Citation
Geomembrane/soil interface shear strengths

Material Information

Title:
Geomembrane/soil interface shear strengths a comparison of test results generated in the 4-inch and 12-inch direct shear boxes
Creator:
Lahti, Kerry L
Publication Date:
Language:
English
Physical Description:
1 volume (various pagings) : illustrations ; 29 cm

Subjects

Subjects / Keywords:
Waste disposal sites ( lcsh )
Heap leaching ( lcsh )
Geomembranes ( lcsh )
Leachate ( lcsh )
Shear strength of soils -- Testing ( lcsh )
Geomembranes ( fast )
Heap leaching ( fast )
Leachate ( fast )
Shear strength of soils -- Testing ( fast )
Waste disposal sites ( fast )
Genre:
bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

Notes

Bibliography:
Includes bibliographical references.
General Note:
Department of Civil Engineering
Statement of Responsibility:
by Kerry L. Lahti.

Record Information

Source Institution:
|University of Colorado Denver
Holding Location:
Auraria Library
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
40274191 ( OCLC )
ocm40274191
Classification:
LD1190.E53 1998m .L34 ( lcc )

Full Text
GEOMEMBRANE / SOIL INTERFACE
SHEAR STRENGTHS:
A Comparison of Test Results
4-inch and 12-inch Direct Shear Boxes
Kerry L. Lahti, P.E.
B.S.C.E. Purdue University, 1992
A thesis submitted to the
University of Colorado at Denver
in partial fulfillment
of the requirements for the degree of
Master of Science
Civil Engineering
Generated in the
by
1998


This thesis for Master of Science
degree by
Kerry L. Lahti, P.E.
has been approved
by
Nien-Yin Chang
Kevin Rens


Lahti, Kerry L. (M.S., Civil Engineering)
Geomembrane / Soil Interface Shear Strengths: A Comparison of Test Results
Generated in the 4-inch and 12-inch Direct Shear Boxes
Thesis directed by Professor N.Y. Chang
ABSTRACT
In the design of waste containment facilities and heap leach pads, geomembranes have
been used as the primary component in the design of a barrier system to prevent
leachate from coming in contact with the underlying foundation soils and/or
groundwater. In addition to the geomembrane, several other soil and/or geosynthetic
materials are used in the barrier system to assist in preventing contamination of the
surrounding areas.
The stability of the barrier system, especially the stability of the materials adjacent to
the geomembrane, is a critical component in the design of waste containment and heap
leach facilities. The stability of the facility is dependent on the degree of interface
shear strength developed between the soil (or geosynthetic) and geomembrane.
One of the most commonly used and widely accepted devices to measure the interface
shear strength is a conventional direct shear box. Currently, there are several different
size direct shear machines available. However, two widely accepted standard test
methods, GRI GS6 and ASTM D 5321, specify the use of a 12-inch square direct shear
box.
1


Because the cost, materials required and time required for performing the test work in
a 12- inch direct shear box is much greater than that required for a 4-inch direct shear
box, this paper focuses on the applicability of determining the soil/geomembrane
interface shear strength using a 4-inch direct shear machine.
A test program was setup involving over 50 direct shear tests. The tests were
performed using 4-inch square and 12-inch square direct shear boxes. The results of
these tests were then reviewed to determine if a correlation could be made between the
test data generated in the 4- and 12- inch direct shear machines.
Several different types of soils and aggregates were selected for testing. The material
types varied from clean gravels to fat clays. The materials tested were selected to
represent different layers (drainage and protective layers and soil liners) typically found
adjacent to geomembranes in waste containment and heap leach facilities.
The results of this test program indicate that the peak interface strength parameters
measured for the 4- and 12- inch samples were found to be insignificantly different.
This abstract accurately represents the content of the candidates thesis. I recommend
its publication.
Signed
Nien-Yin Chang
u


ACKNOWLEDGMENTS
The author would like to thank GSE Lining Technology, Incorporated located in
Houston, Texas for providing the smooth 60 mil HDPE Hyperflex material for testing
and Knight Piesold LLC for allowing the use of their "state-of-the-art" laboratory. In
addition, the author would like to thank the examination review committee for their
help, Dr. N.Y. Chang, Dr. J.T.H. Wu and Dr. K. Rens.
111


CONTENTS
1.0 Introduction ....................................................... 1
1.1 Problem Statement................................................... 1
1.2 Scope of the Study.................................................. 2
2.0 Literature Review 4
2.1 General............................................................. 4
2.2 Soil / Geomembrane Interface Test Work.............................. 4
2.3 Interface Test Procedures 7
2.4 Evaluating Interface Test Results 9
2.5 Comparison of Test Results Generated in Different Size Direct Shear BoxekO
3.0 Direct Shear Test Equipment and Test Methods........................11
3.1 General.............................................................11
3.2 12-inch Direct Shear Box Specifications.............................14
3.3 4-inch Direct Shear Box Specifications..............................14
3.4 Test Methods .......................................................14
3.5 ASTM D5321 Test Procedures..........................................15
4.0 Materials, Material Preparation and Properties......................21
4.1 Geomembrane.........................................................21
4.2 Soils...............................................................22
IV


4.2.1 General ............................................................22
4.2.2 Soil Index Tests....................................................22
4.2.3 Soil Index Test Results.............................................23
4.2.3.1 Gravel........................................................24
4.2.3.2 Sand ........................................................25
4.2.3.3 Clay (sample A)..............................................26
4.2.3.4 Clay (sample B)..............................................27
4.2.3.5 Composite 1 ..................................................28
4.2.3.6 Composite 2..................................................29
4.2.3.7 Composite 3 ..................................................30
4.2.3.8 Composite 4..................................................31
4.2.3.9 Composite 5 ..................................................32
4.2.3.10 Composite 6..................................................33
5.0 Test Program and Procedures.........................................34
5.1 General.............................................................34
5.2 4-inch Direct Shear Machine ........................................35
5.2.1 Sample Preparation and Equipment Setup.............................35
5.2.2 Application of Normal Stress........................................44
5.2.3 Determination of the Displacement Rate for the Gravel, Sand and Composite
1, 2, 3, 4, 5 and 6 Samples .......................................45
5.2.4 Determination of the Displacement Rate for Clay (samples A and B) ... 46
5.2.5 Shearing of the Sample..............................................65
v


5.3 12-inch Direct Shear Machine ........................................66
5.3.1 Sample Preparation and Equipment Setup...............................66
5.3.2 Time Consolidation and Horizontal Displacement Rate .................79
5.3.3 Shearing of the Sample...............................................80
6.0 Analysis of Test Results ............................................82
6.1 General..............................................................82
6.2 4-inch Direct Shear Box .............................................82
6.2.1 Gravel...............................................................82
6.2.2 Sand.................................................................87
6.2.3 Clay (sample A) .....................................................91
6.2.4 Clay (sample B)......................................................96
6.2.5 Composite 1.........................................................102
6.2.6 Composite 2.........................................................106
6.2.7 Composite 3.........................................................110
6.2.8 Composite 4.........................................................114
6.2.9 Composite 5.........................................................117
6.2.10 Composite 6........................................................121
6.3 12-inch Direct Shear Box ...........................................125
6.3.1 Gravel..............................................................125
6.3.2 Sand................................................................129
6.3.3 Clay (sample A) ....................................................132
6.3.4 Clay (sample B).....................................................136
vi


6.3.5 Composite 1....................................................140
6.3.6 Composite 2....................................................145
6.3.7 Composite 3....................................................149
6.3.8 Composite 4....................................................153
6.3.9 Composite 5....................................................156
6.3.10 Composite 6...................................................160
7.0 Comparison of 12-inch and 4-inch Direct Shear Results..........165
7.1 General........................................................165
7.2 Gravel.........................................................165
7.4 Clay (sample A) ...............................................179
7.5 Clay (sample B)................................................186
7.6 Composite 1....................................................194
7.7 Composite 2....................................................201
7.8 Composite 3....................................................207
7.9 Composite 4....................................................213
7.10 Composite 5....................................................219
7.11 Composite 6....................................................225
8.0 Summary, Conclusions and Recommendations.......................231
BIBLIOGRAPHY
vii


LIST OF TABLES
Table 4.1
Table 5.1
Table 5.2
Table 5.3
Table 5.4
Table 5.5
Table 5.6
Table 5.7
Table 5.8
Table 5.9
Table 5.10
Table 5.11
Table 5.12
Table 6.1
Table 6.2
Table 6.3
Table 6.4
Table 6.5
Table 6.6
Table 6.7
Table 6.8
Table 6.9
Table 6.10
Material Index Tests and Applicable Standard Test Methods
t100 for Gravel
t100 for Sand
t100 for Composite 1
t100 for Composite 2
t100 for Composite 3
t100 for Composite 4
t100 for Composite 5
t100 for Composite 6
t100 for Clay (sample A)
t100 for Clay (sample B)
Estimated Displacement Rate for Clay (sample A) Based on the One-
Dimensional Time Consolidation Test Work
Estimated Displacement Rate for Clay (sample B) Based on the One-
Dimensional Time Consolidation Test Work
Interface Friction Results of the 4-inch Direct Shear Test Work on
Gravel
Interface Friction Results of the 4-inch Direct Shear Test Work on Sand
Required Displacement Rates for Shearing of Clay (sample A)
Interface Friction Results of the 4-inch Direct Shear Test Work on Clay
(sample A)
Required Displacement Rates for Shearing of Clay (sample B)
Interface Friction Results of the 4-inch Direct Shear Test Work on Clay
(sample B)
Interface Friction Results of the 4-inch Direct Shear Test Work on
Composite 1
Interface Friction Results of the 4-inch Direct Shear Test Work on
Composite 2
Interface Friction Results of the 4-inch Direct Shear Test Work on
Composite 3
Interface Friction Results of the 4-inch Direct Shear Test Work on
Composite 4
vm


Table 6.11
Table 6.12
Table 6.13
Table 6.14
Table 6.15
Table 6.16
Table 6.17
Table 6.18
Table 6.19
Table 6.20
Table 6.21
Table 6.22
Table 7.1
Table 7.2
Table 7.3
Table 7.4
Table 7.5
Table 7.6
Table 7.7
Interface Friction Results of the 4-inch Direct Shear Test Work on
Composite 5
Interface Friction Results of the 4-inch Direct Shear Test Work on
Composite 6
Interface Friction Results of the 12-inch Direct Shear Test Work on
Gravel
Interface Friction Results of the 12-inch Direct Shear Test Work on
Sand
Interface Friction Results of the 12-inch Direct Shear Test Work on
Clay (sample A)
Interface Friction Results of the 12-inch Direct Shear Test Work on
Clay (sample B)
Interface Friction Results of the 12-inch Direct Shear Test Work on
Composite 1
Interface Friction Results of the 12-inch Direct Shear Test Work on
Composite 2
Interface Friction Results of the 12-inch Direct Shear Test Work on
Composite 3
Interface Friction Results of the 12-inch Direct Shear Test Work on
Composite 4
Interface Friction Results of the 12-inch Direct Shear Test Work on
Composite 5
Interface Friction Results of the 12-inch Direct Shear Test Work on
Composite 6
Percent Strength Loss from Peak Shear Stress to Minimum Shear Stress
for Gravel
Percent Horizontal Displacement at the Peak Shear Stress for Gravel
Gravel/Geomembrane Interface Friction Angles
Percent Strength Lost from Peak Shear Stress to Minimum Shear Stress
for Sand
Percent Horizontal Displacement at the Peak Shear Stress for Sand
Post Test Moisture Content Test Work Results for Clay (sample A)
Percent Horizontal Displacement at the Minimum Shear Stress for Clay
(sample A)
IX


