of failure
are reported for each
specimen. A visual
qualification/disqualifica-
tion criteria, known as the
film tear bond (FTB), is
often reported for each
specimen instead of the
bonded seam breaking load.
TB8* EQUIPMENT I
Constant-Rate-of-Extension
(CRE) tensile testing device
clamps, specimen cutting die
and measuring devices.
t
CLAMP
WELD
SPECIMEN
\
DI-4
-------
VSKTOIUaSCX raOPKKTXl HYDROSTATIC BURSTING RESISTANCE
REFERENCED TEST METHOD: —-
UTBSIOISZTE KBTHODS: DREXEL UNIVERSITY GRI IGH3-87
SCOPE: GEOMEMBRANES
TARGET VXLUE: BURSTING RESISTANCE
mnist % strain, Number of days at
prescribed pressure
suioaunt or mbtbosi
The performance hydrostatic
bursting resistance test
apparatus described is based
on devices fabricated by the
US Bureau of Reclamation and
other organizations in the
US and Europe. The device
consists of a large
cylindrical split chamber
measuring as large as 60 to
90 cm (2 to 3 ft.) in
diameter. A geomembrane
specimen is supported on
flanges at the chamber split.
The lover chamber can be
filled with
soil or other test media.
The upper chamber may be
filled with water and air
pressure applied. The device
may be operated as a large
burst tester if the specimen
is tested to failure.
Performance properties of a
candidate geomembrane can be
examined under simulated
field conditions. The effect
of soil density, surface
uniformity, etc., can be
examined under particular
stress conditions. The
effects of friction, rutting
of a soil subgrade (from
equipment or subsidence),
desslcation cracking, or the
effects of a geotextile
substrate can be examined.
Stress-strain measurements
can be made so
that the limiting geomembrane
strain for field conditions
can be approximated.
Lona-tera hydrostatic
resistance tests can be
conducted to investigate
performance, or even creep
behavior of a geomembrane.
No standard test method
currently exists, but an ASTM
subcommittee has recommended
that this test method be
reviewed and considered for
performance testing.
TKST EQUIPMENT:
Large diameter pressure
chamber; must be custom
fabricated.
DI-5
PERFORMANCE PROPERTY!
REFERENCED TEST XBTEOD I
AI/TERHXTIVS METHODS i
SCOPES
tosses mLtrsj
UNITS:
NONDESTRUCTIVE SEAM EVALUATION -
ULTRASONIC SHADOW METHOD
DREXEL UNIVERSITY GRI IGK1-86
GEOKSKSRANE SEAMS
RELATIVE SEAM SOUND ENERGY
TRANSMISSION
% of Calibrated Standard Maximum
8UXXART 07 KBTHODi
The referenced test method
covers the evaluation of
field or factory seams using
the Ultrasonic Shadow Method
technique. The method is
suitable for all types of
solvent, taped, thermal
(including extruded), and
combination seams. An
indication of the quality of
field seams is recorded and
compared to competent control
seams. The presence of
unbonded sections, voids,
foreign objects, and
nonhomogenlties can be
detected. This technique can
be used to assist in the
selection of locations for
destructive tests. The
Shadow Method apparatus
consists of a high frequency
pulse generator (-1HHZ),
transducers, and a CRT
display. The pulse Is sent
into the upper geomembrane on
one side of the seam and is
received on the lower
geomembrane on the opposite
side of the seam. Roller
mounted transducers or soft
rubber coupling tips can be
used. The system is first
calibrated on unseamed parent
material and then on a
control section of seam known
to be competent. The signal
signature is observed on the
CRT for the control seam and
the amplitude is adjusted to
full screen height (FSH). An
alarm is set for any
amplitude received less than
some minimum allowable
threshold amplitude. The
threshold value is set in
specifications and is
generally in the 15-25* FSH
range. For testing, the seam
is wiped clean with a clean
dry cloth after suitable
curing period of the seam.
The transducers are placed so
that the seamed area(s) is
straddled. The technician
pushes the transducer
assembly and the amplitude
signature is indicated on the
CRT which is transported with
the assembly. A maximum
testing rate of about 2 m/nin
(6 linear ft. per minute) of
seam can be attained.
TEST EQOZSXmt
The ultrasonic shadow system
is commercially available.
DI-6
-------
PERFORMANCE PROPERTY t
UniZHCID STANDARD PRACTICE I
ALTERNATIVE MBTH0D8:
SCOPES
TARGET VALUE I
UNITS:
NONDESTRUCTIVE SEAM EVALUATION -
ULTRASONIC PULSE ECHO TECHNIQUE
ASTM D4437
HOST UNREINFORCED GEOMEMBRANE
SEAMS
INDICATION OF UNBONDED AREA
Abatement of Pulse Energy
SUMMARY OT METHOD:
The referenced standard
practice lists several
destructive and
nondestructive seam
evaluation techniques,
including the ultrasonic
pulse echo technique for most
nonreinforced field seams. A
high frequency (1-15 MHZ)
sound wave passes through the
seam overlap. A continuous
seam will allow a return of
the sound energy to the
single transducer unit, which
is connected to a monitor.
