A generic soil-geosynthetic composite test

Abstract

Geosynthetic-Reinforced Soil (GRS) mass, comprising soil and layers of geosynthetic reinforcement, is not a uniform mass. To examine the behavior of a GRS mass by a laboratory test, a sufficiently large-size specimen of soil and reinforcement is needed to produce a representative soil-geosynthetic composite. This paper presents a generic test, referred to as the Soil-Geosynthetic Composite (SGC) test, for investigating stress-deformation behavior of soil-geosynthetic composites in a plane strain condition. The specimen dimensions, 2.0 m high and 1.4 m wide in a plane strain configuration, were determined by the finite element method of analysis. The configuration, specimen dimensions, test conditions, and procedure of the SGC test are described. In addition, the results of a SGC test with nine sheets of reinforcement, as well as those of an unreinforced soil test conducted in otherwise identical conditions, are presented. In the test, the soil mass was subject to a prescribed value of confining pressure, applied by vacuum through latex membrane covering the entire surface area of the mass in an air-tight condition. Vertical loads were applied on the top surface of the soil mass until a failure condition was reached. The behaviors of the soil masses, including vertical displacements, lateral movement, and strains in the geosynthetic reinforcement, were carefully monitored. The measured data allow the behavior of reinforced and unreinforced soils to be compared directly, provide a better understanding of soil-geosynthetic composite behavior, and serve as the basis for verification of numerical models to investigate the performance of GRS structures. J. Ross Publishing, Inc.

Full text

1. INTRODUCTION
Geosynthetic-Reinforced Soil (GRS) walls have gained
increasing popularity in the U.S. and abroad over the past
few decades. In actual construction, GRS walls have dem-
onstrated many distinct advantages over conventional can-
tilever and gravity retaining walls. GRS walls are generally
more ductile, more flexible (hence more tolerant to differ-
ential settlement and to seismic loading), more adaptable
to low-permeability backfill, easier to construct, require less
over-excavation, and significantly more economical than
conventionalearthretainingstructures(Wu, 1994;Holtzet
al., 1997; Bathurst et al., 1997).
A good understanding of soil-geosynthetic composite
behavior in reinforced soil structures has been lacking. As a
result, current design methods for GRS walls simply consider
the geosynthetic reinforcement simply as an added tensile
element (i.e., “tieback”), and have failed to account for the
interaction between the soil and geosynthetic reinforcement
(Wu, 2001; Adams et al., 2011).
A generic laboratory test, called the “Soil-Geosynthetic
Composite” test, or SGC test, was designed and conducted
to examine the interactive or composite behavior of soil and
geosynthetic in a GRS mass when subject to increasing verti-
cal loads. The SGC test was conducted at the Turner-Fairbank
Highway Research Center, Federal Highway Administration,
in Mclean, Virginia. The setup of the SGC test is shown in
Figure 1.
This paper describes the configuration, conditions, and
procedure of the SGC test. In addition, the results of a SGC
test, as well as those of an unreinforced soil test (in otherwise
identical conditions to the SGC test) are presented. In the test,
Jonathan T. H. Wu,1* Michael Adams,2 Thang Q. Pham,3 San Ho Lee,4 and Christina Y. Ma5
A generic soil-geosynthetic composite test
ABSTRACT: Geosynthetic-Reinforced Soil (GRS) mass, comprising soil and layers of geosynthetic reinforcement, is not a
uniformmass.ToexaminethebehaviorofaGRSmassbyalaboratorytest,asufficientlylarge-sizespecimenofsoilandrein-
forcement is needed to produce a representative soil-geosynthetic composite. This paper presents a generic test, referred to as
the Soil-Geosynthetic Composite (SGC) test, for investigating stress-deformation behavior of soil-geosynthetic composites in a
plane strain condition. The specimen dimensions, 2.0 m high and 1.4 m wide in a plane strain configuration, were determined
by the finite element method of analysis. The configuration, specimen dimensions, test conditions, and procedure of the SGC
test are described. In addition, the results of a SGC test with nine sheets of reinforcement, as well as those of an unreinforced
soil test conducted in otherwise identical conditions, are presented. In the test, the soil mass was subject to a prescribed value
of confining pressure, applied by vacuum through latex membrane covering the entire surface area of the mass in an air-tight
condition. Vertical loads were applied on the top surface of the soil mass until a failure condition was reached. The behaviors of
the soil masses, including vertical displacements, lateral movement, and strains in the geosynthetic reinforcement, were care-
fully monitored. The measured data allow the behavior of reinforced and unreinforced soils to be compared directly, provide
a better understanding of soil-geosynthetic composite behavior, and serve as the basis for verification of numerical models to
investigate the performance of GRS structures.
KEyWORDS: Planestraintest,geosynthetics,reinforcedsoil,composite,soil-reinforcementinteraction,specimensize
*Corresponding Author
1
Department of Civil Engineering, University of Colorado Denver,
CB-113, 1200 Larimer Street, Denver, CO 80217, USA,
e-mail: jonathan.wu@cudenver.edu, Phone: 303-556-8585,
Fax: 303-556-2368
2
Turner Fairbank Highway Research Center, Federal Highway
Administration, 6300 Georgetown Pike, McLean, VA 22101, USA,
e-mail: mike.adams@fhwa.dot.gov, Phone: 202-493-3025,
3
Institute of Geotechnical Engineering (IGE/IBST), Ministry of Construction,
Vietnam, e-mail; phamthangibst@gmail.com, Phone: (+84)437544014
4
Department of Agricultural Civil Engineering,Kyungpook National
University, DAEGU 702-701, South Korea, e-mail: sahlee@knu.ac.kr,
Phone: 82-53-950-5730
5
Consulting Engineer, Greenwood Village, CO 80111,
e-mail: christinama@ymail.com, Phone: 303-556-2364
103
International Journal of Geotechnical Engineering (2012) 6: (103-116)
DOI 10.3328/IJGE.2012.06.01.103-116
J. Ross Publishing, Inc. © 2012

