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Laboratory long-term performance tests for soil-geosynthetic composites

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Title:
Laboratory long-term performance tests for soil-geosynthetic composites
Creator:
Ketchart, Kanop
Place of Publication:
Denver, CO
Publisher:
University of Colorado Denver
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Language:
English
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ix, 156 leaves : illustrations ; 29 cm

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Subjects / Keywords:
Geosynthetics ( lcsh )
Soils -- Creep ( lcsh )
Geosynthetics ( fast )
Soils -- Creep ( fast )
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bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

Notes

Bibliography:
Includes bibliographical references (leaves 151-156).
Thesis:
Submitted in partial fulfillment of the requirements for the degree, Master of Science, Civil Engineering
General Note:
Department of Civil Engineering
Statement of Responsibility:
by Kanop Ketchart.

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|University of Colorado Denver
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|Auraria Library
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All applicable rights reserved by the source institution and holding location.
Resource Identifier:
34845567 ( OCLC )
ocm34845567
Classification:
LD1190.E53 1995m .K48 ( lcc )

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Full Text
LABORATORY LONG-TERM PERFORMANCE TESTS
FOR SOIL-GEOSYNTHETIC COMPOSITES
by
Kanop Ketchart
B.Eng, Chulalongkorn University, Thailand,
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
1992
, 1995


This thesis for the Master of Science
degree by
Kanop Ketchart
has been approved for the
Department of
Civil Engineering
by


Date
Kevin Rens


Ketchart, Kanop (M.S., Civil Engineering)
Laboratory Long-Term Performance Tests for
Soil-Geosynthetic Composites
Thesis directed by Professor Jonathan T.H. Wu
ABSTRACT
Creep behavior is of concern in the design of
geosynthetic-reinforced soil (GRS) structures because
geosynthetics, which are manufactured with various
polymers, are generally considered creep-sensitive. In
the current design methods for GRS structures, creep is
accounted for by performing geosynthetic "element" creep
tests in which sustained loads are applied directly to
the geosynthetic under confined or unconfined condition.
However, field measurement of GRS retaining walls has
clearly indicated that the backfill type and density play
a very significant role in their long-term performance.
In an attempt to investigate the effects of confining
soil on the long-term behavior of a soil-geosynthetic
composite. Wu and Helwany (1996) developed a long-term
iii


soil-geosynthetic performance test device. They performed
two tests using a granular soil and a cohesive soil/ and
concluded that long-term behavior of a soil-geosynthetic
composite is a result of soil-geosynthetic interaction.
To properly assess long-term performance of a GRS
structure, this interaction behavior must be taken into
account.
In this study, a modified soil-geosynthetic
performance test was devised. The test simulates the
predominant deformation behavior of a GRS structure in a
"worst" condition by allowing geosynthetic reinforcement
and its confining soil to deform in an interactive manner
under a sustained surcharge without lateral confinement.
A series of performance tests were performed to
examine test repeatability and to investigate the effects
of soil type, geosynthetic type and sustained load
intensity on the behavior of soil-geosynthetic composite.
A test was instrumented with strain gages to measure
deformation along the length of the geosynthetic. Tests
with soil only were also conducted for comparisons with
soil-geosynthetic composite. In addition, a load-
deformation test with a weak geosynthetic was conducted
IV


to examine the failure mode of the soil-geosynthetic
composites. Many of the tests were conducted at an
elevated temperature of 125F. Element test on the
geosynthetics indicated that the elevated temperatures
typically accelerated creep of the geosynthetic by 100 to
400 folds.
A finite element model was employed to analyze one
of the performance tests. The analytical results were
compared with the measures values.
This abstract accurately represents the content of the
candidate's thesis. I recommend its publication.
Signed
v


ACKNOWLEDGEMENTS
I would like to express my sincerest thanks to
Professor Jonathan T.H. Wu for his guidance and
encouragement throughout my academic and research
program. Special gratitude is also extended to Dr. Sang-
Ho Lee Yottana Kunatorn and Hsu-Kun Cheng for their
helpful assistance. I would also like to thank Robert
Barrett, A1 Ruckman, Steven Steve and Tammy Harper of the
Colorado Department of Transportation. Further thanks are
extended to Amoco Fabrics and Fibers Company for
providing materials.
Finally, I would like to thank my parents and my
sister for providing much needed love and support
throughout mu study.


CONTENTS
Chapter Page
1. Introduction................................. 1
1.1 Problem Statement............................... 1
1.2 Research Objectives............................. 5
1.3 Method of Research.......'................... 6
2. Test'Materials and Material Properties....... 10
2.1 Soils.......................................... 10
2.2 Geosynthetics.................................. 11
2.3 Acceleration of Geosynthetic Creep at
an Elevated Temperature.......................... 22
3. Test Apparatus, Test Procedure,
and Test Program.................................. 27
3.1 Test Apparatus ............................... 27
3.2 Test Procedure ............................... 34
3.3 Test Instrumentation.......................... 36
3.4 Testing Program.............................. 4 0
Vll


4. Test Results and Discussion of Results...... 49
4.1 Verification of Test Method.................... 50
4.1.1 Repeatability Test........................... 50
4.1.2 Failure Mode of the Performance Test...... 56
4.2 Behavior Before Releasing Lateral Support... 56
4.3 Long-Term Behavior of the Performance Test.. 62
4.3.1 Deformed Shape of Test Specimen and
Strain Distribution along the Geosynthetic...... 62
4.3.2 Loads in Geosynthetic Reinforcement......... 64'
4.3.3 The Role of Reinforcement..................... 75
4.3.4 Effect of Geosynthetic Type................... 81
4.3.5 Effect of Soil Type.......................... 90
4.3.6 Effect of Temperature........................ 93
4.3.7 Effect of Sustained Vertical Surcharge... 94
5. Finite Element Analysis of the Performance
Test.............................................. 103
5.1 The Finite Element Model.................... 103
5.1.1 Sekiguchi-Ohta Soil Model................... 104
5.1.2 Generalized Geosynthetic Creep Model........ 105
5.2 Evaluation of Model Parameters.............. 107
5.2.1 Sekiguchi-Ohta Model Parameters............. 107
5.2.2 Generalized Geosynthetic Creep Model........ 112
viii