Table 7.8
Table 7.9
Table 7.10
Table 7.11
Table 7.12
Table 7.13
Table 7.14
Table 7.15
Table 7.16
Table 7.17
Table 7.18
Table 7.19
Table 7.20
Table 7.21
Table 7.22
Table 7.23
Table 7.24
Table 7.25
Percent Horizontal Displacement at the Peak Shear Stress for Clay
(sample A)
Interface Friction Angles and Adhesion for Clay (sample A)
Peak Shear Stress, Minimum Shear Stress, Percent Strength Lost and
Percent Strength Gained for Clay (sample B) Tested in the 4-inch Direct
Shear Box
Peak Shear Stress, Minimum Shear Stress, Percent Strength Lost and
Percent Strength Gained for Clay (sample B) Tested in the 12-inch
Direct Shear Box
Percent Horizontal Displacement at the Peak Shear Stress for Clay
(sample B)
Interface Friction Angles and Adhesion for Clay (sample B)
Percent Strength Lost form Peak Shear Stress to Minimum Shear Stress
for Composite 1
Percent Horizontal Displacement at the Peak Shear Stress for Composite
1
Percent Strength Lost form Peak Shear Stress to Minimum Shear Stress
for Composite 2
Interface Friction Angles for Composite 2
Percent Horizontal Displacement at the Peak Shear Stress for Composite
2
Percent Strength Lost form Peak Shear Stress to Minimum Shear Stress
for Composite 3
Interface Friction Angles for Composite 3
Percent Horizontal Displacement at the Peak Shear Stress for Composite
3
Percent Strength Lost form Peak Shear Stress to Minimum Shear Stress
for Composite 4
Percent Horizontal Displacement at the Peak Shear Stress for Composite
4
Percent Strength Lost form Peak Shear Stress to Minimum Shear Stress
for Composite 5
Interface Friction Angles for Composite 4
x


Table 7.26
Table 7.27
Table 7.28
Table 7.29
Table 8.1
Table 8.2
Table 8.3
Table 8.4
Percent Horizontal Displacement at the Peak Shear Stress for Composite
5
Percent Strength Lost form Peak Shear Stress to Minimum Shear Stress
for Composite 6
Percent Horizontal Displacement at the Peak Shear Stress for Composite
6
Interface Friction Angles for Composite 6
Comparison of Material Index Properties
Comparison of Adhesion and Interface Friction Angles at Peak Shear
Strength
Comparison of Adhesion and Interface Friction Angles at Minimum
Shear Strength
Comparison of Peak and Minimum Shear Strengths
xi


Figure 3.1
Figure 3.2
Figure 4.1
Figure 4.2
Figure 4.3
Figure 4.4
Figure 4.5
Figure 4.6
Figure 4.7
Figure 4.8
Figure 4.9
Figure 4.10
Figure 5.1
Figure 5.2
Figure 5.3
Figure 5.4
Figure 5.5
Figure 5.6
Figure 5.7
Figure 5.8
Figure 5.9
Figure 5.10
Figure 5.11
Figure 5.12
Figure 5.13
Figure 5.14
Figure 5.15
Figure 5.16
Figure 5.17
Figure 5.18
LIST OF FIGURES
Brainard-Killman 12-inch Direct Shear Machine
Geotest Model S2213A 4-inch Direct Shear Machine
Gravel
Sand
Clay (sample A)
Clay (sample B)
Composite 1 (10% clay-sample A)
Composite 2 (20% clay-sample A)
Composite 3 (30% clay-sample A)
Composite 4 (10% clay-sample B)
Composite 5 (20% clay-sample B)
Composite 6 (30% clay-sample B)
4-inch wide by 4-inch long Serrated Aluminum Plate
Gravel Placed in the 4-inch by 4-inch Upper Box
Filter paper and sand placed on top of the gravel to create a level
surface prior to application of the prescribed normal pressure
Prepared and Inundated Gravel Sample for Application of Normal Load
Filling of Lower Box with Water
Compaction Mold and Plate
Compaction Mold and Plate
3/4 inch thick Compacted Sample in Compaction Mold
Placement of Compacted Specimen into Upper Box
Prepared sample, positioned load plate, positioned load application arm
and positioned vertical deformation gauge
Direct Shear Time Consolidation, Gravel
Direct Shear Time Consolidation, Sand
Direct Shear Time Consolidation, Composite 1
Direct Shear Time Consolidation, Composite 2
Direct Shear Time Consolidation, Composite 3
Direct Shear Time Consolidation, Composite 4
Direct Shear Time Consolidation, Composite 5
Direct Shear Time Consolidation, Composite 6
Xll


Figure 5.19
Figure 5.20
Figure 5.21
Figure 5.22
Figure 5.23
Figure 5.24
Figure 5.25
Figure 5.26
Figure 5.27
Figure 5.28
Figure 5.29
Figure 5.30
Figure 5.31
Figure 5.32
Figure 5.33
Figure 5.34
Figure 5.35
Figure 5.36
Figure 6.1
Figure 6.2
Figure 6.3
Figure 6.4
Figure 6.5
Figure 6.6
GeoMatic Consolidometer used for Performing One-Dimensional
Consolidation Tests on the Clay (samples A and B)
One-Dimensional Time Consolidation (ASTM D2435)Clay (sample A)
One-Dimensional Time Consolidation (ASTM D2435) Clay (sample B)
Serrated Aluminum Plate
Secured Geomembrane
4-inch deep by 12-inch wide by 12-inch long Upper Box
Positioned Upper Box
Placed Gravel
Filter Paper to Prevent Migration of Leveling Sand into Gravel
Leveling Sand Placed on Top of Filter Paper
8oz. Non-Woven Geotextile Placed on Top of Leveling Sand
Material Placed in the Upper Box Prior to Compaction
Compaction of Material in the Upper Box
Upper Box and Compacted Material Lifted for Removal of Waxed
Paper and for Filling of the Lower Box with Water
Spacer Plate
Positioned Spacer Plates
Positioned Air Bladder
Post Test Soil Sample Showing that the Water is able to Flow In and
Out of the Soil during Shearing
Results of 4-inch Direct Shear Testwork on Gravel, Shear Stress versus
Horizontal Displacement
Results of 4-inch Direct Shear Testwork on Gravel, Shear Stress versus
Normal Stress
Results of 4-inch Direct Shear Testwork on Sand, Shear Stress versus
Horizontal Displacement
Results of 4-inch Direct Shear Testwork on Sand, Shear Stress versus
Normal Stress
Results of 4-inch Direct Shear Testwork on Clay (sample A), Shear
Stress versus Horizontal Displacement
Results of 4-inch Direct Shear Testwork on Clay (sample A), Shear
Stress versus Normal Stress
xm


Figure 6.7
Figure 6.8
Figure 6.9
Figure 6.10
Figure 6.11
Figure 6.12
Figure 6.13
Figure 6.14
Figure 6.15
Figure 6.16
Figure 6.17
Figure 6.18
Figure 6.19
Figure 6.20
Figure 6.21
Figure 6.22
Figure 6.23
Results of 4-inch Direct Shear Testwork on Clay (sample B), Shear
Stress versus Horizontal Displacement
Results of 4-inch Direct Shear Testwork on Clay (sample B), Shear
Stress versus Normal Stress
Results of 4-inch Direct Shear Testwork on Composite 1, Shear Stress
versus Horizontal Displacement
Results of 4-inch Direct Shear Testwork on Composite 1, Shear Stress
versus Normal Stress
Results of 4-inch Direct Shear Testwork on Composite 2, Shear Stress
versus Horizontal Displacement
Results of 4-inch Direct Shear Testwork on Composite 2, Shear Stress
versus Normal Stress
Results of 4-inch Direct Shear Testwork on Composite 3, Shear Stress
versus Horizontal Displacement
Results of 4-inch Direct Shear Testwork on Composite 3, Shear Stress
versus Normal Stress
Results of 4-inch Direct Shear Testwork on Composite 4, Shear Stress
versus Horizontal Displacement
Results of 4-inch Direct Shear Testwork on Composite 4, Shear Stress
versus Normal Stress
Results of 4-inch Direct Shear Testwork on Composite 5, Shear Stress
versus Horizontal Displacement
Results of 4-inch Direct Shear Testwork on Composite 5, Shear Stress
versus Normal Stress
Results of 4-inch Direct Shear Testwork on Composite 6, Shear Stress
versus Horizontal Displacement
Results of 4-inch Direct Shear Testwork on Composite 6, Shear Stress
versus Normal Stress
Results of 12-inch Direct Shear Testwork on Gravel, Shear Stress
versus Horizontal Displacement
Results of 12-inch Direct Shear Testwork on Gravel, Shear Stress
versus Normal Stress
Results of 12-inch Direct Shear Testwork on Sand, Shear Stress versus
Horizontal Displacement
xiv


Figure 6.24
Figure 6.25
Figure 6.26
Figure 6.27
Figure 6.28
Figure 6.29
Figure 6.30
Figure 6.31
Figure 6.32
Figure 6.33
Figure 6.34
Figure 6.35
Figure 6.36
Figure 6.37
Figure 6.38
Figure 6.39
Figure 6.40
Results of 12-inch Direct Shear Testwork on Sand, Shear Stress versus
Normal Stress
Results of 12-inch Direct Shear Testwork on Clay (sample A), Shear
Stress versus Horizontal Displacement
Results of 12-inch Direct Shear Testwork on Clay (sample A), Shear
Stress versus Normal Stress
Results of 12-inch Direct Shear Testwork on Clay (sample B), Shear
Stress versus Horizontal Displacement
Results of 12-inch Direct Shear Testwork on Clay (sample B), Shear
Stress versus Normal Stress
Results of 12-inch Direct Shear Testwork on Composite 1, Shear Stress
versus Horizontal Displacement
Results of 12-inch Direct Shear Testwork on Composite 1, Shear Stress
versus Normal Stress
Results of 12-inch Direct Shear Testwork on Composite 2, Shear Stress
versus Horizontal Displacement
Results of 12-inch Direct Shear Testwork on Composite 2, Shear Stress
versus Normal Stress
Results of 12-inch Direct Shear Testwork on Composite 3, Shear Stress
versus Horizontal Displacement
Results of 12-inch Direct Shear Testwork on Composite 3, Shear Stress
versus Normal Stress
Results of 12-inch Direct Shear Testwork on Composite 4, Shear Stress
versus Horizontal Displacement
Results of 12-inch Direct Shear Testwork on Composite 4, Shear Stress
versus Normal Stress
Results of 12-inch Direct Shear Testwork on Composite 5, Shear Stress
versus Horizontal Displacement
Results of 12-inch Direct Shear Testwork on Composite 5, Shear Stress
versus Normal Stress
Results of 12-inch Direct Shear Testwork on Composite 6, Shear Stress
versus Horizontal Displacement
Results of 12-inch Direct Shear Testwork on Composite 6, Shear Stress
versus Normal Stress
xv