Discontinuities in the seam
result in an abatement of the
pulse energy below some
threshold energy which
triggers an alarm on the
device.
Continuous surface contact
between the transducer and
the seam must be maintained
and water couplant is
required. For this reason,
this technique is limited for
use on some extruded seams
and extremely time consuming
for double welded seams.
This technique can be used to
detect discontinuities,
foreign matter, etc., but
gives only an empirical
indication of seam quality.
The use of this method in
conjunction with a
destructive technique is
recommended.
TEST EQUIPMENT:
Ultrasonic pulse echo
equipment is commercially
available.
DI-7
PERFORMANCE PROPERTY t
REFERENCED STANDARD PRACTICE:
ALTERNATIVE METHODS:
8COPB!
TARGET VALUE:
UNITS:
NONDESTRUCTIVE SEAM EVALUATION -
VACUUM BOX TECHNIQUE
ASTM D4437
MOST GEOMEMBRANE SEAMS
INDICATION OF UNBONDED AREA
Visual
SUMMARY 07 METHOD!
The referenced standard
practice lists several
destructive and
nondestructive seam
evaluation techniques,
including the use of a vacuum
box. The vacuum box provides
visual evidence of unbonded
areas or continuous voids
across the seam. The
permeability of the seam in
the unloaded (unstressed)
condition is examined, but
the mechanical strength of
the seam is not addressed.
The vacuum box consists of a
metal box with a clear glass
top and a soft rubber gasket
around the perimeter of the
open bottom, the seam is
cleaned and a soap solution
is applied to the seam area.
The box is placed over the _
seam and the entire gasket'
compressed to seal against
the liner. A vacuum is
applied and maintained inside
the box. In areas where
disbonds or voids exist, soap
bubbles are aenerated and are
observed inside the box.
These areas are marked for
repair.
This method is commonly used
at the present time for field
quality control of
geomembrane seams. The
vacuum technique has several
limitation? including use
around penetrations and on
some extruded seams. The use
of the vacuum box testing is
recommended only in
conjunction with full-time
observation and other testing
methods (destructive and/or
nondestructive).
TEST EQUIPMENT:
Generator, vacuum pump and
vacuum box are commercially
available.
DI-8
-------
PERTORKMTCE PROPERTY! NONDESTRUCTIVE SEAM EVALUATION -
PRESSURE TESTING TECHNIQUE
RETBRKHCBD TEST KKTBOSi
ALTERHATIVK KBTHOHSI
8COrE: DUAL THERMALLY FUSED GEOHEMBRAHE
SEAMS WITH AIR GAP
(nonreinforced)
TAKGET VALUE: INDICATION OF UNBONDED AREA
UNITS: Loss of Air Pressure
stnooure or kbthodi
The pressure testing
technique is suited for
testing dual thermally fused
seams in relatively rigid
material, such as
polyethylene. The commercial
technique is patented and is
performed by licensed
installers.
Two parallel seams are made
with a small air gap between,
resulting in a continuous air
channel along the entire
length of the seam. The air
channel is sealed at the ends
and is inflated to a specific
air pressure for a specific
time period. Channel
pressure of 210 kPa (30 psi)
and a period of 30 minutes
are typical. A loss of
pressure (after allowances
for expansion of the
geomenbrane) indicates an
unacceptable seam. The leak
can be located by
systematically halving the
test area and retesting.
This technique can provide an
indication of the mechanical
strength and the
vatertightness of both of the
dual seams. The use of the
pressure technique is limited
in patch areas or
penetrations where dual welds
are not usually constructed.
TEST EQUIPMENT:
Air pump, pressure indicator,
and miscellaneous sealing and
patching equipment.
DI-9
PERFORMANCE PROPBRTYi
RXPBRBNCED STAMDARD PRACTICE!
ALTBRHATIVB METHODS t
8 COPE!
TAJU3BT VALUE I
QUITSI
NONDESTRUCTIVE SEAM EVALUATION
AIR LANCE TECHNIQUE
ASTM D4437
GEOMEMSRANE SEAMS (Flexible
Geomembranes)
INDICATION OF UNBONDED AREA
visual
8BMCAR* or METHODS
The referenced standard
practice lists several
destructive and
nondestructive seam
evaluation techniques,
including the air lance test.
