United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-86/085 Jan. 1987
&EPA Project Summary
Geotextiles for Drainage,
Gas Venting, and
Erosion Control at
Hazardous Waste Sites
Raymond C. Horz
Geotextiles (engineering fabrics) have
proven to be effective materials for solving
numerous drainage and stability problems
in geotechnical engineering, and they can
be used to solve similar problems in the
containment and disposal of solid and
hazardous waste. "Geotextile" is defined
as any permeable synthetic textile product
used in geotechnical engineering.
Important mechanical, hydraulic, and
endurance properties of fabrics are dis-
cussed. Tensile strength and elongation as
measured by the grab tensile test; tearing
resistance as measured by the trapezoidal
tear test; and puncture resistance as meas-
ured by the U.S. Army Corps of Engineers
puncture test are emphasized as being the
most important mechanical properties.
Tests for other mechanical properties such
as creep susceptibility, tear resistance,
f rictional and pull-out resistance with soil,
and seam strength are also reviewed.
The important hydraulic properties of
fabrics are their ability to allow free pas-
sage of fluids, to retain soil particles (pip-
ing resistance) and to resist clogging. The
equivalent opening size (EOS) and gradient
ratio tests used to evaluate these qualities
are discussed, as well as possible causes
of the long-term reduction of fabric hy-
draulic flow capacity.
Fabric resistance to ultraviolet light
and chemicals and to biological degra-
dation is considered .
Applications of geotextiles to (1) landfill
cover drains, leachate collection systems,
and ground-water control systems; (2) gas
venting; and (3) protection of landfill
covers and waste disposal sites from
surface erosion are addressed in detail. In
each of these applications, design consid-
erations, fabric requirements, and con-
struction techniques are discussed. Model
specifications for fabrics in the various
applications are given. For drainage sys-
tems and erosion control, criteria for
selecting fabrics based on the fabric's
piping and clogging resistance are
presented. Strength requirements based
on the severity of the construction environ-
ment and long-term chemical/biological
degradation are addressed.
This Project Summary was developed
by EPA's Hazardous Waste Engineering
Research Laboratory, Cincinnati, OH, to
announce key findings of the research pro-
ject that is fully documented in a separate
report of the same title (see Project Report
ordering information at back).
Introduction
The use of geotextiles (engineering
fabrics) has grown from 12.5 million m2
(15 million yd2) in 1977 to 115 million m2
(138 million yd2) in 1983 in the United
States and Canada alone. In spite of this
rapidly expanding use of geotextiles, their
use and performance in applications
related to waste containment and disposal
has rarely been documented in the open
literature. The information in this report
draws on the experiences of the geotech-
nical field to provide guidance for the use
of geotextiles in land waste disposal
activities.
A geotextile is defined as any permeable
synthetic textile product used in geotech-
nical engineering. Related products such
as plastic grids (geogrids) or composite
products such as drainage panels are also
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discussed because they are used in similar
applications or include geotextiles as part
of their structure.
Types of Geotextiles
Geotextiles are currently being made
from polypropylene, polyester, polyethy-
lene, nylon, polyvinylidene chloride, and
fiber glass, with polypropylene being used
far more than any of the other materials.
The physical properties of all these
materials can be enhanced by adding
additives and by processing the polymer
into fibers.
Geotextiles are usually grouped by
method of construction, the major groups
being woven, knitted, and non-woven.
Construction type has an important bear-
ing on both the mechanical and hydraulic
properties of a geotextile and conse-
quently its potential performance in a
given application. Woven construction is
expensive but tends to produce fabrics
with high strengths and moduli and low
elongations at rupture. Woven construc-
tion also produces fabric with a simple
pore structure and narrow range of pore
sizes or openings between fibers. This is
beneficial in many filtration applications.