Figure 7.1
Figure 7.2
Figure 7.3
Figure 7.4
Figure 7.5
Figure 7.6
Figure 7.7
Figure 7.8
Figure 7.9
Figure 7.10
Figure 7.11
Figure 7.12
Figure 7.13
Figure 7.14
Figure 7.15
Figure 7.16
Figure 7.17
Shear Stress versus Horizontal Displacement Curves for Gravel, A
Comparison of the 12-inch and 4-inch Direct Shear Box Results
Comparison of 12-inch and 4-inch Direct Shear Results at the Peak
Shear Stress, Gravel
Comparison of 12-inch and 4-inch Direct Shear Results at the Minimum
Shear Stress, Gravel
Geomembrane Damage
Shear Stress versus Horizontal Displacement Curves for Sand, A
Comparison of the 12-inch and 4-inch Direct Shear Box Results
Comparison of 12-inch and 4-inch Direct Shear Results at the Peak
Shear Stress, Sand
Comparison of 12-inch and 4-inch Direct Shear Results at the Minimum
Shear Stress, Sand
Shear Stress versus Horizontal Displacement Curves for Clay (sample
A) , A Comparison of the 12-inch and 4-inch Direct Shear Box Results
Comparison of 12-inch and 4-inch Direct Shear Results at the Peak
Shear Stress, Clay (sample A)
Comparison of 12-inch and 4-inch Direct Shear Results at the Minimum
Shear Stress, Clay (sample A)
Shear Stress versus Horizontal Displacement Curves for Clay (sample
B) , A Comparison of the 12-inch and 4-inch Direct Shear Box Results
Comparison of 12-inch and 4-inch Direct Shear Results at the Peak
Shear Stress, Clay (sample B)
Comparison of 12-inch and 4-inch Direct Shear Results at the Minimum
Shear Stress, Clay (sample B)
Shear Stress versus Horizontal Displacement Curves for Composite 1,
A Comparison of the 12-inch and 4-inch Direct Shear Box Results
Comparison of 12-inch and 4-inch Direct Shear Results at the Peak
Shear Stress, Composite 1
Comparison of 12-inch and 4-inch Direct Shear Results at the Minimum
Shear Stress, Composite 1
Shear Stress versus Horizontal Displacement Curves for Composite 2,
A Comparison of the 12-inch and 4-inch Direct Shear Box Results
xvi


Figure 7.18
Figure 7.19
Figure 7.20
Figure 7.21
Figure 7.22
Figure 7.23
Figure 7.24
Figure 7.25
Figure 7.26
Figure 7.27
Figure 7.28
Figure 7.29
Figure 7.30
Figure 7.31
Figure 8.1
Figure 8.2
Figure 8.3
Comparison of 12-inch and 4-inch Direct Shear Results at the Peak
Shear Stress, Composite 2
Comparison of 12-inch and 4-inch Direct Shear Results at the Minimum
Shear Stress, Composite 2
Shear Stress versus Horizontal Displacement Curves for Composite 3,
A Comparison of the 12-inch and 4-inch Direct Shear Box Results
Comparison of 12-inch and 4-inch Direct Shear Results at the Peak
Shear Stress, Composite 3
Comparison of 12-inch and 4-inch Direct Shear Results at the Minimum
Shear Stress, Composite 3
Shear Stress versus Horizontal Displacement Curves for Composite 4,
A Comparison of the 12-inch and 4-inch Direct Shear Box Results
Comparison of 12-inch and 4-inch Direct Shear Results at the Peak
Shear Stress, Composite 4
Comparison of 12-inch and 4-inch Direct Shear Results at the Minimum
Shear Stress, Composite 4
Shear Stress versus Horizontal Displacement Curves for Composite 5,
A Comparison of the 12-inch and 4-inch Direct Shear Box Results
Comparison of 12-inch and 4-inch Direct Shear Results at the Peak
Shear Stress, Composite 5
Comparison of 12-inch and 4-inch Direct Shear Results at the Minimum
Shear Stress, Composite 5
Shear Stress versus Horizontal Displacement Curves for Composite 6,
A Comparison of the 12-inch and 4-inch Direct Shear Box Results
Comparison of 12-inch and 4-inch Direct Shear Results at the Peak
Shear Stress, Composite 6
Comparison of 12-inch and 4-inch Direct Shear Results at the Minimum
Shear Stress, Composite 6
Results of 4-inch Direct Shear Testwork, Peak Shear Stress versus
Normal Stress
Results of 12-inch Direct Shear Testwork, Peak Shear Stress versus
Normal Stress
Results of 4-inch Direct Shear Testwork, Minimum Shear Stress versus
Normal Stress
XVII


Figure 8.4
Figure 8.5
Figure 8.6
Figure 8.7
Figure 8.8
Figure 8.9
Results of 12-inch Direct Shear Testwork, Minimum Shear Stress
versus Normal Stress
Average Difference of Peak Shear Strength
Average Difference of Minimum Shear Strength
Photographs of Geomembrane Coupons, 1 of 3
Photographs of Geoemembrane Coupons, 2 of 3
Photographs of Geoemembrane Coupons, 3 of 3
XVUl


1.0 Introduction
1.1 Problem Statement
The interface shear strength (or friction angle) is an important parameter for designing
facilities on slopes which make use of geosynthetics. The stability of slopes in heap
leach and waste containment facilities depends on the interface shear strengths between
the components of the liner system which may include both geosynthetics and soils.
The most commonly used and widely accepted device to measure the interface shear
strength is a conventional direct shear box. However, there are many factors that
influence the test results including: sample preparation, time allotted for consolidation
of the soil, frictional resistance in the apparatus, the rate at which the application of the
shearing force is applied (especially in fine grained saturated soils) and possible
eccentric loading. These factors contribute to increasing the cost and effort in
performing a reliable interface friction test.
Before 1991, there were no set standards in the industry on how to measure the
interface shear strength between geosynthetics and soils. Several geotechnical
laboratories focused on performing the test using tilt-tables, using direct shear boxes
varying in size (2-inch square to 12-inch square) and performing pull-out tests. In
1991 however, the Geosynthetics Research Institute (GRI) adopted the first
standardized test method for measuring the interface shear strength: GS6 "Interface
Friction Determination By Direct Shear Testing". This test method specifies the use
1


of the 12-inch square direct shear box. In 1992, the American Society for Testing and
Materials (ASTM) developed a standard test method: ASTM D5321 "Determining the
Coefficient of Soil and Geosynthetic or Geosynthetic and Geosynthetic Friction by the
Direct Shear Method" which also specifies the use of the 12-inch square direct shear
box.
While these standards eliminated test method inconsistencies in the industry, they set
a standard on the type of equipment (direct shear machine) and size of the equipment
(12-inch square) to be used in the testing of interface shear strengths. This study
focuses on the applicability of determining interface shear strengths using a 4-inch
square direct shear box. If it is determined that adequate design values of interface
shear strengths may be determined in the 4-inch direct shear box, testing can be
performed at a lower cost and at a faster rate. It should be noted that if adequate
design values are generated in the 4-inch direct shear box the results may be soil type
and size dependent.
1.2 Scope of the Study
This paper will present a study on measuring the interface shear strength between soil
and geomembrane, present a comparison of the test results generated in a 4-inch
square direct shear box and a 12-inch square direct shear box. This study will make
a recommendation on the upper size limit of material that may be tested in a 4-inch
direct shear box while maintaining acceptable results when compared to those
generated by the 12-inch direct shear box. Several different types of soils and
aggregates were selected for testing to represent different layer types used in a heap
2


leach or waste containment facility barrier system. A gravel, sand, clay and several
composite samples of these materials were selected for use in this study.
3


2.0 Literature Review
2.1 General
An extensive effort was made to find references pertaining to soil/geomembrane
interface test work including direct shear test work pertaining to comparing the results
generated by different size direct shear boxes and work pertaining to interface testing
procedures and evaluation of test results. The reference search included the
university's computer assisted research system, CARL, which allowed a search of all
regional libraries, Knight Piesold's library and the Internet.
The reference search found many documents pertaining to test work on soil /
geomembrane interfaces, interface testing procedures and the evaluation of interface
test results. However, only one article was found that discussed comparing the
interface test results generated in different size direct shear machines. These papers
may be referenced in the bibliography.
2.2 Soil / Geomembrane Interface Test Work
Several papers were reviewed which discuss soil / geomembrane interface test work.
The studies were found to be performed in many different types of testing
devices and in many different size direct shear machines. Typically, the studies were
found to analyze a sand (or clay) / geomembrane interface. The findings of a few of
4


the papers which were found to be most applicable to this test work are summarized
below.
"Direct Shear Testing for HDPE / Amended Soil Composites" by H.D. Sharma
and D.E. Hullings
This paper presents the results (peak and residual interface shear strengths) of interface
friction test work performed in a 12-inch direct shear box. The paper was written prior
to the release of the ASTM D 5321 standard test procedures for direct shear interface
test work. The paper stresses the importance of identifying the potentially weak
interfaces in a barrier system and accurately testing the interface shear strength by
simulating field conditions. The study tested many different types of soils and
amended soils adjacent to different geomembranes.
One of the interfaces tested was a bentonite sand adjacent to a smooth HDPE Gundle
product. The bentonite sand had 51 percent of the material passing the No. 200 seve,
a LL of 38, a PI of 22, a maximum dry density of 129 pcf and an optimum moisture
content of 9.6 percent. Upon completion of the direct shear test work, the interface
friction angle at the peak shear strength was found to 19 degrees with zero adhesion
and the residual shear strength was found to be 7 degrees with an adhesion of 29 kPa.
The residual shear strength was measured at a horizontal displacement of 30.5 cm or
10-percent of the original sample length. The distance that the sample was sheared,
10 percent of the original sample length, was selected because no guidelines regarding
the total horizontal displacement the sample should be sheared such that the residual
shear strength has been reached were available. The test was performed for partially
5


consolidated undrained conditions which were assumed to simulate the long term final
slope configuration as if refuse was in place for some time. The interface was
inundated to simulate field conditions due to rain, leachate migration, migration of
water due to consolidation of soil and/or water vapor collecting under the
geomembrane from thermal effects.
"Smooth HDPE-Clay Liner Interface Shear Strengths: Compaction Effects" by
R.B. Seed and R.W. Boulanger
This paper analyzed the effects of compaction effort and moisture content on the
interface shear strength of a clay adjacent to an HDPE geomembrane. The tests were
performed in a direct shear machine with a 4-inch diameter lower box dimension and
a 4-inch square upper box dimension. The specimens were sheared in an
unconsolidated undrained condition with some samples being presoaked for several
days under a light surcharge (250 psf). The results of the test work indicate that the
interface shear strength can change by a factor of 2 or more as a result of minor
variations in the as-compacted dry density and moisture content of the clay.
"Shear Strength of Sand-Geomembrane Interfaces for Cover System and Liner
Design" by S.J. Druschel and T.D. O'Rourke
This study performed 450 sand/geomembrane interface tests in a 60 mm square direct
shear box. The tests were performed at horizontal displacement rates of 0.4 to 0.6
mm/min and at normal stresses of 3.5 to 35 kPa. Four different types of sand were
tested adjacent to many different types of geomembrane. The results of the
6


sand/HDPE interface test work performed, showed no peak shear stress (i.e. the shear
stress versus horizontal displacement curves had no defined peak shear strength). The
study indicated that these results were typical.
2.3 Interface Test Procedures
Several papers discussing interface test procedures were found. The findings of a few
of the papers found to be most applicable to the test work done in this study are
summarized below.
"The Influence of Selected Testing Procedures on Soil/Geomembrane Shear
Strength Measurements" by S.M. Bemben and D.A. Schulze
This paper studied the effects of a single set-up with multiple consolidation and
shearing steps to obtain 3 or more points of a residual stress failure envelope. The
authors found this approach feasible and practical for the following interface tests:
soil/soil, soil/smooth geomembrane and soil/textured geomembrane. They also found
that the ASTM guideline for determining the critical rate of movement (horizontal
displacement rate) was reasonable when they tested interfaces that made use of their
glacial till specimen. The glacial till was a minus Vi inch material found to have very
low plasticity, a maximum dry density of 130 pcf and an optimum moisture content of
8 percent. The test work also indicated that the minimum shear movement required
to reach residual strength increases with increasing normal stresses.
7