The air lance test provides
visual evidence of completely
unbonded seam areas in very
flexible geomembranes. An
air nozzle is held a maximum
of 50 mm (2") from the seam
edge and air at 345 kPa
(50 psi) pressure is directed
toward the seam. The
unbonded seam areas are
observed visually. This
technique is severely limited
and does not provide an
indication of seam strength
or water tightness. Only
large, completely unbonded
areas can be detected using
the air lance. With proper
welding techniques and
quality control, and the use
of other testing methods,
this technique is not
necessary and is not
recommended.
DI-10
-------
PBK70RXUICS PROPERTY!
MOTMHCBO TWBt KBTZOOt
ALTBRHXTXVB METHODS:
SCOPSt
TAKQBT ViLUBJ
TOITS:
EMBEDMENT DEPTH FOR ANCHORAGE
MOBILIZATION
OREXEL UNIVERSITY GRI #GM2-87
GEOMEMBRANES, GEOCOMPOSITES
EMBEDMENT DEPTH
cm (In.)
sunns* op mbthodj
Required In many design
procedures for geomeabranes
and geocomposites is the
embedment depth necessary to
mobilize a certain stress
level. For polyethylene,
this stress level is the
yield stress. For
geomembranes other than
polyethylene, the stress
level will be that required
to reach a certain strain,
e.g., 100%. The specimens
are ISO mm (6") wide and of
variable length. The
specimen length is placed
between steel plates faced
with sandpaper as shown in
the sketch. Normal pressure
is applied to the steel
plates and the free end of
the specimen is tensioned
using a
Constant-Rate-of-Extension
(CRE) tensile testing device.
The embedment depth at which
the targeted stress level
is based on a series of
trials as shown in the figure
below. Normal pressures of
25 to 500 kPa (500 to
10,000 lb/ft } can be applied
resulting in required
embedment depths of 25 to
300 mm (1" to 12").
TEST BQtnPXZHTl
CRE tensile testing device
and custom fabricated jaws
and assembly. Sketches of
jaws and assembly will be
available through GRI.
CLAMPING
HYDRAULIC JACK
SPECIMEN
YIELD ZONE
! I
11
NON-YIELD
ZONE
MOBILIZATION DISTANCE X (In.)
EXAMPLE: STRESS »» MOBILIZATION OISTANCE FOR MOPE
DI-ll
PERFORMANCE PROPERTY!
REFERENCED TEST HBSSODl
MTERHMrVE METHODS!
SCOPE!
TARGET mOBl
UNITS!
BREAKING STRENGTH - WIDE WIDTH
STRIP METHOD
ASTM D4595
GEOTEXTILES, GEOGRIDS
TENSILE STRENGTH AND ELONGATION
N/m (lbf/in), %
SUMMARY or KETHODl
The wide width strip method
utilizes a specimen having a
width of 200 ma {8") and a
gauge length of 100 mm
(4"). This reduces the
effect of high transverse
strains, or "neckdown" common
in the narrow strip or grab
methods. It is widely
believed that this produces
results more closely related
to anticipated field
behavior.
The specimen is gripped along
its entire width in the
clamps of a Constant-Rate-
of-Extension (CRE) type
tensile testing device
operated at a constant strain
rate of 10%/min. Force and
elongation are continuously
monitored as the specimen is
tested to rupture. A minimum
of six specimens in each of
the principle geosynthetic
directions is recommended.
The specimen is discarded if
slippage of the specimen from
the clamps occurs during
testing or if the specimen
breaks at or near the jaws.
Limitations of the jaws and
the need to modify the jaw
face under certain conditions
is addressed.
The tensile strength,
elongation and initial and
secant tensile moduli may be
calculated for each specimen.
Construction of the load -
elongation curve and initial
and secant moduli is
illustrated in the appendix
of the standard.
Modifications of this
procedure are being
considered for use with
geoaembrane specimens.
TEST EQUIPMENT:
CRE tensile testing device,
force and elongation
measuring devices, and clamps
as described in standard.
Illustrations of alternative
clamps are included. Roller
clamps, although not
addressed in the standard,
have been shown to be
effective for high strength
woven geotextiles.
200mm
DII- H
-------
PERTORXXHCB PROPERTY! SEWN SEAM STRENGTH
REFERENCED TEST HBTHODl PROPOSED ASTM
lT.TMmTTCT XBZSODSl ASTM D1682 (modified)
BCOSH GEOTEXTILES, GEOMEMBRANES, SOME
COMPOSITES
TARGE* VALDB: SEAM BREAKING LOAD
omits: kH/n (lbf/in)
801008? or KBTHODI
The referenced tost method
uses the wide strip method
(ASTM D4595) SB its basis.
The sewn seam specimens are
200 mm (8") wide with the
sewn seam centrally located.
A "blockout of 30 ma (1.25")
is left on either side of the
seam along the center of the
specimen as illustrated on
the figure below. The
specimen is failed in tension
in a direction perpendicular
to the seam. The test method
is intended for acceptance
testing of sewn seams, and is
best suited for testing of
sewn geotextile seams. The
suitability of testing sewn
seams or combination
sewn-bonded seams for
geomembtanes or composites
using this test method has
not been determined.