5.3 Finite Element Simulation of the Performance
Test.............................................. 112
5.3.1 Finite Element Simulation................... 112
5.3.2 Results of Finite Element Analysis..........
115
6. Summary and Conclusions....................... 120
6.1 Summary....................................... 120
6.2 Conclusions................................... 122
Appendixes
A. Performance Test Results....................... 127
B. Input Data of Finite Element Analysis.......... 139
Bibliography...................................... 151


1. INTRODUCTION
1.1 Problem Statement
Geosynthetic-reinforced soil (GRS) retaining wall
have become increasingly popular in the construction of
retaining structure because of its many advantages over
conventional reinforced concrete walls, including:
(1) GRS retaining structures are more flexible,
hence more tolerant to foundation settlement.
(2) Construction of GRS retaining structure is rapid
and requires only "ordinary" construction equipment.
(3) GRS retaining structures are generally less
expensive to construct than their reinforced concrete
counterparts.
When a geosynthetic is used as reinforcement in a
"permanent" retaining structure, acceptable performance
of the GRS retaining structure must be satisfied
throughout its design life. The creep behavior is of
concerned in evaluating the long-term performance of GRS
retaining structure because geosynthetic, which are
manufactured with various polymers,
are generally


considered creep-sensitive.
Some current design methods (e.g., AASHTO, 1992) for
GRS retaining structure evaluate the long-term creep
potential of a GRS retaining structure by performing
"element" creep tests on the geosynthetic reinforcement
alone (in either a confined or unconfined mode). Other
design methods simply apply a safety factor or a creep
reduction factor to the ultimate strength of the
geosynthetic reinforcement to account for creep. All
these design methods tacitly assumed that creep of a GRS
retaining structure is due entirely to the geosynthetic
and not affected by the surrounding soil.
Field measurement of GRS retaining walls has
indicated little or no creep when granular backfill is
employed. Some examples of well-instrumented, well-
monitored GRS retaining structure are:
(1) A 41-ft high aeosynthetic-reinforced soil
retaining wall constructed in Seattle in 1989 The creep
strains in the geotextile 11 months after fill placement
were very small (with a maximum creep strain of about
0.13%). The creep rate was 4.5xl01% per day after fill
l
placement, and 2.0xl0~4% per day ten months after fill
placement. The rates were approaching zero, 11 months
2


after placement. The backfill was gravelly sand (Allen,
et al., 1992).
(2) Forty-six aeocrrid-reinforced soil retaining
walls constructed in Tucson. Arizona in 1984 and 1985
Field measurement showed that despite the in-soil
temperature was relatively high (97F), the geogrid
reinforcement experienced a maximum strain of
approximately 1.0% and was stable with time. The measured
creep of the reinforcement in 10-year after construction
was negligible (Collin, et al., 1994).
(3) An 18-ft high aeocTrid-reinforced test wall
constructed in Algonquin. Illinois A number of
instruments were used to monitored the behavior of the
test wall. Measured data indicated that the strain/load
level remained constant(i.e. no creep) throughout the
first five months after construction, and there were no
other time-dependent phenomena deteriorating the geogrid
performance. The backfill was well-graded sand gravel
(Simac, et al., 1990; Bathurst, et al., 1993).
However, the creep reduction factors adopted in the
current design methods are fairly low, regardless of the
backfill type. For example, creep reduction factors
ranging from 0.25 to 0.4, depending on the polymer type
3


of a geosynthetic, were specified in the AASHTO design
method.
To characterized the soil-geosynthetic composite
behavior, Wu (1994) and Wu and Helwany (1996) developed
a soil-geosynthetic long-term performance test, in which
the stresses applied to the soil are transferred to the
geosynthetic in a manner similar to the typical load
transfer mechanism in GRS retaining structures, and both
the soil and the geosynthetic are allowed to deform in an
interactive manner under a constant sustained load. They
reported two carefully conducted long-term performance
tests, one used a clayey backfill and the other a
granular backfill. Using element test on the geosynthetic
alone, the maximum strain in the geosynthetic was
underestimated by 250% in the clay-backfill test, and
over-estimated by 400% in the sand-backfill test. It was
noted that creep deformation essentially ceased within
100 minutes after the sand-backfill test began; whereas,
the clay-backfill test experienced creep deformation over
the entire test period (18 days).
Wu and Helwany (1996) indicated that long-term creep
of a soil-geosynthetic is a result of soil-geosynthetic
interaction. If the confining soil has a tendency to
4


creep faster than the geosynthetic reinforcement along
its axial direction, the geosynthetic will impose a
restraining effect on the deformation of the soil through
the friction and/or adhesion between the two materials.
Conversely, if the geosynthetic reinforcement tends to
creep faster than the confining soil, then the confining
soil will restrain the reinforcement deformation through
the friction/adhesion. This restraining effect is a
direct result of soil-reinforcement interaction where
redistribution of stresses in the confining soil and
changes in axial forces in the reinforcement occur over
time in an interactive manner.
In this study, a modified soil-geosynthetic long-
term performance test was developed. The modified test
was simpler to perform, yet represent a "worst" condition
by providing no lateral constraint to the soil-
geosynthetic composite.
1.2 Research Objectives
The objectives of this research were three-fold. The
first objective was establish a consistent test procedure
for the modified soil-geosynthetic long-term performance
test so that long-term soil-geosynthetic interaction
5


