EPA/600/R-93/171
August 1993
REPORT OF WORKSHOP ON
GEOSYNTHETIC CLAY UNERS
by
David E. Daniel and B. Tom Boardman
University of Texas at Austin
Department of Civil Engineering
Austin, Texas 78712
Cooperative Agreement No. CR-815546-01-0
Project Officer
Robert Landreth
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
Cincinnati, Ohio 45268
RISK REDUCTION ENGINEERING LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
The information in the document has been funded wholly or in part by the United States
Environmental Protection Agency under assistance agreement number CR-815546-01-0. It has been subject
to the Agency's peer and administrative review and has been approved for publication as a U.S. EPA
document. Mention of trade names or commercial products does not constitute endorsement or
recommendation for use.
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FOREWORD
Today's rapidly developing and changing technologies and industrial products and practices
frequently carry with them the increased generation of materials that, if improperly dealt with, can
threaten both public health and the environment. The United States Environmental Protection Agency
is charged by Congress with protecting the Nation's land, air, and water resources. Under a mandate of
national environmental laws, the Agency strives to formulate and implement actions leading to a
compatible balance between human activities and the ability of natural systems to support and nurture
life. These laws direct the U.S. EPA to perform research to define our environmental problems, measure
the impacts, and search for solutions.
The Risk Reduction Engineering Laboratory is responsible for planning, implementing, and
managing research, development, and demonstration programs to provide an authoritative, defensible
engineering basis in support of the policies, programs, and regulations of the U.S. EPA with respect to
drinking water, wastewater,, pesticides, toxic substances, solid and hazardous wastes, and Superfund-
related activities. This publication is one of the products of that research and provides a vital
communication link between the researcher and the user community.
This report documents the available information concerning manufactured materials that
might be utilized in liner and cover systems for landfills, impoundments, site remediation projects, and
secondary containment structures. The information compiled in this report was obtained from
literature, from information supplied by manufacturers, and from discussions at a 2-day workshop held
on June 7 and 8,1992 in Cincinnati. This report will be useful to scientists, engineers, and regulatory staff
who are considering use of these types of materials.
E. Timohty Oppelt
Risk Reduction Engineering Laboratory
111
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ABSTRACT
A workshop was held at the Risk Reduction Engineering Laboratory in Cincinnati, Ohio,
on June 9-10,1992 to discuss geosynthetic clay liners (GCLs). The purpose of the workshop was
to present and discuss the most recent information available on the use of GCLs. This
information will be of use to EPA program and regional officials, state regulatory officials, permit
writers, and designers of waste disposal facilities.
Information about GCLs was first presented by manufacturers. Four commercial GCL
producers manufacture distinctly different products from a variety of materials. One common
feature, however, of all GCLs is a thin layer of bentonite clay. Two of the four manufacturers mix
an adhesive with the clay while the other two use no adhesive but instead needle punch two
geotextiles together with the bentonite sandwiched between the geotextiles. The manufacturers
focused their discussions on technical developments, recent research results, quality control, and
comparison of GCLs to compacted clay liners (CCLs).
Testing procedures were discussed next. A variety of conformance and performance
tests can be performed, but standard test methods are lacking. In addition, no consensus has
been reached on the types of tests that should be required or the appropriate frequency of testing.
Interpretation of test data is not always free of ambiguity due in part to a lack of standard testing
methods.
The performance of geomembrane/GCL composite liners was discussed at length. The
hydraulic contact between the clay and geomembrane was the focus. If a geotextile separates the
clay from the geomembrane (as is the case with most GCLs), and there is a defect in the
geomembrane, some lateral spreading of liquid will take place in the geotextile. Although some
equations are available to estimate the effect of the geotextile, more research is needed to quantify
geomembrane/GCL composite behavior more fully.
Owner/operators of waste disposal facilities described their experiences with GCLs.
Experience varies widely; some companies have used GCLs extensively while others have used
them rarely. Experience seems to have been good to date but concern was expressed about the
need for further refinement of construction quality assurance procedures and resolution of
several technical issues.
Recent research findings at the University of Texas and Drexel University's Geosynthetic
Research Institute were described. The response of GCLs to differential settlement, such as
would be experienced in cover systems placed over compressible waste, has been studied. Most
of the GCLs tested maintained low hydraulic conductivity even when subjected to large
IV
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differential settlement. The hydration, swelling, and strength of the bentonite in GCLs varies
depending upon the fluid (water or leachate) being used. The need to test with the site-specific
liquid was apparent.
The issue of equivalency of a GCL to a CCL was discussed. A number of criteria might
be applied, but only a few seem truly rational. Steady-state water flux and solute flux are
obvious and clear criteria that should usually be part of an equivalency analysis. Other criteria
can be applied but most are much less meaningful in terms of addressing regulatory compliance.
Finally, regulatory acceptance of GCLs was discussed. Although numerous site-specific
approvals of GCLs have been given by regulatory agencies, no blanket approvals or disapprovals
were identified. The EPA's RCRA Subtitle D regulations prescribe a geomembrane/CCL for
unapproved states but in approved states allow for equivalent designs to be accepted by state
regulatory agencies.
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Table of Contents
Disclaimer ii
Foreword iii
Abstract iv
List of Figures xi
List of Tables xiii
1. Introduction \
2. Manufacturer's Information 3
2.1 Bentofix® 3
2.1.1 Benefits of Needle Punching 3
2.1.2 Non-Woven Geotextiles 4
2.1.3 Bentonite 4
2.1.4 Laboratory Measurement of Hydraulic Conductivity 5
2.1.5 Overlaps 5
2.1.6 Installation Procedures 5
2.1.7 Case Histories 6
2.1.8 Supplemental Information 6
2.2 Bentomat® 7
2.2.1 A Brief History of Waste Management Practices 7
2.2.2 The Potential Role of Geosynthetic Clay Liners in Landfills 8
2.2.3 Future Directions for Research and Discussion 8
2.2.3.1 Intimate Contact 8
2.2.3.2 Puncture Concerns 12
2.2.3.3 Construction Quality Assurance 12
2.2.3.4 Research Directives 12
2.2.3.5 Test Standards 13
2.2.4 Conclusion 13
2.3 Claymax® 13
2.3.1 Benefits of Using a GCL 14
2.3.2 Quality Management .16
2.3.3 Available Information on Claymax® 16
2.4 Gundseal® 16
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2.4.1 Gundseal® Composite System 21
2.4.1.1 Hydraulic Conductivity 21
2.4.1.2 Overlapped Seams 21
2.4.1.3 Composite Action 22
2.4.1.4 Internal Shear Strength 22
2.4.1.5 Interfacial Friction Resistance 25
2.4.2 Gundseal® as a Single Liner System 25
2.4.2.1 Soil Suction 25
2.4.2.2 Hydraulic Conductivity 25
2.4.2.3 Internal Shear Strength 26
2.4.2.4 Seams 27
2.4.2.5 Geotextile Separator 27
2.4.3 Conclusion 28
3. Testing Procedures 29
3.1 Quality Assessment for Bentonite Sealants 29
3.1.1 Bentonite 29
3.1.2 Primary Test Methods 31
3.1.2.1 Permeameter Testing 31
3.1.2.2 Swell Tests 31
3.1.2.2.1 Free Swell Test 31
3.1.2.2.2 Modified Free Swell Index Test 32
3.1.2.2.3 Swelling Pressure Test 32
3.1.2.3 Plate Water Absorption (PWA) Test 33
3.1.2.4 Liquid Limit Test 33
3.1.3 Secondary Test Methods 34
3.1.3.1 Apparent Colloid Content Test 34
3.1.3.2 X-Ray Diffraction (XRD) Mineralogical Analysis 34
3.1.3,3 Cation Exchange Capacity (CEC) 35
3.1.3.4 Specific Surface Area 35
3.1.3.5 Chemistry 35
3.1.4 Conclusion 35
3.2 Conformance Testing of Geosynthetic Clay Liners 36
3.2.1 Testing Options 37
3.2.1.1 Shear Strength 38
3.2.1.2 Tensile Properties 38
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3.2.1.3 Puncture Resistance 38
3.2.1.4 Biaxial Stresses 38
3.2.1.5 Freeze-Thaw and Desiccation 39
3.2.2 Suggested List of Conformance Tests for GCLs 39
3.2.2.1 Hydraulic Conductivity Testing 39
3.2.2.2 Shear Strength Testing 39
3.2.2.3 Tensile Property Testing 44
3.2.2.4 Biaxial Stress Testing 46
3.2.3 Testing Frequency 47
3.2.4 Conclusion 47
3.3 The Determination and Interpretation of Shear Strength 47
3.3.1 Test Conditions 48
3.3.1.1 Normal Stress 48
3.3.1.2 Hydration Conditions 48
3.3.1.3 Rate of Shear 49
3.3.1.4 Method of Failure 50
3.3.2 Conclusion 59
4. Intimate Hydraulic Contact with Geomembrane 51
4.1 Intimate Contact for GCL/Geomembrane Composite Liner Systems 51
4.1.1 In-Situ Behavior of a GCL 51
4.1.2 The Case for Geotextile Placement Within a Composite Liner 52
4.1.3 Evaluation of Potential Leakage Rates 52
4.1.4 Ongoing Research 53
4.2 Questions from the Audience 54
4.3 Final Comments 55
5. Owner/Operator Experiences and Concerns 55
5.1 Clarke Lundell, Representing Waste Management of North America, Inc 56
5.2 Charles Rivette, Representing Browning-Ferris Industries (BFI) 56
5.3 Kurt Shaner, Representing Chambers Development Comany, Inc 58
5.4 John Workman, Representing Laidlaw Waste Systems 59
6. Recent Research ^Q
6.1 The Hydraulic Conductivity of Large Scale Intact, Overlapped, and Composite
Geosynthetic Clay Liners 60
6.2 The Effect of Differential Settlement on the Hydraulic Conductivity of Geosynthetic
Clay Liners 62
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6.3 Stability of Final Covers Placed on Slopes with Geosynthetic Clay Liners 68
6.4 The Hydration Behavior and Mid-Plane Shear Strength of Four Geosynthetic Clay
Liners 72
7. Equivalency 76
7.1 Equivalency 76
7.1.1 Potential Applications 76
7.1.2 Differences Between CCLs and GCLs 77
7.1.3 Criteria for Equivalency 79
7.1.4 Hydraulic Issues 79
7.1.4.1 Steady Flux of Water 79
7.1.4.2 Steady Solute Flux 82
7.1.4.3 Adsorption Capacity 85
7.1.4.4 Time to Initiate Discharge of Water from Base of Liner 87
7.1.4.5 Breakout Time for Solute 88
7.1.4.6 Production of Consolidation Water 88
7.1.5 Physical/Mechanical Issues 89
7.1.5.1 Freeze/Thaw Resistance 89
7.1.5.2 Wet/Dry Effects 89
7.1.5.3 Response to Total Settlement 90
7.1.5.4 Response to Differential/Settlement 90
7.1.5.5 Stability on Slopes 90
7.1.5.6 Vulnerability to Erosion 91
7.1.5.7 Bearing Capacity 91
7.1.6 Construction Issues 91
7.1.6.1 Puncture Resistance 91
7.1.6.2 Effect of Subgrade Condition 92
7.1.6.3 Ease of Placement or Construction 92
7.1.6.4 Speed of Construction 92
7.1.6.5 Availability of Materials 92
7.1.6.6 Weather Constraints 93
7.1.6.7 Quality Assurance Requirements 93
7.1.7 Summary of Equivalency Issues 93
7.2 Discussion 95
8. Technical Concerns 96
8.1 The Effect of Freezing on Saturated Sodium Bentonite 96
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8.2 The Flow of Bentonite out of a GCL on a Side Slope 95
8.3 Designing for Side Slopes 97
8.4 Possibility of Overlap* Pulling Apart Due to Wet/Dry Cycles 97
8.5 Steep Slopes 9?
8.6 Long Term Physical Stability 9g
8.7 Long Term Shear Strength 9g
8.8 Biotic Instabilities
"o
9. References and Publications Related to GCLs 99
10. Appendix : List of Attendees 102
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List of Figures
Figure Title Page No.
2.1 Needle Punched System of Bentofix® 3
2.2 Potential Double Composite Liner System 9
2.3 Potential Single Composite Liner System 9
2.4 US EPA Recommended Landfill Cover Design 15
2.5 Potential Landfill Cover Design Incorporating a GCL 15
2.6 Clem Quality Management Program Summary 17
2.7 Composite Action Test with Overlying Defective Geomembrane 23
2.8 Variations in Bentonite Water Content beneath a Defective Geomembrane 24
2.9 Water Content vs. Time for Samples of Gundseal® Placed Within Sands of
Varying Water Content 26
3.1 Flexible-Wall Apparatus 40
3.2 Rigid-Wall Apparatus 41
3.3 Large Diameter Rigid-Wall Apparatus 42
3.4 Typical Direct Shear Friction Apparatus 43
3.5 Geosynthetic/Geosynthetic Direct Shear Testing 43
3.6 Wide Width Tensile Test Schematic 44
3.7 Cross Section of a Horizontal Containment Box in a Confined Creep Test
Mode 45
3.8 Biaxial Test Apparatus Schematic 46
6.1 Cross Sectional View of Test Set Up 61
6.2 Cross Sectional View of Modified Test Set Up 63
6.3 Plan View of Tank and Deflatable Bladder 63
6.4 Hydraulic Conductivity vs. Time for Intact Bentomat® Sample IHS-2-D 64
6.5 Hydraulic Conductivity vs. Deformation for Intact Bentomat® Sample
IHS-2-D 64
6.6 Hydraulic Conductivity vs. Time for Overlapped Bentomat® Sample
OHS-2-C 65
6.7 Hydraulic Conductivity vs. Deformation for Overlapped Bentomat®
Sample OHS-2-C 65
6.8 Hydraulic Conductivity vs. Time for Intact Claymax® Sample IHS-l-A 66
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6.9 Hydraulic Conductivity vs. Deformation for Intact Claymax® Sample
IHS-l-A „
oo
6.10 Hydraulic Conductivity vs. Time for Overlapped Claymax® Sample
OHS-l-F ,_
o/
6.11 Hydraulic Conductivity vs. Deformation for Overlapped Claymax®
Sample OHS-l-F 67
6.12 Hydraulic Conductivity of Bentomat® after a Large Settlement Prior to
Hydration 69
6.13 Hydraulic Conductivity of Gundseal® after a Large Settlement Prior to
Hydration ,„
6.14 Typical Profile of Final Cover with Geosynthetic Clay Liners 70
6.15 Profile of the Slope Used for Computations 70
6.16 Relationship between Maximum Interfacial Displacement and Minimum
Interfacial Friction Angle for a 3:1 Slope 71
6.17 Relationship between Tension in the Geogrid and the Minimum Interfacial
Friction Angle for a 3:1 Slope 71
6.18 Hydration of GCLs Using Different Liquids 73
xn
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List of Tables
Table Title Page No.
2.1 Measurement of Hydraulic Conductivity for GCLs 5
2.2 Summary of Triaxial Permeability Test Data on Bentomat® 10
2.3 Summary of Direct Shear Test Data on Bentomat® 11
2.4 Claymax® Mineral Performance Testing 18
2.5 Claymax® Backing Material Testing 18
2.6 Claymax® Inspection andTesting 18
2.7 Claymax® GCL Material Specifications 19
2.8 Partial List of Claymax® Hydraulic Conductivity Testing Data 20
2.9 Partial List of Claymax® Frictional Resistance Data 20
2.10 Permeability to Various Hydrocarbons as a Function of Initial Bentonite
Water Content 27
6.1 Direct Shear Test Results Summary 75
7.1 Differences Between GCLs and CCLs 78
7.2 Potential Equivalency Issues 80
7.3 Summary of Equivalency Assessment 94
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CHAPTER 1
INTRODUCTION
On June 7-8, 1990, the United States Environmental Protection Agency
(EPA) held a workshop to discuss the use of alternative barriers in the design of
cover and/or liner systems. The focus of the workshop was on the potential use
of geosynthetic clay liners (GCLs) as an alternative barrier. Since that
introductory conference, a significant amount of information has been gathered
through research and field applications. For this reason, another workshop on
the use of GCLs was held on July 9-10, 1992 at the EPA's Risk Reduction
Engineering Laboratory in Cincinnati, Ohio.
The purpose of the second workshop was to present and discuss the most
recent research available on the use of GCLs. As the use of GCLs has expanded
dramatically over the last few years, it is important that EPA program and
regional officials, state regulatory officials, permit writers, and designers keep up
to date on the latest information available on the use of these products.
The information discussed at the workshop held on July 9-10,1992 was as
follows:
1) Manufacturer's Information. A compilation of information available on
each of the major GCL products was presented by the manufacturing
sector. (Presented by representatives for Bentofix®, Bentomat®,
Claymax®, and Gundseal®)
2) Testing Procedures. The use of different testing methods and procedures
to determine the physical properties of GCLs was discussed. (Presented
by Richard Brown, John Boschuk, and Robert Bachus)
3) Intimate Contact. The mechanisms of intimate hydraulic contact between
geomembranes and GCLs were discussed. (Presented by John Bove)
4) Owner/Operator Experiences. An overview of information on the field
application of GCLs was presented by owner/operators of landfills.
(Presented by representatives of Waste Management of North America,
Browning-Ferris Industries, Chambers Development, and Laidlaw)
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5) Recent Research. The most recent research carried out by Drexel
University and the University of Texas at Austin was discussed.
(Presented by Robert Koerner, David Daniel, Mark LaGatta, B. Tom
Boardman, and Hsin-Yu Shan)
6) Equivalency. The equivalency of a GCL to a compacted clay liner was
discussed. (Presented by David Daniel)
7) Technical and Regulatory Concerns. An open discussion was held on the
technical concerns of the use of GCLs. (Presented by David Daniel and
Robert Landreth)
The purpose of this report is to summarize the information presented at
the GCL workshop held on July 9-10, 1992. This report does not represent the
full extent of the information available on geosynthetic clay liners. Readers are
directed to the summary of the GCL workshop held on June 7-8, 1990 for
additional information (EPA 600/2-91/002). Rather, this report augments the
proceedings from the first workshop.
Information on Bentofix®, Bentomat®, Claymax®, and Gundseal® is
presented in Chapter 2. Testing Procedures are discussed in Chapter 3. Intimate
contact is discussed in Chapter 4. Owner/operator experiences are listed in
Chapter 5. Recent university research is discussed in Chapter 6. Equivalency
concerns are addressed in Chapter 7. Technical concerns are voiced in Chapter 8.
A list of references and published papers and reports on GCLs is included in
Chapter 9. A list of attendees is presented in the Appendix.
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CHAPTER 2
MANUFACTURER'S INFORMATION
At the present time, there are four major products available on the
geosynthetic clay liner (GCL) market. These four products are Bentofix®,
Bentomat®, Claymax®, and Gundseal®. Each product has its own unique
properties.
The manufacturer of each product was asked to speak about technical
discoveries that had been made since the previous meeting. The information
presented in this chapter was provided by the manufacturer's speaker.