the soil mass was subject to a confining pressure, applied by
vacuum through latex membrane covering the entire surface
area of the soil mass in an air-tight condition. Vertical loads
were applied on the top surface of the soil mass until failure
occurred. The tests were conducted in a well-controlled
condition, and the behaviors of the soil masses, including
vertical displacements, lateral movement, and strains in the
geosynthetic reinforcement, were carefully monitored. The
measured data allow the differences between reinforced and
unreinforced soils to be compared directly, provide a better
understanding of soil-geosynthetic composite behavior, and
serves as the basis for verification of numerical models to
investigate the performance of GRS structures.
2. SPECIMEN DIMENSIONS AND TEST
PROCEDURE
A soil mass reinforced by layers of geosynthetic reinforce-
ment is not a uniform mass. To investigate the behavior of a
GRS mass by a laboratory test, it is imperative to determine
the minimum specimen dimensions that will provide an ade-
quate representation of reinforced soil behavior. Moreover,
since most GRS structures resemble a plane strain condition,
the test specimen needs to be tested under that condition.
2.1 Specimen Dimensions – Finite Element
Analysis
To determine the specimen dimensions for the SGC test, a
series of finite element analyses, using the computer code
PLAXIS 8.2 (Plaxis, 2002), were performed. The aim of the
analyses was to determine the minimum dimensions of a
generic soil-geosynthetic composite that will produce load-
deformation behavior sufficiently close to that of a typical
reinforced soil mass in actual construction, referred to as the
reference reinforced soil mass. The reference reinforced soil
mass was taken to be 7.0 m high and 4.9 m wide at reinforce-
ment spacing of 0.2 m (a typical reinforcement spacing of
GRS walls) in a plane strain condition.
Four different sizes of GRS composites were analyzed:
specimen heights, H = 7.0 m, 2.0 m, 1.0 m and 0.5 m, while
the width, W, of the specimen was kept as 0.7(H). The width-
to-height ratio of 0.7 corresponds to a common practice of
employing a reinforcement length equals to 0.7 of the wall
height in GRS walls. In these analyses, the soil was a dense
sand. The reinforcement was a medium-strength woven
geotextile at 0.2 m vertical spacing. Two confining pressures,
0 kPa and 30 kPa, were used (note: the confining pressure of
30 kPa is approximately the lateral stress at the mid-height of
a 7.0 m high wall).
Figures 2 and 3 show the stress-strain and volume
changecurvesofthe different specimensizesfor confining
pressures of 0 and 30 kPa, respectively. The volume change
curve is expressed as vertical strain (εv) versus volumetric
strain (ΔV/Vo, change in volume divided by initial volume).
The Figures indicate that specimen heights H = 1.0 m and 0.5
m will be too small to provide an adequate representation of
the reference reinforced soil mass. Also, a better representa-
tion can be obtained with a confining pressure of 30 kPa than
unconfined (under 0 kPa). Specimen dimensions of height =
2.0 m and width = 1.4 m, under a confining pressure of 30
kPa, were therefore selected for the SGC test.
For comparison purposes, another series of finite ele-
ment analyses were performed for unreinforced soil. It is
interesting to see, as shown in Figure 4, that a specimen
height as small as 0.5 m (a commonly used specimen size
for triaxial and plane strain testing of soils with a maximum
grain size less than 1/6 of specimen diameter) will yield
nearly the same stress-strain-volume change relationships as
those of the reference soil mass of H = 7.0 m when reinforce-
ment is not present.
104 International Journal of Geotechnical Engineering
Figure 1. The Soil-Geosynthetic Composite (SGC) Test Setup.