creep behavior can be assessed in a reliable manner. The
second objective was to examine the soil-geosynthetic
interaction creep behavior for various soils and
geosynthetics under different conditions, including
accelerated creep at an elevated temperature. The third
objective was to analyze the load transfer mechanism in
the long-term performance test.
1.3 Method of Research
This research was divided into two phases: an
experimental phase and an analytical phase.
1.3.1 Experimental Study
Long-term performance tests were performed to
examine the soil-geosynthetic interactive creep behavior
in various conditions of soils, geosynthetics, sustained
vertical surcharges, and temperatures.
Two types of soil, a road base and a clayey soil
with 43% of fines, were employed as backfill for the
tests. The road base is a silty sandy gravel (GM) It has
been widely used as backfill for construction of road
ways and retaining walls. The clayey soil has. a
plasticity index of 11 and a higher tendency to deform
6


with time than the road base.
Three types of geosynthetic, Amoco 2044, Amoco 2002,
and Typar 3301, were selected as reinforcement for the
tests. Amoco 2044 and Amoco 2002 are woven-prolypropylene
geotextile with tensile strength of 400 lb/in. and 120
lb/in.,respectively. Amoco 2044 presents a strong
reinforcement, while Amoco 2002 presents a weak
reinforcement. Typar 3301 is a heat-bonded nonwoven-
prolypropylene geotextile. This fabric was selected
because of its relatively smooth surface which make
mounting of strain gages much easier.
The test specimen comprised a cuboid of soil and a
layer of geosynthetic reinforcement embedded at the mid-
height of the soil. The soil-geosynthetic composite was
prepared inside the apparatus. The soil was prepared at
2% wet-of-optimum moisture and compacted to 95% relative
density for every test conducted in this study. For
comparison, tests without geosynthetic (i.e., soil only)
were also conducted.
Six long-term performance tests were conducted at an
elevated temperature of 125F to accelerate creep of the
geosynthetics. Tests under ambient temperature were also
conducted to examine the effects of temperature on soil-
7


geosynthetic composites.
A sustained average vertical pressure of 15 psi was
applied to all of the performance tests except one test
which was subjected to a sustained pressure of 30 psi.
The test under 30 psi pressure was performed to examine
the effects pressure intensity on the soil-geosynthetic
composites.
The lateral and vertical displacements of the soil-
geosynthetic composite were monitored by LVDTs (Linear
Voltage Displacement Transducers) and mechanical
displacement dial gages. In one test, strain gages were
installed along the length of the geosynthetic to measure
the distribution of axial strain with time. The measured
results were also used for verification of a finite
element analytical model.
1.3.2 Analytical Study
A finite element model developed by Helwany and Wu
(1995) was employed to analyze the experimental results.
The finite element model incorporated an elasto-
viscoplastic soil model and a generalized creep model.
The generalized creep model was developed by Helwany and
Wu(1992) to simulate creep characteristics of
8


geosynthetics. The elasto-viscoplastic soil model was
developed by Sekigushi and Ohta (1977). The finite
element model has been verified with the measured
behavior by Iizuka and Ohta (1987), Chou (1992) and
Helwany and Wu (1995).
9


2. TEST MATERIALS AND MATERIAL PROPERTIES
2.1 Soils
A Road Base and a clayey soil with 43% of fines
were selected for the tests. The road base has been
widely used as backfill for construction of roadways and
retaining walls. The clayey soil represents a natural
soil which deforms significantly with time.
2.1.1 The Road Base
This soil was classified as A-l-B(O). The grain size
distribution curve is shown in Figure 2.1. The material
has 7 6% passing the standard sieve No. 4 and 19% passing
No. 200. The specific gravity of the soil solids was
2.67. The maximum dry unit weight of the soil was 134
lb/ft3 and the optimum moisture content was 7.2%. The
Road Base was prepared inside the test apparatus by
compaction with a 8-pound Proctor hammer. The soil was
compacted to 95% relative density and 2% wet-of-optimum
moisture content.
Three consolidated-drained (CD) triaxial compression
tests at confining pressures of 15, 30, 45 psi were
10


conducted. The test specimen was prepared at a density of
126 lb/ft3 and a moisture content of 8.5%. Each specimen
was loaded at a constant deformation rate of 0.3xl0~3 in.
per hour. The stress-strain relationship is shown in
Figure 2.2. The internal friction angle of the road base
was 32.
2.1.2 The Clayey soil
This soil was classified as A-6. The grain size
distribution curve is shown in Figure 2.3. The material
has 100% passing the standard sieve No. 4 and 43% passing
No. 200. The plasticity index and liquid limit were 11
and 26, respectively. The maximum dry unit weight was 120
lb/ft3 and the optimum moisture content was 11%. The
clayey soil was prepared inside the test apparatus in the
same as that of the road base.
2.2 Geosynthetics
2.2.1 Amoco 2044
AMOCO 2044 is a woven polypropylene geotextile with
some of its index properties listed in Table 2.1. The
wide width Tensile test with Curtis Sure-Gripe with 16
11


Percent finer, %
0.01 0.1 1. 10
Particle diameter, mm
Figure 2.1 : Grain Size Distribution of the Road Base
12


Deviatoric Stress, psi
Axial Strain, %
Figure 2.2 : Consolidated Drained Triaxial Test Results
of the Road Base
13


Percent liner, %
Particle diameter, mm
Figure 2.3 : Grain Size Distribution of the Clayey Soil
14


inch gage length and 0.5 inch per minute cross head speed
was conducted by the manufacturer. The load-deformation
relationship is shown in figure 2.4.
The element creep tests with 4 inch diameter roller
grips and a 8 inch wide specimen were also conducted by
the manufacturer. The element creep curves of AMOCO 2044
in the fill direction under 22%, 25%, 30% of the ultimate
load are shown in figure 2.5, 2.6, and 2.7, respectively.
Each figure shows the creep curves at temperature of
70F, 100F, and 120F.
2.2.2 Amoco 2002
Amoco 2002 is a woven polypropylene geotextile.
Creep test data was not available through the
manufacturer because the main function of Amoco 2002 was
not for reinforcement. The index properties of Amoco
2002 are listed in Table 2.1.
2.2.3 Typer 3301
Typar 3301 is a heat-bonded nonwoven polypropylene
geotextile. This geotextile was selected because of
easiness for strain gage installation and accuracy for
15