Modified grab methods may be
considered. Harrow
strip-type specimens may not
yield reproducible results.
S3
<
K
<
>
ui
-i
a
<
5
5
For the wide strip method, a
minimum of six seam specimens
are tested and the average is
reported as the average peak
load applied to the specimen,
in units of kH/m (lbf/in),
For multiple stitch seams or
combination seams, multiple
peaks may be reported.
TBST 1QOIPMKHTJ
Constant-Rate-of-Extension
Tensile Testing Device (CRE),
specimen clamps, as described
in ASTM D4595, or roller
clamps, and a specimen
cutting template (optional).
SEAM TEST SPECIMEN
CENTER OF,
seam •'
60mm /.'•
~]
30
mm
200mm
30
mm
DII-13
PERJTOR1CUICB PROPERTY s
RiFSRKKCED TEST METHODI
AI.TERHATTVB METHODS S
SCOPSI
TARGET VKLmtt
OMITS S
COEFFICIENT OP SOIL/GEOSYNTHETIC
FRICTION
PROPOSED ASTM
GEOSXNTHETICS
COEFFICIENT OF FRICTION
DIMENSIONLESS
SUMMARY Of METHODS
The test method referenced
covers the determination of
the coefficient of soil/geo-
synthetic friction by the
direct shear method. The
procedure, which is similar
to that used for testing of
soils, can also be used to
determine the coefficient of
geosynthetic/geosynthetic
friction. When testing the
gaosynthetic specimens alone,
the test functions as an
index test. Because of the
variability of the soils and
conditions tested and the
presence of several possible
failure mechanisms, soil/geo-
synthetic friction tests are
intended to produce design
data.
The direct shear apparatus
proposed is square or
rectangular with a minimum
width of 300 mm (12") and
depth of 50 mm (2"). A shear
force is applied to a
traveling container while a
normal compressive stress is
applied to the overlying
stationary container. The
soil is placed into each
container as specified by the
user. The geosynthetic
specimen can be placed in
such a way that the soil is
in contact with one or both
sides of the specimen. The
specimen is sheared at a rate
selected by
the user, but a maximum rate
of 5 am/min (0.2"/min) for
geosynthetic/geosynthetic
tests and 1 mm/min
(0.0«"/min) for soil/geo-
synthetic tests is currently
recommended. The shear load
is measured and plotted as a
function of displacement,
until a constant shear force
is observed (usually defor-
mations of 25 to 75 am [1 to
3"] are required). The
specimen is carefully
examined to determine the
location and mode(s) of shear
failure. The peak shear
stress recorded is plotted
against normal compressive
stress for at least 3
different normal stresses.
The slope of the line formed
by connecting the data points
is the coefficient of
friction of the specimen
tested. The y-intercept of
the plot is the adhesion of
the specimen tested.
TEST EQUIPMENT:
large scale direct shear
apparatus, loading and
recording devices. This
standard is in the early
stages of development at this
time, so no standard equip-
ment has been identified.
Equipment is currently custom
fabricated.
011-14
-------
performance property i
REFERENCED TEST KBTBOD:
ALTERNATIVE METHODS:
scope:
TARGET VALUE!
units:
PUNCTURE STRENGTH (CBR PLUNGER)
MODIFIED DIN 54 307
DREXEL UNIVERSITY GRI #GSl-8 6
GEOSYNTHETICS
PUNCTURE RESISTANCE
N (lbf)
SUMMARY OT METHOD I
The referenced test method is
a modified CBR plunger test
using the test appparatus
described in the German DIN
standard. The test is
performed in a CBR mold
(inner diameter 150 mm [6"])
that is modified to hold a
geosynthetic specimen. The
plunger is a flat-tipped
cylinder with a diameter of
50 mm (2") which moves at a
rate of 60 mm/min (2.5"/min)
until the specimen is
ruptured. A force-deflection
curve is plotted during
testing. From this
information, a load-
deformation plot for the
specimen is plotted.
Since the CBR apparatus is
commonly used in geotechnical
engineering, this procedure
can easily be modified to
generate design oriented
performance data. Since the
puncture resistance of a
geosynthetic specimen may be
very different when tested
against soil as opposed to in
the unsupported condition (as
in the index test) the
addition of soil to the CBR
mold is a possibility. The
soil can be compacted to a
known density at a known
moisture content and tested
in a saturated condition.
the test conditions may be
selected by the user to model
particular field conditions.
The load-deformation behavior
of the geosynthetic/soil
system may be compared (with
great care) to the soil
tested alone. For special
studies, the geosynthetic
specimen can be overlain by
another geosynthetic, a layer
of soil or other material.