A generic soil-geosynthetic composite test 105
2.2 Plane Strain Condition
To generate a plane strain condition for the tests, the test
bin was made very rigid so that there would be negligible
deformation in the longitudinal direction upon load appli-
cations. In addition, the friction between the backfill and
the side panels of the test bin (in the longitudinal direction)
wasminimizedtonearlyzero.Thesidepanelsweremadeof
transparent plexiglass that fitted inside a steel tubing frame to
form the side surfaces of the test bin. A lubrication layer was
created over the interior surfaces of the plexiglass. The lubri-
cation layer consists of a 0.5-mm thick latex membrane cov-
ered with an approximately 1-mm thick lubrication agent.
This procedure has been used successfully in numerous plane
strain tests conducted by Tatsuoka and his associates at the
University of Tokyo (e.g., Huang and Tatsuoka, 1990) and by
the lead author and his associates in many large-scale experi-
ments (e.g., Wu, 1992; Wu and Helwany, 2001; Ketchart and
Wu, 2002). The friction angle between the lubricant layer
and plexiglass, as determined by direct shear tests, is approxi-
mately one degree.
2.3 Test Procedure
The procedure for preparation of a soil-geosynthetic com-
posite specimen for the SGC test can be described by the
following steps:
(a)
(b)
0
250
500
750
1,000
1,250
1,500
0.0 2.5 5.0 7.5 10.0 12.5 15.0
Deviatoric Stress, ı1 - ı3 (kPa)
Global Vertical Strain, İv (%)
7.0 m x 4.9 m
2.0 m x 1.4 m
1.0 m x 0.7 m
0.5 m x 0.35 m
-2
-1
0
1
2
3
4
5
6
0.0 2.5 5.0 7.5 10.0 12.5 15.0
*OREDO9ROXPHWULF6WUDLQ¨99
Global Vertical Strain, İv (%)
7.0 m x 4.9 m
2.0 m x 1.4 m
1.0 m x 0.7 m
0.5 m x 0.35 m
Figure 2. (a) Global Stress-Strain Curves and (b) Global Volume
Change Curves for Different Sizes of Soil-Geosynthetic Composites
under a Confining Pressure of 0 kPa.
(a)
(b)
0
250
500
750
1,000
1,250
1,500
0.0 2.5 5.0 7.5 10.0 12.5 15.0
Deviatoric Stress, ı1 - ı3 (kPa)
Global Vertical Strain, İv (%)
7.0 m x 4.9 m
2.0 m x 1.4 m
1.0 m x 0.7 m
0.5 m x 0.35 m
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
0.0 2.5 5.0 7.5 10.0 12.5 15.0
*OREDO9ROXPHWULF6WUDLQ¨99
Global Vertical Strain, İv (%)
7.0 m x 4.9 m
2.0 m x 1.4 m
1.0 m x 0.7 m
0.5 m x 0.35 m
Figure 3 (a) Global Stress-Strain Curves and (b) Global Volume Change
Curves for Different Sizes of Soil-Geosynthetic Composites under a
Confining Pressure of 30 kPa.