2.1 Bentofix® (By Georg Heerten, Naue-Fasertechniik GmbH & Co.)
Bentofix®, which was developed in 1987, is produced by the German
company Naue-Fasertechnik and was introduced to the North American market
in 1991 through the joint venture company Albarrie Naue Ltd. establishing an
additional production facility in Canada. Bentofix® is designed as a layer of
loose granular or powdered bentonite held between two non-woven geotextiles
by a series of thin needle punched fibers (Fig. 2.1). Needle punching keeps the
bentonite in place before and after hydration, and the needle punching is said to
increase the internal shear strength of the GCL.
woven or
non-woven
bentonite
non-woven
Figure 2.1 Needle Punched System of Bentofix®
2.1.1 Benefits of Needle Punching
Naue-Fasertechnik's purpose for needle punching a layer of loose
bentonite between two non-woven geotextiles was to create a sturdy GCL that
could withstand the rigors of installation. The needle punching helps to keep the
bentonite in place even after hydration. For this reason, the manufacturer states
that Bentofix® can be installed during rainy conditions or underwater.
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A GCL bound by needle punched fibers is said to allow for the installation
on steep slopes (up to 1.5 :1), by preventing sliding between the components of
the GCL, while also increasing the internal shear strength of the GCL as a whole.
2.1.2 Non-Woven Geotextiles
The manufacturer stresses the importance of the robustness of the
geotextiles incorporated into the GCL. To allow the GCL to be needle punched
together, at least one layer must be a non-woven geotextile. Both geotextile
components must pass filter criteria in order to prevent the migration of
bentonite out of the GCL. The upper layer non-woven geotextile must also be
puncture resistant. For this reason, the top cover layer geotextile must have a
minimum mass/area of .25 kg/m2 and pass a German puncture test. However, a
.12 kg/m2 woven geotextile may also be used. The manufacturer has not had the
opportunity to measure the hydraulic conductivity of a deformed section of
Bentofix® after passing the puncture test. This is still being investigated.
To avoid lateral wicking in the upper non-woven geotextile, when a
geomembrane is placed on the GCL to form a composite liner, the pore space of
the upper geotextile is filled with powdered bentonite. The bentonite powder is
said to be fixed by a patented system which fills the non-woven pores. This
system is also said to improve the intimate contact between a GCL and an
overlying geomembrane by reducing the amount of loose powdered bentonite
dust where the two come in contact.
2.1.3 Bentonite
Bentofix® can be manufactured with powdered bentonite with 87% of the
mixture having a grain size less than 0.002 mm, or as a granular bentonite in the
size range of 0.5 to 4 mm. Due to its finer grain size, the powdered bentonite will
hydrate much quicker than a granular bentonite. Granular bentonite used to be
necessary when Bentofix® was used in conjunction with a geomembrane because
the powdered bentonite would create welding difficulties for the overlying
geomembrane. The manufacturer is said to have solved the problem of loose
powdered bentonite influencing the welding process of geomembranes by fixing
the bentonite to the geotextile, which addresses the intimate contact issue at the
same time.
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2.1.4 Laboratory Measurement of Hydraulic Conductivity
The manufacturer recommends that the procedures outlined in Table 2.1
be observed for the proper measurement of the hydraulic conductivity of a GCL.
Differences in GCL sample preparations can lead to large variations in the
measured value of hydraulic conductivity.
Table 2.1 Measurement of Hydraulic Conductivity for GCLs
Procedure Important Steps Possible Problems
Sampling 1) Exact Cutting (Stamping) 1) Flow around edge
2) No bentonite loss on edges 2) Air encapsulation
3) Edge wetting
Installation 1) Soaking filter plate 1) Air slows down
swelling
2) Applying flexible 2) Loss of bentonite
membrane carefully
Test Procedure 1) Proper saturation time 1) Inadequate water
(50 hours minimum) Adsorption
2) Cell pressure
(30 kPa minimum)
3) Hydraulic gradient
Calculation 1) Measurement of 1) Incorrect calculation
hydrated sample thickness
2.1.5 Overlaps
In the past, the overlapping seams had to be filled with loose powdered
bentonite or a hydrated bentonite paste. This will not be necessary in the future
due to the upper layer non-woven geotextile being filled with bentonite powder.
This system is said to provide a more intimate contact along the GCL overlap.
A prefabricated velcro system has also been designed to prevent
displacement along the overlaps due to movements during or after the covering
process.
2.1.6 Installation Procedures
Bentofix® will have the printing on the upper geotextile as well as an
overlap mark. Naue-Fasertechnik has also developed an installation manual
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which is delivered to each customer in advance. According to the manufacturer
a correct overlap can be achieved, and wicking in the non-woven plane can be
prevented, if the installation instructions are followed correctly.
2.1.7 Case Histories
1) Geomembrane Protection. In an effort to prevent the puncture of an
underlying geomembrane by the placement of a granular drainage material with
large particles (16 to 32 mm), Bentofix® has also been used as a cushion layer
over the geomembrane. The GCL not only protects the geomembrane, but
provides an additional seal, as well.
2) Vertical Gas Barrier. In an effort to prevent the seepage of landfill gas and
leachate, Bentofix® was placed in a vertical cutoff trench surrounding a landfill.
Apparently the soil moisture was sufficient to hydrate the bentonite resulting in a
sufficient gas barrier.
3) Sealing a Canal. In an effort to seal a canal and cofferdam, Bentofix® was
successfully installed in an underwater operation. The manufacturer states that
the needle punching allowed the GCL to withstand the immediate swelling and
the following installation procedure all while underwater.
4) Groundwater Protection System. In an effort to catch the run off from de-
icing impurities at the Munich II Airport, over 700,000 m2 of Bentofix® was
installed. The project has proved successful to date.
2.1.8 Supplemental Information
After the conference, Mr. Klaus Stief submitted additional information.
Because Bentofix® was developed in Germany, the manufacturer has followed
German and European regulations for landfills particularly closely. The
following is a summary of Mr. Stief's perspective on European policy on landfill
linings.
The Commission of the European Communities published in May 1992 a
proposed set of regulations for landfills. The proposal calls for liner systems,
leachate collection systems, and engineered cover systems. The lining system
may consist of natural, low-permeability soil, or lacking such soil, engineered
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liners must be used. There are no specific requirements for engineered liners; the
use of GCLs is in no way restricted.
Current German regulations are more stringent. The general liner
requirement in Germany is for a single composite liner consisting of a
geomembrane placed on 0.75 to 1.5 m of low-permeability compacted soil.
Similar requirements exist for the cap, although the soil liner component has a
smaller minimum thickness (0.5 m).
2.2 Bentomat® (By Robert Trauger, CETCO)
Bentomat® is manufactured by the Colloid Environmental Technology
Company (CETCO), which is a subsidiary of the American Colloid Company.
The representative from CETCO briefly discussed the results of recent
laboratory testing on Bentomat®, but mainly concentrated on the highlights and
advantages of the use of GCLs in the waste management industry.
2.2.1 A Brief History of Waste Management Practices
For several decades, the only practical means of waste containment was
the construction of a hydraulic barrier consisting of a layer of compacted clay.
Unfortunately, the possibility of complete containment to the extent that a 1977
US EPA report on landfill liners suggested a "different approach/' whereby
"pollution would be lessened by designing landfill liners for higher permeability
and by selectively attenuating the most toxic pollutants from the leachate../'
This novel idea of emphasizing attenuation over containment was never
implemented due to the emergence of geomembrane technology in the 1980's.
The near zero hydraulic conductivity of geomembranes made the concept of true
containment appear attainable. After a decade of technical progress,
geomembranes are now accepted by most designers as a required component of
landfill liners. The composite liner system, in which a geomembrane is placed
over a clay layer, was another fundamental advance as designers abandoned
attenuation considerations in favor of containment. Leakage rates through well
constructed composite liners are far lower than through geomembranes or
compacted clay liners (CCLs) alone. The only development missing in the shift
to containment oriented landfills was a series of federal regulations for landfill
liner design.
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The US EPA has just recently released the long awaited federal rules on
landfill design for municipal solid waste landfills. Unfortunately, GCLs were not
well established when the rules were drafted, so there is not yet a federal policy
on the role of GCLs in landfills.
2-2-2 The Potential Role of Geosynthetic Clay Liners in Landfills
Some have suggested that GCLs are not merely a convenient substitute for
clay liners but instead represent the next step towards the goal of total waste
containment. GCLs have an extremely low, uniform hydraulic conductivity and
are not subject to the many materials and construction related problems that
commonly plague CCLs. Potential landfill liner cross sections reflecting this
design goal are shown in Fig. 2.2 and 2.3.
2-2-3 Future Directions for Research and Discussion
The GCL is an important innovation in lining technology, but its
performance can be undermined by poor design and installation. As with any
emerging technology, additional field and laboratory research is necessary to
strengthen the feedback loop for better designs, installations, and products.
Since the last GCL workshop held two years ago, a vast amount of useful data
has been obtained for Bentomat®. Some of the data are shown in Tables 2.2 and
2.3. More work needs to be done, however, to realize the full performance
capabilities of GCLs. Some of the most important remaining issues which the
technical, regulatory, and manufacturing communities must address are
discussed in succeeding subsections.
2.2.3.1 Intimate Contact
Concern has been expressed that the upper geotextile of a GCL could
prevent intimate contact between the geomembrane and the bentonite clay and
facilitate lateral movement along the interface. Overall leakage could
consequently increase because liquid is distributed over a broader area.
However, lateral movement may only occur at low confining stress, and the
quantification of the phenomenon is incomplete. When considering this issue
one must assess the theoretical advantages of geomembrane/CCL intimate
contact with respect to the many performance and installation advantages of a
geomembrane/GCL liner system.
-------
0.6 m Select Fill
Separator Geotextile
0.6 m Granular LCS
Cushioning Geotextile
Geomembrane
0.3 m Granular LDS
Geomembrane
0.6 m Structural Fill (or Clay)
SUBBASE
Figure 2.2 Potential Double Composite Liner System
0.6 m Select Fill
Separator Geotextile
0.6 m Granular LCS
Cushioning Geotextile
Geomembrane
GCL
0.6 m Structural Fill (or Clay)
SUBBASE
Figure 2.3 Potential Single Composite Liner System
-------
Table 2.2 Summary of Triaxial Permeability Test Data on Bentomat®
TEST LAB* DATE
J & L 07-05-90
J&L 09-21-90
J & L 12-17-90
Geosyntec 12-20-90
J & L 01-08-91
ACC 05-02-91
J&L 07-05-91
D&M 07-15-91
Geosyntec 07-31-91
Nelson 09-04-91
ACC 06-18-91
Notes:
T P. I _ I O. I TV,.*'
PRODUCT MAX. EFFECTIVE
CONF. STRESS(KPA)
SS 56.5
73
90.9
107
CS 56.5
73
90.9
107
SS 56.5
73
90.9
CS N/A
CS N/A
CS 129
CS 207
SS 255
PL 393
PL 34
SS 34
SS 34
HEAD(M)
.3
3.7
7.3
11
.3
3.7
7.3
11
.3
3.7
7.3
9.1
4.6
11
2.1
2.7
16
2
3.7
7.0
GRADIENT
30
380
760
1100
35
450
900
1315
30
400
800
2250
N/A
1800
200
530
217
160
360
840
TOTAL
TIME(HRS)
26
6
13
4
62
19
46
2
36
28
7
25
72
25
216
4
190
720
1440
3600
PERMEABILITY
(CM/SEC)
2.1 x 10'9
7.5 x 10'10
5.8 xlO'10
6.6 xlO'10
5.6 x 10'9
l.lxlO'9
9.8 xlO'10
2.6 x 10'9
7.3 xlO-10**
7.3 x lO'10
1.4 x 10'9
1.4 xlO'9
2.0 x 10'9
1.6 x lO'9
3.6 x 10'9t
2.1 x 10'10
6.8xlO-10tt
3.0 xlO-9**
3.5 x 10'9*
3 0 x 10-9$
J & L = J&L Testing Company, Inc., Canonsburg, PA
Geosyntec = Geosyntec Consultants, Norcross, GA
D & M = Dames & Moore, Salt Lake City, UT
ACC = American Colloid Company, Arlington Heights, IL
Nelson = Robert L. Nelson & Associates, Schaumburg, IL
Permeant was landfill leachate
' Permeant was salt water
'f Permeant was 600 ppm NaCN
•*• Permeant was liquid fertilizer
10
-------
Table 2.3 Summary of Direct Shear Test Data on Bentomat®
LAB DATE
J & L 05-30-90
STS 09-11-90
J&L 11-06-90
GRI 04-18-91
STS 05-28-91
UTA 08-12-91
J&L 09-09-91
TRI 05-06-92
Notes:
INTERFACE
NW/Sand
NW/Sand
NW/Clay
NW/Clay
NW/1 mm Text. HOPE
NW/2 mm Text. HOPE
W/2 mm Text. HOPE
NW/Sandy Soil
Internal
NW/1 mm Text. HDPE
W/2 mm Text. HOPE
Internal
W/Soil Cover
W/Geonet
NW/2B Stone
W/1.5mmText. VLDPE
W/1.5mmSm. VLDPE
NORMAL
STRESSES(KPA)
7/14/21
240/360/480
14/24/34
3/7/14/34/69/140/240
0.83/3/7/34/69
0.83/3/7/34/69
240/360/480
41/62/96/130
4/8.6/13.0
14/55/96
14/55/96
MOISTURE
CONDITION'''
Hydrated
Dry
Hydrated
Dry
Dry
Dry
Dry
Dry
Dry
Hydrated
Hydrated^
Hydrated
Hydrated
Hydrated
Hydrated
Hydrated
Hydrated
Hydrated
Hydrated
SHEAR RATE FRICTION
ANGLE(DEG)
0.5 mm/min
5 mm/min
0.5 mm/min
0.89 mm/min
5 mm/min
0.5 mm/min
0.89 mm/min
1 mm/min
35
28
41
31
18
37
24
23
42
37
39
20
19
26
22.5
17
53
22
14
J & L = J & L Testing Company, Inc., Canonsburg, PA (used a 75 mm Wykeham Farrance direct shear device)
STS = STS Consultants Ltd., Northbrook, IL (used a custom-made 300 mm shear box)
GRI = Geosynthetic Research Institute, Drexel University, Philadelphia, PA (used a Wykeham Farrance device)
UTA = University of Texas at Austin, Civil Engineering Laboratory (used a 60 mm direct shear box)
TRI = TRI Environmental Inc., Austin, TX (used a 300 mm direct shear box)
NW = Non-woven geotextile of Bentomat
W = Woven geotextile of Bentomat
T "Dry" = sample tested in the as-received moisture state.
"Hydrated" = sample was hydrated prior to testing, although the actual hydration methods vary.
Samples were hydrated with distilled water unless otherwise noted.
'* Hydrated in leachate.
11
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2.2.3.2 Puncture Concerns
There has been a great deal of concern over the potential for a GCL to be
more susceptible to puncture damage. This concern is often cited by regulators
as reason not to allow the use of GCLs. Liner systems in today's modern landfills
are more controlled than ever before and great care is usually taken to prevent
the possibility of puncture from above and below the liner. With GCLs, these
practices must be even more strongly emphasized, especially in the post
construction stage. The construction of a sound foundation and the placement of
cover material over the liner system must be rigidly controlled. If deemed
necessary, additional cover layers should be placed on the liner system to further
preclude the possibility of puncture. In other words, puncture prevention should
be emphasized during the construction process.
2.2.3.3 Construction Quality Assurance
GCLs can be easily and rapidly installed in comparison to geomembranes
and CCLs, yet a stringent construction quality assurance (CQA) plan must be
implemented. The best design and the most explicit project specifications mean
nothing if the installation is faulty. Comprehensive and realistic CQA programs
should be developed by GCL manufacturers and engineers. These programs
should detail installation criteria as well as materials conformance criteria. The
certification program under development by the National Institute for
Certification of Engineering Technologists (NICET) will be extremely valuable
for providing trained GCL installers, but more input is needed from installers
regarding methods of installation which minimize the potential for GCL damage.
2.2.3.4 Research Directives
The long term compatibility of a hydra ted bentonite layer with the
variety of organic and inorganic chemicals it may encounter needs to be
investigated. Due to time constraints, these tests are inconvenient to run in a
controlled, repeatable fashion. New test methods may need to be developed to
provide meaningful data in a reasonable period of time. Results of this research,
however, could lead to improvements in contaminant resistant clays.
Direct shear testing is another area requiring additional research. There is
a seemingly limitless variety of soil and geosynthetic materials which may be
used in conjunction with a GCL. Each interface has its own unique frictional
12
-------
characteristics, and the designer needs a reliable evaluation of the applicable
friction angles to perform a slope stability analysis. A relatively sizable database
is already available, but more information is needed.
A long term, full scale field study of GCLs would also be informative. The
effects of freeze/thaw, desiccation, and settlement could all be observed on a
large scale.
2.2.3.5 Test Standards
The engineering and performance characteristics of GCLs are typically
evaluated using ASTM methods for soils and geosynthetics. For the geosynthetic
components of GCLs, these test methods are already acceptable or only require
minor modifications. Unfortunately there are no currently recognized standards
for preparing GCL test samples, for determining the quality of the bentonite
component, or for testing the entire product as a whole. At this time, all of the
major GCL manufacturers are working with ASTM to develop the necessary
standards.
2.2.4 Conclusion
The rapid increase in the use of GCLs over the past two years has made
intrepid pioneers out of manufacturers, regulators, and installers. Still, a
watchful eye must be maintained over the types of applications and designs in
which GCLs are specified. A poorly conceived design, or a careless installation,
can only serve to undermine the credibility that the industry has striven to
attain. In the coming years, everyone is urged to share his information and
experiences so that the state of the art can be advanced to the benefit of everyone
involved with geosynthetic clay liners.
2.3 Claymax® (By Walter Grube, Jr., James Clem Corporation)
Claymax® is manufactured by the Clem Environmental Corporation,
which is a branch of the James Clem Corporation. Claymax® was the first GCL
product to be designed and introduced onto the market.
Claymax® produces two products. The Claymax® 200R is the original
product which consists of a layer of granular sodium bentonite sandwiched
between an upper primary woven geotextile and a lower secondary open weave
13
-------
geotextile. Other materials can be specified for the lower backing depending on
site specific needs. Claymax® 200R is normally installed with the primary
geotextile on top, but this may be reversed depending on site-specific
requirements. Claymax® 500SP has recently been introduced as a material with
high shear and tensile strength properties. The increase in strength has been
achieved by stitch-bonding the primary and secondary backing materials
together and by increasing the tensile strength of the backing materials
themselves.
2.3.1 Benefits of Using a GCL
The manufacturer discussed four reasons to use a GCL. These reasons are
discussed in more detail below.
1) Stop Seepage. In an effort to reduce seepage, a GCL can be used to fulfill the
low permeability requirement and as a design alternative to a compacted clay
liner. In order to attain this low permeability, the in place overlapping GCLs
must have seam integrity and the ability to successfully self heal.
2) Quality Control. The high degree of quality assurance/quality control
(QA/QC) in the materials and manufacture of the GCL make.it an attractive
alternative to compacted clay liners. The manufacturer also states that they will
provide field and technical support to ensure QA/QC. Also, the GCL customer
may perform independent conformance testing.
3) Standards of the Industry. Both the bentonite and geosynthetic industries
have a history of reliable standards and guidelines. The GCL manufacturers are
working with various standard-writing organizations in an effort to ensure a
high level of QA/QC.