The standard plunger can be
replaced by another plunger
designed to simulate gravel,
crushed stone, shot rock,
etc.
TEST equipment!
Constant-Rate-of-Extension
(CRE) testing device,
modified CBR mold and
plunger.
DII-15
PERFORMANCE PROPERTY!
REFERENCED TEST METHOD t
ALTERNATIVE METHODS I
8C0PBS
TARGET VALUE!
UNITS!
IN-PLANE FLOW
ASTM 4 617
SEVERAL EUROPEAN
GEOTEXTILES, GEONETS, GEOGRIDS,
GEOCOMPOSITES
HYDRAULIC TRANSMISSIVITY
n /sec-m (gpm/ft)
SUMMARY OF METHOD!
Hydraulic transmissivity is
determined by measuring the
quantity of water which pass
through the specimen in a
specific time interval under
particular conditions
selected by the user. A
specimen width of 300 mm
(12") with an aspect ratio of
at least 1 is suggested.
Hydraulic gradients and
normal compressive stresses
selected for testing are site
or application specific for
this constant'head method.
For acceptance testing or
general use, gradients
ranging from 0.1 to 1.0 and
compressive stresses from 25
to 250 kPa (500 to 5000 psf)
are given as guidelines.
Minimum seating periods of
15 minutes are suggested,
although the need for longer
periods is addressed. The
use of site specific sub and
superstrata, such as rigid
plates, other geosynthetics
or soil, is recommended.
Transmissivity for each test
is reported as an average
flow rate per unit width per
unit gradient for the
conditions examined. All
values are corrected for
temperature. Results are
presented as plots of
hydraulic transmissivity
versus normal compressive
stress, or hydraulic
transmissivity versus time
for constant stress levels.
TEST EQUIPMENT!
Equipment must be custom
fabricated. No details are
available at this time.
DII-16
-------
perporxahcs PBOPBarsrs
REPEKEHCZD TEST XESHODl
XLTSmim KBTB0D8!
SCOPEt
XXRSBS VALUE:
OTITSi
WATER PERMEABILITY UNDER STRESS
PROPOSED ASTM
GEOTEXTILES
PERMITTIVITY
sec
SDXKMCX OP KETBODI
Thia method covers the
determination of the water
permeability ot a single or
multiple geotextile speciaen
under a normal compressive
stress by the permittivity
method. Because of the
compressibility of the
specimens, the permittivity,
not permeability, is measured
directly. The method can be
used as an index test or as a
design test in limited
applications. It is intended
to measure the effect of
normal compressive stress on
the permittivity of a
geotextile specimen.
The test apparatus is a
modified version of the one
detailed in ASTH D4491. A
piston applies a normal force
to distributor plates
overlying the geotextile
specimen(s). The specimen
thickness can be monitored
during testing. The
hydraulic gradient across
the specimen is measured
using manometers. Deaired
water is recommended for
testing. The test is
performed using an initial
normal compressive stress of
2kPa (0.29 psi), and
additional stresses selected
by the user are applied. The
seating period for each
applied stress is selected by
the user. The rate of flow
measurements and the
permittivity calculations are
performed as indicated in the
draft procedure, and are
identical to those presented
in ASTH D4491. The
permittivity under load
reported is the average for
at least five specimens.
TB8T EQUIPMENT J
Modified permittivity device
(see ASTM D4491), water
deairing system. Details of
permittivity apparatus will
be provided with the
completed test method when
published.
Quoad pi.»tim
, /
V; 8Ptc»MiN
Z
mxM
illiUiliilr
DISTRIBUTOR
DII-17
PERFORMANCE PROPERTY:
REFERENCED TBBT METHOD:
ttTBRXMXVZ METHODS s
SCOPE!
TARGET
TOITSl
summary or kbtbodi
A circular geotextile
specimen (111 am or 4-3/8"
diameter) is placed within a
clear plastic permeameter over
an open mesh support ring.
About 1000 graas of dry soil,
selected by the user, is
placed loosely to a depth of
75 mm (3") over the geotextile
specimen. The permeameter is
assembled and all manometer
ports (see figure) are
attached. The
soil/geotextile specimen is
slowly saturated and then
purged of oxygen with carbon
dioxide to reduce the
occurrence of air bubbles.
In addition, it is
recommended that the test be
run using deaired water at
room temperature.
Successive hydraulic
gradients of 1,0, 2.5, 5.0,
7.5 and 10.0 are placed on
the specimen for 24 hours
each. Additional hydraulic
gradients or testing times
can be applied if required.