"The Influence of Testing Procedures on Clay/Geomembrane Shear Strength
Measurements" by S.M. Bemben and D.A. Schulze
The focus of this paper was to evaluate the test procedures outlined in ASTM D5321
with regard to sliding suction and initial capillary suction.
Initial capillary suction is thought to occur when the soil specimen is tested at the
optimum or natural moisture content as opposed to inundated conditions simulated by
filling the lower box with water. Flooded boundary conditions during soaking and
shearing prevent the development of initial capillary suction.
Sliding suction is thought to develop on the bottom of a wet clay specimen moving over
a smooth surface membrane. A film of water typically exists at the interface of the
clay and the membrane at the end of consolidation. During shearing the clay specimen
tends to slide on this film of water. If drained state stress behavior is sought, the test
results indicate that the sliding suction effects can be offset by using a "sufficiently
slow rate of horizontal movement." It was thought that ASTM D5321, as it qpplies to
clay/geomembrane interface testing, provides an acceptable method for determining a
safe rate of horizontal movement. The authors found that this sufficiently slow rate of
movement will produce consolidated-drained behavior during shearing for tests on
textured geomembrane not on smooth geomembrane. The authors believe that a
"sufficiently slow rate of movement" to minimize/eliminate soil suction can be
developed by having an initial degree of saturation of 90 percent or higher, flooded
boundary conditions, a safe rate of movement as defined in ASTM D5321, and similar
test procedures and equipment as described in the paper.
8


2.4 Evaluating Interface Test Results
Several papers discussing the evaluation of interface test results were found. The
findings of two of the papers found to be most applicable to the test work done in this
study are summarized below.
"Geosynthetic Interface Friction: A Challenge for Generic Design and
Specification" by R.F. Lopes, P.A. Smolkin and P.J. Lefebvre
This paper discusses the factors influencing design and specification and performance
of liner systems. The conclusion of the paper states that interface friction values
obtained from laboratory shear test work are very sensitive to the test apparatus and
the physical characteristics of the specific materials being tested.
"Interface Shear Strength in not for the Uninitiated" by M.E. Smith and K.
Criley
This paper discusses the complexity of interface shear strength testing. The authors
think the key factors in obtaining good quality shear strength test results requires
finding a reliable laboratory, specifying the required test procedures in detail, use
parameters that are accurate and job-specific and if the data doesn't make sense, ask
questions.
9


2.5 Comparison of Test Results Generated in Different Size Direct Shear Boxes
The following paper is the only article found that discusses comparing interface test
results generated in different size direct shear machines.
"Soil-Geosynthetic Interface Strength Characteristics: A Review of State-of-
the-Art Testing Procedures" by D.L. Takasumi, K.R. Green and R.D. Holtz
This paper focused on comparing the difference in test results due to the different types
of interfaces tested and the variation of test procedures used. Part of the focus of this
study was to evaluate the interface test results produced in various size shear box test
apparatus. The box sizes varied from 2.4 inches square to 12-inches square. Interface
test work performed on an Ottawa sand and concrete sand contact with a smooth HDPE
geomembrane at low (< 100 kPa) to high (<480 kPa) normal stresses in direct shear
boxes varying in size (from 2 inches to 12-inches square) were found to have similar
friction efficiencies. Friction efficiency is the ratio of the measured interface friction
angle to the soil friction angle. However, additional research in this area was
recommended.
10


3.0 Direct Shear Test Equipment and Test Methods
3.1 General
As stated previously, the purpose of this study is to compare the results of
soil/geomembrane interface shear strengths recorded in a 4-inch and 12-inch direct
shear apparatus. The 4-inch direct shear apparatus, used in this test work, is
manufactured by Geotest Instrument Corporation (Model S2213A) and the 12-inch
direct shear box is a Brainard-Killman LG-114 distributed by Boart Longyear.
Both the 4-inch and 12-inch direct shear machines used in this test work allow for
totally fixed conditions. This type of test condition allows for the geomembrane to be
"fixed" to the lower box either by clamping or gluing the geomembrane to a rigid
substrate that fits tightly into the lower box. The results of test work performed under
these conditions are considered to be lower bound values of the interface shear
resistance, thus yielding slightly conservative results when used in stability analyses.
Both machines have a stationary upper box while the lower box rides on roller
bearings. The lower box is also slightly longer than the upper box (4-inch or 12-inch)
to allow the area of contact between the upper and lower boxes to be constant during
the test. Figures 3.1 and 3.2 show the 12-inch direct shear apparatus and the 4-inch
direct shear machine, respectively.
11




13


3.2 12-inch Direct Shear Box Specifications
The LG-114 direct shear box was assembled by Brainard-Killman with the following
specifications:
Horizontal Displacement Speed Range: 0.0001 to 0.2 inches/minute
Maximum Allowable Horizontal Travel in Lower Box: 4 inches
Maximum Normal Load: 10,000 lbf (100 psi) applied by air
Normal Compressive Loads: Applied via air bladder
Maximum Shear Force: 10,000 lbf
Upper Box Measurements: 12 inch wide x 12 inch long x 4 inch high
Lower Box Measurements: 12 inch wide x 16 inch long x 4 inch high
3.3 4-inch Direct Shear Box Specifications
As stated previously, the 4-inch direct shear apparatus used in the test work was
manufactured by Geotest Instrument Corporation, Model S2213A. This direct shear
machine conforms to the following standards:
Horizontal Displacement Speed Range: 0.00003 to 0.15 inches/minute
Maximum Allowable Horizontal Travel in Lower Box: 0.9 inches
Maximum Normal Load: 2,250 lbf (140.6 psi) applied by air/nitrogen
Normal Compressive Loads: Applied via rigid plate
Maximum Shear Force: 2,250 lbf
Upper Box Measurements: 4 inch wide x 4 inch long x 1 inch high
Lower Box Measurements: 4 inch wide x 5 inch long x 1 inch high
3.4 Test Methods
Two widely known direct shear test methods have been followed by the industry for
the past several years. The two methods are:
14


Geosynthetic Research Institute (GRI) Test Method GS6, "Interface
Friction Determination by Direct Shear Testing."
American Society for Testing and Materials (ASTM) D5321,
"Determining the Coefficient of Soil and Geosynthetic or Geosynthetic
and Geosynthetic Friction by the Direct Shear Method."
In general, the test procedures and scopes of each method are similar. In fact, the GRI
test method was developed to give engineers and lab technicians a method to follow
until an ASTM method was developed. Therefore, the ASTM test method was
followed, in general, when performing the direct shear tests conducted for this study.
A copy of each method may be referenced in Appendix A.
3.5 ASTM D5321 Test Procedures
ASTM D5321 is the "Standard Test Method for Determining the Coefficient of Soil
and Geosynthetic or Geosynthetic and Geosynthetic Friction by the Direct Shear
Method." This method was followed for the interface test work performed for this
study.
As required by ASTM, the interface shear strength between a soil and a Geosynthetic
shall be determined in a 12-inch square direct shear box. A normal compressive load
and a shear force are applied to the specimen. The shear force is applied to one end
of the box such that one section of the container move with respect to the other sectbn
thus recording shear force versus horizontal displacement. ASTM specifies that a
15


minimum of three tests be performed under different normal stresses. The peak and/or
residual shear stress is then plotted against the appropriate normal stress. From this
plot, the interface friction angle may be determined.
The ASTM procedure requires a minimum dimension of the upper and tower boxes to
be 12-inches. In addition, it is recommended that the minimum depth be 2 inches or
6 times the maximum particle size when soil is tested adjacent to a geosynthetic.
As stated previously, a 4-inch direct shear box will be used for some of the direct shear
interface test work as the purpose of this paper is to establish a correlation between the
interface shear results generated in a 4-inch and 12-inch direct shear box. Therefore,
the minimum box dimension as stated in the ASTM test method will not always be
adhered to for the test work performed for this study.
In addition to not meeting the minimum box dimension criterion, the minimum depth
criterion has not been met. For this test work, the 4-inch direct shear apparatus used
has an upper box depth of one inch. While this depth is adequate when testing fine
grained soils and sands (i.e. the box depth is greater than 6 times the maximum particle
size), several materials tested have particle sizes that are larger than 1/6 times the depth
of the soil placed in the upper box. The effect that the depth of the soil sample, in the
upper box, has on the interface shear strength was not studied.
The ASTM test method also states several allowable equipment tolerance limits. The
tolerances are as follows:
16


The normal load device must maintain a uniform normal stress on the
specimen within + or 2-percent during testing.
The shear force loading device must maintain a constant rate of displacement
in a direction parallel to the direction of travel of the container. The rate of
displacement should be controlled to an accuracy of + or 10 percent.
The horizontal displacement indicator should have a sensitivity of 0.001
inches.
These equipment tolerances are met with the equipment used in this test work.
In general, the test setup and procedures for measuring the interface shear strength of
soil and geosynthetic friction described above are as follows:
The geomembrane specimen is placed flat over a rigid metal substrate in the
lower shear box. Due to machine constraints, the manner in which the
geomembrane is fixed in each box differs. In both machines, however, the
geomembrane remains in a fixed condition during testing. In the 12-inch direct
shear box, the geomembrane is clamped at one end such that the material
remains fixed during the test. In the 4-inch direct shear box, the geomembrane
specimen is glued to a serrated aluminum plate such that it remains fixed for the
duration of the test. Devcon 5 Minute Epoxy was used to glue the
geomembrane to the rigid plate. The epoxy was allowed to set for a minimum
of 24 hours prior to testing.
17