4) Lack of Clay Reserves. Many regions do not have significant clay reserves.
As an example, the landfill cover design recommended by the US EPA, shown in
Fig. 2.4, is considered. As an alternative to a compacted clay liner, the
manufacturer recommends the landfill cover design shown in Fig. 2.5, which has
been modified to incorporate a GCL.
14
-------
vegetation/soil
top layer
drainage layer
low hydraulic conductivity
geomembrane/soil layer
\\A v\// \\/,
T
60 cm
I
30cm
waste
filter layer
0.5 mm (20 mil)
geomembrane
Figure 2.4 US EPA Recommended Landfill Cover Design (EPA/625/4-91 /025)
vegetation/soil
top layer
drainage layer
GCL(<10'9 cm/sec)
fine-textured soil, compacted
to 95-100% Standard Proctor,
wet of optimum moisture
content
waste
\\A
\\L
filter layer
0.5 mm (20 mil)
geomembrane
Figure 2.5 Potential Landfill Cover Design Incorporating a GCL
15
-------
2.3.2 Quality Management
While data can be collected from small scale samples in the laboratory,
how will the product perform as a whole in the field? This is where construction
quality assurance for the GCL product becomes important.
The manufacturer states that the Clem quality management program is
independent of manufacturing, and follows all applicable and relevant standard
ASTM/API test methods. With each product sent to a client, a certification of
compliance is included detailing the properties of that particular shipment.
A summary of the quality management program undertaken at the James
Clem Corporation is shown in Fig. 2.6, and in Tables 2.4, 2.5, 2.6, and 2.7. Two
partial lists of available testing data are shown in Tables 2.8 and 2.9.
2.3.3 Available Information on Claymax®
The manufacturer states that the following information is available on the
Claymax® product:
1) Case histories
2) Laboratory data
a) Compatibility studies
b) Shear resistance
c) Overlapped seam/damaged liner permeability tests
d) Freeze/thaw tests
3) Customer assistance
a) Engineers guide to GCL specifications
b) Engineers guide to GCL CQA programs
4) Design models and comparison studies
a) Slope stability analyses
b) Comparative flows (clay vs. Claymax®)
c) Composite liner system comparative flow rates
d) Bentonite quantity calculations at seams
2.4 Gundseal® (By James Anderson, Gundle Lining Systems, Inc.)
Gundseal® is manufactured by Gundle Lining Systems, Inc. The
Gundseal® GCL consists of a layer of bentonite (5 kg/m2) adhered to a
geomembrane. Depending on the types of fluids that may come in contact with
16
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Mineral Performance
Testing
Mineral Performance
Testing
Evaluation of
Supplier QC Data
Testing of Raw
Materials
Testing of Adhesive
Materials
Testing of Adhesive
Mixture
Acceptance of Raw
Materials
Incorporation into
Process
Process Monitoring
100% Inspection of
Finished Product
Finished Product
Testing
Testing of Backing
Materials
Testing of Finished
CLAYMAX Product
Acceptance of Finished CLAYMAX Product
Shipment of
CLAYMAX Product
Field/Technical
Service
Fig. 2.6 Clem Quality Management Program Summary
17
-------
Table 2.4 Claymax® Mineral Performance Testing
TEST
Gradation
Moisture
Content
PH
Plate
Water
Adsorption
Free Swell
Fluid Loss
Performed?
X
X
X
X
X
X
AS DELIVERED
Criteria Frequency
per specs 8- 10 per rail car
< 10%
8-10.5
860% min.
25 ml min. "
18 ml max. "
AS REMOVED FROM FINISHED CLAYMAX
Performed? Criteria Frequency
-
X
X
X
X
X
-
25% max.
-
-
27 ml min.
12 ml max.
-
2000 m2 max.
»
»
»
••
Table 2.5 Claymax® Backing Material Testing
TEST SUPPLIER
TESTED
Grab Tensile Strength
Grab Tensile Elongation
Puncture Strength
Mullin Burst
Unit Weight
Wide Width Tensile
X
X
X
X
X
X
CLEM TESTED ACCEPTANCE
CRITERIA
(MARV)
X 400 N
X 15%
X 220 N
1700 kPa
0.12kg/m2
1 1 N/mm
CLEM TESTING
FREQUENCY
7-10 per delivered
truckload
"
"
"
„
Table 2.6 Claymax® Inspection andTesting
TEST
Bentonite Content
Composite Thickness
Bentonite Thickness
Permeability
Overlapped Seam Permeability
(no granular bentonite)
MINIMUM TESTING
FREQUENCY
2000 rn2
2000 rn2
2000 rn2
70,000 m2
70,000 m2
ACCEPTANCE CRITERIA
4.6 kg/m2 MARV
5.0 mm MARV
4.3 mm MARV
< 5 x 10'9 cm/sec @ 14 kPa
< 5 x 10-9 cm/sec @ 14 kPa
18
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Table 2.7 Claymax® GCL Material Specifications
PROPERTY
BENTONTTE
PROPERTIES
**
ADHESIVE
PHYSICAL
PROPERTIES
HYDRAULIC
PROPERTIES
Sodium
Montmorillonite
Content
Free Swell
Fluid Loss
Moisture Content f
Adhesion
Thickness (excluding
fabric)
Composite Thickness
Wide Width Tensile
Grab Tensi le
Bentonite Content f
@ 20% moisture
Shear Resistance
Hydrated
Dry
Permeability
A) 14 kPa Effective Stress
B) 200 kPa Effective Stress
Permeability
(14 kPa effective stress)
C) 50 mm Overlapped
Claymax (without the use
of granular bentonite
between the seams)
D) Damaged Claymax
(3 each, 25 mm holes)
E) Claymax underneath
damaged HOPE geo-
membrane (25 mm hole)
F) after 3 Wet/Dry Cycles
G) after 5 Freeze/Thaw
Cycles
TEST
METHOD *
X-Ray
Diffraction
USP-NF-XVII
API 13 B
ASTM D4643
Visual
ASTM D1777
ASTM D1777
ASTM D4595
ASTM D4632
Weigh
1 2" X Roll Width
ASTM
D35.01.81.07
(draft)
ASTM D5084
ASTM D5084
ASTM D5084
ASTM D5084
ASTM D5084
ASTM D5084
ASTM D5084
UNITS
%
ML
ML
%
MM
MM
N/MM
N
KG/M2
DEC
DEC
CM/S
CM/S
CM/S
CM/S
CM/S
CM/S
CM/S
CLAYMAX STYLE
200R
90 (typ)
27 (MARV)
12 (Max. A.R.V.)
20 (typ)
Continuous Adhesion
to Backing Material
4.3 (MARV)
5 (MARV)
11 (typ) tt
400 (MARV) ft
4.6 (MARV)
>10
>35
5 x lO'9 (Max. A.R.V.)
< 5 x lO'10 (typ)
< 5 x 10'9 (typ)
<5xlO'9 (typ)
< 5 x lO'9 (typ)
< 5 x 10'9 (typ)
<5xlO'9 (typ)
CLAYMAX STYLE
500SP
90 (typ)
27 (MARV)
12 (Max. A.R.V.)
20 (typ)
Continuous Adhesion
to Backing Material
4.3 (MARV)
5 (MARV)
18 (typ)
400 (MARV) tt
4.6 (MARV)
>40
>40
5 x lO'9 (Max. A.R.V.)
< 5 x 10'10 (typ)
< 5 x 10'9 (typ)
N/At
N/A*
N/At
N/At
* Standard test methods modified where appropriate to facilitate testing a Geosynthetic Clay Liner (GCL).
** Properties of bentonite removed from finished GCL product.
t D4643 modified to included wet weight as the denominator.
tt Machine (warp) direction of primary backing.
t Testing in progress.
19
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Table 2.8 Partial List of Claymax® Hydraulic Conductivity Testing Data
RANGE OF RESULTS
Standard
CLAYMAX 200R
CLAYMAX 500SP
25 mm hole prior to hydration*
50 mm overlapped seam*
2-4 x 10'9 cm//sec
2-4 x 10'9 cm/sec
3-5 x 10~9 cm/sec
3-5 x 10~9 cm/sec
* = self-healing tests on damaged liner and tests on overlapped seams were performed on both CLAYMAX 200R and
CLAYMAX 500SP.
Testing Parameters (ASTM D5084)
• 100-150 mm permeameter cells
• 5 kPa during hydration
• 14 kPa effective stress during consolidation
Table 2.9 Partial List of Claymax® Frictional Resistance Data
INTERFACE
PBM: smooth HOPE
PBM: textured HOPE
SBM: smooth HOPE*
SBM: textured HOPE*
SBM: textured VLDPE
PBM: sand
PBM: #57 stone
INTERNAL
CLAYMAX 200R
CLAYMAX 500SP
FRICTION ANGLE (°)
12
22
11
24
30
29
31
FRICTION ANGLE (°)
12
N/A
ADHESION (KPA)
1
1.9
3
1.4
2.4
0
1.6
COHESION (KPA)
0.2
24
PBM = Primary Backing Material
SBM = Secondary Backing Material
* = test done on CLAYMAX 500SP
20
-------
the GCL, the bentonite can either be a Wyoming sodium bentonite or a treated,
contaminant-resistant bentonite. The geomembrane can be either a HOPE or
VLDPE with a thickness ranging from 20 to 80 mils (0.5 to 2.0 mm). Textured
geomembranes can be used, as well.
Gundseal® can be installed in two ways. The first configuration is with
the geomembrane side facing downward against the subgrade, and with the
bentonite side facing upward against an overlying geomembrane, forming a
composite system. The second configuration is with the bentonite side facing
downward against the subgrade. Certain design criteria must be applied
depending on how the Gundseal® is to be installed.
2.4.1 Gundseal® Composite System
When Gundseal® is applied underneath a geomembrane with the
bentonite side facing upward, a composite liner system is formed. The success of
the composite system is a function of the hydraulic conductivity of the system,
the effectiveness of overlapped seams, the degree of intimate contact with
overlying geomembrane, the internal shear strength of the bentonite, and the
interfacial friction resistance between the components of the system.
2.4.1.1 Hydraulic Conductivity
The hydraulic conductivity of an intact specimen of Gundseal® has been
reported to be less than 4x10'12 cm/s. Researchers at the University of Texas
(Daniel & Shan, 1992) and at GeoSyntec Consultants (1991) have reported that
the bentonite element of Gundseal® alone has a hydraulic conductivity between
IxlO'9 and IxlO'10 cm/s. Therefore, the 3 mm thick layer of bentonite, when
considered by itself, is equivalent to at least 300 mm of IxlO'7 cm/s clay. The
Gundseal® system, consisting of the geomembrane and the layer of bentonite, is
equivalent to well over 900 mm of IxlO'7 cm/s clay.
2.4.1.2 Overlapped Seams
When Gundseal® panels are overlapped, close contact is developed
between the bentonite portion of one panel and the geomembrane portion of the
other. Researchers at the University of Texas (Estornell, 1991) investigated the
effectiveness of this overlap by performing large scale tests on two separate
overlapping specimens. One sample had an overlap of 40 mm, while the other
21
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sample had an overlap of 75 mm. Two feet of gravel and one foot of water were
placed over each of the specimens. During the five-month-long test, no outflow
was noted through either of the overlapping specimens. Additional testing has
been performed by GeoSyntec Consultants (1991) and no flow was noted
through the overlapped seams after one hundred hours.
2.4.1.3 Composite Action
The effectiveness of the overlapped seams indicates that a good composite
action is formed between a geomembrane and the hydrated bentonite.
Additional research at the University of Texas (Estornell, 1991) has shown that
the bentonite portion of Gundseal® is able to seal off defects in an overlying
geomembrane. At the University of Texas, slits and holes were cut into a
geomembrane. This geomembrane was placed on top of the bentonite portion of
Gundseal®, and the system was covered with gravel and water. These tests were
performed for five months, during which time no flow was observed through the
system. After five months, the tests were dismantled and the condition of the
GCL was observed. Around the largest hole (75 mm diameter) in the
geomembrane, only a 130 mm diameter area was wetted on the bentonite, thus
indicating excellent intimate contact and composite action (Fig. 2.7).
The effectiveness of intimate contact between Gundseal® and an
overlying geomembrane was also investigated by the engineers at GeoSyntec
Consultants (1991). Their results indicated that the hydrated bentonite can
effectively seal a defect in an overlying geomembrane. Water contents were
taken from the bentonite portion of Gundseal® directly beneath a 1 mm diameter
hole. The water content tests indicated a significant reduction in the water
content of the bentonite radially away from the hole (Fig. 2.8).
2.4.1.4 Internal Shear Strength
The internal shear strength of the bentonite portion of Gundseal® has
been investigated by both the Geosynthetic Research Institute (1991) and the
University of Texas (Daniel and Shan, 1992). The internal friction angle for the
bentonite portion of Gundseal® in an unhydrated state (water content = 17%)
was found to range from 22° to 26°. The manufacturer states that due to the
effectiveness of composite action with an overlying geomembrane, the bentonite
portion of Gundseal® will remain basically unhydrated. Thus the internal
22
-------
T
2.4m
I
Hydrated Areas
75 mm Diameter
Unhydrated Area
100-125 mm
Figure 2.7 Composite Action Test with Overlying Defective Geomembrane
(after Estornell, 1991)
23
-------
Initial Specimen Conditions:
Final Specimen Conditions:
Water Content - 7.3%
Water Contents:
- Section A- 77.2%
- Section B - 30.2%
- Section C - 24.0%
Figure 2.8 Variations in Bentonite Water Content beneath a Defective
Geomembrane (after Geosyntec Consultants, 1991)
24
-------
friction angle of 22° to 26° can be used by designers if the bentonite remains
"dry/7
2.4.1.5 Interfacial Friction Resistance
The interfacial friction angle between the smooth sheet geomembrane
portion of Gundseal® and the subgrade soil can be assumed to be approximately
16° (Koerner, 1990). If a higher interfacial friction resistance is necessary, the
interfacial friction angle between a textured geomembrane portion of Gundseal®
and the subgrade soil can be assumed to range from 25° to 32° (Koerner, 1990).
The interfacial friction angle between the dry bentonite portion of
Gundseal® and the overlying geomembrane can be assumed to be 16° for smooth
sheet (Koerner, 1990) and 32° for a textured sheet (Westinghouse Inc., 1991).
2.4.2 Gundseal® as a Single Liner System
In some cases, engineers and designers desire to use Gundseal® as a
single liner system. This can occur in liner systems for reservoirs, disposal sites,
and at hydrocarbon storage tank facilities. The major factors affecting the
performance of Gundseal® in these areas are soil suction, hydraulic conductivity,
internal shear strength, and subgrade contamination.
2.4.2.1 Soil Suction
The University of Texas (Daniel and Shan, 1992) recently completed a
study on the effect of subgrade moisture content on the bentonite portion of
Gundseal® when the GCL was installed beneath a layer of medium grained sand
with the bentonite side of Gundseal® in contact with the sand. It was found that
the dry bentonite has a very high suction value of 7500 kPa and will draw
moisture from the sand. The amount of moisture "sucked up" by the bentonite
depends upon the moisture in the sand. Equilibrium can be reached between the
bentonite and the sand in a period varying from 2 to 14 days (Fig. 2.9).
2.4.2.2 Hydraulic Conductivity
If the bentonite side of Gundseal® is placed in contact with the subgrade
soil, the bentonite will hydrate. Depending on the initial water content on the
subgrade soil, the final water content of the bentonite can range from 50% to
over 145%.
25
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.t=J
I
I
i
3
Water Content of Sand = 1%
10
20 30
Time (days)
40
50
Figure 2.9 Water Content vs. Time for Samples of Gundseal® Placed Within
Sands of Varying Water Content (Daniel & Shan, 1992)
The hydraulic conductivity of the bentonite portion of Gundseal® as a
function of the initial water content of the bentonite was recently studied at the
University of Texas (Daniel and Shan, 1992). Various hydrocarbons were used as
the permeant liquid in the study. The results are shown in Table 2.10.
2.4.2.3 Internal Shear Strength
The internal shear strength of the bentonite portion of Gundseal® has
been investigated by both the Geosynthetic Research Institute (1991) and the
University of Texas (Daniel and Shan, 1992). The internal friction angle for the
bentonite portion of Gundseal® in a hydrated (wet) state was found to 19° at a
total normal stress less than 36 kPa, and 7° at higher normal stresses. Therefore,
care must be taken to take into account the effect of normal stress when using a
friction angle in a stability analysis.
26
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Table 2.10 Permeability to Various Hydrocarbons as a Function of Initial
Bentonite Water Content (Daniel & Shan, 1992)
PERMEANT LIQUID
Benzene
Gasoline
Methanol
MTBE
TCE
Water
WQ = 17%
3 x 1(T5
4xlO'5
3 x 1(T5
2xl(T5
4xlO-5
2 x 1(T9
PERMEABILITY (CM/S)
WQ = 50% wo = 100% WQ = 125%
2 x 10'5 5 x 10'9 No Flow
4 x 10'5 4 x 10'9 No Flow
3 x 10'5 3 x 10'9 No Flow
3 x 10'6 <1 x 10-9 No Flow
4 x 10'5 3 x ID'8 No Flow
..
WQ = 145%
No Flow
No Flow
No Flow
No Flow
No Flow
--
2.4.2.4 Seams
When Gundseal® is installed with the bentonite side facing down, the
manufacturer recommends that tape be placed along the seam to prevent
overlying cover soils from separating the seams.
Alternatively, the overlapping geomembrane of the Gundseal® can be
heat seamed with fillet extrusion welding, or cap strip seams, to form a seamed
membrane composite barrier.
2.4.2.5 Geotextile Separator
When placed in contact with the subsoil, the bentonite portion of
Gundseal® will draw in moisture and become hydrated. While this reduces the
permeability to hydrocarbons, it also reduces the internal friction angle of the
bentonite. Therefore, in order to maintain the integrity of the bentonite and to
prevent contamination from the lower soils, it may be necessary, in cases of
nonuniform subgrades, to use a geotextile to maintain a separation between the
bentonite and the lower subgrade soils.
27
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2.4.3 Conclusion
Research has indicated that Gundseal® is an effective replacement for clay
in landfill liner systems and covers. Concern has been expressed, upon occasion,
by engineers, contractors, and regulators that the thin geosynthetic clay liners,
such as Gundseal®, are susceptible to damage during installation. However, the
installation of geosynthetic clay liners is much easier than the construction of
compacted clay liners, and when the contractors utilize the same care that is
needed to install a geomembrane, an effective liner or cover system is in place
and protecting the environment.
28
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CHAPTER 3
TESTING PROCEDURES
As GCLs are still relatively new to the market, the methods used to test
and to interpret these tests are still in their initial stages. Each of the major GCL
manufacturers is currently working to create standard methods of testing these
products. Until these standards are completed, it will be up to testing companies
and design engineers to decide how to set up and interpret the results of testing
on GCLs. The major problem is variable results arising from different testing
procedures.
Three speakers were given the opportunity to speak directly about testing
procedures. The first spoke about the number of different ways one can assess
the quality of the bentonite being used in the GCL product. The second spoke
about the number of laboratory tests one can perform in order to determine the
basic design parameters necessary to decide whether the product will perform as
anticipated. The third spoke specifically about how to determine and interpret
the shear strength of a GCL.