The system flow rate and
static head at several levels
within the soil/geotextile
specimen are monitored. The
gradient ratio for each set
of manometer readings is
calculated. The gradient
ratio is defined as the ratio
of the head loss across the
downstream 1" of the test
soil and the geotextile to
CLOGGING POTENTIAL
GRADIENT RATIO METHOD
{Proposed ASTH)
LONG-TERM FLOW TESTS
GEOTEXTILES
GRADIENT RATIO
DIMENSIONLESS
the head loss across the
upstream 50 am (2") of the
test soil. The gradient
ratio values are a function
of the geotextiles, soil and
test conditions. The
relationship between test
results and actual field
conditions has not been
established. The
reproducibility of test
results using a "standard"
soil is being investigated by
an ASTM D-35 Task Group. The
test device is also suitable
for long-term soil/geotextile
permeability tests.
TEST EQUIPMENT:
Permeameter-drawings will be
available from ASTH. Mater
deairing system
(recommended).
FLOW IN
h»hj
SOIL
SPECIMEN
GEOTEXTILE
SPECIMEN
Dii-ib
-------
PROPERTYI
ssraszjrcsD •net method«
alternative methods:
STOPS I
TARGET TALDBS
CHITSI
LONG TERM CLOGGING POTENTIAL
DREXEL UNIVERSITY GRZ IGS 1-86
GEOTEXTILES
LONG TERM FLOW HATE
Liters/day (gal/day)
somosx or method»
The referenced test method
covers the evaluation of tha
long tarn flow rata of a
soil/geotaxtile system. The
trend of the long term flow
rate provides an Indicator of
the clogging potential of the
system.
The test is essentially a
constant head test using
specially build apparatus.
Testing devices used for the
Gradient Ratio or
permittivity under stress
tests can also be used. The
pre-conditioned specimen is
placed in the device and ISO
mm (6") of the test soil is
placed over the specimen.
Undisturbed or remolded soils
can be used,, although there
are some limitations on soil
compaction. Anti-seep
collars are used to reduce
the development of
preferential flow paths along
the outer perimeter of the
soil sample. Hater is then
introduced and maintained at
a constant head selected by
the user. Tha flow data is
recorded immediately to
establish the initial portion
of the curve. A detergent or
bleach (such as Chlorox) must
be added to the test water on
a daily basis to eliminate
bacteria growth within the
specimen.
The flow rata will initially
decrease with time due to
damnification of tha soil.
At some time, the flow rate
will appear to stabilize.
This transition time is
dependent on the type of soil
used and the initial soil
density. The slope of the
flow rate versus time line
for data recorded after the
transition time provides an
indication of clogging
potential of the system.
Three lona term conditions
are described in the test
procedure: Equilibrium,
Partial Clogging, and
Complete Clogging. These
conditions are illustrated on
the figure below which is a
plot of the system flow rate
versus log of time. Several
tests run concurrently can
provide a direct comparison
of several candidate
geotextiles using the same
soil, or a single geotextile
may be tested with serveral
different soils.
TEST EQUIPKBHTl
Flanged plexiglass column
with specimen support capable
of maintaining a constant
head on the specimen. Device
can easily be custom
fabricated, or a Gradient
Ratio device can be used.
*f OUjlllRIUM*
LOO TIM«, I
DII-19
P1R*08J0UKSB PROPERTY S
rezerehced *ist methodi
A1TERHATXVE METHODS!
SCOPEI
TASSET VAX.OB:
OMITS I
TENSILE CREEP
PROPOSES ASTM
TIME TO FAILURE OR TOTAL STRAIN
Hours or %
SUMtXRT OF XBTBODI
Synthetic polymers used in
geosynthetics are prone to
creep, 91 increased
elongation with time for a
constant tensile lead. The
geosynthetic can ultimately
rupture at loads signifi-
cantly less than tha breaking
strength recorded using other
methods.
The proposed ASTM procedure is
in its initial draft stage at
this time; therefore, details
of the test will not be
discussed. A general creep
testing procedure is
presented. For an overview
of creep testing procedures
and terminology for testing
of plastics, a review of ASTM
D2990 is recommended.
The breaking load of the
geosynthetic is determined by
a standard tensile test, ASTM
D4595 (Wide Strip Method), is
recommended. An identical
set of specimens are loaded
in tension by a system of
dead weights at load levels
of a known percentage of the
ultimate breaking load. The
load levels and other test
conditions (such as temper-
ature) are selected by the
user to best model antici-
pated field conditions. The
elongation of the specimens
are monitored under the
sustained tensile load. The
strain or strain rate is
recorded and plotted against
the log of test time. The
testing time is generally
user and application
specific. From a family of
creep curves, the creep
behavior may be extrapolated
for the life of the appli-
cation, or a safe load level
(i.a., one where excessive
creep of the specimen is not
observed over the time
tested) is selected for
design. Caution is advised
in interpreting
time-dependent visco-plastic
behavior of geosynthetics
(creep or stress relaxation)
since this behavior is
dependent on many factors and
is difficult to extrapolate
in plastics.