106 International Journal of Geotechnical Engineering
1. Prepare a lubrication layer over the side surfaces
of the test bin by applying an approximately 1-mm
thick lubricating agent evenly on the interior
plexiglass surfaces of the test bin, and covering
the plexiglass with a sheet of 0.5-mm thick latex
membrane (with a pre-printed grid system on the
membrane);
2. Lay a course of facing blocks on the open ends of
the test bin, place and compact backfill behind
facing blocks until it reaches the top edge of the
blocks, and check (and adjust, if needed) the fill
placement moisture and density by a nuclear den-
sity gage;
3. Place a layer of geosynthetic reinforcement to
cover the top surface area of the compacted fill and
facing blocks;
4. Repeat Steps 2 and 3 until the full height of the soil
mass is attained;
5. Place a sheet of latex membrane to cover the top
surface of the soil mass and attach (with adhesive)
it to the top of the two latex membranes on the
plexiglass of Step 1;
6. Remove all facing blocks and trim off excess geo-
synthetics extruding from the soil mass;
7. Apply vacuum to the soil specimen through the
latex membrane until a prescribed value of confin-
ing pressure is reached, check for air leaks under
vacuum, and measure actual specimen dimen-
sions.
3. TEST CONDITIONS AND TEST MATERIALS
3.1 Test Conditions
The reinforced soil mass (i.e., SGC mass) and unreinforced
soil mass were both tested at a confining pressure of 34 kPa
under a plane strain condition. The soil masses were sub-
ject to vertical loads, through a 30 cm-thick concrete pad
that conformed to the top surface of the soil mass, by using
a hydraulic jack with a capacity of 4.4 x 106 N (1 million
pounds). The loads were applied in equal increments, with
10 minutes elapsed time between increments to allow for
equilibrium and for measurement of internal displacements,
until a failure condition developed. For the unreinforced
soil test, which is perhaps the largest plane strain test ever
performedonasoil,thespecimenwasunloadedtozeroafter
it was loaded to 250 kPa, then reloaded to failure. This was
carried out to assess unloading-reloading stiffness of the soil.
It should be noted that the vertical pressures reported in this
paper were obtained by dividing the applied vertical loads by
the top surface area of the soil mass. The weight of the con-
crete pad was included in the reported values.
3.2 Test Materials
(a) Backfill
The backfill used in the tests was a crushed diabase, a well-
graded gravelly soil, obtained from a source near Washington
D.C. Before conducting the tests, a series of laboratory tests
were performed to determine the basic properties of the
backfill, including gradation test, specific gravity test, absorp-
tion test of the coarse aggregates, standard Proctor compac-
tion test with rock corrections. The following properties were
(a)
(b)
0
20
40
60
80
100
120
140
0.0 1.0 2.0 3.0 4.0 5.0
Deviatoric Stress, ı1 - ı3 (kPa)
Global Vertical Strain, İv (%)
7.0 m x 4.9 m
2.0 m x 1.4 m
1.0 m x 0.7 m
0.5 m x 0.35 m
-0.4
-0.2
0.0
0.2
0.4
0.6
0.8
1.0
0.0 1.0 2.0 3.0 4.0 5.0
*OREDO9ROXPHWULF6WUDLQ¨99
Global Vertical Strain, İv (%)
7.0 m x 4.9 m
2.0 m x 1.4 m
1.0 m x 0.7 m
0.5 m x 0.35 m
Figure 4. Theoretical formulation of inflection point method. (a) ΔUr/Δ
log Tr) V/s log Tr curves. (b) (ΔUr/Δ log Tr) V/s Ur curve.