3.1 Quality Assessment for Bentonite Sealants (By Richard K. Brown,
WYO-BEN, Inc.)
The use of bentonite as an environmental sealant in the development of
low permeability horizontal barriers to fluid movement has become an accepted
and standard practice in landfill and lagoon construction for waste containment.
Despite this, and despite the fact that there are an abundance of methods
available for assessing quality in bentonite, there is as yet no standard practice or
accepted criteria for assessing the quality of the bentonite which is used in this
capacity. This paper presents a summary of those methods which may be used
for this purpose, along with a brief discussion of the suitability of each method
for this task.
3.1.1 Bentonite
Any discussion of test methods used to define bentonite quality would be
incomplete without a brief discussion of what bentonite is and how it works.
29
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Bentonite is a clay composed primarily of the crystalline, hydrous
alumino-silicate mineral montmorillonite. As a result, the unique
physicochemical characteristics of montmorillonite define the performance
capabilities of bentonite. Montmorillonite particles typically exist as minute,
very broad, extremely thin, three-layered crystals which have negative electrical
charges expressed on their surfaces. The presence of these charges causes
inorganic cations and polar molecules, such as water, to be attracted by and
absorbed to the montmorillonite crystal surfaces. There is strong evidence to
indicate that water which is absorbed by montmorillonite crystals becomes
bound in layers many molecules in thickness in a crystalline or quasi-crystalline
arrangement similar to that found in ice. The thickness of the bound water layer
is controlled by the negative electrical charge density on the montmorillonite
crystal surfaces. This is modified, however, by the effect of the particular
absorbed cations which are present, with sodium ions (Na+) enhancing the effect
while all other cations diminish it to varying degrees.
In dry bentonite, montmorillonite crystals tend to be arranged in a densely
packed surface to surface facing structure similar to the arrangement of cards in a
deck of cards. Water added to dry bentonite will be absorbed onto the crystal
surfaces causing adjacent crystals to move further apart. This expansion will
continue, as more water is added to the system up to the adsorption limits of the
montmorillonite. This process is the cause of the swelling phenomenon observed
when bentonites are wetted.
Studies have shown that the crystalline nature of the water absorbed by
montmorillonite crystals appears to cause it to be immobile or to act as a highly
viscous fluid, depending upon the hydraulic gradient under which it is placed. It
is this resistance to flow found in the absorbed water layer on montmorillonite
crystals which is the fundamental basis for the sealing capability exhibited by
bentonite.
As a result, those test methods which can be used to define the water
adsorption and swelling capability of bentonite should offer the best possibility
of indicating sealing capability. This statement holds true only for natural,
untreated bentonite or bentonite products, however. Many of the additives
which are commonly used to treat bentonite sealants mask this mechanism
making the definition of bentonite quality very difficult to accurately determine.
30
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3.1.2 Primary Test Methods
The methods presented here are those which, directly or indirectly, define
the sealing capability of bentonite and appear to offer the most promise, either
singularly or in combination, for defining quality in bentonite sealants.
3.1.2.1. Permeameter Testing
By far the best, most accurate and most direct way of assessing the quality
of a bentonite sealant would be to test its hydraulic conductivity under a
standard set of test conditions. Several bentonite manufacturing companies
have, in fact, established permeability performance tests specific for their own
products. Unfortunately, these tests often vary in their methods and conditions
making broad comparisons between products difficult. Although a standard test
method now exists to facilitate this type of testing (ASTM D 5084-90) there has, to
date, been no unified effort by any group to establish test conditions under which
such quality testing might be accomplished. Nevertheless, standard test
conditions for permeameter testing can be adopted by testing firms for project
specific comparison testing in order to determine relative quality of competing
bentonite sealant products.
The absence of any standardized hydraulic conductivity test data for
bentonite sealant products, coupled with the high equipment cost for
permeameters and slowness in obtaining test results, has led to the use of a
number of other test methods which serve as indirect indicators of sealing
capability.
3.1.2.2 Swell Tests
Swell tests measure the ability of a bentonite to adsorb water by
measuring the increase in volume of a mass of bentonite which occurs during the
adsorption process. Several methods are available which allow measurement of
various aspects of the swelling characteristic.
3.1.2.2.1 Free Swell Test
This test method measures the swollen volume of a sample of powdered,
dried bentonite which has been added in numerous small increments over a
period of time to 100 ml of distilled water in a 100 ml graduated cylinder.
Measurement of bentonite volume is made from the gradations on the cylinder.
31
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Typically, this measurement is taken after the cylinder has set, undisturbed, for 2
to 24 hours following the final bentonite addition. In theory, this procedure gives
the test bentonite the opportunity to adsorb water and swell in an uninhibited
and unconfined fashion yielding a good representation of the swelling capacity
of the clay. This method is easily used, requires little equipment, and typically
has good reproducibility, Variations in the rate of bentonite addition, the
amount of bentonite added at each addition, and the setting time allowed can all
affect the result, however. Despite this, the results of this test method appear to
correlate well with the results of hydraulic conductivity testing. Although no
standard method currently exists for this test, one is now being developed by
ASTM.
3.1.2.2.2 Modified Free Swell Tndp*
This test method, developed by Sivapullaiah et al. (1987) for clays
generally, measures the settled volume of clay sediment resulting from 3
additions of clay which have been mixed into a volume of water, typically 100
ml, in a graduated cylinder of suitable size, and then allowed to set, undisturbed,
for 24 hours. The sediment volume is measured using the graduations on the
cylinder. The resulting volume is then used to calculate the "Modified Free Swell
Index" of the clay using a formula which takes into account both the weight and
specific gravity of the solids used. This test is relatively simple to conduct and
appears to have good reproducibility for most bentonite materials. The
definition of sediment layer boundaries can be a problem when testing some
high quality natural sodium bentonites as well as with some treated bentonite
products, however. Reschke and Haug (1991) report that the results of this test
method show good correlation with the results of hydraulic conductivity testing
for compacted soil /bentonite mixtures (not pure bentonite).
3.1.2.2.3 Swelling Pressure Test
This test is included here because intuition suggests that swelling pressure
should inversely correlate strongly with hydraulic conductivity. No published
data have been found which establishes this correlation, however. Measurement
of the pressure exerted by hydrating bentonite as it adsorbs water and swells in a
confined space is typically done using consolidometers (Oscarson, et al., 1990).
32
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As a result, this test requires both sophisticated equipment and personnel in
order to properly conduct it. This may limit the wide spread use of this method.
3.1.2.3 Plate Water Absorption (PWA) Test
This test method measures the ability of a sample of powdered, dried
bentonite to "absorb" water when placed on a piece of filter paper on a porous
stone in a covered, water filled tray for 18 hours. The procedure for conducting
this test has been standardized as ASTM E 946. When properly conducted this
test is accurate to approximately ± 5%, with test values for bentonites ranging
from 200 to 1100. The test is very sensitive to a number of conditions, such as
variations in the thickness of the bentonite sample on the filter paper, the number
of samples placed on each porous stone, the water level within the test tray, and
to even minor fluctuations in temperature during the period of the test. Failure
to adequately control these can result in swings in test results and very poor
reproducibility. As a result experienced personnel are required for this test in
order to obtain consistent results. Results from this test method appear to
correlate well with the results from hydraulic conductivity testing and with the
results of free swell testing. There appears to be very poor correlation between
PWA test results and modified free swell test results, however.
3.1.2.4 Liquid Limit Test
This test, as standardized in ASTM D 4318, sets forth a method for
determining the water content of a soil at the boundary between the soil's plastic
and liquid states. This method provides us another way to measure the water
adsorption capability of bentonite. Sivapullaiah et al. (1987) state that the liquid
limit, when expressed on a volume basis (volume of water to volume of soil),
shows a strong correlation with the modified free swell index test results.
Limited data presented by Reschke and Haug (1991) suggests a strong
correlation between liquid limit (as normally calculated) and both the modified
free swell index and hydraulic conductivity test results for high quality sodium
bentonites. These same data suggest little correlation for low quality sodium
bentonites. The simplicity of this test makes it a desirable one for use in
assessing sealing bentonite quality. However, additional testing is necessary to
establish the relationship between liquid limit and hydraulic conductivity.
33
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3.1.3 Secondary Test Methods
The methods described here are those which may be used in addition to
the primary test methods to further assist in defining quality in bentonite
sealants. These methods do not, by themselves, yield enough information to be
used as independent tests. As a result these tests should never be used as the
sole criterion in determining bentonite quality.
3.1.3.1 Apparent Colloid Content Test
This test method measures the fraction of a 2% water-dispersed sample of
bentonite that remains in suspension after an 18 to 24 hour settling period. In
theory, this test should be capable of measuring the montmorillonite content of a
bentonite sample because montmorillonite crystals should all be smaller than the
0.5 micron size threshold delimiting colloidal size particles which, by definition,
are small enough to stay permanently in aqueous suspension. Unfortunately,
factors such as incomplete sample dispersion, flocculation due to chemical
contaminants, and the effects of various additives all act to bias the test results.
In effect this test is simply a larger version of the Modified Free Swell Index Test
which was previously described, although different methods of analysis are used
in this method. When analyzed using the criteria of the Modified Free Swell
Index Test the results produced by the apparent Colloid Content Test do not
duplicate the results of the other test. Further, the Apparent Colloid Content Test
does not correlate strongly with the any of the primary tests, exhibiting only
moderate correlation with the Free Swell Test and the PWA Test.
3-1-3.2 X-Ray Diffraction (XRD) Mineralogical Analysis
X-Ray Diffraction analysis of a bentonite sample can be used to determine
its approximate mineralogical composition. However, because XRD is a semi-
quantitative method absolute percent compositions are not possible. Further,
while some inferences can be drawn from the results of this test as to the quality
of the montmorillonite crystals in a sample it is not possible to make any accurate
statements about sealing capabilities of the bentonite sample being tested based
solely on XRD results. At best, this method can be expected to provide only a
close approximation of the amount of montmorillonite present in a sample.
34
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3.1.3.3 Cation Exchange Capacity (CEC)
The methods used to determine CEC measure the negative charge present
on the montmorillonite crystals in a bentonite. Although other, more accurate
methods are available, the CEC of bentonite is most often measured by
determining the ability of a sample to adsorb the positively charged dye,
methylene blue. The Methylene Blue Dye Test has been standardized by the
American Petroleum Institute. The Methylene Blue Dye Test is capable of
yielding consistent, reproducible results when properly performed, although
these results are generally slightly lower than those produced by other CEC
determination methods.
3.1.3.4 Specific Surface Area
This test provides a measure of the montmorillonite crystal surface area
upon which water can potentially be adsorbed. Generally, higher surface area
values should be indicative of high quality bentonites having low hydraulic
conductivity. Limited data presented by Reschke and Haug (1991) show only
moderate correlation between surface area and hydraulic conductivity.
3.1.3.5 Chemistry
Definition of the gross chemical composition of bentonite, using X-Ray
Fluorescence or wet chemistry techniques, as well as definition of the
exchangeable cations present, using both wet chemistry and flame photometry,
can offer insights into bentonite quality. For example, Reschke and Haug (1991)
found that a strong correlation existed in the bentonites they tested between the
SiO2Al2O3 ratio and the quality of the material, while Alther (1986) found the
ratio of exchangeable sodium, calcium and magnesium had a significant effect on
the rheological and contamination resistance properties of bentonite. It must be
remembered, however, that the results of bentonite chemical analysis are only
useful when they are evaluated in the context of the results from other testing. A
wide variety of relationships between gross chemical and exchangeable cation
chemistries which would yield similar quality bentonites are no doubt possible.
3.1.4 Conclusion
Quality in bentonite sealants is specifically defined by the level of
impermeability or hydraulic conductivity achievable by a particular bentonite.
35
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Permeameter testing under a set of standard test conditions, therefore, offers the
most direct method of determining the quality of a bentonite sealant product.
Where this cannot be done, the water adsorption and swelling capabilities of a
bentonite, which are both fundamental characteristics of the sealing process, may
also be tested as indirect indicators of sealing effectiveness. A variety of test
methods may also be employed to define other bentonite characteristics such as
mineralogical composition, specific surface area, cation exchange capacity, and
others which, in combination with the results of water adsorption and/or
swelling tests, can serve to give a more complete picture of the quality of
bentonite sealants. However, additional test methods do not provide sufficient
information about the mechanism of the sealing process to enable them to be
used independently or as the principal method for determining bentonite sealant
quality.
3.2 Conformance Testing of Geosynthetic Clay Liners (By John Boschuk, Jr.,
J & L Engineering, Inc.)
As part of important construction activities using man-made or natural
materials, the engineer needs verification that specific materials for the project
conform to the design requirements and will perform as anticipated. Over the
past several years, a number of basic tests for each of the major geosynthetic
types have evolved and are included in specifications as conformance tests.
These tests are typically performed on material samples taken from the rolls as
they are manufactured or from the rolls on-site before the material is deployed.
Geosynthetic clay liners are increasingly being used in many projects and
may be considered relatively new to many engineers and regulators.
Conformance testing for these products is not yet well defined. The purpose of
this discussion is to suggest guidelines for testing methods and test frequencies
necessary to verify conformance of the materials with the design engineer's
requirements.
Unlike most other single-material-component geosynthetics, GCLs are a
combination of two or three different elements fused together to create a single
composite material. Two of the three elements consist of man-made
geosynthetics and the third is a processed natural material containing additives
36
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to bond the particles, assist in fusing the material to the geosynthetic or to
improve performance of the bentonite.
Considering the differences in the products, two basic choices exist for
conformance tests:
1) Test the individual elements of the composite.
2) Test the composite as a single material.
The first option is generally very difficult to exercise since the components
are bonded together. Separating the layers to perform tests on each material
component would probably damage the components and yield misleading test
results. Consequently, it is more logical to test the products as a composite.
Furthermore, the designer selected the material to function as a composite and
the design is based on the geosynthetic working as a composite.
3.2.1 Testing Options
As part of the research for this paper, the author queried the major users
of the material to determine what conformance tests they typically perform on
GCLs. Not surprising, testing has generally been limited to hydraulic
conductivity of the GCL, coupled with manufacturer's certifications. Often no
conformance testing is performed and verification is limited only to
manufacturer's certifications.
Further research indicates that no specific conformance, or even quality
control, testing of these products is typically specified other than hydraulic
conductivity. Verification is usually limited to visual inspections and visual field
checks to insure the material is not saturated until it is sealed and covered with a
confining load.
Before suggesting test protocols, an evaluation of the engineering
properties is warranted. First and foremost, the GCL products are being
marketed as a low permeability barrier. Consequently, hydraulic conductivity
and compatibility with the liquid to be retained should be emphasized.
However, there are several other important considerations, e.g., shear strength.
37
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3.2.1.1 Shear Strength
As part of the design, the engineer may need to evaluate shear strength of
the composite and develop design properties for the material. Once production
of the material commences, verification of conformance to performance
characteristics would then be warranted.
3.2.1.2 Tensile Properties
For some designs the product may be subject to short term tensile stresses
such as during deployment. In this case the engineer would determine what
allowable tensile loads can be applied to the product without adversely affecting
other properties. Once these maximum allowable stresses are determined,
conformance testing would be specified to insure that the production materials
meet these standards.
In other instances, a design may require the product to be subjected to
unavoidable long term or residual stresses. If this is the case, long term creep
strains may occur and reduce its performance characteristics. Once the engineer
determines the maximum allowable sustained stress, criteria can be established
for design testing to verify material capabilities. Due to the duration of creep
testing, conformance testing is probably not warranted if the design carefully
considers these conditions.
3.2.1.3 Puncture Resistance
These products all have some puncture resistance capability. The
engineer's design testing program would evaluate how the material will perform
under the design conditions. Conformance testing is most likely not warranted
to verify this property. Competent field visual observations to insure that the
GCL is installed properly should suffice to insure performance.
3.2.1.4 Biaxial Stresses
Under certain conditions GCLs may be subject to differential settlements
such as in landfill cover systems. As part of the design, the engineer may
perform tests to assess performance and to establish design parameters. These
assessments may include biaxial stress tests followed by other engineering tests
on the stressed material. With these properties established, conformance testing
38
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under biaxial conditions may be warranted to verify material compliance with
critical design criteria.
3.2.1.5 Freeze-Thaw and Desiccation
GCLs contain bentonite which can be subjected to freeze-thaw and
desiccation that may affect performance. As part of the design process, these
conditions are evaluated and the design adjusted to accommodate these
concerns. Although conformance testing may be warranted under certain unique
conditions, bentonite supplied for these products is generally very uniform and
accompanied by supplier certifications and supplier QC testing. Research to date
also indicates that bentonite has unique healing properties after freeze-thaw and
desiccation. Proper design to accommodate freeze-thaw and desiccation,
coupled with supplier testing and certification documents, will most likely be
sufficient to insure satisfactory performance.
3.2.2 Suggested List of Conformance Tests for GCLs
Considering these design and performance elements a suggested list of
conformance tests is presented as a recommendation to design engineers:
3.2.2.1 Hydraulic Conductivity Testing
Two types of hydraulic conductivity tests are available: flexible-wall
permeameters (ASTM D5084) and rigid-wall permeameters. A schematic of each
is presented in Fig. 3.1 and 3.2. A modified large-scale rigid wall apparatus,
which is large enough to test seams in these products, is shown in Fig. 3.3. When
specifying these tests, it is recommended that the permeant be similar to the
liquids which will be exposed to the in-place material. Hydraulic gradients and
pressures should be specified by the engineer. Extreme care should be exercised
to insure the material is saturated and sealed at the sample edges.
3.2.2.2 Shear Strength Testing
Direct shear tests through the plane of bentonite can be performed on
either the standard 100 mm shear box or 305 mm shear box. J&L Engineering has
performed comparative tests with these products using both types of apparatus
and found the 100 mm shear box to be satisfactory for GCL materials. The
engineer should specify normal loads, rates of strain, liquid of saturation, fixity
39
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conditions, and preferred size of sample. Figures 3.4 and 3.5 present schematics
of the test configurations and fixity conditions.
Vent Port
Top Plate
Acrylic Tube
Porous Disks
Geosynthetic Clay
Liner (GCL)
66 to 150 mm
Dia. Sample
Base Pedestal
Base Drain
Top Drain
O-Ring
O-Ring
Latex Membrane
Sand
O-Ring
Bottom Plate
Base Drain
Top Drain
Figure 3.1 Flexible-Wall Apparatus
40
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Pressure
Chamber
Line
Vent Line
Influent Line
Pressure
Chamber
Porous
Disks
Sand
Loading
Piston
Geosynthetic Clay
Liner (GCL)
64 mm Dia. Sample
Silicon Seal
Effluent Line
Vent Line
Figure 3.2 Rigid-Wall Apparatus
41
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Piston
Overlap
ofGCL
Pressure
Chamber
Line
Vent
Influent Line
Effluent Line
Water under
Pressure to Apply
Confining Load
O-Ring Seals
Porous Disk
GCL
Figure 3.3 Large Diameter Rigid-Wall Apparatus
42
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(Fixed)
Normal Stress Loading Device
Normal Stress Indicator
Clamp
Shear
Force
Loading
Device
(Fixed)
Upper (Fixed) Box
(300 mm x 300 mm min.)