Table 2.1 Some Index Properties of Geosynthetics
Amoco 2044 Amoco 2002 Typar 3301
Polymer type Polypropylene Polypropylene Polypropylene
Manufacturing Method Woven Woven Non-woven
Wide width strength (ASTM D-4595) 400 lb/in. 120 lb/in. 35 lb/in.
Elongation at break (%) (ASTM D-4595) 18% 10% 60%
Grab tensile (ASTM D-4632) 600 lb 200 lb 120 lb
Elongation at break (%) (ASTM D-4632) 20% 15% 60%
16


Load/Wldth, Ib/in.
Strain, %
Figure 2.4 : Load-Deformation Behavior of Amoco 2044
(Courtersy of Rick Valentine,
Amoco Fabrics and Fibers Company)
17


20
00
Elapsed Time, hours
70"F 100 *F 120*F
Figure 2.5 : Creep Curves of Amoco 2044 Geotextile
in the Fill Direction at 22% of Ultimate
Load (Courtersy of Tom Baker/
Amoco Fabrics and Fibers Company)


70 *F 100 *F 120 *F
Figure 2.6 : Creep Curves of Amoco 2044 Geotextile
in the Fill Direction at 25% of Ultimate
Load (Courtersy of Tom Baker,
Amoco Fabrics and Fibers Company)


Elapsed Time, hours
70*F 100*F 120*F
Figure 2.7 : Creep Curves of Amoco 2044 Geotextile
in the Fill Direction at 30% of Ultimate
Load (Courtersy of Tom Baker,
Amoco Fabrics and Fibers Company)


measurement. The index properties of Typar 3301 are shown
in Table 2.1.
The load-deformation behavior of Typar 3301 is shown
in Figure 2.8. Specimens 30 cm in width and 3.75 cm in
gage length were tested under three conditions: (1)
unconfined (in-isolation), (2) confined by a sand, and
(3) confined by a rubber membrane. For the confined tests
(i.e. test conditions 2 and 3), an effective normal
stress of 11 psi was applied on the geosynthetic. All the
tests were conducted at a strain rate of 2% per minute
(Wu, 1992).
The confined tests were conducted in a manner that
the soil-reinforcement interface friction will not be
inadvertently mobilized throughout the test. Detailed
test procedures and test conditions have been presented
by Wu (1991).
Since the load-deformation behavior of the heat-
bonded geotextile is hardly affected by the confinement,
as seen in Figure 2.8, the creep tests were conducted
with the geotextile in isolation (unconfined). The
specimen size used in the creep tests was 6 in. wide and
1 in. long. Both ends of the test specimen were glued
between two sets of thin metal plates to facilitate
21


application of loads. The sustained loads used in the
tests were 96, 140, and 180 lb/ft (approximately 24%,
35%, and 45% of the short-term ultimate strength,
respectively). The results of the creep tests are shown
in Figure 2.9.
2.3 Acceleration of Geosynthetic Creep at an Elevated
Temperature
A Higher temperature tends to accelerate creep in a
polymer. Hence, creep tests should be conducted to cover
a range of temperatures in the anticipated in-service
condition of the structure. This does, however, require
extensive testing at different temperatures over
considerable time periods. In absence of such
information, time-shifting techniques may be utilized
(with caution) to account for the effect of temperature.
Morgan and Ward (1971) have found that the creep
curves from element creep test at a certain temperature
can be obtained by a simple horizontal shift from creep
curve at different test temperature under the same
sustained load. A number of element creep tests at
different temperatures must be conducted to establish a
time shifting factor for a certain change in temperature.
22


Element creep curves for Amoco 2044 subject to three
different sustained loads (at 70F, 100F and 120F), as
shown in Figure 2.5, 2.6, and 2.7, were used to determine
the time shifting factor as shown in Table 2.2. The
factor varies approximately between 100 to 400 for
temperatures changing from 70F to 120F.
For instance, a strain of 5% of 70F in the fill
direction at 30% of ultimate load was measured at an
elapsed time of about 25 hours for Amoco 2044. At 120F,
under otherwise identical conditions, the same strain was
measured at an elapsed time of only 0.1 hour, which
results in a time shifting factor of 250 (see Figure
2.7) For a strain of 5% in the fill direction at 25% of
ultimate load, the measured elapsed time was about 100
hours at 70F. At 120F, under otherwise identical
conditions, the same strain was measured at an elapsed
time of about 1 hour (see Figure 2.6), which gives a time
shifting factor of 100.
23


Load / NidLh, 11b/fLI
Figure 2.8 : Load-Deformation Behavior of Typar 3301
( Wu, 1992)
24


total strain
K
Figure
2.9 : Creep Behavior of Typar 3301 Geotextile
(Wu, 1992)
25


t\J
CTl
Sustained Load (% of Wide Width Tensile Strength) Strain (%) Elapsed Time Time Shifting Factor
At 70*F (hours) At 100F (hours) At 120T (hours) 70T/100T 70*F/ 120T
22% 4 140 1.4 0.3 100 466.7
5 1200 14 3 85.7 400
6 4000 150 12 26.7 333.3

25% 4 14 0.1 0.016 140 875
5 100 2 1 50 100
6 700 16 6 43.8 116.7

30% 4 4 0.016 0.01 250 400
5 25 0.6 0.1 41.7 250
6 90 3 0.5 30 180
Table 2.2 Time Shifting Factors Due to Elevated Temperatures of Amoco 2044