A generic soil-geosynthetic composite test 107
determined: specific gravity of soil solids = 3.0, absorption
= 0.43, percentage of fines (passing No. 200 U.S. Standard
sieve) = 14.6%, maximum dry unit weight = 24.1 kN/m3 , and
optimumwatercontent=5.2%. In addition, fivelarge-size
(diameter = 152 mm, height = 305 mm) consolidated drained
triaxial tests at different confining pressures were conducted
on the soil at the maximum dry unit weight of 24.1 kN/m3
and optimum moisture content of 5.2%. The stress-strain
curves of the triaxial tests are shown in Figure 5. The Mohr-
Coulomb strength parameters are: c (cohesion) = 71 kPa,
ϕ (angle of internal friction) = 50° for confining pressures
between 0 and 200 kPa, and c = 242 kPa, ϕ = 38o for confin-
ing pressures between 200 and 750 kPa.
(b) Geosynthetics
The geosynthetic used in the SGC test was a woven poly-
propylene geotextile. The strength properties as provided by
the manufacture are: wide width tensile strength (per ASTM
D-4595) = 70 kN/m, and wide-width ultimate elongation =
10% in both warp and fill directions.
(c) Facing Block
The facing blocks used in the tests was a hollow concrete
block with exterior dimensions of 397 mm (width) by 194
mm (height) by 194 mm (depth), and an average weight of
0.18 kN. Note that the facing blocks were employed only dur-
ing specimen preparation and were removed prior to testing.
4. INSTRUMENTATION
The test specimens were instrumented to monitor their
performance during testing. The number and type of instru-
ments used include the following:
(a) Three Linear Variable Displacement Transducers
(LVDT) and two digital dial indicators were installed
on the top of the concrete pad to measure vertical
displacements during loading.
(b) Ten LVDTs and two digital dial indicators were
installed along the height of the specimen (i.e., on
two open faces of the test specimen) to measure
lateral displacements during loading. Figure 6 shows
LVDTs being used to measure lateral displacements
of a test specimen under vacuum. The lateral dis-
placements reported in this paper are the average
values on the two open faces of the specimen.
(c) The internal movement of the specimen was traced
by marking on the plexiglass new positions of pre-
selected grid points on latex membrane after each
load increment.
(d) High elongation strain gages were mounted along
the length of the geosynthetic sheets to measure
reinforcement deformation in the SGC test. Each
strain gage was glued to the geosynthetic only at
two ends to avoid inconsistent local stiffening of
geosynthetic sheet due to the adhesive used for gage
mounting. Because of uneven surface of the geosyn-
thetic used for the test, each gage was first mounted
0
50
100
150
200
250
300
350
400
450
500
550
600
01234567891011
Axial Strain (%)
Deviatoric Stress (psi)
5 psi
15 psi
30 psi
70 psi
70 psi - Ketchart
110 psi - Ketchart
Figure 5. Stress-Strain Curves of Backfill under Different Confining Pressures, Obtained from Triaxial Compression Tests (adapted after Wu et al.,
2011)

108 International Journal of Geotechnical Engineering
on a 25 mm by 76 mm patch of a lightweight heat-
bonded nonwoven geotextile. Each patch was then
glued to the geosynthetic sheet, again only at two
ends. Microcrystalline wax and rubber coating were
used to protect the gages from moisture. To ensure
reliability of the moisture-protection technique, a
geosynthetic specimen mounted with strain gages
was tested after immersing in water for 24 hours.
This technique was proven to be excellent. Before
backfilling, each gage was covered with a butyl rub-
ber tape to protect it from being damaged during
compaction. Calibration tests were performed to
establish the relationship between gage strains and
actual strains.
5. TEST RESULTS AND DISCUSSIONS
The only difference between the two tests conducted in this
study was that the SGC mass contained nine sheets of a geo-
textile at vertical spacing of 0.2 m, while the unreinforced
soil mass contained no reinforcement. The test results and
discussions of results are highlighted as follows:
Global Stress-Strain Relationship
Figure 7 shows the global stress-strain relationship of the
SGC mass and unreinforced soil mass leading to and post
failure. The values of secant stiffness of the SGC mass and
unreinforced soil mass at 1% vertical strain were 62,000
kPa and 30,000 kPa, respectively, indicating an increase in
the stiffness of about 100% due to the reinforcement. The
unloading/reloading stiffness of the unreinforced soil mass
was approximately 80,000 kPa, which suggests a very sig-
nificant benefit of preloading on the granular soil; its effect
is even somewhat greater than that due to the reinforcement.
The SGC mass failed at an applied vertical pressure
of 2,740 kPa, about 250% higher than that of the unrein-
forced soil mass (failure pressure = 770 kPa). Due to the
reinforcement, the increase in strength is seen to be much
more pronounced than the increase in stiffness. The vertical
displacement for the SGC mass at failure was 125 mm (6.5%
vertical strain), as compared to 60 mm (3.0% vertical strain)
for the unreinforced soil mass. The presence of the reinforce-
ment has significantly increased the ductility of the soil mass.
Shear Bands in the SGC Mass at Failure
Figure 8 shows the shear bands developed in the SGC mass
at failure. At failure, the shear bands of the SGC mass were
in diagonal lines, as visible through the plexiglass side walls.
Along the shear bands, the grids printed on latex membrane
were severely distorted. All except the lowest layer of rein-
forcement in the SGC mass were found to have ruptured. An
0
500
1,000
1,500
2,000
2,500
3,000
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
Applied Vertical Stress, ıkPa)
Global Vertical Strain, İ
SGC mass
Unreinforced
soil mass
Figure 7. Global Stress-Strain Relationships of the SGC Mass and
Unreinforced Soil Mass.
Figure 6. LVDTs on the Open Face of Soil Mass under Vacuum.