Knitted construction is rarely used for
geotextiles, although some filtration fab-
rics and some experimental reinforcement
fabrics are made by this method. Non-
woven fabrics are those which are neither
woven nor knitted. In non-woven con-
struction, the fibers are placed with a
random orientation and the properties of
the finished product can vary greatly
depending on the fiber density and meth-
od of bonding the fibers together. The
fibers may be either continuous or staple
(short length) and are bonded by needle
punching (needling), heat bonding, resin
bonding, or a combination of those
processes.
Functions
In geotechnical and waste management
engineering, geotextiles perform one or
more of the following functions: filtration,
drainage, separation, reinforcement, and
erosion control. As applied to geotechnical
engineering, filtration is the process of re-
taining a soil or other particulate material
in place while allowing liquid or gas to
escape. Geotextiles are used in leachate
collection systems where they act as a
filter between the overlying waste and the
drainage layer of gravel or synthetic
drainage material.
A geotextile, when used as a drain, acts
as a conduit for liquids or gases. Special
grid products have successfully replaced
sand and gravel as drainage layers in
leachate collection and gas venting ap-
plications. Separation is the function of
keeping two dissimilar materials from mix-
ing, but differs from filtration in that there
is no requirement for allowing liquids or
gases to pass. Reinforcement is the proc-
ess of increasing the mechanical strength
of the geotechnical structure by including
the geotextile in the system. Capping a
waste lagoon with a geotextile overlain by
soil illustrates both the separation and rein-
forcement functions. A geotextile per-
forms in erosion control by preventing the
tractive forces of wind or water from
displacing soil or waste particles. Fabric
placed in a drainage ditch and covered
with gravel is an example of a fabric per-
forming erosion control. In many applica-
tions, a geotextile performs more than one
of the functions just described. Each func-
tion requires consideration of different
fabric properties and different tests to
evaluate the qualities of importance.
The material costs for geotextiles may
vary greatly depending on the intended
function and on installation practices. The
cost of fabric for a specific project will also
depend on current supply and demand and
such factors as the prestige or significance
of a particular project. It is often less costly
to the project as a whole to select a fabric
having a higher initial cost, if the fabric has
properties which expedite construction,
reduce labor costs, and reduce the
chances of damage that must be repaired
later.
Evaluation of Geotextile Properties
A geotextile may be evaluated on its
general physical properties, mechanical
properties, hydraulic properties, and envi-
ronmental endurance properties. General
physical properties include fiber composi-
tion, fabric construction, weight per unit
area, thickness, and roll weight and dimen-
sions. These properties are often cited in
product literature and are useful for distin-
guishing between fabrics. They are also
useful when considering ease of handling.
However, properties that relate to the
actual application must be known to
properly design a system using fabric.
The mechanical properties of geotex-
tiles include tensile strength, tensile
stress-strain relationship (modulus), punc-
ture and burst resistance, penetration
resistance, creep resistance, abrasion
resistance, tear resistance, flexibility, soil-
fabric sliding resistance, and fatigue resis-
tance. These qualities are most important
to reinforcement applications of geotex-
tiles and to the survivability of the fabric
during installation. Ease of installation is
also affected by such qualities c
flexibility.
Puncture and burst failures of geote:
tiles are caused by localized stressing <
the fabric and failure depends largely c
the omnidirectional strength and elong.
tion characteristics of the geotextile.
Once a break has formed in a fabric, te.
resistance is a measure of the force n
quired to propagate the break. The tea
ing resistance of geotextiles can b
evaluated by the trapezoidal tear test.
Soil-fabric friction is of vital importanc
in reinforcement applications. For othi
applications such as drainage and erosic
control, soil-fabric friction is a factor in tr
ability of a fabric to remain in place on
sloping surface as when used in cpnjuni
tion with rip-rap in an erosion contr
application or on a landfill cover slope.
Fabric panels can be joined by overlai
ping, stapling, heat welding, or sewing. (
these methods, sewing is used where tr
two fabric panels must withstand tensi
stresses or where the security of the seai
is critical. Several types of sewn searr
can be produced in the field and the
selection will depend on the fabric beir
sewn and the strength requirements fi
the seam.