3. TEST APPARATUS, TEST PROCEDURE, AND TEST PROGRAM
3.1 Test Apparatus
Wu (1994) and Wu and Helwany (1996) developed a
long-term soil-geosynthetic performance test to
investigate long-term interactive behavior of soil-
geosynthetic composite. A schematic diagram of the test
device is shown in Figure 3.1, in which a reinforced soil
unit was placed inside a rigid container with transparent
plexiglass side walls. The reinforced soil unit comprised
a geosynthetic reinforcement, two vertical flexible steel
plates, and confining soil. The confining soil confined
the geosynthetic reinforcement at both top and bottom.
The two ends of the geosynthetic reinforcement were
securely attached to the two vertical steel plates, each
of 1 mm in thickness, at their mid-height. The transverse
direction of the reinforced soil unit was fitted between
two lubricated plexiglass side-wall of a rigid container
in such a manner that the reinforced soil unit was
restrained from movement in the direction perpendicular
to the plexiglass side walls (i.e., in a plane strain
27


-<------ L -------->
Dimensions: Legends:
Sand-Backfill Test: a Geosynthetic Reinforcement
L = 813 cm b Soil
H = 30.5 cm c Steel Plate
d Rigid Container with Lubricated Side Walls
Clay-Backfill Test: e Sustained Load
L = 45.7 cm H = 25.4 cm f Rigid Plate
Figure 3.1 : Schematic Diagram of the Long-Term
Soil-Geosynthetic Performance Test Device
(Helwany and Wu, 1996)
28


configuration) On the top surface of the confining soil,
another sheet of geosynthetic was used to connect the top
edge of the vertical steel plates. Upon the application
of a sustained vertical surcharge to the top surface of
the reinforced soil unit, the geosynthetic reinforcement
and its confining soil will deform in an interactive
manner over time. Namely, there will be an interactive
retraining effecting on deformation between the
geosynthetic reinforcement and the soil.
To maintain plane strain condition throughout the
test, the interface between the rigid plexiglass and the
soil was minimized to near frictionless. This was
accomplished by creating a lubrication layer at the
interface of the plexiglass side-wall and the soil. The
lubrication layer consists of a 0.02 mm thick membrane
and a thin layer of a silicon grease. This procedure was
developed by Tatsuoka at the University of Tokyo. The
friction angle between the lubrication layer and
plexiglass as determined by the direct shear test was
less than one degree (Tatsuoka, et al., 1984).
In this study, a modified apparatus was developed to
simplify sample preparation and load application. A
photograph and a schematic diagram of the modified long-
29


term performance test apparatus are shown, respectively,
in Figures 3.2 and 3.3. The modified apparatus differs
from the original device in five aspects:
(a) Dimension of test apparatus The modified test
apparatus is 1-ft high, 2-ft wide, and 2-ft long, which
was smaller than the original apparatus depicted in
Figure 3.1. Test specimen was reduced to 1-ft high, 1-ft
wide, and 2-ft long. The test specimen was prepared at
the center of the test apparatus.
(b) Moveable Lateral Supporting Panels The longitudinal
direction of the test specimen was fitted between two
lubricated plexiglass panels. These two lateral
supporting panels can be moved horizontally. The movement
was controlled by an air cylinder attached to each panel.
After the lateral supporting panels were released (i.e.,
moved away from the soil) the test specimen was free to
move in the longitudinal direction in an unconfined
condition. This represents a "worst" condition as any
lateral confinement will undoubtedly reduce lateral
deformation of the soil-geosynth^tic composite.
(c) Attachment of Geosvnthetic The geosynthetic
reinforcement at the mid-height as well as at the top
surface were simply laid horizontally without attaching
30


to the vertical plates (not present in the modified
apparatus) as in the original apparatus. Such a manner
greatly simplifies sample preparation and eliminate
possible bucking of the vertical plate.
(d) Load Application Mechanism In the modified test, the
sustained vertical load was applied with a self-contained
loading mechanism which consisted of a rigid frame and a
Conbel pneumatic loader. The rigid loading frame was used
as the reaction for the load application. To distribute
a concentrate load to the top surface of the specimen,
rigid plexiglass plates of different sizes were assembled
in a pyramid configuration. The moveable supporting
panels were released after the sustained vertical load
was applied for a given period of time.
(e) Measurement of Lateral Deformation The lateral
deformation of test specimen was measured by LVDT's
(Linear Voltage Deformation Transducers) at the mid-
height, where the geosynthetic reinforcement was located.
Mechanical displacement dial gage was used to measure the
vertical displacement of the specimen.
31


Legends:
A Air Cylinder
B Conbel Pneumatic Loading Device
C Loading Plate
D Lateral Movable Supporting Panel
E LVDT Supporting Tube
Figure 3.2 : The Modified Long-Term Soil-Geosynthetic
Performance Test Device
32


sustained pressure
(a) Before Releasing Lateral Supporting Panels
sustained pressure
(b) After Releasing Lateral Supporting Panels
Figure 3.3 : Schematic Diagram of the Modified
Long-Term Soil-Geosynthetic Performance
Test Device
33


3.2 Test Procedure
The procedure for the Long-Term Soil-Geosynthetic
Performance test can be described in the following steps:
1. prepare the soil at the desired moisture content
(2% wet-of-optimum in this study) and cure the soil
overnight in a sealed container inside a high humidity
room.
2. apply lubrication layers, each consist of a latex
membrane and a thin layer of a silicon grease, on all
four sides of the plexiglass.
3. restrain movement of the moveable supporting
panels with a high air pressure (80 psi) through air
cylinders. A pair of carpenter's clamps were also used to
prevent movement of the supporting panel during soil
compaction. This creates a cuboidal volume of 1 ft by 1
ft by 2 ft, within which a sample can be prepared.
4. place a layer of geosynthetic (1 ft by 2 ft in
size) at the bottom of the test device, and compact the
soil in lifts until it reaches the mid-height (i.e., 0.5
ft), and lay a layer of geosynthetic ( 1 ft by 2 ft in
size) covering the soil surface.
5. compact soil in lifts over the geosynthetic layer
until it reaches 1 ft height, and cover the top surface
34


with a layer of geosynthetic.
6. remove the carpenter's clamps, and mount the
LVDT's and dial indicator, and set the readings to zero.
7. cover the test specimen with a plastic sheet to
keep a constant moisture content.
8. apply a sustained vertical load through a loading
plate placed on the top surface of the geosynthetic layer
(see Figure 3.3(a)).
9. release the moveable supporting panels (the
supporting panels are retracted and the lateral
confinement is removed) after the sustained vertical load
has been applied for a given amount of time (see Figure
3.3(b)), and take a reading of the immediate response.-
10. take measurement periodically by a data
acquisition system.
In case of testing at elevated temperature (125DF),
tests were performed in a heat chamber at constant
temperature and humidity (provided by humidifier), as
shown in Figure 3.4. In order to achieve consistent
elevated temperature of test specimen, test specimen in
test apparatus was placed in the heat chamber for 2 days
before load application.
35