Clamp
Direction of Travel
Shear Force Indicator
Displacement Indicator
Lower (Travelling) Box
(300 mm x 300 mm min.) Bearings
Figure 3.4 Typical Direct Shear Friction Apparatus Schematic
FIXED/FIXED
Failure Constrained to
G eosynthetic/Geosynthetic
Interface
FKED/FREE
Failure along
S upeistrate/Geosynthetic
Interface Prevented
FREE/FREE
Unconstrained Failure
Figure 3.5 Geosynthetic/Geosynthetic Direct Shear Testing
43
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3.2.2.3 Tensile Property Testing
For short term peak stress considerations, wide-width tensile testing per
ASTM D4595 is the most appropriate nationally recognized test procedure
available (Fig. 3.6). Care must be exercised to insure that the multiple composite
is properly clamped. The engineer may have to specify the grip type to insure
comparable results between the design and conformance tests, which may be
performed by different laboratories. As previously discussed, peak stresses may
develop during deployment of the GCL. Therefore, this testing would be
performed on the dry products.
Deflection
Gage
200mm
i
!
k
r
Load Cell
Sample
100mm
Clamp (typ.)
Figure 3.6 Wide Width Tensile Test Schematic (Source: John Boschuk)
Creep testing is probably not warranted in that the design addresses this
issue and creep testing requires a long period of time to perform. If required to
insure compliance, the material should be saturated with the same type of liquid
the product will be exposed to in the field (Fig. 3.7).
44
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45
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3.2.2.4 Biaxial Stress Testing
Biaxial testing per GRI Test Method GM4 can be specified as a
conformance test to assess material bonding performance under conditions
similar to those in the field. The fluid used in the test should be similar to the
fluid the material will be exposed to in the field. The engineer should specify the
fluid, pressures, rate of pressure increase and allowable deflections (Fig. 3.8).
Water
Inlet
Original
GCL
Pressure
Gauge
Deformation
Rod
Air Vent
Vent
Deformed
GCL
Figure 3.8 Biaxial Test Apparatus Schematic (Source: John Boschuk)
46
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3.2.3 Testing Frequency
Typically, conformance tests are performed at a rate of one test series per
9000 m2 of product manufactured during a single run. If products are obtained
from a stockpile consisting of materials from different runs, testing frequencies
should be increased to insure that all runs are adequately tested. Recently, at
several projects of which Mr. Boschuk is aware, the testing frequency has been
increased to one test series per 4600 m2 of product. The engineer may have to
negotiate this frequency with regulatory authorities.
3.2.4 Conclusion
GCLs are relatively new to the industry and conformance tests are still
evolving. This presentation attempts to present technical considerations to
establish a conformance test program for GCLs which focuses on verification of
the designed performance properties of the product for its specific application.
Testing frequencies have also been suggested based on the testing frequencies
used for other geosynthetic materials.
It is important to note that these products are still evolving.
Manufacturers may be adjusting and changing the geosynthetics used in their
products, adjusting the methods of bonding the materials and even the types and
distribution of the bentonite used in the products. It is important that whatever
product is evaluated in the design be the same product used in the field.
Specifications need to address this issue and the manufacturer should be
consulted to insure the product tested in the design is the same product used
during construction.
3.3 The Determination and Interpretation of Shear Strength (By Robert
Bachus, GeoSyntec Consultants)
The topic of shear strength is familiar to anyone associated with
geoenvironmental engineering. With the development of geosynthetic clay liners
(GCLs), engineers are now faced with the task of evaluating the ability of GCLs
to transmit shear at an interface, or through the liner system. The solution to this
is to simulate expected field conditions in the laboratory in an attempt to model
and test the expected mode of shearing failure. The problem is that the "shear
strength" of the GCL is actually composed of three distinct components (internal
47
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shear strength, interfacial frictional resistance, and tensile strength). This
breakdown into the different components of shear strength coupled with the fact
that lab and/or field conditions greatly influence their value, makes the
fundamentals of shear strength much more complex than most people realize.
3.3.1 Test Conditions
The shear strength of a GCL must be determined under conditions
matching those anticipated in the field. When incorporating a friction angle into
a slope stability analysis one cannot expect any degree of accuracy if that friction
angle was determined under conditions varying widely from those in the field
analysis. The variation in normal stresses, degree and type of fluid hydration,
rate of shear, and method of failure are all important variables that a designing
engineer must consider.
3.3.1.1 Normal Stress
Over a small range of normal stresses there may appear to be a linear
relationship between normal stress and shear stress at failure (Mohr-Coulomb
failure envelope), but if taken over a broader range of normal stresses, this
relationship may not be linear. Therefore, the shear strength parameters of angle
of internal friction (<&') and cohesion (c') are not constant and depend upon the
range of normal stresses over which they are determined. Unfortunately, friction
angles and cohesion values are often published without any reference to the
normal stress at which they were determined. One must remember that O' and
c' are not inherent properties of a GCL, but rather a convenient way of
representing the shear and normal stresses acting along a plane at the time of
failure.
3.3.1.2 Hydration Conditions
In addition to the type of fluid and the length of time for hydration, the
method used to hydrate the GCL can affect the measured internal shear strength.
For example, prior to direct shear testing, a GCL sample can be hydrated under a
normal load in or out of the shear box. Due to sample disturbance caused by
unloading and reloading, the sample hydrated outside the shear box will have a
different shear strength than the undisturbed sample hydrated within the shear
box.
48
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Another concept to consider is when should a hydrated GCL be
considered saturated? The bentonite within a GCL is generally a non-
homogeneous mixture of individual nodules. These nodules will tend to adsorb
any free water. Thus, at what water content will adsorption cease, and the
sample be considered saturated?
3.3.1.3 Rate of Shear
One of the testing variables most often overlooked is the rate at which the
sample is sheared. The slower a hydrated sample is sheared, the more time
excess pore water pressures have to dissipate. Thus the shear strength of a
saturated GCL is directly related to how quickly the sample is sheared.
This is why geoenvironmental engineers specify whether the shear
strength parameters O' and c' are for drained or undrained conditions. If a
hydrated sample is loaded slowly enough that excess pore water pressures have
time to dissipate, then the test is considered drained. If an engineer performs a
long term slope stability analysis (i.e. drained conditions), he must test a
representative sample under drained conditions as well. Due to the low
hydraulic conductivity of sodium bentonite, a direct shear test cannot be carried
out in a day on a GCL. Using the methods proposed by Gibson and Henkel
(1954), the time to failure can be estimated for very soft clays as tfaiiure = SOtso,
where t5o is the time required to achieve 50% consolidation under the normal
stress being used. Using a constant shear rate of 0.02 mm/hr (1.31xlO-5 in/min),
researchers at the University of Texas (Daniel & Shan, 1991) found that the peak
shear stress was typically reached after 5 to 20 days of shearing for GCLs
incorporating sodium bentonite. Only two samples failed in less than five days.
Based on previous consolidation tests, the calculated minimum time to failure
was approximately 3 days. Thus, for these tests, the rate of shearing was slow
enough to ensure full dissipation of excess pore water pressure at the time of
failure.
Hydrated sodium bentonite clays have also been known to be susceptible
to creep. What effect does the long term sustained transmission of shear loads
have on the shear strength of a hydrated GCL? This question requires further
study.
49
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3.3.1.4 Method of Failure
The type of testing equipment can predetermine the mode of failure of a
GCL. A direct shear test would be used to determine the internal shear strength
of a GCL, while an inclined tilt table would be used to measure interfacial friction
resistance. Finding the tensile or internal shear strength of a stitch bonded or
needle punched GCL can be more difficult due to localized stress concentrations
caused by the stitching. Direct shear tests have been modified in order to force
the failure plane through the stitch or needle punch bonding.
3.3.2 Conclusion
While a lot of time and money can be put into measuring the shear
strength of GCLs, this information will not be very effective if it is not interpreted
correctly. One must remember that there is a non-linear relationship between
normal stress and shear stress at failure (curved failure envelope). Not only are
O' and c' affected by normal stress, but also by the degree and fluid of hydration.
The testing conditions must always be specified when determining the shear
strength of a GCL. These testing conditions not only should match anticipated
field conditions, but should also be listed with the final results in order that
others may understand how to interpret the results.
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CHAPTER 4
INTIMATE HYDRAULIC CONTACT WITH GEOMEMBRANE
4.1 Intimate Contact for GCL/Geomembrane Composite Liner Systems (By
John Bove, Hazen and Sawyer, P.C.)
The concept of "intimate contact" within composite liner systems for
waste disposal and storage facilities is not a new one. The intimate contact
approach is intended to minimize the lateral migration of fluid that may pass
through defects in the geomembrane, which is typically the upper component of
the composite liner. This concept enhances the contribution of the soil liner
component of the composite system in minimizing leakage through the liner and
discourages the use of a geotextile directly beneath the geomembrane.
Empirical and theoretical analyses of composite liner performance
persuasively highlight the advantages of intimate contact. Analyses indicate that
the presence of a high transmissivity drainage medium directly below the
geomembrane may increase the leakage rate through the liner by several orders
of magnitude compared with a composite system with good contact between the
components.
4.1.1 In-Situ Behavior of a GCL
Depending on the in situ conditions, the GCL may exhibit behavior
similar to anything ranging from a thin geotextile to a compacted soil liner in
good contact with the geomembrane. When considering the use of a GCL as a
substitute for the compacted soil component, it is important to understand the
mechanisms that may interrupt the ability to attain "intimate contact." Possible
mechanisms include:
• Excessive transmissivity within the upper GCL geotextile (e. g., an
excessively thick upper geotextile)
• Gaps, cracks, or breaks in GCL or at GCL panel ends
• Imperfections in overlapped GCL seams
• Localized wrinkles in GCL and/or geomembrane
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• Uneven GCL subgrade surface
If a designer, owner/operator, or regulator believes that the presence of
the mechanisms listed above, or any others not listed, will prevent "intimate
contact," the use of GCLs in place of soil may be restricted. This provides a
challenge to the producers and users of GCLs.
4.1.2 The Case For Geotextile Placement Within a Composite Liner
The use of a thin geotextile between the soil and geomembrane
components of the soil liner system, while providing a drainage pathway, can
only transmit a finite quantity of fluid that has passed through a geomembrane
defect. This quantity is one or two orders of magnitude less than the upper
bound theoretical volume predicted by research conducted by the EPA
(assuming that the quantity of leachate at a given hydraulic head is always
available at the defect location). For thinner geotextiles with relatively low
hydraulic transmissivity, the volume of fluid that can be laterally transmitted
may be smaller than the quantity of fluid potentially generated by consolidating
soils or the dehydration of a GCL.
Even though a quantity of fluid can be transmitted laterally, it must still
pass through the bentonite component of a GCL before it can be considered as
leakage through the composite liner. For an intact GCL having a hydraulic
conductivity in the range of IxlO'9 to lxlO-10cm/s, this is a difficult task. In
reality though, the flow through the system is most likely to be controlled by the
apparent hydraulic conductivity and transmissivity of GCL seams and defects,
rather than the upper layer geotextile alone.
In an effort to increase slope stability, a separate geotextile placed between
the geomembrane and the underlying soil liner may actually allow for the
dissipation of excess pore water pressures. Thus, an increase in the internal shear
strength is realized at the expense of an increase in lateral flow.
4.1.3 Evaluation of Potential Leakage Rates
A significant step in understanding the future role of GCLs in composite
liner systems would be to define "intimate contact" in terms that may be
measured in the laboratory or the field. Clearly a composite system can allow
"some" volume of lateral drainage and still function as intended. The Action
Leakage Rate (ALR) quantity of 187 L/hectare/day often used for double lined
52
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systems with leak detection layers can provide some perspective on allowable
leakage rates per defect.
For the evaluation of localized fluid transmission at the
geomembrane/GCL interface (i.e. where "intimate contact'' has not been
attained), the quantity of leakage through a defect is a function of the hydraulic
head, size of the defect, and the properties of the GCL. If a defect having an area
of 1 cm2 is considered with a constant head of 30 cm (1 ft), then the leakage
quantity through a GCL specimen is mainly a function of the following GCL
properties:
• Initial transmissivity of the upper GCL geotextile
• Rate of hydration of the bentonite
• Extrusion of bentonite into the upper GCL geotextile (i.e. long term
transmissivity of the upper GCL geotextile)
• Continuity of the leakage source (i.e. steady state)
• Vertical percolation rate through the GCL (initial and long term)
If it is assumed that bentonite can intrude into the pores of the upper
geotextile, the hydraulic transmissivity of that interface will decrease. While the
rate of leakage may be initially high, it could decrease with time to a level that is
insignificant in terms of the leakage quantities through the composite liner.
4.1.4 Ongoing Research
The issue of whether migrating bentonite can reduce the transmissivity of
the upper geotextile has been evaluated in laboratory research funded by the
GCL manufacturers. There has been a lot of attention paid to the initial leakage
rates as opposed to the longer term rate. With relatively small scale laboratory
GCL specimens (150 to 300 mm diameter), the fluid initially introduced to the
GCL through the geomembrane defect often flows out of a radial flow device
before the GCL can hydrate. If the test specimens were larger in diameter (600 to
1500 mm), it is conceivable that lateral flow from the edge of the specimens
would not be observed even from the GCL specimens with the highest initial
leakage rate. From a design standpoint, this is the critical behavior to quantify.
53
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To begin to define the role of a GCL in an "intimate contact" composite
liner, the investigation of the rates of hydration of larger GCL specimens at the
geomembrane interface should be coupled with ongoing research on GCL seams
and shrink/swell behavior to estimate the effective radius of saturation of a GCL.
This radius will determine the area that has been essentially saturated such that
vertical percolation through the bentonite component of the GCL will begin to
occur. This area can be used to estimate long term leakage through the
composite liner. This is the quantity that is of the greatest concern to the waste
industry and will provide the information necessary to evaluate the use of GCLs.
If the maximum computed leakage is acceptable, then GCLs can be considered as
a replacement for portions of or all of the compacted soil component.
4.2 Questions from the Audience
Upon the conclusion of his lecture, Mr. Bove held a question/answer
session where several important topics were discussed.
1) From the point of view of intimate contact, what is the difference between a
compacted clay liner and a GCL?
Ans) The use of a GCL potentially introduces an interface that allows flow. The
important point though, is how much flow occurs, and can we get sufficiently
low flow with either the compacted clay or the GCL?
2) As the upper geotextile of a hydrated GCL is said to be "plugged up" with
migrating bentonite, why is there such a concern for the transmissivity of the
upper geotextile?
Ans) From a regulatory standpoint, a geotextile is a geotextile whether it is
incorporated into a GCL or not. And if the placement of a geotextile beneath a
geomembrane is unacceptable, then the same goes for a GCL incorporating an
upper layer geotextile. One could make the geotextile thin enough that lateral
flow does not become a big issue over time, or one could have the mentality that
there is no geotextile that is satisfactory.
While manufacturers and testing companies may claim that once
hydrated, a GCL makes good contact with an overlying geomembrane, until this
is demonstrated on a full scale sample, some skepticism will remain.
54
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3) Could a layer of condensed water between a geomembrane and a compacted
clay liner be a potential pathway for lateral transmission?
Ans) Depending on the overburden stress, it would most likely provide a
localized pathway as opposed to a continuous one.
4) Which provides better intimate contact, a smooth or textured geomembrane?
Ans) This is a difficult question that depends on a lot of factors. For example, if
one has a very hard compacted clay liner and a textured geomembrane under
low normal loading, one could easily imagine high levels of lateral flow if the
geomembrane does not penetrate the liner.
5) If the concern revolves around a damaged geomembrane, why not place a
thick geotextile or a GCL protection layer on top of the geomembrane in order to
prevent damage as it is done in Germany?
Ans) This is a good point in that designers need to get out of the mode that a
GCL will just replace the layer of compacted clay. A new design philosophy is
necessary to realize the full potential use of a GCL.
4.3 Final Comments
Part of the purpose of displaying ranges of geotextile transmissivity data
was to show that the amount of water that can potentially move laterally the
geotextile component of a GCL is very small. Furthermore, the distance traveled
by this liquid is limited by GCL hydration. Mr. Bove stated that the risk of
significant leakage through a GCL in this mode is very small, especially in
double composite liner systems.
The question of intimate contact between a geomembrane and a
compacted clay liner was raised by several people. It was pointed out that
wrinkles in the geomembrane make intimate contact with a compacted clay liner
questionable.
55
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CHAPTER 5
OWNER/OPERATOR EXPERIENCES AND CONCERNS
Representatives from four waste disposal companies were given the
opportunity to voice their opinions on the use and performance of GCLs. While
one company representative was very confident of the ability of GCLs to
perform, the others expressed concerns over several technical issues.
5.1 Clarke Lundell, Representing Waste Management of North America, Inc.
Up to now, the use of GCLs has been limited to a backup role. Typically,
GCLs are placed as a redundant seepage barrier in secondary liner systems for
which only a single geomembrane liner is required. The company is reluctant to
make a general statement about whether a GCL can be used alone in the primary
liner when no secondary liner is present. This decision would be dependent on
the geologic conditions at the site.
There needs to be more information gathered about GCLs. While it
appears that the products do work, more work is needed to determine why they
work.
Some of the issues that need to be investigated are:
• Intimate contact with a geomembrane
• Frictional properties
• Hydration and swelling
• Quality assurance
• Storage
• Deployment
—What equipment should be used?
-What about soft subgrade?
—Weather factors
5.2 Charles Rivette, Representing Browning-Ferris Industries (BFI)
While GCLs have been used within the company, there is not a general
consensus on them yet. If one polled a representative from each of their 100
landfill sites, one would most likely get 100 different answers. Within their sites
56
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in the United States, the use of GCLs has mostly been limited to sumps, header
pipes, and as secondary containment for leachate and fuel storage. However, in
Italy, BFI has some sites in use, or permitted for later use, where a GCL is the
primary seepage barrier. The most likely future use of GCLs will be in cover
systems used to cap older landfills that were closed in the 1960s.
The company still has some concerns about the products. Some of these
concerns are:
• Construction
—There is still some concern about how to successfully install a GCL. An
example was given describing a site in Louisiana where a GCL was
installed below an HOPE geomembrane. Before installers could
completely seal off the upper geomembrane, a sudden rain storm
hydrated the yet unfinished liner. The effort involved in the ensuing clean
up and reinstallation was enormous.
• Quality assurance/quality control (QA/QC)
--QA/QC is not only important for construction, but for the
manufacturing of the products, as well.
• Cost
—Due to the high costs of clay in the Northeast, and along the West coast,
GCLs are more likely to be used. In the South and Midwest, where
suitable clay is readily available, compacted clay liners are going to
continue to be used extensively.
• Interface friction
—The use of canyons and valleys for landfill sites has become more
common. Unfortunately, during interim fill conditions there exists the
possibility of a massive wedge failure for bottom slopes of only 2 to 4 %.
While they would like to attain a factor of safety of 2 for their designs,
they often cannot even achieve a factor of 1.5 when using current interface
friction values in their analysis.
—The values of interfacial friction angles measured so far have been
highly variable. They would like to see more repeatability of results.
At the present time, BFI has one site in use and at least three liners in the
process of design and/or obtaining a permit where a composite HOPE/GCL
57
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system is serving as the primary liner. In each case, the design is necessary due
to the lack of local clay soils at the site.