The upper box is then placed in the proper position.
A predetermined weight of soil is placed in the upper box according to standard
soil testing practices where the soil type, unit weight, density and moisture
content are recorded. Care was taken to avoid damaging the geomembrane
specimen during soil placement.
A piece of filter paper and a porous stone, or other means of allowing drainage,
are placed above the soil specimen and rigid stratum is placed over the porous
stone to ensure a uniform normal stress is applied over the entire test area.
If required, the geomembrane/soil interface is inundated by filling the direct
shear box with distilled water and allowing the soil/geosynthetic interface to
become wet and the soil specimen to become saturated. Interfaces area
inundated to simulate field conditions due to rain, leachate migration, migration
of water due to consolidation of soil and/or vapor collecting under the
geomembrane from thermal effects.
The normal loading system is assembled and load and displacement indicators
are installed and set to zero.
The desired normal load may now be applied and the sample is allowed to
consolidate according to the procedures outlined in ASTM D3080 "Standard
Test Method for Direct Shear Tests of Soils Under Consolidated Drained
18


Conditions." The soil is allowed to consolidate to simulate long term
conditions, i.e. as if the heap leach or waste containment facility had been in
place for some time.
Once the specimen has consolidated, while maintaining the required normal
load, the shear force is applied using a constant rate of displacement. The
shear force shall be applied at a rate slow enough to dissipate soil pore
pressures. The rate of displacement is calculated by using the information
generated from the time consolidation graph.
In the 12-inch direct shear box, the shear force is measured as a function of a
specified time interval (every 6 seconds) while the shear force in the 4-inch
direct shear box is recorded as a function of horizontal displacement.
The test shall be run until the applied shear force remains relatively constant
with increasing displacement (residual shear strength).
Once the shear force is removed, the normal load shall be removed and the
device carefully disassembled. The test is then performed with at least two
additional normal stresses, selected by the user, using new soil and geosynthetic
specimens.
The data from the tests are then analyzed and the results are plotted with the
shear stress versus horizontal displacement. It should be noted that the test
measures the shear force, however, shear stress may be calculated as follows:
19


T = Fs/Ac
where:
T = shear stress (psf)
Fs = shear force (lbs)
Ac = corrected area of soil specimen in coitact with the
geomembrane (sf)
Note: For the tests performed in this study, the contact area
does not decrease with horizontal displacement, therefore the
contact area is the area of the soil specimen.
Either a peak or residual shear stress may be obtained from the shear stress versus
horizontal displacement graph knowing the corresponding normal stress. This
information may be plotted on a second graph with normal stress versus shear stress.
From this plot, a linear or non-linear (hyperbolic or parabolic) fit is made using the
data such that the interface friction angle and adhesion may be determined at a given
normal stress.
A more detailed description of the test setup and procedures in the 4-inch and 12-inch
boxes is discussed in Section 5.0.
20


4.0 Materials, Material Preparation and Properties
4.1 Geomembrane
A smooth 60 mil High Density Polyethylene (HDPE) geomembrane was selected for
the interface test work. Although there are many different types of geomembrane (higjh
density polyethylene, linear low density polyethylene, polyvinyl chloride, etc), material
thicknesses, texturing, and reinforcing; a smooth 60 mil HDPE product was selected
since this product is one of the most widely used products in design and construction
of waste containment and heap leach facilities.
If test work shows that acceptable interface shear strengths can be obtained in the 4-
inch direct shear box when compared to those produced in the 12-inch direct shear box
using a smooth 60 mil HDPE product, similar results (comparison of results between
the 4-inch and 12-inch direct shear boxes not interface shear strengths) are expected
to be achieved using the different types and thicknesses of geomembranes. However,
additional test work, beyond the scope of this study, may be performed to confirm this
position.
The smooth 60 mil HDPE product used in this study was supplied by GSE Lining
Technology, Incorporated located in Houston, Texas. The manufacturer certification
sheet associated with the product used in this test work is included in Appendix B.
21


4.2 Soils
4.2.1 General
The barrier systems designed for waste containment and heap leach facilities have
several different types of soil and aggregate adjacent to a geomembrane. For example,
a fine grained, low permeability soil, such as a silt or a clay, is typically found beneath
the geomembrane to prevent or discourage seepage of leachate into the groundwater
in the event the geomembrane is punctured. Several different types of soils and
aggregates may be found above geomembranes. For example, if high loads are
expected on the geomembrane, as in many heap leach facilities, a protective layer, such
as a sand, may be placed on top of the geomembrane. In facilities where high loads
are not expected and puncturing of the geomembrane is not of concern, a gravel with
minimal fines may be placed on top of the geomembrane to promote drainage of
leachate.
The interface shear strength between these soils and/or aggregates and the
geomembrane is a critical component when performing stability analyses for the
facility. Therefore, all of the above mentioned soils and aggregates were selected for
use in the test program. In addition, several composite materials (suchas a clayey sand
with gravel) were manufactured for testing.
4.2.2 Soil Index Tests
Prior to performing the direct shear test work, material index testing was performed
such that the soils and aggregates could be classified in the appropriate engineering
22


category. All test work was performed in Knight Piesold's geotechnical laboratory
located in Denver, Colorado. The material index testing included the following tests
and applicable ASTM test methods:
Table 4.1
Material Index Tests and Applicable Standard Test Methods
TEST ASTM TEST METHOD
Particle Size Distribution D 422
Atterberg Limits D 4318
Moisture Density Relationship D 698
Specific Gravity (Fine Grained Soils) D 854
Specific Gravity (Aggregate) C 127
Moisture Content D 2216
Classification of Soils D 2487
Time Consolidation D 2435
Relative Density C 29 / C29M / D4253 / D4254
4.2.3 Soil Index Test Results
The results of the index testing are summarized below for each material type studied.
23


4.2.3.1
Gravel
For testing purposes, a gravel was manufactured to meet the following specification:
minus 3/4 inch, plus No. 4 sieve. The minus 3/4 inch material was selected to
represent an upper bound on size of material that may result in the production of
reliable and comparable interface shear strengths in the 4-inch and 12-inch direct shear
boxes. Based on the particle size distribution analysis, the unified soil classification
system (USCS) classifies this material as a poorly graded gravel, GP. The uniformity
coefficient. Cu, was found to be 2.5 and the coefficient of curvature, Cc, is 1.1. The
specific gravity of the aggregate was found to be 2.61, according to ASTM C 127.
Since the material has less than one percent passing the No. 200 sieve, minimum and
maximum relative density tests were performed on the material and found to be 94.4
pcf and 105.7 pcf, respectively. Index test data sheets may be referenced in Appendix
C.l.
Figure 4.1 Gravel
24


4.2.3.2
Sand
As per ASTM D 422, particle size distribution test method, the sand was found to have
99.9 percent of the material passing the No. 4 sieve and 98.1 percent of the material
retained on the No. 200 sieve. Based on these test results, this material classifies as
a poorly graded sand, SP. The uniformity coefficient, Cu, and the coefficient of
curvature, Cc, were found to be 5 and 0.5, respectively. The specific gravity of the
sand was found to be 2.65, as per ASTM D 854. Minimum and maximum relative
density tests were performed on this material since, the material has less than two
percent passing the No. 200 sieve. The test work was performed according to ASTM
D4253 and D4254. The results of the test work indicate a minimum relative density
of 106 pcf and a maximum relative density of 115.6 pcf. Index test data sheets may
be referenced in Appendix C.2.
Figure 4.2 Sand
25


4.2.3.3
Clay (sample A)
As per ASTM D 422, a particle size distribution analysis was performed on the clay.
Results of the gradation and hydrometer analyses indicate that 100-percent of the soil
passes the No. 4 sieve and approximately 90-percent of the soil passes the No. 200
sieve. The results of the Atterberg Limits test indicate this material has a liquid limit
(LL) of 90.5 and a plasticity index (PI) of 51.3. The results of this test work indicate
the material classifies as a fat clay, CH, as per ASTM D 2487. The specific gravity
of the material was found to be 2.61 and the moisture-density relationship of the clay
indicated a maximum dry density of 69 pcf and an optimum moisture content of 42.6
percent. Index test data sheets may be referenced in Appendix C.3.
Figure 4.3 Clay (sample A)
26


4.2.3.4
Clay (sample B)
Index test work performed on this soil, according to ASTM standards, indicates that
approximately 98-percent of this soil passes the No. 200 sieve. Atterberg limit test
work indicates this soil has a LL of 59.0 and a PI of 41.1. Based on this information,
this soil classifies as an fat clay, CH. Specific gravity analyses on this material
indicate a specific gravity of 2.66. The moisture-density relationship information
indicates a maximum dry density of 91.5 pcf and an optimum moisture content of 19
percent. Index test data sheet may be referenced in Appendix C.4.
Figure 4.4 Clay (sample B)
27


4.2.3.5
Composite 1
This material was manufactured to have approximately equal parts of gravel and sand
with 10 percent of the material passing the No. 200 sieve. The material passing the
No. 200 sieve consists of the clay (sample A) material. Once manufactured, grain size
analyses indicate that 45.3 percent of the material is gravel, 44.6 percent of the
material is sand and 10.1 percent of the material is clay. The uniformity coefficient,
Cu, was determined to be 80 and the coefficient of curvature, Cc, is 1.6. Based on this
information, Composite 1 was classified as a well graded gravel with clay and sand,
GW-GC. Since the material was found to have 10-percent passing the No. 200 sieve,
minimum and maximum relative density tests were performed on the material and were
found to be 110.3 pcf and 123.4 pcf, respectively. The index test data sheets may be
referenced in Appendix C.5.
Figure 4.5 Composite 1 (10% clay sample A)
28


4.2.3.6
Composite 2
As with Composite 1, this material was manufactured to have approximately equal
parts of gravel and sand. The material was also manufactured to have approximately
20 percent of the material passing the No. 200 sieve. The material passing the No. 200
sieve consists of the clay (sample A) material. Once manufactured, grain size analyses
indicate that 35.6 percent of the material is gravel, 44.4 percent of the material is sand
and 19.9 percent of the material is clay. Based on this information, Composite 2 was
classified as a clayey sand with gravel, SC. Since the material was found to have 20-
percent passing the No. 200 sieve, a standard proctor test was performed. The results
of this test indicate a maximum dry density of 113 pcf and an optimum moisture
content of 16 percent. The index test data sheets may be referenced in Appendix C.6.
Figure 4.6 Composite 2 (20% clay sample A)
29


4.2.3.7
Composite 3
This material was manufactured to have approximately equal parts of gravel and sand
with approximately 30 percent of the material passing the No. 200 sieve. The material
passing the No. 200 sieve consists of the clay (sample A) material. Once
manufactured, grain size analyses indicate that 33.3 percent of the material is gravel,
41.6 percent of the material is sand and 25 percent of the material is clay. Based on
this information, Composite 3 was classified as a clayey sand with gravel, SC. Since
the material was found to have 25-percent passing the No. 200 sieve, a standard
proctor test was performed. The results of this test indicate a maximum dry density
of 108.7 pcf and an optimum moisture content of 19 percent. The index test data
sheets may be referenced in Appendix C.7.
Figure 4.7 Composite 3 (30% clay sample A)
30