3.3 Test Instrumentation
The instruments used in the test are LVDT and
mechanical displacement dial gage. With the exception of
one test (Test D-l), two LVDT's were used to measure the
lateral deformation of test specimen, a dial gage was
used to measure the vertical displacement. A typical
layout of instrumentation is depicted in Figure 3.5.
3.3.1 Linear Voltage Deformation Transducer (LVDT)
Linear Voltage Deformation Transducer (LVDT) was
placed in a horizontal position used to measure lateral
movement of the soil-geosynthetic composite. The stylus
of LVDT was set to just touch the mid-height of the
composite, where the reinforcement layer was placed. Two
LVDT's were employed in each test, one on each side of
the composite. Reading of. the LVDT's was recorded
periodically by an automated data acquisition interfaced
with a personal computer.
3.3.2 Mechanical Displacement Dial Gage
Mechanical displacement dial gage was used to
measure the vertical displacement of the soil-
geosynthetic composite. The tip of the dial gage was set
36


Figure 3.4 : The Modified Long-Term Soil-Geosynthetic
Performance Test Device at Elevated
Temperature
37


Legend
linear voltage displacement transducer
9 mechanical displacement dial gage
Figure 3.5 : Layout of Instrumentation
38


to touch the top of the loading plate. The accuracy of
the dial gage was +0.001 in.
3.3.3 Strain Gage
i
High-elongation strain gages were used to measure
the strain distribution of the Typar geotextile in one of
the tests (Test D-l). Two additional layout of the
instruments in such test is depicted in Figure 3.6.
A total of 10 strain gages were mounted along the
length of geosynthetic on two parallel lines to provide
redundancy of the measurement. To avoid inconsistent
local stiffening of the geotextile by the adhesive, the
strain gage attachment technique developed by Billiard
and Wu (1991) was employed by gluing only the two ends of
a strain gage to the surface of geotextile with two-ton
epoxy. This technique has been used successfully by Wu
(1992) and Helwany (1994).
Because the soil contained gravel and was moist. A
microcrystalline wax material was used to protect the
gages from soil moisture. For five of the strain gages,
an extensible neoprene rubber patch was used to cover
each strain gage (see Figure 3.7) to prevent the expected
mechanical damage during compaction. Helwany (1994)
39


conducted two uniaxial tension tests, one with and the
other without the protective cover (wax material plus
Neoprene patch), to examine the effect of the protective
cover on the extensibility of the geotextile. The results
indicated that the protective material had little effect
on the extensibility of the geotextile.
A uniaxial tension test with two strain gages on a
geotextile specimen was performed to obtain the
calibration curve. The calibration curves for the two
strain gages, as shown in Figure 3.8, are nearly
identical.
3.4 Testing Program
The testing program was designed to examine the
effects of various factors on long-term behavior of soil-
geosynthetic composites. These factors included soil
type, geosynthetic type, temperature, and sustained
vertical surcharge. To demonstrate the validity of the
test method, repeatability tests and load-deformation
tests were also performed. A summary of these tests is
presented in Table 3.1. The test conditions are described
briefly as following:
40


Legend
LI strain gage
~3-1 linear voltage displacement transducer
mechanical displacement dial gage
Figure 3.6 : Layout of Instrumentation of Test D-l
41


42


gage 1
gage 2
Strain, %
Figure 3.8 : Calibration Curves for Strain Gages on
Typar 3301 Geotextile
43


Table 3.1 Test Program
Test Designation Soil Reinforcement Temp. Sustained Average Vertical Pressure Total Elapsed Time
(F) (psi) (days)
C-l c.s. None 70 15 30
C-2 c.s. Amoco 2044 70 15 30
D-l R.B. Typar 3301 70 15 15
H-l R.B. Amoco 2044 125 30 30
R-l R.B. Amoco 2044 70 15 30
R-2 R.B. Amoco 2044 125 15 30
R-3 R.B. Amoco 2044 125 15 30
S-l R.B. None 70 15 30
S-2 R.B. None 125 15 30
U-l R.B. Amoco 2002 70 failure failure
W-l R.B. Amoco 2002 125 15 30
Note: R.B.= road base
C.S.= a clayey soil with 43% of fines and PI=11
44


3.4.1 Repeatability Tests
Two tests were conducted in identical conditions to
examine repeatability of the performance test. Tests R-2
and R-3 were conducted with the road base and Amoco 2044
reinforcement. The tests were conducted under a sustained
average vertical pressure of 15 psi, and at a constant
temperature of 125F.
3.4.2 Failure Mode of the Performance Test
In order to investigate failure mode of the
performance test, a soil-geosynthetic composite (with the
road base and Amoco 2002) was subjected to an increasing
applied load at a constant rate of 0.6 in. per minute,
using a MTS-810 loading machine, until a failure
condition developed. This test was designated as Test
U-l.
3.4.3 Deformed Shape of Test Specimen and Strain
Distribution along the Geosynthetic
To' examine strain distribution along the
geosynthetic reinforcement and deformed shape of the test
specimen, a Test designated as Test D-l was conducted.
45