A generic soil-geosynthetic composite test 109
aerial view of the nine reinforcement sheets exhumed from
the SGC mass after testing is shown in Figure 9. The number
next to each sheet is the layer number starting from the top
of the SGC mass. The locations of the rupture lines in the
reinforcement sheets agree precisely with the shear bands in
the soil mass shown in Figure 8. It is to be noted that well-
defined shear bands were not observed in the unreinforced
soil mass.
Lateral Displacement Profiles
Figure 10 shows the lateral displacement profiles along the
height of the open face under different vertical pressures
for the two tests. As may be expected, the magnitude of the
lateral displacements was much smaller in the SGC mass
than in the unreinforced soil mass. At lower applied pres-
sures (less than 200 kPa), the lateral displacement was fairly
uniform, as the pressure increased, “bulging” began to occur.
At an applied pressure of 200 kPa, a typical design bearing
pressure for GRS bridge abutments (Elias et al., 2001; Wu et
al, 2006), the maximum lateral displacements were about 1
mm and 4 mm for the SGC mass and unreinforced soil mass,
respectively. At an applied pressure of 770 kPa, at which
time the unreinforced soil mass had just reached a failure
condition, the maximum lateral displacement was 46 mm in
the unreinforced soil mass; while it was merely 5 mm in the
SGC mass.
The deformed shape was also rather different for the
two soil masses. The largest lateral displacement for the SGC
mass occurred approximately at the mid-height; whereas it
was lower than the mid-height for the unreinforced soil mass
(at approximately 0.35H, H = total specimen height) from
the base. At failure, the maximum lateral displacements were
about 60 mm (at pressure = 2,740 kPa) in the SGC mass, and
about 47 mm (at pressure = 770 kPa) in the unreinforced soil
mass.
Strain Distributions in Reinforcement Layers
Figure 11 shows the strain distributions in all reinforcement
layers of the SGC mass. Most of the strain gages appear to
have performed very well for strains up to 4.0%. Beyond
4.0%, the gages were either dead or the measured values
were judge to be not as reliable. The locations of maximum
Rupture Lines
Figure 9. Aerial View of the Nine Reinforcement Sheets Exhumed from
the SGC Mass [the number next to each sheet is the reinforcement layer
number, starting from the top of the SGC mass].
Shear Bands
Figure 8. Shear Bands in the SGC Mass at Failure.

110 International Journal of Geotechnical Engineering
(a)
(b)
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
0 10 20 30 40 50 60
Height (m)
Lateral Displacement (mm)
200 kPa 400 kPa 600 kPa
770 kPa 1,000 kPa 1,250 kPa
1,500 kPa 1,750 kPa 2,000 kPa
2,250 kPa 2,500 kPa 2,740 kPa (failure)
Applied
Pressure:
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
2.00
0 10 20 30 40 50
Height (m)
Lateral Displacement (mm)
200 kPa
400 kPa
600 kPa
700 kPa
770 kPa
Applied Pressure:
Figure 10. Lateral Displacements along the Open Face in (a) SGC Mass, and (b) Unreinforced Soil Mass.

A generic soil-geosynthetic composite test 111
Figure 11. Strain Distribution in Reinforcement Sheet at (a) 0.2 m and (b) 0.4 m from the Base.
(a)
(b)
0.0
0.5
1.0
1.5
2.0
2.5
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Strain (%)
Distance from the Edge of the SGC Mass (m)
200 kPa
400 kPa
600 kPa
800 kPa
1,000 kPa
1,250 kPa
1,500 kPa
Applied Pressure:
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Strain (%)
Distance from the Edge of the SGC Mass (m)
200 kPa
400 kPa
600 kPa
800 kPa
1,000 kPa
1,250 kPa
1,500 kPa
Applied Pressure:

112 International Journal of Geotechnical Engineering
Figure 11 (continued). Strain Distribution in Reinforcement Sheet at (c) 0.6 and (d) 0.8 m from the Base
(c)
(d)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Strain (%)
Distance from the Edge of the SGC Mass (m)
200 kPa
400 kPa
600 kPa
800 kPa
1,000 kPa
1,250 kPa
1,500 kPa
Applied Pressure:
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Strain (%)
Distance from the Edge of the SGC Mass (m)
200 kPa
400 kPa
600 kPa
800 kPa
1,000 kPa
Applied Pressure:

A generic soil-geosynthetic composite test 113
Figure 11 (continued). Strain Distribution in Reinforcement Sheet at (e) 1.0 m and (f) 1.2 m from the Base.
(e)
(f)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Strain (%)
Distance from the Edge of the SGC Mass (m)
200 kPa
400 kPa
600 kPa
800 kPa
1,000 kPa
Applied Pressure:
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Strain (%)
Distance from the Edge of the SGC Mass (m)
200 kPa
400 kPa
600 kPa
800 kPa
1,000 kPa
Applied Pressure:

114 International Journal of Geotechnical Engineering
Figure 11 (continued). Strain Distribution in Reinforcement Sheet at (g) 1.4 m and (h) 1.6 m from the Base.
(g)
(h)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Strain (%)
Distance from the Edge of the SGC Mass (m)
200 kPa
400 kPa
600 kPa
800 kPa
1,000 kPa
1,250 kPa
Applied Pressure:
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Strain (%)
Distance from the Edge of the SGC Mass (m)
200 kPa
400 kPa
600 kPa
800 kPa
1,000 kPa
1,250 kPa
Applied Pressure:

A generic soil-geosynthetic composite test 115
strains recorded in all reinforcement layers are in agreement
with the locations of shear bands shown in Figure 8 and the
ruptured lines shown in Figure 9. This suggests that the mea-
sured strains are likely reliable.
The locations of the maximum strain in the reinforce-
ment were different among different layers. For reinforce-
ment layers in the mid-section of the SGC mass (i.e., between
0.6 m and 1.0 m from the base), the maximum reinforcement
strains occurred near the centerline of the soil mass. For rein-
forcement layers near the top and bottom of the GRS mass,
the maximum reinforcement strains occurred about 0.3 m to
0.5 m from the edge of the SGC mass.
6. CONCLUDING REMARKS
A Geosynthetic-reinforced soil (GRS) mass, comprising soil
and layers of geosynthetic reinforcement, is not a uniform
mass. To examine the behavior of a GRS mass by a laboratory
test, a sufficiently large-size specimen of soil-geosynthetic
composite is needed to be representative of field behavior. A
generic test, referred to as the Soil-Geosynthetic Composite
(SGC) test, has been developed for investigating the stress-
deformation behavior of soil-geosynthetic composites. The
specimen dimensions capable of adequately representing a
typical GRS wall at 0.2 m reinforcement spacing have been
determined to be 2.0 m high and 1.4 m wide under a confin-
ing pressure of 30 kPa and in a plane strain condition.
The results of two tests: one on a SGC mass with nine
layers of geosynthetic reinforcement at 0.2 m spacing, and
the other on an unreinforced soil mass in otherwise identical
conditions, provide a direct comparison between reinforced
and unreinforced soil behavior. Both tests were loaded until
a failure condition was reached. The tests demonstrated that
the reinforcement increased the overall stiffness by approxi-
mately 100%, increased the ultimate load carrying capacity by
about 250%, and increase the ductility (in terms of strain at
failure) by a little over 100%. Also, under a vertical pressure
of 200 kPa (a typical design pressure for bridge abutments),
the presence of the reinforcement reduced the maximum lat-
eral displacement very pronouncedly, by approximately four
folds. Under a vertical pressure of 770 kPa, where the unre-
inforced soil mass had reached a failure state, the maximum
lateral displacement in the unreinforced soil mass was nearly
10 times as large as in the reinforced soil mass.
The measured data show the differences between rein-
forced and unreinforced soils, provide a better understand-
ing of soil-geosynthetic composite behavior, and serve as the
(i)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Strain (%)
Distance from the Edge of the SGC Mass (m)
200 kPa
400 kPa
600 kPa
800 kPa
Applied Pressure:
Figure 11 (continued). Strain Distribution in Reinforcement Sheet at (i) 1.8 m from the Base.

116 International Journal of Geotechnical Engineering
basis for verification of numerical models to investigate the
performance of GRS structures.
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