4.2.3.8
Composite 4
This material was manufactured to have approximately equal parts of gravel and sand
with 10 percent of the material passing the No. 200 sieve. The material passing the
No. 200 sieve consists of the clay (sample B) material. Once manufactured, grain sire
analyses indicate that 49 percent of the material is gravel, 40.9 percent of the material
is sand and 10.1 percent of the material is clay. The uniformity coefficient. Cu, was
determined to be 93.3 and the coefficient of curvature, Cc, is 0.13. Based on this
information, Composite 4 was classified as a well graded gravel with clay and sand,
GW-GC. Since the material was found to have 10-percent passing the No. 200 sieve,
minimum and maximum relative density tests were performed on the material and were
found to be 110.3 pcf and 120.8 pcf, respectively. The index test data sheets may be
referenced in Appendix C.8.
Figure 4.8 Composite 4 (10% clay sample B)
31


4.2.3.9
Composite 5
As with Composite 4, this material was manufactured to have approximately equal
parts of gravel and sand. The material was also manufactured to have approximately
20 percent of the material passing the No. 200 sieve. The material passing the No. 200
sieve consists of the clay (sample B) material. Once manufactured, grain size analyses
indicate that 42.7 percent of the material is gravel, 40.6 percent of the material b sand
and 16.7 percent of the material is clay. Based on this information, Composite 4 was
classified as a clayey gravel with sand, GC. Since the material was found to have 17-
percent passing the No. 200 sieve, a standard proctor test was performed. The results
of this test indicate a maximum dry density of 127.5 pcf and an optimum moisture
content of 9 percent. The index test data sheets may be referenced in Appendix C.9.
32


4.2.3.10 Composite 6
This material was manufactured to have approximately equal parts of gravel and sand
with approximately 30 percent of the material passing the No. 200 sieve. The material
passing the No. 200 sieve consists of the clay (sample B) material. Once
manufactured, grain size analyses indicate that 28.3 percent of the material is gravel.
39.4 percent of the material is sand and 32.3 percent of the material isclay. Based on
this information, Composite 6 was classified as a clayey sand with gravel, SC. Since
the material was found to have 32-percent passing the No. 200 sieve, a standard
proctor test was performed. The results of this test indicate a maximum dry density
of 120.8 pcf and an optimum moisture content of 11 percent. The index test data
sheets may be referenced in Appendix C.10.
Figure 4.10 Composite 6 (30% clay sample B)
33


5.0 Test Program and Procedures
5.1 General
In general, the test work on each material type was performed at four normal stresses
(25, 50, 75 and 100 psi). The maximum normal stress, 100 psi, is an upper limit of
the allowable normal stress that may be applied by the 12-inch direct shear box. While
the 25 psi represents a lower bound that is considered reliable since there is some
concern in the industry on the reliability of direct shear box tests at low normal
pressures.
The four points sheared for each sample were performed with an inundated interface
between the soil and the geosynthetic. The interface was inundated by filling the box
with water and allowing the interface between the soil and geomembrane to become
inundated. This condition results in a lower bound of the interface shear strength and
simulates field conditions due to rain, leachate migration, migration of water due to
consolidation of soil and/or water vapor collecting under the geomembrane from
thermal effects.
As stated previously, the tests were sheared until the residual shear strength and/or 15-
percent horizontal displacement was reached.
34


5.2 4-inch Direct Shear Machine
5.2.1 Sample Preparation and Equipment Setup
Based on material index test information, soil sample weights and moisture contents
were measured such that a soil sample could be placed in the upper box of the shear
machine either at a relative density of 65 percent or at the maximum dry density and
optimum moisture content. The required sample weight was calculated using the
moisture density relationship or relative density information and the following upper
box dimensions: 4-inches wide by 4 inches long by 0.75 inches high. The above
stated density/moisture content requirements are typical of construction specifications
for placement of similar materials found adjacent to geomembranes in heap leach or
waste containment facilities.
A minimum of 24 hours prior to performing the shear test a 4-inch wide by 5-inch long
coupon of geomembrane was glued to a serrated aluminum plate, as shown on Figure
5.1.
The 60 mil HDPE geomembrane/serrated aluminum plate was placed in the lower box
and the edges of the box were greased with Dow Corning high vacuum grease to
minimize frictional resistance between the Teflon feet of the upper box and the lower
box during shearing. The upper box was positioned, secured against the load cell and
the Teflon feet were adjusted such that the upper box was level and there was a slight
gap between the base of the upper box and the 60 mil HDPE geomembrane,
approximately 0.06".
35


Figure 5.1 4-inch wide by 5-inch long Serrated Aluminum Plate
The following paragraph describes the placement procedures used for the gravel, sand
and Composite 1 and 4 materials.
As shown on Figure 5.2. the material was then placed into the upper box. The
material was dry rodded in place such that the sample was approximately 0.75
inches high and had a relative density of 65-percent.
36


The following paragraph describes the placement of the filter paper and leveling sand
for the gravel material.
A 4-inch by 4-inch sheet of wetted filter paper was placed on top of the gravel
and a thin layer of sand was placed on top of the filter paper. The sand was
placed such that the voids on the top surface of the gravel were filled and a
level surface was created, as shown on Figure 5.3. The level surface was
required such that a uniform normal load could be applied to the gravel.
37


Figure 5.3 Filter paper and sand placed on top of the gravel to create a level
surface prior to application of the prescribed normal pressure.
The following paragraph describes the placement of the filter paper and porous stone
for the sand and Composite 1 and 4 materials.
A 4-inch by 4-inch sheet of Filter paper was placed on top of the sand and a
0.25-inch thick by 4-inch wide by 4-inch long porous stone was placed on top
of the filter paper to allow for dissipation of pore pressures during shearing.
38


The following paragraph describes how an inundated interface was obtained for the
gravel, sand and Composites 1 and 4.
As shown on Figure 5.4, distilled water was then poured into the box such that
the material voids were filled with water and the soil sample / HDPE interface
was inundated.
Figure 5.4 Prepared and Inundated Gravel Sample for Application of Normal Load
39


The following paragraphs describes the compaction and placement processes for the
clay (samples A and B) and Composite 2, 3, 5 and 6 materials.
Once the upper box was positioned, the lower box was then filled with distilled
water such that the geomembrane was covered with approximately 1/8 inch of
water, see Figure 5.5.
The soil samples were then prepared for direct shear testing. Based on the
moisture density test work, a sample of predetermined weight at optimum
moisture content was compacted into a 1-inch high by 4-inch wide and 4-inch
40


long mold to achieve the predetermined maximum dry density. During
compaction, the height of the sample was measured several times to ensure a
sample height of 0.75 inches. Refer to Figures 5.6, 5.7 and 5.8 for the sampfe
preparation process in the compaction mold.
Once the material was compacted into the mold, the soil sample was then
placed into the upper box by pushing the specimen into the upper box using the
compaction plate, see Figure 5.9. Distilled water was then poured to the top
level of the upper box and a 4-inch by 4-inch sheet of filter paper and 0.25-inch
porous stone were placed on top of the clay.
Figure 5.6 Compaction Mold and Plate
41


Figure 5.7 Compaction Mold and Plate
42


Figure 5.9 Placement of Compacted Specimen into Upper Box
The following paragraph relates to equipment setup for all soil samples tested.
The load plate, load application arm and vertical deformation gauge were
positioned, as shown on Figure 5.10 and the required normal load and
estimated rate of horizontal displacement were input.
43


Figure 5.10 Prepared sample, positioned load plate, positioned load application arm
and positioned vertical deformation gauge.
5.2.2 Application of Normal Stress
The required normal load was then applied to the sample (the horizontal load remained
off) and the sample was allowed to consolidate. Manual vertical deformation readings
were taken against time such that a consolidation curve for the sample could be plotted
and the time for 100-percent of the pore pressure dissipation (t^) could be determined.
The samples were allowed to consolidate according to the procedures outlined in
ASTM D3080 "Standard Test Method for Direct Shear Tests of Soils Under
Consolidated Drained Conditions" and ASTM D2435 "Standard Test Method for One-
44


Dimensional Consolidation Properties of Soil." The gravel, sand and Composite 1, 2,
3, 4, 5 and 6 samples were allowed to consolidate for a minimum of 30minutes and
the Clay samples A and B were allowed to consolidate for a minimum of 60 minutes
prior to application of the shear stress.
5.2.3 Determination of the Displacement Rate for the Gravel, Sand and Composite
1, 2, 3, 4, 5 and 6 Samples
Since the permeability of a these materials is relatively high, the time required for 100-
percent consolidation (or 100-percent dissipation of pore pressure) after a normal load
is applied is relatively instantaneous. Since the readings of vertical deformation versus
time were taken manually, by the time the first reading was taken (at 6 seconds), most
of the consolidation had occurred. Therefore, if these data were used, calculations for
determining the time for 100 percent consolidation would be extremely over estimated
and the allowable test displacement rate would be much slower than required.
The time consolidation plots developed for the gravel, sand and Composites 1, 2, 3,
4, 5 and 6 are shown on Figures 5.11 through 5.18.
Because it is difficult, if not impossible, to manually take readings of vertical
deformation versus time such that an accurate time consolidation plot can be developed,
ASTM Standard D 5321 states:
"If excess pore pressures are not anticipated, and in the absence of a material
specification, apply the shear force at a rate of 1 mm/min or 0.04 in/min."
45


Assuming a displacement rate of 0.04 in/minand a conservative displacement at failure
of 0.03 inches (a conservative estimate based on engineering judgement and previous
test work), the time to failure would be:
tf = df/dr = 1.33 minutes
Head, K.H., (1989), Soil Technicians Handbook Volume II, Pentech Press, London
The time at 100-percent consolidation can therefore be estimated as:
tioo ~ tf / 12.7 = 0.105 minutes
Head, K.H., (1989), Soil Technicians Handbook Volume II, Pentech Press, London
To verify that the time for 100 percent consolidation is extremely over estimated using
the time consolidation plots created for each sample sheared, the calculated time for
100-percent consolidation are summarized on Tables 5.1 through 5.8.
As seen on these tables, the time to 100-percent consolidation calculated from the time
consolidation plots are much larger than that estimated from the default displacement
rate stated in the ASTM standard (0.105 minutes). This confirms that the initial belief
that the manual readings of vertical displacement versus time were not taken fast
enough to create the time-consolidation curve correctly.
5.2.4 Determination of the Displacement Rate for Clay (samples A and B)
Prior to performing the direct shear test work, a one-dimensional time consolidation
test was performed on the material. A one-dimensional time consolidation test was
performed because these types of materials have lower permeabilities than sands and
46


1 less Recorded Deflection (in)
FIGURE 5.11
DIRECT SHEAR TIME CONSOLIDATION
GRAVEL
0 1 2 3 4 5 6 7
_______________________________Square Root of Time (min)______________________________
N=100psi o N=75 psi A N=50 psi
N=25 psi -> N=25 psi (dry interface)
| N = Normal Stress]
GRAVEL.WK4
12/19/97