Creep resistance can be a significai
consideration for applications where a fal
ric must withstand high loads for long pei
ods. This is considered for reinforcemei
applications but not normally for drainac
or erosion control. Research has show
that polyester fabrics are less susceptib
to creep than polypropylene fabrics.
Abrasion resistance is the ability of
fabric to resist wear by friction. It can t
a consideration in slope protection applic
tions where wave wash or water curren
may cause repeated movements of stor
or block protection elements against
fabric.
The hydraulic properties of a geotexti
are those properties which govern i
ability to pass liquids (and gases) ar
retain solid particles. Hydraulic propertit
encompass piping resistance, permeabilil
and clogging resistance.
Piping resistance is the ability of a fabr
to retain solid particles and is related to tt
sizes and complexity of the pores or ope
ings in the fabric.
When geotextiles are used in fiftratic
and drainage applications they must ha'
a flow capacity adequate enough to pr
vent significant hydrostatic pressure buil
up in the soil being drained and must I
able to maintain that flow capacity for tl
range of flow conditions for that particul
installation.
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Clogging is the reduction in permeability
f a geotextile because of fabric pores
eing blocked by soil particles or by
acterial or chemical encrustations. To
ome degree, clogging takes place with all
abrics in contact with soil and this is why
ermeabilities of fabrics measured in isola-
ion are of only limited usefulness.
Whenever a soil is suspected of being
nternally unstable, the particular soil-
abric combination can be evaluated by a
ioil-fabric permeability apparatus and its
slogging tendency quantified by the
Gradient Ratio.
The ability of certain fabrics and certain
special products such as grids, meshes,
md panels to transmit significant quanti-
ies of fluids in the plane of their structure
offers one of the greatest potential uses
Df these materials in the waste manage-
nent area. The flow capacity of thin planar
materials parallel to their plane can be
expressed by Darcy's Law in the same way
as flow perpendicular to the plane.
The environmental endurance properties
of geotextiles are those properties which
determine whether the fabric can continue
:o function for the life of the project.
All the polymers used in the manufac-
ure of engineering fabrics are subject to
degradation from exposure to the ultra-
violet (UV) light portion of sunlight. The
polymers vary in their resistance to UV
radiation but all can be made much more
resistant to UV attack by incorporating
certain additives into the polymer
formulation.
Geotextiles will come into contact with
chemical leachate when used in leachate
collection systems and in cover designs
where, for example, they will be used as
part of a gas venting system. Extensive
tabulations are available showing the
resistance of the common geotextile poly-
mers to a wide range of chemicals. Unfor-
tunately, this data can only be considered
useful for screening purposes. Differences
in plastic formulations and type and levels
of additives can have a significant effect
on a given plastic's reaction to a given
chemical. It cannot be assumed that a
plastic fiber or fabric will behave the same
with similar chemicals.
Table 1, compiled from data available
from manufacturers' literature and other
sources, provides a summary of responses
of geotextile plastics to a variety of chem-
icals. This type of information should only
be used for preliminary screening purposes,
and tests simulating conditions to be
expected in the specific application are
recommended where the geotextile is to
be exposed to a known chemical environ-
ment for an extended period.
There are no known instances of geo-
textile failure due to attack by soil
microorganisms, even though some geo-
textile installations are over 20 years old.
Certain microorganisms are known to
cause gelatinous iron precipitates to form
in drainage systems including those using
geotextiles.
The effects of temperature extremes,
repeated freezing and thawing, and long-
term water immersion on the performance
of geotextiles have been investigated and
no significant detrimental effects have
been recorded for these conditions.