The soil-geosynthetic composite consisted of the road
base and Typar 3301 reinforcement. Ten strain gages were
installed along the length of the geotextile to measure
the distribution of strain with time under an average
vertical pressure of 15 psi and at ambient temperature.
LVDT's were used to measure horizontal displacement of
the specimen at Points 1, 2, and 3, as shown in Figure
3.7. The vertical movement was measured by a mechanical
displacement dial gage.
3.4.4 Roles of Reinforcement
Tests C-l, S-l were conducted with the clayey soil
and the road base only, respectively, under a sustained
average vertical pressure of 15 psi at 70F. Comparisons
between Test C-2 and C-l, and between R-l and S-l were
made to assess the role of reinforcement in the long-term
performance test. Test C-2 and R-l were conducted under
the same conditions as Tests C-l and S-l, except that
Test C-l and R-l are with Amoco. 2044 reinforcement. To
investigate the roles of reinforcement at an elevated
temperature, Test S-2 was performed with the road base
only, under a sustained average vertical pressure of 15
psi at 125F to compare with Test R-2 which was conducted
46


under the same conditions as Test S-2 except a sheet of
Amoco 2044 was incorporated in Test R-2.
3.4.5 Effect of Soil Type
To assess the behavior of the performance test
with different soil types, the clayey soil and the road
base were employed in.Tests C-2 and R-l, respectively.
Both tests used Amoco 2044 reinforcement and were
conducted under a sustained average pressure of 15 psi at
70F.
3.4.6 Effect of Temperature
The creep behavior of the performance test at
ambient and elevated temperatures was examined by Tests
R-l and R-2. Test R-l was conducted at 70F, while Test
R-2 was at 125F. Both Tests R-l and R-2 used the road
base and Amoco 2044 reinforcement and both were subjected
to a sustained average pressure of 15 psi.
3.4.7 Effect of Geosynthetic Type
Amoco 2002 and Amoco 2044 are manufactured by the
same method and with the same polymer except that the
47


same method and with the same polymer except that the
ultimate tensile strength of Amoco 2002 is about 3 times
lower than Amoco 2044. Test W-l, consisted of the road
base and Amoco 2002 reinforcement, were conducted to
assess the effect of reinforcement strength by with Test
R-2 which was conducted under the same conditions except
with Amoco 2044 reinforcement.
The effect of reinforcement type can be also be
examined by comparing Tests D-l and R-l which were
conducted under the same conditions (with the road base
under a sustained average pressure of 15 psi at 70dF) .
Typar 3301 and Amoco 2044 were used as reinforcement in
Test D-l and R-l, respectively.
3.4.8 Effect of Sustained Vertical Surcharge
Test H-l was designed to examine the behavior of the
i
performance test under a higher sustained vertical load.
An average sustained vertical pressure of 30 psi was
applied in Test H-l which was conducted under the same
condition as test R-2 except for the average sustained
vertical pressure.
48


4. TEST RESULTS AND DISCUSSION OF RESULTS
In this research, a number of performance tests were
conducted with different soils, geosynthetics, sustained
vertical surcharges, and at different temperatures.
Lateral and vertical displacements of the soil-
geosynthetic composite were recorded periodically
throughout each test. The term lateral displacement,
unless otherwise specified, is referred to the total
lateral displacement on both sides of the test specimen
at the mid-height of the soil-geosynthetic composite
(i.e. at the location of the reinforcement). The time, t,
is referred to the elapsed time after the supporting
panels were removed. Strain distributions along
geosynthetic with time were measured in one test only
(Test D-l). The test data presented in this chapter are
tabulated in Appendix A.
49


4.1 Verification of Test Method
4.1.1 Repeatability tests
Figures 4.1(a) and 4.1(b) show the lateral and
vertical displacements versus time relationships of
Tests R-2 and R-3, respectively. The two tests were
conducted under the same condition (road base with Amoco
2044 reinforcement, under a sustained average pressure of
15 psi, at 125F) to examine the repeatability of the
performance test.
Because of the electrical interference of data
acquisition system, significant reading scatters of LVDT
readings were experienced. To examine the extent of the
electrical interference, two LVDT's with their stylus
touching a rigid wall (i.e., presumably a zero
displacement) were tested in the heat chamber. The
readings, as shown in Figure 4.2, are seem to deviate
from zero with an accuracy of +0.4xl0-2 in. To accommodate
these scatters, curve fittings were performed on the test
data to allow comparison of lateral and vertical
displacements versus time for Tests R-2 and R-3.
Initial vertical displacements at t= 10 min. of
0.018 in. and 0.020 in., and initial lateral
displacements of 0.028 in. and 0.013 in. were measured
50


displacements of 0.028 in. and 0.013 in. were measured
for Tests R-2 and R-3 after releasing of lateral
supports, respectively. The differences are mostly due to
the differences in the degree of restraint of the
supporting panels.
The magnitudes of creep deformation over 43,200 min.
(30 days) and the rates of creep in both directions for
Tests R-2 and R-3 were similar. As shown in Table 4.1,
the creep deformation in vertical and lateral directions
at t=43,200 min. were, respectively; 0.054 in. and 0.055
in. for Test R-2; and were 0.055 in. and 0.054 in. for
Test R-3. The creep rates decreased at fast decreasing
rate in both vertical and lateral direction in both
tests. The repeatability of the performance test is
considered satisfactory.
It is of great important to note that, under the
elevated temperature condition of which the creep rate
accelerated more than 100 folds, the creep deformation
was very small and essentially ceased after t=30,000
minutes. This behavior conferred with those observe in
full-scale tests (see section problem statement in
Chapter 1) that creep was negligible.
51


Displacement, In.
Figure4.1(a) Lateral Displacements Versus Time
Relationships of Tests R-2, R-3
52


0.20
0.10 -
u
0.00 -------1--------1--------1--------1--------
0 10 20 30 40 50
(Thousands)
Elapsed Time, min.
R-2 R-3
Figure 4.1 (b)
Vertical Displacements Versus Time
Relationships of Tests R-2, R-3
53