1 less Recorded Deflection (in)
FIGURE 5.12
DIRECT SHEAR TIME CONSOLIDATION
SAND
3 4
Square Root of Time (mint
N = 100 psi o N = 75 psi * N = 50 psi
N = 25 psi N = 25 psi (dry interface)
| N = normal stress |
SAND.WK4
12/19/97


1 less Recorded Deflection (in)
FIGURE 5.13
DIRECT SHEAR TIME CONSOLIDATION
COMPOSITE 1
0 1 2 3 4 5 6
________________________________Square Root of Time (min)__________________________________
N = 100psi o N = 75psi A N = 50psi
N = 25psi N = 25psi (dry interface)
| N = normal stress |
COMP1.WK4
12/19/97


1 less Recorded Deflection (in)
FIGURE 5.14
DIRECT SHEAR TIME CONSOLIDATION
COMPOSITE 2
0 1 2 3 4 Square Root of Time (min)
N = 10Opsi N = 25psi O N = 75psi A N = 50psi > N = 25psi (dry interface)
| N = normal stress |
COMP2.WK4
12/19/97


1 less Recorded Deflection (in)
FIGURE 5.15
DIRECT SHEAR TIME CONSOLIDATION
COMPOSITE 3
COMP3.WK4
12/19/97


1 less Recorded Deflection (in)
FIGURE 5.16
DIRECT SHEAR TIME CONSOLIDATION
COMPOSITE 4
0 1 2 3 4 5 6
________________________________Square Root of Time (min)__________________________________
N = 100psi N = 75psi a- N = 50psi
N = 25psi N = 25psi (dry interface)
| N normal stress |
COMP4.WK4
12/19/97


1 less Recorded Deflection (in)
FIGURE 5.17
DIRECT SHEAR TIME CONSOLIDATION
COMPOSITE 5
_______________________________Square Root of Time fmin)__________________
N = 100psi N = 75psi -a N = 50psi
N = 25psi -e- N = 25psi (dry interface)
N = normal stressl
COMP5.WK4
12/19/97


FIGURE 5.18
DIRECT SHEAR TIME CONSOLIDATION
COMPOSITE 6
Lft
Square Root of Time (min)
- N = 100psi O N = 75psi a N = 50psi
N = 25psi ^ N = 25psi (dry interface)
N = normal stress |
COMP6.WK4
12/19/97


Table 5.1
MOO for Gravel
Normal Stress (nsf) Tangent Square Root ofTime !.15*Square Root ofTime 1-1)90 (inches) DO (inches) 1/9*(D90-D0) (inches) D100 (inches) tlOO (min)l
25 l.l 1.2650 0.969 0.0048 0.0029 0.0339 >36
50 0.55 0 6325 0942 0.0000 0.0064 0.0644 >36
75 0.4 0 4600 0 919 0 0014 0.0088 0,0898 >36
100 0,35 0.4025 0 913 0.0003 0,0096 0 0966 >36
25 (drv) 1.05 1.2075 0.969 0.0001 0.0034 0 0344 >36
Table 5.2
<-* tlOO for Sand
Normal Stress 25 0.55 0 6325 0.970 0.0023 0.0031 0.0331 >36
50 0.55 0 6325 0 967 0 0021 0.0034 0.0364 >36
75 0.45 0 5175 0 962 0.0013 0.004 1 0 0421 >36
100 0 35 0.4025 0 952 0.0010 0,0052 0.0532 >36
25(drv) 0.6 0.6900 0.973 0.0003 0.0030 0.0300 >36
Note: I) The 1100 values calculated area extremely overestimated due to the fact that these materials will experience 100-percent consolidation
rclati\ely instantaneously and the fact that the vertical deformation readings versus time were taken manually See Section 5 2 3 lor a discussion
03/04 '98
TIOO.WK4


Table 5.3
11 CIO for Composite I
Normal Stress (I'sf) Tangent Square Root of Time L15*Square Root of Time 1-1)90 (inches) 00 (inches) 1/9*(090-00) (inches) DI00 (inches) tlOO (min)l
25 0.8 0.9200 0 959 0.0001 0.0046 0.0461 >30
50 0.6 0.6900 0 943 0.0000 0.0064 0.0639 >30
75 0 5 0.5750 0 929 0 0005 0.0078 0.0788 >30
100 0.35 0.4025 0 906 0.0002 0.0105 0.1050 >30
25 (drv) 1.55 1.7825 0.978 0 0000 0.0024 0.0244 9
LA
Os
Table 5.4
tlOO for Composite 2
Normal Stress (I'sO Tangent Square Root of Time !.15*Squarc Root ofTimc 1-D90 (inches) DO (inches) 1/9*(D90-D0) (inches) D100 (inches) (100 (min)
25 0.875 1 0063 0 973 0 0000 0.0030 0.0300 9
50 0.55 0,6325 0.958 0 0000 0,0047 0.0467 >30
75 0.45 0.5175 0 953 0.0000 00052 0.0522 >30
100 0.4 0.4600 0.948 0.0000 0.0058 0.0583 30
25 (drv) 1 1.1500 0.978 0.0001 0.0025 0.0250 >30
Note: I) The 1100 values calculated area extremely overestimated due to the fact that these materials will experience 100-percent consolidation
relatively instantaneously and the fact that tlte vertical deformation readings versus time were taken manually. See Section 5.2.3 for a discussion.
03 04 98
TI00 WM


Tublc 5.5
1100 for Composite 3
Normal Stress 0>sD Tangent Square Root of Time M5*Squarc Root of Time 1-090 (inches) no (inches) 1/9*(D90-D0) (inches) D100 (inches) (100 (min)l
25 0.6 0.6900 0.962 0 0000 0,0042 0.0422 4
50 0.6 0 6900 0.956 0 0001 0,0049 0.0489 9
75 0.32 0.3680 0 930 0 0000 0.0078 0,0778 9
100 0,25 0.2875 0.910 0.0002 0.0100 0.1000 16
25 (drv) 0.75 0.8625 0 970 0.0000 0.0033 00333 36
Table 5.6
J
1100 for Composite 4
Normal Stress (I>s0 Tangent Square Root of Time 1.^Square Root ofTinte 1-D90 (inches) DO (inches) l/9*(D90-D0) (inches) D100 (inches) tioo (min)
25 1.2 1.3800 0 970 0 0000 0.0033 0,0333 >30
50 0.55 0 6325 0.938 0.0000 0.0069 0.0689 >30
75 0.45 0 5175 0.925 0 0001 0 0083 0.0833 >30
100 0.38 0 4370 0.907 0 0001 0.0103 0 1033 >30
25 (dry) 1.05 1.2075 0.965 0 0006 0.0038 0.0388 >30
Note: I) The 1100 values calculated area extremely overestimated due to the fact that these materials will experience 100-pcrccni consolidation
relatively instantaneously and the fact that the vertical deformation readings versus lime were taken manually. Sec Section 5.2.3 for a discussion
03.0-1/98
II00 Wk-I


Tabic 5.7
MOO for Composite 5
Normal Stress (l>sf) Tangent Square Root ofTimc LI5*Squarc Root ofTimc 1-D90 (inches) DO (inches) 1/9*(D90-I)0) (inches) D100 (inches) tlOO (min)l
25 1.15 1.3225 0.979 0.0000 0.0023 0 0233 >36
50 0.7 0.8050 0.966 0.0001 0.0038 0.0378 >36
75 0.5 0.5750 0.955 0.0000 0.0050 0.0500 >36
100 0 43 0.4945 0.948 0.0000 0.0058 0.0578 >36
25 (drv) 1.2 1 3800 0.982 0.0000 0 0021 0.0206 9
L* Table 5.8
00
tlOO for Composite 6
Normal Stress (|)sf| Tangent Square Root ofTimc !.15*Squarc Root ofTimc I-D90 (inches) DO (inches) I/9*(D90-D0) (inches) DI00 (inches) tint) (min)l
25 0.45 0.5175 0.967 0.0000 0.0037 0,0367 16
50 0 3 0.3450 0 952 0.0002 0 0053 0.0533 16
75 0.25 0.2875 0.939 0.0000 0.0068 0.0678 9
100 0.3 0.3450 0 94 8 0.0000 0.0058 0.0578 4
25 (drv) 0.6 0 6900 0 972 0.0000 0.0031 0.031 1 4
Sole: 1) The 1100 values calculated area extremely overestimated due to the fact that these materials will experience 100-percent consolidation
relatively instantaneously atid the fact that the vertical deformation readings versus time were taken manually See Section 5.2 3 lor a discussion
03 0-1 98
TlOO WK4


gravels, therefore resulting in slower required displacement rates during shearing such
that pore pressures are dissipated. It was thought that performing the time
consolidation test work in an "approved" time consolidation test machine would result
in better, more accurate consolidation curves and estimates of the time to failure.
The one dimensional time consolidation test was performed according to ASTM D
2435 "Standard Test Method for One-Dimensional Consolidation Properties of Soils"
(Method B) using a GeoMatic Consolidometer shown on Figure 5.19.
Figure 5.19 GeoMatic Consolidometer used for Performing One-Dimensional
Consolidation Tests on the Clay (samples A and B)
59


Vertical deformation versus the square root of time curves were developed for each of
the normal loads to be applied during direct shear testing. These curves are shown on
Figures 5.20 and 5.21 for clay (sample A) and clay (sample B), respectively.
From each of the curves, the time for 100-percent consolidation was calculated and is
summarized on Tables 5.9 and 5.10.
Based on the information generated from the one-dimensional time consolidation
curves, the rate of displacement could be estimated for each point tested.
The first step is to estimate the time to failure, tf. From t^, an estimated time to
failure, tf, can be determined where:
tf = 12.7 t1()0 (min)
Head, K.H., (1989), Soil Technicians Handbook Volume II, Peniech Press, London
In addition to determining the time to failure, the deformation at failure, df, is required
such that a displacement rate, d^, may be determined, where:
dr = d,-/ tf (inches/min)
Head, K.H., (1989), Soil Technicians Handbook Volume II, Pentech Press, London
For the clay (sample A) material, at a normal load of 25 psi, the deformation at failure,
dr, was estimated to be 0.03 inches. It should be noted that this is an estimate based
on previous interface test work and engineering judgement and is thought to be a
conservative estimate. Prior to testing points two through five, the deformation to
60


1 less Recorded Deflection (in)
FIGURE 5.20
ONE DIMENSIONAL TIME CONSOLIDATION (ASTM D2435)
CLAY (sample A)
012345678
Square Root of Time (min)
| N = normal stress |
N=100psi o N = 75 psi a N = 50 psi b N = 25 psi
CLAY-CON.WK4
12/19/97


1 less Recorded Deflection (in)
FIGURE 5.21
ONE DIMENSIONAL TIME CONSOLIDATION (ASTM D2435)
CLAY (sample B)
0.82
0.81
0.8
0.79
0.78
0.77
0.76
0.75
0.74
0.73
0.72
0.71
0.7
0.69
0 68
X
-SQ-
-a-