TEST EQUXFKXHTi
Creep frame, loading system,
elongation monitoring
equipment, suitable clamps,
and a Constant-Rate-of-
Extension (CRE) tensile
testing device for determin-
ation of the geosynthetic
breaking load.
Diii-20
-------
CHSTOSIOBCB PROPERTY
REFERXHCED TEST METHODJ
M.TBBHXCZV1 METHODSt
BCOEBt
taught vxibb:
touts I
COMPRESSIVE CREEP
DREXEL UNIVERSITY GRI #GS 4-87
ALL GEOSWTHETICS
TIKE DEPENDENT THICKNESS
UNDER STRESS
turn - hr (inches - hr)
SUHXAM or METHODS
The referenced test method
covers the determination of
the compressive creep of
geosynthetics, especially
geocoaposites, geonets and
geotextiles. The
tine-dependent specimen
thickness is recorded for a
constant compressive stress,
or a series of compressive
stresses. For index testing,
seating periods of 100 hours
and load levels of 20, 40 and
60% of the specimen breakdown
or crush strength are
suggested. For design
testing, seating periods of
1000 hrs and load levels of
100, 200 and 300% of design
stresses are selected. Site
specific fluid or elevated
temperatures may be used in
testing.
Geosynthetic specimens,
measuring at least 150 am (6
in) square are placed between
two rigid platens in a device
similar to a soil
consolidoaeter. The
deformation of the specimen
under constant normal stress,
selected by the user, is
recorded. At the end of the
seating period, the next
(greater) stress level is
applied and the deformation
is recorded. For multiple
stress levels, a family of
creep curves is generated, as
shown in the figure below.
The strain rate nay be
calcualted for use in creep
prediction models.
TEBT BQOIPKEHTt
Device capable of applying
and maintaining a constant
normal compressive stress to
the specimen, and dial gauge
or LVDT to measure
deformation. Modified soil
consolidoaeters, which are
commercially available, are
satisfactory for most
geosynthetics.
*eo% eifiax »'*«#»
300% pmON STRESS
100% DESIOH
1 000
D1II-21
SERTOSMAHCB SSOSERTXt
SZ7XKEHCBD TEST METHODS
ALTERNATIVE METHODS t
SCOPES
TARGET VALUEJ
TOUTS S
FLOW CHANNEL INTRUSION
DREXEL UNIVERSITY GRI *GS 5-87
GEONETS AND GEOCOKPOSITES
REDUCTION IN OPINING AREA
»
amooxi or kbtbodi
The above refereced method
covers the determination of
the degree of intrustion of
an adjacent geotextile or
geomembrane into the openings
of a geonet or geocomposite.
The goal is to measure the
decrease in cross-sectional
open area available for
planar flow of fluids.
On-site soil or other
surfaces can be used to model
field conditions. At this
time, no prediction regarding
the reduction of planar flow
capacity of the specimen is
made. The mechanisms of
intrusion and core or net
deformation may be visually
identified.
The normal compressive stress
and seating period are
selected by the designer to
best model field conditions.
Specimens are 150 mm (6")
sguare and are caulked around
their perimeter with a flex-
ible silicon caulk. A soil
substrate, If desired, is
placed on the rigid base of
the test device and the geo-
synthetic specimen is placed
over it. Two rigid tubes are
placed within the
geonet or core to serve as
the inlet and outlet for an
epoxy resin.• The soil
superstratum is placed
over the specimen. The normal
compressive stress is applied
for a period of at least 15
minutes. A quick setting
epoxy is then injected into the
specimen until the specimen
is completely inpregnated.
The resin is allowed to set
under the constant
compressive stress for at
least 24 hours. The specimen
is removed from the holder
and sectioned for
observation. Photographs of
the sections may be taken and
the reduction in void area
may be calculated.
ZEST EQUIPXKNTt
Testing device capable of
applying and maintaining
normal compressive loads up
to 50 kN (10,000 Ibf), steel
specimen holder and eopxy
resin injection equipment.
DIII-22
-------
PERFORMANCE PROPERTY I
RSTEREHCED TEST XZTEODl
ALTERNATIVE KETH0D8:
SCOPE t
TARSET VALUES
DHIT »S
GEOCOMPOSZTE BOND STRENGTH
ASTM F904
GEOCOMPOSITES
FORCE TO SEPARATE PLIES
gm/25 mm (lbf/in)
SUMMARY 07 METHODS
The referenced test method
was developed to compare bond
strength or ply adhesion of
similar laminates from such
materials as paper, plastic
film and foil. This test
method has been used to
determine the ply adhesion of
geotextiles to geonets or
drainage cores. Although a
peel adhesion load is
recorded, this method is not
recommended for determining
the performance of a
geocomposite in cases where
the bond could fail in shear
(such as for geocomposites
placed on the sidewalls of a
waste cell).