5.3 Kurt Shaner, Representing Chambers Development Company, Inc.
At the present time, Chambers operates or is in the process of permitting
20 municipal solid waste landfills. GCLs are incorporated into the liner system at
10 of these sites. Of these 10, 5 sites are in operation, 3 are permitted with
construction ongoing, and 2 are in the permitting process. The most common
application of the GCLs has been in the formation of primary composite liners at
double lined sites.
While the company views GCLs as a positive development in the area of
liner technology, is still has some concerns. Some of these concerns include:
• Quality Assurance Standards
-Uniform procedures for the QA/QC of the manufacturing and
installation of GCLs are needed.
• Shear Strength Determination
-Repeatable results for the testing of internal and interface friction need to
be determined. This testing should account for variables such as normal
stress, shear rate, amount of hydration, hydration liquid, etc. Potentially,
a data base could be created to correlate between each of the variable
parameters and frictional resistance.
• Construction Considerations
-Some problems with premature hydration have been encountered due to
leaking trailers and precipitation events. While not a problem with the
performance of the material, it does illustrate a difficulty with the
installation of the product.
Perhaps the greatest benefit of the use of GCLs is the ease of their
installation compared to CCLs. The installation of GCLs does not require
compaction nor the control of moisture content and can be completed in cold
weather. The non-applicability of these factors improves the probable quality of
an installation, especially when placed to form a primary composite liner.
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5.4 John Workman, Representing Laidlaw Waste Systems
Due to the abundance of clay at each of their sites, Laidlaw has never
incorporated GCLs into any of their designs. For GCLs to be used at a future
date, the reliability of the product will have to be well established. Some of the
criteria used to ensure this reliability are discussed below:
• Efficiency
—The efficiency of a liner system refers to its ability to shed water.
Efficiency is a measure of the amount of leachate diverted to a drainage
sump versus the amount that percolates through the liner.
• Damage resistance
—There is the human element of big, bulky equipment being operated at
sites. This equipment, if improperly handled, can damage a liner.
• Long term performance
—Chemical resistance
—Leakage potential
—Break through potential
• Constructability
• Availability
-The company is not opposed to the use of GCLs. It has just always
had a readily available source of clay at its sites. There are some sites that
do not have clay, and the use of a GCL may be warranted at these sites.
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CHAPTER 6
RECENT RESEARCH
Representatives from the University of Texas and Drexel University were
given the opportunity to discuss the results of the most recent research
undertaken at their respective universities. Research at the University of Texas
has tended to focus on large-scale hydraulic conductivity testing and on the
stability of final covers. Research at Drexel University has concentrated on the
hydration behavior, swelling characteristics, and internal shear strength of GCLs.
6.1 The Hydraulic Conductivity of Large Scale Intact, Overlapped, and
Composite Geosynthetic Clay Liners (By David Daniel University
of Texas)
The hydraulic conductivity of three 2.8 m2 geosynthetic clay liners (GCLs)
was measured. The apparatus is shown in Fig. 6.1. Tests were performed on
Bentomat®, Claymax® 200R, and Gundseal. The GCLs were placed above a
drainage medium and covered with 0.3 or 0.6 m of gravel. A constant hydraulic
head of 0.3 or 0.6 m was established. Tests were conducted on either a single
piece of material (control sample) or on two pieces of material that were
overlapped 37 or 75 mm. (Gundseal) or 75 or 150 mm. (Bentomat® and
Claymax® 200R). Tests showed that overlapped panels self sealed; flow rates
through the overlapped GCLs were about the same as those through the control
samples.
A defective high density polyethylene (HOPE) geomembrane was placed
on top of samples of GCL material, covered with gravel, and then flooded with
water. Effective composite behavior did not occur with those GCLs that
contained a geotextile between the defective geomembrane and bentonite but did
occur for the GCL in which the defective geomembrane was in direct contact
with the bentonite in the GCL.
Further details on this research is provided by Estornell (1991) and
Estornell and Daniel (1992).
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Water
Surface
Geosynthetic
Clay Liner
(GCL)
Drainage
Hole
Drainage Layer
Acrylic Strip
Bentonite Seal
Drainage Outlet
System
.X Collection
Container
Note: Not to Scale
CORNER DETAIL
Bentonite
n
$&&$w^^^^^
Drainage
Material
Acrylic Strip
75 mm
Figure 6.1 Cross Sectional View of Test Set Up
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6.2 The Effect of Differential Settlement on the Hydraulic Conductivity of
Geosynthetic Clay Liners (By Mark LaGatta and B. Tom Boardman,
University of Texas)
One of the more likely future uses of a GCL is as a component in the final
cover of a municipal solid waste landfill. Subsidence generally occurs beneath
the final cover due to biochemical decay of waste, collapse of underlying
materials, or consolidation of saturated waste material. Unlike a wide
embankment fill, the landfill will most likely not settle as a uniform mass. There
will be localized settlements randomly distributed across the cover.
Unfortunately, these localized settlements tend to cause the most damage to a
flexible cover due to tensile strains caused by large differential settlement.
In an attempt to determine the effects of settlement on the hydraulic
conductivity of a GCL, Mr. LaGatta modified the steel tanks developed originally
by Estornell. A wood frame and a large, deflatable, water-filled bladder were
placed in the bottom of each tank to allow settlement to occur. By opening a
valve beneath each tank, the rate and amount of settlement could be controlled
after the installation of the GCL (Fig. 6.2 and 6.3).
Both intact and overlapping samples were tested. A conservative overlap
of 225 mm was used. The overlapping samples were aligned with the overlap
running parallel to the length of the tank and the deflatable bladder. A non
symmetrical bladder was used to ensure one dimensional distortion and tensile
strains.
Mr. LaGatta has studied the effects of differential settlement on a hydrated
GCL. The full size GCL samples were hydrated within the tank after the GCLs
had been covered with 0.6 m of gravel. The valve to the bladder was then
opened, and a series of incremental settlements were induced beneath the GCL.
The effect of each incremental settlement on the hydraulic conductivity of the
deformed GCL was then closely monitored.
Intact and overlapping samples of Bentomat®, Claymax® 200R, and
Gundseal were tested. The effective normal stress was approximately 7.6 kPa for
each test. The results are shown in Fig. 6.4 through 6.11. There was no measured
outflow for either the intact or overlapping samples of Gundseal at any
deformation.
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•V;-V^^.-X'-V;- GCL Specimen .V;.Vy/y..
O-Seal Straight Thread
Male Connector
Granular
Bentonite
Side Seal
Valve;
1/8-in. O.D. Inflation/
Deflation Line
. Copper
Union Outlet Tube
1/8-to 3/8-in. Tee
Reducer
Figure 6.2 Cross Sectional View of Modified Test Set Up
Steel Weather L 2x2xl/4
Tank 7ealf|er- Steel
strip Tape Frame
Granular
Bentonite
Seal
Pea Gravel
Drainage
Course
2x 10
Wood 4x4 Wood
Frame Support
1.2m i
2.4m
Figure 6.3 Plan View of Tank and Deflatable Bladder
63
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10
10
P 10
o
-6
-7
-8
8 10-9
£ 10
o
10
-10
-11
2nd Deflation
(2) 59.8 days,
A =» 46 mm
4th Deflation
(2) 87.0 days,
A = 74 mm
3rd Deflation
(5) 73.0 days,
A = 60 mm
Y\k
\l
0 10 20 30 40 50 60 70 80 90 TOO 110
TIME (days)
Figure 6.4 Hydraulic Conductivity vs. Time for Intact Bentomat® Sample
IHS-2-D
10
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
DEFORMATION, A / L
Figure 6.5 Hydraulic Conductivity vs. Deformation for Intact Bentomat® Sample
IHS-2-D
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4th Deflation
@ 69.9 days,
A »107mm
3rd Deflation
56.9 days,
A » 86 mm
1st Deflation
22.8 days,
A ~ 8 mm
10
20 30 40 50 60 70
TIME (days)
80 90
Figure 6.6 Hydraulic Conductivity vs. Time for Overlapped Bentomat® Sample
OH5-2-C
Note: Loose 0.25 Ib/ft bentonite placed along outer edge of overlap as opposed to centerline of
overlap
0.0
0.1
0.2 0.3 0.4
DEFORMATION, A / L
0.6
Figure 6.7 Hydraulic Conductivity vs. Deformation for Overlapped Sample
OHS-2-C
65
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O
=>
O
O
O
O
1 st Deflation
@ 26.2 days,
A = 16 mm
3rd Deflation
@ 55.9 days,
A « 69 mm
2nd Deflation
42.0 days,
A = 25 mm
0
30 40 50
TIME (days)
Figure 6.8 Hydraulic Conductivity vs. Time for Intact Claymax® Sample IHS-l-A
10
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
DEFORMATION, A/L
Figure 6.9 Hydraulic Conductivity vs. Deformation for Intact Claymax® Sample
IHS-l-A v
66
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I
.O,
>•
O
0
O
O
DC
O
X
2nd Deflation
@ 42.1 days,
A «22mm
0 10 20 30 40 50 60 70
TIME (days)
10
Figure 6.10 Hydraulic Conductivity vs. Time for Overlapped Clavmax® Sample
OHS-l-F
CO
o.
£
a
Q
O
O
OC
O
-91. ... 1 - ... I.. . -
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35
DEFORMATION, A/L
Figure 6.11 Hydraulic Conductivity vs. Deformation for Overlapped Sample
OHS-l-F
67
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Mr. Boardman is studying the effects of differential settlement on
unhydrated, overlapping GCLs. After the installation of the dry GCL, a large
settlement is induced beneath the sample. The deformed GCL is then slowly
hydrated over a span of several days. The ability of the deformed sample to self
heal at the overlap is then closely monitored. The results of two tests are shown
in Fig. 6.12 and 6.13. Both intact and overlapping samples of Bentomat®,
Claymax®, and Gundseal will be tested to determine the effect of the overlap. A
conservative overlap of 225 mm is being used. More details may be found in
LaGatta (1992).
6.3 Stability of Final Covers Placed on Slopes with Geosynthetic Clay Liners
(By Hsin-Yu Shan, University of Texas)
There has been some concern about the use of GCLs in sloping final cover
systems. Even with geogrid reinforcement, a GCL will lose strength and
potentially deform once hydrated. This concern needs to be addressed as GCLs
are expected to be more common in final cover systems.
A typical profile of a final cover incorporating a GCL is shown in Fig. 6.14.
The current slope design method is the limit equilibrium method. Unfortunately,
there is no way to predict the amount of deformation with this method. In an
effort to predict this deformation, Mr. Shan developed a numerical model
incorporating the properties of the top soil, geogrid, GCL, and cover soil. The
profile of the slope used in the model is shown in Fig. 6.15.
The model has been simplified by reducing the number of possible
interfacial friction values to the most critical one and by representing the tensile
resistance of all of the geosynthetics by one material (a geogrid). The top soil is
assumed to be 0.9 m thick and to have a unit weight of 15.7 kN/m3. For the
range of expected normal stresses, ' and c' are assumed to be 30° and 4.8 kPa,
respectively, for the top soil. The degree of hydration of the GCL can be varied.
The numerical model was developed as a finite element program. Some
results of the model are shown in Fig. 6.16 and 6.17. As expected, for a given
slope, the lower the minimum interfacial friction angle, the higher the relative
displacement, and the higher the tension within the geogrid.
68
-------
10
10
-5
-6
u
3
o
u
u
I-H
J
p
<
OS
a
o
10
10
-8.
-9
.
.
1
i
Bentomal
230 mm (
Unhydrat
A/L = 0.3
a
®OUS-1-H
)f Overlap
ed Settlement o
3
"
f 75 mm
3 5 10 15 20 25 3
TIME (days)
Figure 6.12 Hydraulic Conductivity of Bentomat® after a Large Settlement Prior
to Hydration
10
-7
^
>
P
Q
Z
O
u
u
HH
J
p
<
c<
Q
O
10
do
1
V>
10
Gundseal® OUS-l-F
230 mm of Overlap
Unhydrated Settlement of 75 mm
= 0.33
10
15 20
TIME (days)
25
30
Figure 6.13 Hydraulic Conductivity of Gundseal® after a Large Settlement Prior
to Hydration
69
-------
Top Soil
Drainage
Layer
FML
Geosynthetic
Clay Liner
Cover Soil
Waste
Figure 6.14 Typical Profile of Final Cover with Geosynthetic Clay Liners
Top Soil
1 Geogrid
GCL
Cover Soil
Figure 6.15 Profile of the Slope Used for Computations
70
-------
U.b
£ 0.4
o 0.3
Q A 0
7: 0.2
'x
2 0.1
.0
1
•
0
1
1
2
'
1
•
j
4
1
6
1
8
2
Interfacial Friction Angle (°)
Figure 6.16 Relationship between Maximum Interfacial Displacement and
Minimum Interfacial Friction Angle for a 3:1 Slope
3UUUU
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£ 20000
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£.
10000
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14 16
Interfacial Friction Angle (c
18
20
Figure 6.17 Relationship between Tension in the Geogrid and the Minimum
Interfacial Friction Angle for a 3:1 Slope
71
-------
While this analysis is still in its initial stages, it is hoped that by running
the model over a range of conditions one can draw conclusions about:
• The probable short and long term shear strength parameters of GCLs
• The possibility of using GCLs on slopes without excessive deformation
occurring
• The usefulness of design schemes to reinforce the slope
6.4 The Hydration Behavior and Mid-Plane Shear Strength of Four
Geosynthetic Clay Liners (By Robert Koerner, Drexel University)
The focus of GCL research and development at Drexel University's
Geosynthetic Research Institute (GRI) is on the hydration behavior of the various
products and on their mid-plane shear strength. Work is ongoing with four
different commercially available products: Bentofix®, Bentomat®, Claymax®,
and Gundseal®. Each of these products have been evaluated in five different
liquids: distilled water, tap water, mild leachate, harsh leachate, and diesel fuel.
The first series of tests focused on the hydration behavior under varying
normal stresses. These hydration tests were conducted on 150 by 150 mm
samples contained in steel boxes with perforated loading plates so that the
hydrating liquid was available to hydrate the entire surface area of the test
samples. The deformation curves shown in Fig. 6.18 display the following
information:
• The products swelled from highest to lowest amounts in the following
order: distilled water or tap water, mild leachate, harsh leachate, and
diesel fuel
• For a given hydration liquid, Claymax® swells the most, followed by
Gundseal®, Bentomat®, and Bentofix® in descending order. Clearly, the
needle punching of Bentomat ® and Bentofix® restrained the swelling in
these latter two products
Upon completion of the hydration tests, the samples were carefully
removed from their respective test devices and trimmed to fit in a 100 by 100 mm
direct shear test device. The location of the shear plane was set at the mid-plane
of each of the test specimens. The test specimens were sheared at a strain rate of
72
-------
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73
-------
0.9 mm/min and were designated as "constrained-swell" tests. Direct shear tests
were conducted on all samples and counterpointed against parallel sets of tests
in the dry (or as received) state and also against "free-swell" tests in which the
test specimens were hydrated in the same liquids but without any normal stress.
The direct shear tests produced the shear strength parameters and c shown in
Table 6.1. The data indicate the following trends.
• The products are strongest in the dry "as-received" condition and the
weakest in the free-swell condition. The constrained-swell condition is
intermediate betwt?en the two extremes.
• Needle-punching significantly increases shear strength.
• The hydrating liquid can affect strength.
• Hydration with distilled water yields the lowest shear strength and can
be used as a conservative liquid.
• Products with fiber reinforcement required much larger displacements
than unreinforced products to reach their limiting shear stress.
74
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Table 6.1 Direct Shear Test Results Summary (Drexel University)
Hydrating Fluid
Distilled
Water
Tap
Water
Mild
Leachate
Harsh
Leachate
Diesel
Fuel
GCLType
Claymax
Gundseal
Bentomat
Bentofix
Claymax
Gundseal
Bentomat
Bentofix
Claymax
Gundseal
Bentomat
Bentofix
Claymax
Gundseal
Bentomat
Bentofix
Claymax
Gundseal
Bentomat
Bentofix
Measured Property
0 (degrees)
C(kPa)
0 (degrees)
C(kPa)
0 (degrees)
C(kPa)
0 (degrees)
C(kPa)
0 (degrees)
C(kPa)
0 (degrees)
C(kPa)
0 (degrees)
C(kPa)
0 (degrees)
C(kPa)
0 (degrees)
C(kPa)
0 (degrees)
C(kPa)
0 (degrees)
C(kPa)
0 (degrees)
C(kPa)
0 (degrees)
C(kPa)
0 (degrees)
C(kPa)
0 (degrees)
C(kPa)
0 (degrees)
C(kPa)
0 (degrees)
C(kPa)
0 (degrees)
C(kPa)
0 (degrees)
C(kPa)
0 (degrees)
C(kPa)
Dry*
37
6.9
26
50
42
14
36
68
37
6.9
26
50
42
14
36
68
37
6.9
26
50
42
14
36
68
37
6.9
26
50
42
14
36
68
37
6.9
26
50
42
14
36
68
Constrained Swell**
16
3
19
5
37
6
31
7
18
3
18
5
43
6
34
6.9
24
6
18
5
39
8.3
43
5
19
6
13
7.6
45
5
39
4
44
4
24
4
42
6
51
4
Free Swell***
0
4
0
3
23
5
10
9.0
0
3
0
3
26
10
15
7
4
3
13
4
25
14
20
12
0
3
0
3
32
12
30
8.3
38
6
29
6
40
5
46
5
Notes:
* Dry refers to product as-received, placed under desired normal stress, then sheared at midplane.
** Constrained swell refers to product hydrated under desired normal stress, i.e., constrained swell, then
sheared at midplane.
'** Free swell refers to product hydrated under zero normal stress, then placed under desired normal stress, and
then sheared at midplane.
75
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CHAPTER 7
EQUIVALENCY
7.1 Equivalency (By David Daniel, University of Texas)
7.1.1 Potential Applications
If one wants to substitute a geosynthetic clay liner (GCL) for a required
compacted clay liner (CCL), one will generally have to demonstrate that the
proposed GCL will provide equivalent or better performance to a CCL.
Equivalency analyses may be required for:
• Final Cover Systems:
• Single GCL Versus Single CCL Liner
• Geomembrane/GCL Composite Liner Versus Geomembrane/CCL
Composite Liner
• Single Liner Systems:
• Single GCL Versus Single CCL Liner
• Geomembrane/GCL Composite Liner Versus Geomembrane/CCL
Composite Liner
• Double Liner Systems:
• Geomembrane/GCL Composite Liner Versus Geomembrane/CCL
Composite Liner in Primary Liner
• Geomembrane/GCL Composite Liner Versus Geomembrane/CCL
Composite Liner in Secondary Liner
The Solid Waste Disposal Facility Criteria found at 40 CFR Part 258 apply
to municipal solid waste landfills and treat the area of "equivalency" differently
for final covers and liners. Final cover systems are to be designed to minimize
infiltration and erosion, therefore, designs other than the minimum requirements
of §258.60 (a) could be approved using an "equivalency" demonstration.