Design of Filters and
Drainage Systems
Rules for designing filters and drainage
systems using sand and gravel are well
established and have been used success-
fully for many years. When substituted for
granular filters in these applications, geo-
textiles must fulfill the same requirements
imposed on granular filters: the fabric must
prevent piping of the soil to be drained
while remaining sufficiently permeable
over the life of the project to prevent the
buildup of hydrostatic pressures. There
have been numerous approaches to devel-
oping filter criteria for geotextiles. At least
in the United States, most hydraulic
criteria for geotextiles are based in whole
or in part on tests and criteria originally
proposed by the U.S. Army Corps of
Engineers.
Recommended geotextile selection cri-
teria for filtration and drainage applications
in hazardous waste landfills are given in
the main report and include mechanical,
hydraulic, and environmental requirements.
Gas Venting
Thick geotextiles with significant in-
place permeability have been used as a
venting layer beneath impermeable syn-
thetic membrane liners at liquid impound-
ments for over a decade. In landfills, gases
generated by decomposition of organic
matter or volatilization of chemicals can
lead to undesirable gas migration with
consequent dangers of explosions and poi-
soning of people and vegetation. Geotex-
tiles with sufficient gas transmissivity can
relieve this problem.
Erosion Control
In landfill cover protection, erosion most
commonly occurs in sheet form when veg-
etative cover is inadequate or in localized
areas where rainwater runoff concentrates
in surface depressions, swales, and
ditches. Removal of cover soils leads to
exposure of synthetic membrane covers
with consequent deterioration of the cover
from ultraviolet light or mechanical dam-
age. Layers of stones or rip-rap (broken
rock) can prevent surface erosion on cover
slopes or areas of concentrated runoff but
these stones must be supported and pro-
tected from sinking into the underlying
soils. Traditionally, a bedding layer of sand
or gravel has been used, but a properly
selected geotextile can be substituted for
Table 1.
Effects of Various Chemicals on Geotextile Plastics"
Chemical
Acetic Acid
Sulphuric Acid
Sodium Hydroxide
Aniline
Acetone
Ethylene Glycol
Isooctane
Xylene
Chlorobenzene
Methylene chloride
Idichloromethane)
Ferrous sulphate
Concentration
Percent
100 (glacial)
10* (pH = 1)
70* fpH = 12.4)
100
100
100
100
100
100
100
Saturated
Effect of Chemicals on
Polyester
None
None
Destroyed
None
None
None
None
Some
Some
None
Polypropylene
None
None
None
None
None
None
Some
Some
Some
Substantial
Nylon
Substantial
Substantial
None
—
None
None
—
None
None
None
None
None
Consensus of data available to the author for room temperature exposure of at least one
month.
Aqueous solution.
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the sand and gravel bedding layer. Gener-
ally, fine sands, silty sands, and silts are
most susceptible to erosion and are in
most need of protection.
In drainage ditches and culvert outlets,
fabric should be selected and placed as
landfill covers. In cases where erosion
potential is less severe, specialized mat-
like geotextile related products may be
installed as a supplemental root anchor to
maintain vegetative cover. This should
only be used where vegetative cover can
be established to provide adequate perma-
nent protection. Where stone is used in
conjunction with geotextiles to line
ditches and protect culvert outlets, proper
preparation of the soil surface and proper
alignment of fabric panels are essential.
The full report was submitted in fulfill-
ment of Interagency Agreement No.
AD-96-F-1-400-1 by the U.S. Army
Engineer Waterways Experiment Station
under sponsorship of the U.S. Environ-
mental Protection Agency.
RaymondC. Horzis with the U.S. Army Engineer Waterways Experiment Station,
Vicksburg, MS 39180.
Jamet M. Houthoofd is the EPA Project Officer (see below).
The complete report, entitled "Geotextiles for Drainage, Gas Venting, and
Erosion Control at Hazardous Waste Sites," (Order No. PB 87-129 557/AS;
Cost: $18.95, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
UaOFHOALW/
EPA
Official Business
Penalty for Private Use $300
EPA/600/S2-86/085
0000329 PS
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