- 0
o

2
3
4 5
Square Root of Time (min)
|N = normal stress!
N = 100psi o N = 75psi A N = 50psi f;-j N = 25psi
CLYB-CON.WK4
12/19/97


Table 5.9
tlOO for Clay (sample A)
(as determined from the One-Dimensional Time Consol idation Test ASTM D243S)
Normal Stress (psO Tangent Square Root of Time l.l5*Square Root of Time 1-D90 (inches) DO (inches) 1/9*(D90-D0) (inches) DI0O (inches) tlOO (min)
25 2.5 2.8750 0.711 0 2834 0.0007 0.2902 1
50 1.2 1.3800 0.698 0.2925 0.0011 0 3033 1
75 1.55 1.7825 0 689 0.3064 0.0005 03118 0.49
100 0.95 1.0925 0679 0.3161 0.0006 0.3219 049
Table 5.10
tlOO for Clay (sample B)
(as determined from the One-Dimensional Time Consolidation Test ASTM D2435)
Normal Stress Tangent Square 1.15*Square Root of Time 1-D90 DO 1/9*(D90-D0) D100 tlOO
(psf) Root of Time (inches) (inches) (inches) (inches) (min)
25 76 8.7400 0.803 0 1920 0.0006 01981 0.49
50 1.9 2.1850 0.779 0.2021 0.0021 0.2231 0.4225
75 1.4 1.6100 0.741 0.2354 0.0026 0 2616 0.4225
100 1 1 1500 0.703 0.2806 0.0018 02988 0.49
12/19/97
T100.WK.4


failure will be reevaluated based on the data, gathered during shearing, for d, at the
previous point. The estimated displacement to failure and rate of displacement for all
normal loads to be applied during shearing is summarized in Tables 5.11 and 5.12.
Table 5.11
Estimated Displacement Rate for Clay (sample A)
Based on the One-Dimensional Time Consolidation Test Work
Normal Stress (psi) Time to Failure (minutes) Estimated Displacement to Failure (inches) Calculated Rate of Displacement (in/min)
25 12.7 0.031 0.0024
50 12.7 0.062 0.0047
75 6.2 0.062 0.0097
100 6.2 0.052 0.0081
Notes:
1 Estimated based on previous test work and engineering judgement.
2 Determined from results of test work on the previous point.
A conservative displacement rate of 0.0024 inches per minute was selected for shearing
of the clay (sample A) material at all normal pressures.
64


Table 5.12
Estimated Displacement Rate for Clay (sample B)
Based on the One-Dimensional Time Consolidation Test Work
Normal Stress (psi) Time to Failure (minutes) Estimated Displacement to Failure (inches) Calculated Rate of Displacement (in/min)
25 6.2 0.05' 0.008
50 5.4 0.082 0.015
75 5.4 0.072 0.013
100 6.2 0.072 0.011
Notes:
1 Estimated based on previous test work and engineering judgement.
2 Determined from results of test work on the previous point.
A conservative estimate of the displacement rate of 0.007 inches per minute was
selected for shearing of clay (sample B) material at all normal pressures.
5.2.5 Shearing of the Sample
Once the sample consolidated and the deformation rate was determined, the material
was sheared. Readings of horizontal load (lbs) and vertical deformation (inches) were
taken for each of the following readings of horizontal displacement:
from 0.000 inches to 0.030 inches at every 0.005 inches
0.030 inches to 0.200 inches at every 0.010 inches
0.200 inches to 0.300 inches at every 0.020 inches
0.300 inches to 0.500 inches at every 0.025 inches
65


0.500 inches to 0.600 inches at every 0.050 inches
Data calculation sheets for the materials tested may be referenced in Appendix D.
Upon completion of shearing, the vertical and horizontal loads were removed and the
soil sample and geomembrane were carefully removed from the machine. The
moisture content of the soil sample at the completion of the test was recorded.
The machine was then cleaned and prepared for shearing of the next sample.
5.3 12-inch Direct Shear Machine
5.3.1 Sample Preparation and Equipment Setup
Based on index test information, soil sample weights and moisture contents were
measured such that the soil sample could be placed in the upper box of the shear
machine either at a relative density of 65 percent or at the maximum dry density and
optimum moisture content. The required sample weight was calculated using the
moisture density relationship or relative density information and the following upper
box dimensions: 12 inches wide by 12 inches long by 0.75 inches high. These
density/moisture content requirements are typical of construction specifications for
placement of similar materials found adjacent to the geomembrane in a heap leach or
waste containment facilities.
The first step in setting up the direct shear machine for shearing of a soil /
geomembrane interface was to place a tight fitting serrated aluminum plate in the lower
box. A 12-inch wide by 16-inch long coupon of 60 mil HDPE geomembrane was
66


placed on the top of the serrated aluminum plate and bolted to the lower box, such that
the membrane remained in a fixed condition during shearing. The serrated aluminum
plate and secured geomembrane are shown on Figures 5.22 and 5.23, respectively.
The following paragraph pertains to the placement of the gravel, sand and Composites
1 and 4 in the upper box.
The upper box was then positioned and secured to the lower box. Prior to
positioning the upper box, 0.1025-inch spacers were positioned such that there
was a slight gap between the base of the upper box and the 60 mil HDPE
geomembrane / lower box. Photographs showing the upper box and the
positioned upper box are shown on Figures 5.24 and 5.25, respectively.
The material was then placed in the upper box such that it achieved the required
relative density (65 percent) and thickness. Figure 5.26 shows the placed
gravel.
67


68


Figure 5.25 Positioned Upper Box
69


The following paragraph pertains to the placement of filter paper and leveling sand for
the gravel only.
A 12-inch by 12-inch piece of filter paper was then placed on top of the gravel
and a thin layer of sand on top of the filter paper to provide a level surface of
application of the normal load. The purpose of the filter paper as to prevent the
migration of the leveling sand into the gravel during shearing. Figures 5.27
and 5.28 show the placed filter paper and sand, respectively. A 12-inch by 12-
inch piece of 8 oz. non-woven geotextile was then placed on top of the sand to
allow for dissipation of pore pressure and is shown on Figure 5.29.
70


The following paragraph pertains to the placement of the 8 oz. non-woven geotextile
on the sand and Composites 1 and 4.
A 12-inch by 12-inch piece of 8 oz. non-woven geotextile was then placed on
top of the material to allow for dissipation of pore pressure during shearing.
Figure 5.27 Filter Paper to Prevent Migration of Leveling Sand into Gravel
71


72


The following paragraphs pertain to the placement of the Clay (samples A and B) and
Composites 2, 3, 5 and 6 in the upper box.
A 12 inch wide by 14 inch long piece of waxed paper was placed on top of the
geomembrane and the upper box was lowered in place, but not damped down.
The waxed paper was used to protect the geomembrane during the compaction
of the material (soil). Figure 5.30 shows the material placed in the upper box,
prior to compaction.
The material was compacted in the upper box such that it achieved the required
maximum dry density and thickness (0.75 inches). Figure 5.31 shows the
material being compacted in the upper box. Since density measurements could
not be taken after compaction of the sample, the weight of material was
measured prior to placement in the upper box such that, in a compacted state,
the material thickness would be 0.75 inches. During the compaction process,
sample thickness measurements were taken to verify that the material was
placed and compacted near the maximum dry density.
Once the material was compacted, the upper box and compacted sample were
lifted up and the waxed paper sheet was removed, as shown on Figure 5.32.
In addition, water was poured into the lower box such that there was
approximately 0.25 inches of water above the geomembrane. This allowed for
the interface between the soil sample and the geomembrane to be inundated
during shearing. The upper box and clay sample were then lowered back into
place and secured.
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A 12-inch by 12-inch piece of 8 oz. non-woven geotextile was then placed on
top of the material to allow tor dissipation of pore pressure during shearing.
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Figure 5.32 Upper Box and Compacted Material Lifted for Removal of Waxed
Paper and for Filling of the Lower Box with Water
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The following paragraphs pertain to the equipment setup for all samples.
Several '/2-inch spacer plates, shown on Figure 5.32, were then positioned on
the top of the geotextile such that the total depth of the material and spacers was
slightly greater than 4 inches (depth of upper box). In addition, since the 12
and 4-inch direct shear machines were designed to have the normal load applied
in different manners (air bladder and rigid plate), the spacer plates used in the
12-inch direct shear box allowed for the normal load to be applied to the soil
sample similar to that by a rigid plate. Therefore, allowing for a better
comparison of the test results generated in each box. Figure 5.33 shows the
positioned spacer plates.
The air bladder was then placed on top of the upper most spacer and secured.
The positioned air bladder is shown on Figure 5.34. A thin sheet of PVC was
between the upper most spacer and the air bladder to provide puncture
protection to the air bladder when inflated.
The following paragraph pertains to the filling of the lower box with tap water for the
gravel, sand and Composite 1 and 4 materials.
Tap water was then poured into the lower box such that the soil sample/HDPE
interface was inundated. It should be noted that the lower box was designed
such that filling of the lower box with water would also place a portion of the
upper box under water. The 0.1025 inch gap between the upper and lower box
allowed the water to flow into the gravel voids.
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Figure 5.33 Spacer Plate
Figure 5.34 Positioned Spacer Plate
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Figure 5.35 Positioned Air Bladder
The following paragraph pertains to the filling of the lower box with tap water for the
clay (samples A and B) and Composite 2, 3, 5 and 6 materials.
Additional tap water was then poured into the lower box such that the entire
lower box was filled with water. It should be noted that the lower box was
designed to allow for a portion of the upper box to be under water during
testing. The 0.1025-inch gap between the upper and lower box allowed for
some water to flow into the clay voids. Figure 5.35 shows a post test soil
sample with the geotextile, spacer plates and air bladder removed. This figure
shows that the 0.1025-inch gap is sufficient for water to flow in and out of the
sample during shearing.
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Out of the Soil during Shearing (The materials post test moisture content is much
higher than the pre test moisture content.)
The following paragraph pertains to the equipment setup for all samples.
The horizontal displacement rate and maximum horizontal displacement were
then input into the computer.
5.3.2 Time Consolidation and Horizontal Displacement Rate
Due the machine setup constraints, a one-dimensional time consolidation curve could
not be developed for the sample. Therefore, the time for 100 percent consolidation and
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the required displacement rate calculated from results of the time consolidation
analyses performed in the 4-inch direct shear box were used for testing in the 12-inch
direct shear box.
5.3.3 Shearing of the Sample
Once the sample had consolidated, the material was sheared. Readings of horizontal
load (lbs) and horizontal displacement (inches) were taken every 6 seconds for the
gravel, sand and Composite 1, 2, 3, 4, 5 and 6 materials.
Horizontal load (lbs) and horizontal displacement (inches) readings were not taken as
frequently for the Clay (samples A and B) materials since the total test time (due to the
slower displacement rate) was much greater for these materials.
The horizontal load (lbs) and horizontal displacement (inches) readings taken as follows
for Clay (sample A):
For the first 160 minutes of shearing (approximately 0.4 inches
of total horizontal displacement), one reading was taken every
2 minutes.
For the next 585 minutes of shearing (approximately 1.4 inches
of total horizontal displacement), one reading was taken every
10 minutes.
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