Five specimens are cut to a
width of 25 mm (1 in.) and a
length of 250 mm (10 in.)
Specimens are tested in the
machine and cross-machine
direction. Separation of the
plies is initiated by the
user manually or by the use
of a softening solvent. The
specimens are clamped and
pulled at a rate of 2S0
mm/min (11 in/min). The
force required to separate
the first inch is ignored and
the average force to separate
the following 2 inches of
bond is determined. The
average force is expressed in
gm/25 mm (lbf/in).
TEST EQUIPMENT
Constant-Rate-of-Extension
(CRE) Tensile Testing Device,
grips.
DIIt-23
-------
INDEX
Allowable Leachate Head II1-4
Alkalinity III-8
Anchorage 111-21,V-3,VI-13
Apparent Opening Size(AOS) II1-7
Arrhenius Model VII-1
Asthetics V1I-20
Bedding Layer I-iO
Berms IV-4
Biaxial Tension V-19
Biological Growth 1-4,10,V-13,
VII-3,13
Biotlc Barrier V-12
Chemical Attack VII-1,10
Clogging III-8,VI-26
Coefficient of Uniformity III-7
Composite Liner 1-6
Compressive Creep III-5
Concrete VI-15
Construction FML:VI-8, LCR;VI-28
Cover System 1-8,V-l
CPE(Chlorinated Polyethylene) 1-2,
111-19,20,V-10
Creep(Relaxation) VII-10
CSPE(Chlorosulfonated Polyethylene)
I-2,VI-5,12
Darcy's Equation 1-1,111-2,11
Design Ratio 11-1,111-6,25
De Minimis I-6,7,111-10,12,V-8
Direct Shear Test III-9
Downdrag IV-5,6
Drainage Layer 1-10,111-3
Environmental Stress Cracking
VI-4.VII-6
Environmental Stress Rupture
VII-7
Extrusion Weld VI-12
Fabrication VI-6
Pick's Law I11-11
Filter 1-10,111-7,8,V-6
Fine-Finish of Subgrade ¥1-30
Freeze-Thaw 111-25,IV-2,V-3
Gas 111-27,V-3,12,15
Geocomposites 1-4
Geomembrane 1-1
Geonets 1-4
Geotextiles 1-4
Gradient Ratio Test III-8
HDPE(High Density Polyethylene)
1-2,111-14,16,18,IV-6,V-10,16,
VI-3,5,8,ll,VII-9
HSWA 1-1,5,10
Hydrolysis VI1-15
Impact Test 111-20
Index Tests II-l
In-plane Flow II-l
Installation FML;VI-15, LCR:VI-27
Leachate II1-2
Liquids Management 1-8
Manpower VI-8
Melt Index VI-3
Monitor(LCR) IV-8 to 11
MTG(Minimium Technology Guidance)
1-5,8,111-1,2,3,8,10,V-l,8,15
NDT VI-5
NSF 54 1-2
Ozone VII-2
Panels VI-7,9,22
Peel Test 111-16
Percolation Velocity III-4
Performance Tests II-l
Permittlvitty VII-11
Post Closure 1-6
PVC(Polyvinyl chloride) 1-2,V-10,
16,VI-5,VI1-9,13
Puncture Test 111-17
Quality Assurance VI-1,17,21,31
Quality Control VI-1,17,21
Ramp IV-1
RCRA 1-5,8,9,V-l,3,5
Resin VI-3
Roadway IV-1
Rodents V-8,12.VII-19
Roots V-8,V-12,VII-17
Sample Size VI-20
Sampling Strategies VI-19,27
Scrim 111-10
Seams 111-10,15,V-10,VI-2,6,11,12
Seam Repair VI-24
Sealing VI-2,15
Secondary Containment III-l
Secure Landfill 1-5
Settlement 111-9,13,V-3,7,9
Shear Test 111-16
SIAR(Surface Impoundment Assesment
Report) 1-9
Soil Cover I11-26
Soli Burial VII-8,15
Specifications FML:VI-12, LCR:VI-25
Standpipe IV-5,8
Sterilization of Soil VI-29
-------
Surface Impoundment 1-9
SWCR(Surface Water Collection/
Removal) V-5
Survivability III-19.V-11
Tear Test 111-17
Thermal 111-15,VI-10,VII-5,14
Thermoplastic 1-2
Topsoil V-2
TGD(Technical Guidance Document)
VI-1,25
Transmissivity 111-2,3,5,27,V-5,15
VI-26
UV(Ultraviolet)Aging 1-2,111-19,
20.V-10,VII-2
Ultrasonic Side Shadow VI-5
Uplift VI-13
Vegetation V-l
Vent Pipe V-16
Wind II1-25,V-l,VI-5,10,13,VI1-17,
19
WVT(Water Vapor Transmission)
III-ll,V-8
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