However, alternatives to the composite liner design in §258.40 (a) (2) are not
approved based on "equivalency" demonstrations but must meet the
performance standard at §258.40 (a) (1). Different standards apply to facilities
76
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that receive hazardous waste regulated under Subtitle C of RCRA and to
CERCLA clean-up sites.
The designs for Subtitle C and CERCLA are evaluated based on the site-
specific design. Innovative use of modern materials is encouraged, providing
they meet the requirements of the law.
7.1.2 Differences Between CCLs and GCLs
Some of the differences between compacted clay liners and geosynthetic
clay liners are listed in Table 7.1. Some of the potentially important (depending
upon specific application) relative advantages of CCLs and GCLs may be
summarized as follows:
• Advantages of compacted clay liners (CCLs):
• The large thickness of CCLs makes them virtually puncture
proof
• The large thickness of CCLs makes them relatively insensitive
to small imperfections in any one lift
• The large thickness of CCLs gives them substantial capacity for
adsorption of leachate
• The large thickness of CCLs delays the discharge of water and
solutes from the base of liners
• There is a long history of use of CCLs
• Intimate hydraulic contact with a geomembrane is not an issue
for CCLs
• Many regulatory agencies require CCLs; use of another type of
liner may require demonstration of equivalency to a CCL.
• A CCL is a logical choice if suitable clay is available locally
• Testing procedures are reasonably well established for CCLs.
• Advantages of geosynthetic clay liners (GCLs):
• Small thickness of GCLs leads to low consumption of space
• Construction of GCLs is rapid and simple
• Heavy equipment is not needed to install a GCL, which is
beneficial if the GCL is underlain by a geosynthetic material
77
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Table 7.1 Differences Between GCLs and CCLs
Characteristic
Geosynthetic Clay Liner
Compacted Clay Liner
Materials
Bentonite Clay, Adhesives,
Geotextiles, and
Geomembranes
Native Soils or Blend
of Soil and Bentonite
Construction
Manufactured and Then
Installed in the Field
Constructed in the
Field
Thickness
Approximately 10 mm
Approximately 0.5 to
1.0m
Hydraulic
Conductivity
of Clay
10'10 to 10"8 cm/s
(Typical)
10'8 to ID'7 cm/s
(Typical)
Speed and Ease
Construction
Rapid, Simple
Installation
Slow, Complicated
Construction
Water Content
at Time of
Construction
Essentially Dry;
Cannot Desiccate
During Construction
and Produces No
Consolidation Water
Nearly Saturated;
Can Desiccate and
Can Produce
Consolidation
Water
Cost
$5 to $11
per Square Meter
Highly Variable
(Estimated Range:
$8 to $32 per
Square Meter)
Experience
Level
Limited Due to
Newness
Has Been Used for
Many Decades
78
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• Some inclement weather delays (e.g., freezing temperatures)
that stop construction of CCLs are not experienced with GCLs
• Because a GCL is a manufactured material, a consistent and
uniform material can be produced
• Because GCLs are manufactured materials many of the
specialized performance properties can be determined and need
not be repeatedly re-determined
• GCLs can accommodate large differential settlement
• Quality assurance is simpler for a GCL compared to a CCL
• GCLs are more easily repaired than CCLs
• GCLs can probably better withstand freeze/thaw and wet/dry
cycles than CCLs
• Unlike CCLs, GCLs are not vulnerable to desiccation damage
during construction
7.1.3 Criteria for Equivalency
Three issues should be addressed when one compares a GCL to a CCL
and considers the equivalency of a GCL to a CCL:
1. Hydraulic issues
2. Physical/mechanical issues
3. Construction issues
The specific issues that might have to be addressed for a specific site are listed in
Table 7.2.
7.1.4 Hydraulic Issues
Hydraulic issues are the easiest to quantify. The criteria are discussed
separately.
7.1.4.1 Steady Flux of Water
Flux of water is usually assessed by comparing the long-term, steady state
water flux for the CCL and GCL. The flux of water (v) through an individual
layer of porous material is defined from Darcy's Law as:
79
-------
Table 7.2 Potential Equivalency Issues
Category
Hydraulic
Issues
Physical/
Mechanical
Issues
Construction
Issues
Criterion for Evaluation
Steady Flux of Water
Steady Solute Flux
Adsorption Capacity
Breakout Time:
-Water
-Solute
Production of Consolidation Water
Freeze-Thaw
Wet-Dry
Total Settlement
Differential Settlement
Slope Stability
Erosion
Bearing Capacity
Puncture Resistance
Subgrade Condition
Ease of Placement
Speed of Construction
Availability of Materials
Weather Constraints
Quality Assurance
Relevant for:
Liners Covers
X
X
X
X
X
X
X*
X**
X**
X*"
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Notes:
* Relevant only until liner is covered sufficiently to prevent freezing
** Settlement of liners usually of concern only in certain circumstances, e.g., vertical expansions
*** Stability of liner may not be relevant after filling (except canyon landfills)
80
-------
, H+L /rr-M
v= k —F— (7.1)
where k is the hydraulic conductivity, H is the depth of liquid ponded on the
liner, and L is the thickness of the liner. The water pressure on the base of the
liner is assumed to be zero in Eq. 7.1.
For a GCL, Eq. 7.1 is applicable only for flow through the bentonite
component; if the GCL contains a geomembrane, water flux will be controlled by
water vapor diffusion through the geomembrane component. The geomembrane
component, if present, should be considered in the equivalency analysis and in
computation of water flux. Also, Eq. 7.1 applies to a CCL or GCL liner alone;
composite action with a geomembrane is considered later.
The flux ratio for water, Fw, is defined as:
w
w VCCL
or:
H+LGCL
F"= H+LCCLCL <™
kCCL LCCL
For example, for a GCL without a geomembrane component, if:
kGCL = 1 x 10'9 cm/s = 1 x 10"11 m/s
H = 0.3 m (1 ft)
LGCL = 7 mm = 0.007 m
KCCL = 1 x 10"7cm/s = 1 x 10'9 m/s
= 0.9 m (3 ft)
then Fw from Eq. 7.3 equals 0.3. So long as Fw < 1, equivalency in terms of water
flux is demonstrated, i.e., the rate of water flow through the GCL is less than or
equal to that through the CCL. Most GCLs can be shown to be equivalent to a
CCL that has a hydraulic conductivity of 1 x 10~7 cm/s in terms of steady water
81
-------
flux. If the GCL contains a geomembrane, the flux ratio will be even less than
that computed from Eq. 7.3.
A composite liner consists of a geomembrane placed in contact with a low-
permeability soil. A geomembrane/GCL composite may be considered as an
alternate to a geomembrane/CCL composite. If so, flow through the composite
should be analyzed. Flow through a flaw in a geomembrane in a composite liner
depends on the hydraulic conductivity of the clay component, the hydraulic
gradient across the clay component, the hydraulic contact between the
geomembrane and the clay component, and the presence of a geomembrane
within the GCL. No equations have been published for computing flow rates
through a defect in a geomembrane component of a geomembrane/GCL
composite liner. However, published information can be used to make
comparative estimates. Equivalency evaluations would clearly be product and
perhaps site specific.
7.1.4.2 Steady Solute Flux
The maximum flux is the steady-state flux. Long-term, steady solute flux,
which is relevant only for liners, may be analyzed on the basis of advection
alone, diffusion alone, or advection plus diffusion. As will be seen later, the
assumptions necessary to analyze steady diffusion and steady advection-plus-
diffusion are inconsistent with the processes themselves, and only the case of
advection is relevant for steady-state conditions. Nevertheless, for completeness,
the methods for analyzing steady diffusion and steady diffusion-plus-advection
are presented so that these processes can be understood.
It is assumed that the concentration of a solute of concern in the leachate
remains constant. The advective mass flux, vm/A/ is:
H-f L
vm,A ~ cleachate ^ L (7.4)
where qeachate is the concentration of the solute of interest in the leachate. The
advective mass flux ratio, Fm/A is defined as:
vm A(GCL)
(7.5)
m
82
-------
or:
+ LGCL
,
cleachate kGCL
H + LCCL (7>6)
Cleachate ^CCL LCCL
or:
H+LGCL
KGCL
It is noted that qeachate cancels out of Eq. 7.6. Because Fm/A = Fw (Eq. 7.7), if one
has demonstrated equivalency of steady water flux, one has also demonstrated
equivalency of steady mass flux of solute caused by advection.
Solutes in leachate can also migrate through clay liners by molecular
diffusion. Steady diffusion of solutes is usually analyzed with Pick's first law,
which states that:
VD = D 8 -~ (7.8)
where VD is the diffusive mass flux, D is the diffusion coefficient for the solute of
interest, 0 is the volumetric water content, Ac is the difference in concentration of
the solute between the top and bottom of the liner, and L is the thickness of the
liner.
The diffusive mass flux ratio (Fmj)) is defined as
„ FmD(GCL) /p_
Fm'D - (7'9)
or:
Ac
DGCL 0GCL
FmD = =^ (7.10)
? A/"*
DCCL 0CCL LCCL
83
-------
or:
DGCL
(7.11)
Limited data exist on diffusion coefficients in clay liners. Data developed for
compacted kaolinite at the University of Texas indicate that D= 6 x lO'10 m2/s
for the non-reactive solute chlorine. For one GCL tested, the diffusion coefficient
for the bentonite in the GCL was approximately 2 x lO'10 m2/s. If, for example,
one assumes:
DGCL 2xio-iQ
DCCL ~ 6x10-™
0GCL _ 06
0CCL " 0.4 ~L5
LCCL 0.9 m
= 129
LGCL 0.007 m
then one computes a diffusive mass flux ratio of:
Fm,D = (033) (1.5) (129) = 64
In this example, the GCL is not equivalent to the CCL since there would be more
diffusive mass flux through the GCL than CCL. In general the calculated steady,
diffusive mass flux through the bentonite within the GCL is always expected to
be greater than the steady, diffusive mass flux through the CCL. However, for
those GCLs that have a geomembrane component, the geomembrane, which has
an extremely low diffusion coefficient for most solutes, should be considered and
will tend to greatly reduce the steady, diffusive mass flux.
As mentioned earlier, the assumptions necessary for computing steady
diffusive flux are inconsistent with the process itself. The problem is that a
contradiction exists in the boundary conditions. Diffusion is driven by a
concentration gradient, Ac. Over time, the solute of interest in the leachate will
84
-------
diffuse to the base of the liner, and the concentration at the base of the liner will
eventually equal the concentration on top of the liner, i.e., the concentration in
the leachate (which is assumed to be constant). Thus, the diffusion-driving
concentration gradient becomes zero and diffusive transport ceases. The only
way that steady diffusion could develop through a liner would be for fresh water
to continually flush the underside of the liner to maintain a concentration
gradient across the liner. For nearly all sites, the case of steady diffusion will be
irrelevant and need not be considered.
It may be argued that neither advection alone nor diffusion alone is
important ~ solutes will migrate through soil liners by advection plus diffusion.
The total mass flux due to advection plus diffusion (vm/A+D) is generally
assumed to be:
vm,A+D = vm/A + vm/D (7.12)
and the ratio of advective plus diffusive mass flux, Fm/A+o/mav ^e defined as:
VmA+D(GCL) ,7,~x
Fm'A+D= vmA+D(CCL) (7'13)
Although Eq. 7.13 can be applied, it should not be applied because the
assumed conditions are physically impossible for long-term, steady conditions.
If advection carries solutes downward through the liner, then at steady state the
base of the liner must necessarily be saturated with leachate. If the base is
saturated with leachate, then Ac = 0 and vm/o =0. Thus, when one analyzes long-
term, steady mass flux of a solute through a GCL or CCL, only advective
transport need generally be considered.
In some cases, one may wish to analyze transient conditions that lead up
to steady conditions, in which case both advective and diffusive transport should
be considered. If the GCL contains a geomembrane, the presence of the
geomembrane should be taken into account.
7.1.4.3 Adsorption Capacity
The adsorption capacity of a clay liner may be relevant only for liners (not
covers). Regulations generally have no specific adsorption requirements.
85
-------
Adsorption of organics tends to be different from adsorption by inorganics.
Adsorption of inorganics is controlled by cation exchange reactions and
geochemical processes such as precipitation. Adsorption of organic solutes is
generally assumed to be controlled by the amount of organic carbon in the soil
and a partition coefficient for the solute (which is characterized by the octanol-
water partition coefficient or water solubility of the organic species).
For inorganics, the maximum adsorbed mass per unit cross-sectional area
of liner (C) resulting from cation exchange processes may be defined as follows:
C = CECpdL (7.14)
where CEC is the cation exchange capacity (maximum mass of solute sorbed per
unit mass of dry soil), pd is the dry mass density of the soil, and L is the
thickness of the liner. The ratio of thickness of a typical GCL to a CCL is small
(on the order of 0.01). Thus, in order for a GCL to have equivalent cation
adsorption capacity to a CCL, the adsorption coefficient of the GCL would have
to be at least 100 times that of the CCL.
The cation exchange capacity of bentonite clay is typically on the order of
100 to 150 meq/lOOg. Natural soil materials used to construct CCLs have typical
CECs in the range of 3 to 30 meq/lOOg. The ratio of cation adsorption capacities,
denoted
V CGCL CECGCL pdGCL LGCL
FCEC = =
For the typical range of values, FCEC would be expected to be in the range of 0.03
to 0.75. It appears unlikely that equivalency can be demonstrated for cation
adsorption capacity using the expressions just presented. However, it must be
understood that adsorption of inorganic species is a complex process. Cation
exchange is just one of several processes that can affect adsorption. Precipitation
of inorganic solutes can be a far more important mechanism than cation
exchange, and pH is often a dominant variable controlling precipitation
processes in many geochemical environments. Thus, site-specific factors, and not
just simple comparisons of CECs and relative soil masses, will often need to be
considered when relative adsorption capacities are compared.
86
-------
Non-polar organic solutes are sorbed by carbon present in the soil. The
carbon content of bentonite in GCLs is capable of estimation, but CCLs will be
highly variable in their organic carbon content. Although site-specific
assessments would be required (due to variability of CCLs), equivalency of a
GCL to a CCL probably cannot be demonstrated in terms of capacity to adsorb
non-polar constituents in leachate to the bentonite because the mass of bentonite
present in a GCL is far less than the mass of soil present in a CCL.
Adsorption is only relevant in the short term. When steady state mass
transport is reached, adsorption capacity is exhausted. Equivalency in terms of
adsorption, if evaluated at all, should be evaluated in terms of a specified
performance period. For example, suppose the performance period being
considered is 30 years. If the adsorption capacity of neither the CCL nor the GCL
is exhausted after 30 years, both types of liner have "reserve" adsorption capacity
and may be considered equivalent for the performance period. Alternatively, if
either or both is exceeded, breakthrough of solute will occur and other issues,
e.g., steady state solute flux, will require consideration.
7.1 A A Time to Initiate Discharge of Water from Base of Liner
GCLs are initially unsaturated with water whereas CCLs are often very
close to saturation. When liquid first enters the upper surface of the liner, no
liquid initially discharges from the base of the liner. The GCL might be
compared to the CCL in terms of time to achieve discharge of water from the
bottom of the liner. Again, for those GCLs that contain a geomembrane, the
presence of the geomembrane should be taken into account.
The time to achieve discharge of water from the base is difficult to
describe in general terms. For CCLs, the time depends greatly upon the
hydraulic conductivity, initial water content, and tendency to swell. For GCLs,
the time is usually fairly short (a few weeks), although for GCLs that contain a
geomembrane, the time may be much greater. A comparison of time to initiate
discharge of water from the base of the liner would have to be performed on a
site specific basis.
The time to initiate discharge of water from the base of a liner is not
relevant in the long term and often will not be relevant even in the short term.
Most designs assume that water will be discharged from the base of a liner and
do not make any assumptions about how long this process will take.
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7.1.4.5 Breakthrough Time for Solute
The breakthrough time for a solute, which is not relevant for covers, is the
time required for a solute to travel from the top to the bottom of a liner.
However, theoretically, the time required for an infinitely small concentration of
solute to breakthrough to the base of a liner is zero for a thick or thin liner.
Thus, breakthrough time is not a uniquely defined parameter - the time depends
upon the concentration of interest. In this section, it is assumed that the
breakthrough time for a GCL is compared to that of a CCL for the same
concentration at the base of the clay liner.
Because of the thinness of GCLs, diffusion will generally cause the
breakthrough time of a thin layer of bentonite to be less than for a CCL. Even for
GCLs that contain a geomembrane, diffusion of organic solutes across the
geomembrane tends to occur quickly, but at a very low mass flux. However,
diffusion of inorganics through the geomembrane would be nil. Equivalency
depends on the GCL and the chemicals of concern.
One must carefully consider whether the breakthrough time for solutes is
relevant. In the long term, breakthrough time is irrelevant - breakthrough will
eventually occur in all liner systems with an outward gradient. The important
long-term issue is solute flux.
Steady-state flux represents a worst-case scenario, i.e., largest mass flux.
Time-dependent flux, before steady state, also may need to be considered in
certain situations.
7.1.4.6 Production of Consolidation Water
When clayey soils are loaded, water tends to be slowly squeezed out of the
soil via a process known as "consolidation." The production of consolidation
may or may not be of any concern, depending upon site-specific conditions.
Examples of potential problems associated with the production of consolidation
water include reduced stability at the geomembrane/clay liner interface (the
consolidation water from the clay liner tends to reduce stability through
increased water pressure at the interface) and collection of liquids in a leak
detection layer for double composite liners.
Compacted clay liners are nearly saturated with water at the time of
construction. When CCLs are loaded, substantial quantities of water are often
squeezed out of the liner. For example, if a 1-m-thick liner is saturated with
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water and compresses just 2 percent of its original thickness due to consolidation,
the amount of water squeezed out of the liner would be approximately 200,000
liters of water per hectare (20,000 gallons per acre).
Geosynthetic clay liners are essentially dry when they are constructed and
cannot produce consolidation water unless they are first soaked with water and
then compressed. Normally, GCLs do not have an opportunity to become
saturated before they are loaded. However, a saturated GCL will produce far
less consolidation water than a saturated CCL. Thus, GCLs are superior to CCLs
in terms of minimizing production of consolidation water.
7.1.5 Physical/Mechanical Issues
The physical/mechanical issues that might be considered in an
equivalency analysis include freeze/thaw effects, wet/dry effects, response to
total settlement, response to differential settlement, stability on slopes, and
vulnerability to erosion. Some issues are relevant for liners but all are relevant
for covers (Table 7.2).
7.1.5.1 Freeze/Thaw Resistance
Compacted clay liners are known to be vulnerable to large increases in
hydraulic conductivity from freeze/thaw. Limited laboratory data indicate that
GCLs do not undergo increases in hydraulic conductivity as a result of
freeze/thaw (Shan and Daniel, 1991). In addition, for those GCLs that contain a
geomembrane, the geomembrane is unaffected by freeze/thaw. Thus, from the
available data, GCLs appear to be superior to CCLs in terms of freeze/thaw
resistance.
7.1.5.2 Wet/Dry Effects
Wetting and drying of CCLs and GCLs can cause either type of clay liner
to swell or shrink. The main concern with clay liners that are wet and then dry
out, is that desiccation can lead to cracking and an increase in hydraulic
conductivity.
Limited laboratory data indicate that when dry, cracked CCLs are
rewetted, the clay swells and any cracks are partially closed, leading to partial
recovery of the original, low hydraulic conductivity. In contrast, the available
data show that the high swelling of bentonite results in full self healing and full
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recovery of the original, low hydraulic conductivity when dried, cracked GCLs
are rewetted. In addition, for those GCLs that contain a geomembrane, the
geomembrane is insensitive to wet/dry effects. Thus, GCLs appear to be more
than equivalent to CCLs in terms of ability to self-heal if the material is wetted,
dried, and then rewetted.
7.1.5.3 Response to Total Settlement
Total settlement refers to block-like settlement without significant bending
or distortion. It is believed that GCLs and CCLs would respond similarly to total
settlement.
7.1.5.4 Response to Differential Settlement
Recent research by LaGatta (1992) indicates that some GCLs maintain their
low hydraulic conductivity even when subjected to large differential settlements.
In all probability, GCLs are more resistant to damage from differential settlement
than CCLs (LaGatta, 1992). For example, for a depression with a diameter of 1 m
that subsides 0.5 m, the liner will undergo approximately 10% tensile strain.
While the data discussed in LaGatta (1992) suggests that GCLs can function
under such conditions, it is known that CCLs cannot and will suffer tension
cracks at 1% tensile strain or less.
7.1.5.5 Stability on Slopes
The shear strength of GCLs is very sensitive to the water content and type
of GCL (Shan and Daniel, 1991; and Daniel and Shan, 1992). Water-saturated
GCLs that have adhesive-bonded bentonite have angles of internal friction for
consolidated-drained conditions of approximately 10 degrees. Dry materials are
2 to 3 times as strong as water-saturated GCLs. Also, needle-punched and stitch-
bonded GCLs tend to have high strengths. The shear strength of CCLs varies
widely, depending on materials, water content, and compaction conditions.
In stability analyses, one often must consider not only internal shear
failure but interfacial shear with an adjacent layer, e.g., a geomembrane. Also,
shear strength may be of short-or long-term concern, or both. No general
statement can be made about probable equivalency of a GCL to a CCL because
the assessment depends on specific materials, the degree to which the bentonite
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can wet, consolidation water generated by CCLs, the slope angle, and other site-
specific conditions.
7.1.5.6 Vulnerability to Erosion
Erosion resistance may be of concern in final covers if inadequate cover
soil is present. Because of the presence of erosion-resistant geosynthetic
materials in GCLs, GCLs can potentially be more resistant to erosion than CCLs.
However, if the clay liner is exposed to erosive forces, the bentonite may be
washed out of some GCL materials. Thus, equivalency depends upon the
specific materials being considered. For many sites, erosion will not be of any
concern, e.g., for a GCL underlying a geomembrane or a GCL containing a
geomembrane that overlies the bentonite.
7.1.5.7 Bearing Capacity
A clay liner must have adequate bearing capacity to support loads, e.g.,
wheel loads from construction equipment. The clay liner must not thin or pump
clay into adjacent layers under static or dynamic (e.g., traffic) loads. Hydrated
bentonite is not as strong as most materials used in constructing CCLs.
Equivalency is heavily dependent upon site-specific conditions.
7.1.6 Construction Issues
The construction issues that might be considered in an equivalency
analysis include puncture resistance, effect of subgrade condition on
constructability, ease of placement, speed of construction, availability of
materials, weather constraints, and quality assurance requirements.
7.1.6.1 Puncture Resistance
Thick CCLs cannot be accidentally punctured during construction, but
thin GCLs can. Some GCLs have the capability of self-sealing around certain
types of puncture objects, e.g., penetration of the GCL with a sharp object such as
a nail. The swelling capacity of bentonite gives GCLs this self-healing capability.
The more significant type of puncture for a GCL would be puncture
caused by construction equipment. For example, if the corner of the blade of a
bulldozer accidentally punctures the GCL during spreading of cover material,
the GCL would probably not self seal at the puncture. A thick CCL could not be
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punctured by a piece of construction equipment. Thus, GCLs will not have
equivalent puncture resistance to CCLs. However, quality assurance and quality
control procedures can be established and implemented to make the probability
of a puncture during construction extremely low. Ultimately, site-specific
conditions and quality assurance procedures will determine whether puncture is
a relevant issue that deserves serious consideration.
7.1.6.2 Effect of Subgrade Condition
Compacted clay liners are constructed with heavy equipment. If the
subgrade is compressible (e.g, solid waste), the GCL, which can be installed with
light-weight equipment, will be easier to construct. On the other hand, stones
and rocks can puncture a GCL but not a CCL; if the subgrade contains stones or
rocks, the integrity of the GCL may be compromised. Thus, equivalency of a
GCL to a CCL in terms of the effect of subgrade depends on the condition of the
subgrade and will have to be evaluated on a site-specific basis.
7.1.6.3 Ease of Placement or Construction
A GCL will always be easier to place than a CCL, unless weather
conditions are adverse (e.g., constant rain), in which case even a CCL will also be
difficult to construct. In general, GCLs are equivalent to or better than CCLs in
terms of ease of placement or construction.
7.1.6.4 Speed of Construction
Geosynthetic clay liners can be placed much more quickly than CCLs.
Equivalency is obvious.
7.1.6.5 Availability of Materials
Suitable clays for construction of a CCL may or may not be available
locally, depending on the site. Because GCLs are a manufactured material, they
are readily available and can be shipped to a site quickly. The cost of shipment is
not a large percentage of the total cost of a GCL. Thus, GCLs will often be
superior to CCLs in terms of availability of materials.
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7.1.6.6 Weather Constraints
Compacted clay liners are difficult to construct when soils are wet, heavy
precipitation is occurring, the weather is extremely dry (clay desiccates); the soil
is frozen, or the temperature is below freezing. Geosynthetic clay liners are
difficult to construct during precipitation. Weather constraints generally favor
GCLs.
Some GCLs must be covered before they get wet. If a geomembrane will
be placed over the GCL, the GCL must be covered almost immediately with the
geomembrane. Additional weather constraints, e.g., wind speed, may apply to
the geomembrane and, indirectly, influence the GCL. The fact that many GCLs
must be covered before they are hydrated is a significant weather constraint for
GCLs that does not exist for CCLs. However, CCLs have weather constraints,
too: CCLs must not be allowed to freeze or desiccate (GCLs cannot desiccate
during construction because they are dry, and dry GCLs are unaffected by
freezing temperatures).
Equivalency in terms of weather constraints must be considered on a site-
specific basis, but weather constraints generally favor GCLs over CCLs.
7.1.6.7 Quality Assurance Requirements
Quality assurance (QA) requirements are less extensive for GCLs
compared to CCLs, but no less critical. There is no reason to suspect that QA is
more difficult for a GCL than a CCL. However, testing procedures and
observational techniques are well established for CCLs but are not for GCLs. The
GCL industry and the Geosynthetic Research Institute (GRI) are working hard
through GRI and ASTM to established testing methods. While it would appear
that GCLs and CCLs are equivalent in terms of QA requirements, more work
needs to be done to establish standard test methods for GCLs.
7.1.7 Summary of Equivalency Issues
Table 7.3 summarizes the preceding discussion of equivalency.
Equivalency can be demonstrated generically in many categories. However, in
two categories, equivalency probably cannot be demonstrated: (1) GCLs do not
have adsorption capacity equivalent to CCLs; and (2) GCLs do not have the
puncture resistance of CCLs. The adsorption capacity has no relevancy to covers.
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Table 7.3 Summary of Equivalency Assessment
Category
Criterion for Evaluation
Equivalency of GCL to CCL
Probably Probably Product or
Equivalent Not Equivalent Site Specific
Hydraulic
Issues
Steady Flux of Water
Steady Solute Flux
Adsorption Capacity
Breakthrough Time:
-Water
-Solute
Consolidation Water
X
X
X
X
Physical/
Mechanical
Issues
Freeze-Thaw
Wet-Dry
Total Settlement
Differential Settlement
Slope Stability
Erosion
Bearing Capacity
X
X
X
X
X
X
X
Construction
Issues
Puncture Resistance
Subgrade Condition
Ease of Placement
Speed of Construction
Availability of Materials
Weather Constraints
Quality Assurance
X
X
X
X
X
X
94
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For liners, the issue of adsorption capacity may or may not be relevant,
depending on project-specific details. Although thin GCLs can be punctured
during construction, the problem is of more concern for liners (due to higher
stresses), and careful QA may be capable of addressing this potential problem for
both liners and covers.
As suggested by Table 7.3, many equivalency issues depend on the GCL
product and the particular conditions unique to a given site. Equivalency will
clearly have to be evaluated on a case-by-case basis.
7.2 Discussion
A brief discussion took place after the presentation. Comments were
made that there is a large need to establish criteria for analysis of equivalency.
The potential criteria are numerous, but many may not apply. Also, differences
in liners and covers were emphasized and the special problems in analyzing
geomembrane/clay liner composites were briefly discussed.
95
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CHAPTER 8
TECHNICAL CONCERNS
Even though a wide variety of research has been performed on
geosynthetic clay liners (GCLs), many people expressed concern about how
GCLs will perform in the field. The research, while providing some insight into
the properties of GCLs, can often be difficult to interpret and relate back to a real-
life field condition. Because of this, there are still unanswered questions and
concerns relating to the full-scale field behavior of GCLs. In an effort to identify
and address specific concerns, an open discussion was held.
8.1 The Effect of Freezing on Saturated Sodium Bentonite
The hydraulic conductivity of one GCL incorporating sodium bentonite
has been shown to be unaffected by several freeze/thaw cycles in one series of
laboratory experiments (Shan and Daniel, 1991). Similar results have been
obtained for other GCLs in tests performed in commercial laboratories. Thus, the
limited laboratory data show no detrimental effects from freeze-thaw but there
have been no full scale field tests performed to verify the results of laboratory
tests.
8.2 The Flow of Bentonite out of a GCL on a Side Slope
Bentonite would most likely not flow out of a GCL on a slope because:
• If a GCL is installed with an overlying geomembrane, the chances are
that the GCL will never get sufficiently hydrated to allow the clay to
"flow".
• If the GCL did become hydrated, consolidation would take place due
to the stress of cover soils, and the internal shear strength of the GCL
would go up.
• If a needle punched or stitch bonded GCL is used it is difficult to
imagine the clay moving between the confining geotextiles.
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8.3 Designing for Side Slopes
Two sets of data are needed to design for side slope stability when using
GCLs:
1) Shear strength test data simulating the failure mode deemed important
by the designing engineer:
• Short term direct shear tests
• Long term creep tests
2) Wide width tensile strength data. When conducting this test, one must
consider the effect of confining stress on the results. Research at Drexel
University (1992) has shown that the confining stress will not influence
the tensile strength of a GCL incorporating a woven slit film geotextile.
8.4 Possibility of Overlaps Pulling Apart Due to Wet/Dry Cycles
This is why GCLs should always be installed with some sort of
overburden stress. Mot only can the overburden soil prevent damage to the
GCL, but over burden will also prevent the overlap width from changing if moist
GCLs dry and shrink. The GCL products can also be modified to prevent
overlap movement. Bentofix® can be made with a velcro strip along the overlap,
Claymax® or Bentomat® can be sewn (by hand) along the overlap as a prayer
seam with a strong monofilament thread, and the geomembrane components of
Gundseal can be welded together.
8.5 Steep Slopes
The use of geogrids and high strength geotextiles should be considered, as
the long term shear and tensile strength of a GCL is questionable.
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8.6 Long Term Physical Stability
Which will physically last longer, a GCL or a CCL? This depends on the
environment to which the liner will be exposed. While CCLs have traditionally
had problems due to desiccation cracking in hot, arid climates, GCLs have shown
the ability to quickly swell and self-heal even after being dried out. The mineral
components of both the CCL and GCL would hypothetically last forever as clay
is in the final stage of weathering. The long-term performance of the geotextiles
and needle punching is questionable, though.
8.7 Long Term Shear Strength
The internal shear strength of a GCL will go down as the bentonite
hydrates. How long will it take for a GCL to become hydrated? Is it reasonable
to assume that the entire GCL becomes hydrated?
8.8 Biotic Instabilities
How does one prevent animals and plants from burrowing into the final
cover? While a thick CCL could prevent damage, how can a thin GCL prevent
damage from occurring? One could possibly place a wire screen in the upper
layer, but how effective would this really be?
98
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CHAPTER 9
REFERENCES AND PUBLICATIONS RELATED TO GCLs
Alther, G. R. (1986), "The Effect of the Exchangeable Cations on the
Physiochemical Properties of Wyoming Bentonites," Applied Clay Science,
Vol. 1, pp. 273-284.
Bruton, D. (1991), "Bentonite Mats Meet Secondary Containment Standards,"
Geotechnical Fabrics Report, Vol. 9, No. 4, pp. 26-27.
Clem, J. (1992), "GCLs Used Successfully in Hazardous Waste Containment,"
Geotechnical Fabrics Report, Vol. 10, No. 3, pp. 4-7.
Daniel, D. E., and P. M. Estornell (1991), "Compilation of Information on
Alternative Barriers for Liner and Cover Systems," U. S. Environmental
Protection Agency, EPA 600/2-91/002, Cincinnati, Ohio.
Daniel, D. E. ,and R. M. Koerner (1991), "Landfill Liners from Top to Bottom,"
Civil Engineering, Vol. 61, No. 12, pp. 46-49.
Daniel, D. E., and H. Y. Shan (1992), "Effects of Partial Wetting on Strength and
Hydrocarbon Permeability," Geotechnical Engineering Center, Univ. of
Texas, Austin, Texas, 56 p.
Daniel, D. E. and R. M. Koerner (1993), "Final Cover Systems," Geotechnical
Practice for Waste Disposal., D.E. Daniel (Ed.), Chapman & Hall, London, in
press.
Daniel, D. E. (1993), "Clay Liners,"Geotechnical Practice for Waste Disposal , D.E.
Daniel (Ed.), Chapman & Hall, London, in press.
Eith, A. W., J. Boschuk and R. M. Koerner (1991), "Prefabricated Bentonite Clay
Liners," Landfill Closures: Geosynthetics, Interface Friction and New
Developments. Elsevier Applied Science, London, pp. 1193-218.
Elzea, J. M. and H. H. Murray (1990), "Variation in the Mineralogical, Chemical
and Physical Properties of the Cretaceous Clay Spur Bentonite in Wyoming
and Montana (U. S. A.)," Applied Clay Science, Vol. 5, pp. 229-248.
Estornell, P. (1991), "Bench-Scale Hydraulic Conductivity Tests of Bentonitic
Blanket Materials for Liner and Cover Systems," M.S. Thesis, University of
Texas, Austin, Texas.
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Estornell, P., and D. E. Daniel (1992), "Hydraulic Conductivity of Three
Geosynthetic Clay Liners," Journal of Geotechnical Engineering, Vol. 118, No.
10, pp. 1592-1606.
GeoSyntec Consultants (1991), "Final Report Laboratory Testing of Gundseal®,"
Report to Gundle Lining Systems, Inc., Norcross, Georgia, June 15, p. 62.
GeoSyntec Research Institute (1991), "Swelling Behavior and Shear Strength of
Gundseal®, in Distilled Water and Leachate," Report to Gundle Lining
Systems, Inc., Philadelphia, Pennsylvania April 18, p. 20.
Gibson, R.E. and D.J. Henkel (1954), "Influence of Duration of Tests at Constant
Rate of Strain on Measured 'Drained' Strength," Geotechnique, Vol. 4, pp. 6-
15.
Grim, R. E. (1968), Clay Mineralogy, McGraw Hill, New York.
Grube, W. E., Jr. (1991), "Soil Barrier Alternatives," Proceedings of the 17th Annual
RREL Hazardous Waste Research Symposium on Remedial Action, Treatment and
Disposal of Hazardous Waste, EPA/600/9-91/002, Cincinnati, pp. 436-444..
Grube, W. E., Jr. and D. E. Daniel (1991), "Alternative Barrier Technology for
Landfill Liner and Cover Systems," Paper No. 91-5.9,84th Annual Meeting,
Air & Waste Management Association, Pittsburgh, 10 pp.
Grube, W. E., Jr. (1992), "Geosynthetic Liners Offer Cover Option," Environmental
Protection, May. pp. 29-33.
Koerner, R. M. (1990), Designing with Geosynthetics, Second Edition, Prentice-Hall,
Englewood Cliffs, NJ, 659 p.
Koerner, R. M. and D. E. Daniel (1992), "Final Cover Systems for Landfills," Civil
Engineering, Vol. 63, No. 5, pp. 55-57.
LaGatta, M. D. (1992), "Hydraulic Conductivity Tests on Geosynthetic Clay
Liners Subjected to Differential Settlement," M.S. Thesis, University of
Texas, Austin, Texas.
Oscarson, D. W., Dixon, D. A., and M. N. Gray (1990), "Swelling Capacity and
Permeability of an Unprocessed and a Processed Bentonite Clay,"
Engineering Geology, Vol. 28, pp. 281-289.
Reschke, A. E., and M. D. Haug (1991), "The Physio-Chemical Properties of
Bentonites and the Performance of Sand-Bentonite Mixtures," Proceedings,
44th Canadian Geotechnical Conference, Calgary, Vol. 2, pp. 62-1 - 62-10.
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Ross, C. S., and S. B. Hendricks (1945), "Minerals of the Montmorillonite Group,
Their Origin arid Relation to Soils and Clays," U.S. Geological Survey
Professional Paper 205-B, U. S. Dept. Interior, 79 pp.
Scheu, C., K. Johannssen, and F. Saathoff (1990), "Non-Woven Bentonite Fabrics-
A New Fibre Reinforced Mineral Liner System," Geotextiles, Geomembranes
and Related Products., D. Hoet (Ed.), Balkema, Rotterdam, Vol. 2, pp. 467-472.
Schubert, W. R. (1987), "Bentonite Matting in Composite Lining Systems,"
Geotechnical Practice for Waste Disposal '87, R. D. Woods (Ed.), ASCE, New
York, pp. 784-796.
Shan, H.Y. (1990), "Laboratory Tests on a Bentonitic Blanket," M.S. Thesis,
University of Texas, Austin, Texas.
Shan, H. Y., and D. E. Daniel (1991), "Results of Laboratory Tests on a
Geotextile/Bentonite Liner Material," Geosynthetics '91, Industrial Fabrics
Association International (IFAI), St. Paul. Vol. 2 pp. 517-535.
Simpson, M. J. (1991), "A Prefabricated Bentonite Clay Liner,"'Landfill Closures:
Geosynthetics, Interface Friction and New Developments. Elsevier Applied
Science, London, pp. 187-192.
Sivapullaiah, P. V., et al. (1987), "Modified Free Swell Index for Clays,"
Geotechnical Testing Journal, Vol. 10, No. 2, pp. 80-85.
Struve, F. (1990), "Geomembrane-Clay Composite Liners," Landfill Closures:
Geosynthetics, Interface Friction and New Developments. Elsevier Applied
Science, London, pp. 177-180.
Trauger, R. (1991), "Geosynthetic Clay Liner Installed in a New Municipal Solid
Waste Landfill," Geotechnical Fabrics Report, Vol. 9, No. 8, pp. 6-17.
Trauger, R. (1992), "Geosynthetic Clay Liners: An Overview," Pollution
Engineering, May 15, pp. 44-47.
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