Displacement (in.)
LVDT No.1
LVDT No.2
Elapsed Time (min.)
Figure 4.2 : Examination of Electrical Interference to LVDT


Test R-2 Test R-3
Elapsed Lateral Avg. Incremental Vertical Avg. Incremental Lateral Avg. Incremental Vertical Avg. Incremental
Time Dlsp. Lateral Creep Dlsp. Vertical Creep Dlsp. Lateral Creep Dlsp. Vertical Creep
Rate Rate Rate Rate
(min.) (In.) (%/dav) (In.) (%/dav) (In.) (%/dav) (In.) (%/day)
60 0.042 0.4E+OO 0.028 5.6E+00 0.025 5.0E+00 0.028 5.6E+00
400 0.048 2.1E-01 0.030 7.1E-02 0.034 3.2E-01 0.036 2.0E-O1
1000 0.049 2.0E-02 0.032 4.0E-02 0.037 6.0E-02 0.038 4.0E-02
10000 0.053 5.3E-03 0.046 1.9E-02 0.047 1.3E-02 0.039 1.3E-03
20000 0.054 1.2E-03 0.053 0.4E-O3 0.051 4.0E-O3 0.045 7.2E-03
30000 0.055 1.2E-03 0.054 1.2E-03 0.052 1.2E-03 0.053 9.6E-03
40000 0.055 0.0E+00 0.054 O.OE+OO 0.054 2.4E-03 0.055 2.4E-03
Table 4.1 Displacements and Average Creep Strain Rates of Tests R-2,
R-3


4.1.2 Failure Mode of the Performance Test
Figure 4.3 shows the applied vertical load versus
time curve of Test U-l (the road base with Amoco 2002
reinforcement). This test was conducted with a metal test
apparatus because of the anticipate high load intensity.
Part of the curve has to be estimated because the maximum
load capacity of the MTS-810 machine was preset at 20
kips. The ultimate load was approximately 24 kips (i.e.,
an average pressure of 80 psi) As the force in the
geotextile reached its ultimate strength, the
geosynthetic reinforcement ruptured along the center
line, as shown in Figure 4.4, which clearly indicated
that the maximum force in reinforcement occurred along
the center line of geosynthetic specimen. This behavior
also conforms with the anticipated load distribution in
the performance test.
4.2 Behaviors Before Releasing Lateral Support
After each test specimen was prepared, a sustained
vertical load was applied. The transverse movement of the
soil-geosynthetic composite was restrained by the side
walls of the test device, while the longitudinal movement
56


Vertical Load, kips
Elapsed Time, sec.
Figure 4.3: Applied Vertical Load Versus Time
Relationships of Test U-l
300
57


Figure 4.4
Rupture of Amoco 2002 Geotextile, Test U-l
58


of the composite was restrained by the lateral supporting
panels with an air pressure of 80 psi.
In addition to vertical displacement, because of
the high vertical load, some appreciable (longitudinal)
lateral displacements occurred before the lateral
supporting panels were released due to soil compaction
pressure. The measured displacements immediately before
releasing the movable supporting panels are presented in
Table 4.2. From Table 4.2, the following observations
were made:
1. Comparisons of Test S-l (the road base only,
under a sustained average pressure of 15 psi, at 70F),
Test R-l (same as Test S-l except with Amoco 2044
reinforcement), and Test D-l (as Test R-l except with
Typar 3301 reinforcement) indicated-that the geosynthetic
reinforcement played a significant role in restraining
the lateral movement of the composite, but insignificant
in reducing the vertical movement before releasing of the
lateral supports.
2. Comparisons of Test C-2 (the clayey soil with
Amoco 2044 reinforcement, under a sustained average
pressure of 15 psi, at 70F) and Test R-l (same
conditions as Test C-2 except with the road base)
59


Table 4.2 Lateral and Vertical Displacements Before
Releasing Lateral Supports
Test Designation Soil Reinforcement Temp. (F) Sustained Average Vertical Pressure (psi) Lateral Disp. (in. ) Vertical Disp. (in. )
C-l c.s. None 70 15 0.122 0.36
C-2 c.s. Amoco 2044 70 IS 0.066 0.67
D-l R.B. Typar 3301 70 15 0.130 0.376 .
H-l R.B. Amoco 2044 125 30 0.24 0.464
R-l R.B. Amoco 2044 70 15 0.136 0.325
R-2 R.B. Amoco 2044 125 15 0.066 0.260
R-3 R.B. Amoco 2044 125 15 0.025 0.264
S-l R.B. None 70 15 0.329 0.416
S-2 R.B. None . 125 15 0.303 0.257
W-l R.B. Amoco 2002 125 15 0.396 0.230
Note: R.B.= road base
C.S.= a clayey soil with 43% of fines and
PI=11
60


indicated that the clayey soil was more compressible than
the road base, thus, Test C-2 exhibited about twice as
much vertical displacement than Test R-l. The lateral
displacement of Test C-2 was, however, only one half of
that occurred in Test R-l. This may be because the
compaction effect in Test C-2 was much smaller.
3. At ambient temperature, Test R-l (the road base
with Amoco 2044 reinforcement, under a sustained average
pressure of 15 psi, at 70F) and test D-l (same condition
as Test R-l except Typar 3301 was.used as reinforcement)
exhibited nearly the same lateral and vertical
displacements. However, at 125F temperature, Test R-2
(same as R-l except at 125F) showed six times smaller
lateral displacement than Test W-l (under the same
condition as Test R-2 except Amoco 2202 was used as
reinforcement), although their vertical displacements
were comparable.
4. Test R-l (the road base with Amoco 2044
reinforcement, under a sustained average pressure of 15
psi, at 70F) showed twice as much lateral displacement
i
as Test R-2 (under the same condition as R-l except at
125F). The vertical displacement of Test R-l was only
slightly larger than Test R-2.
61


5. The effect of the sustained load can be assessed
by comparing Test R-2 (the road base with Amoco 2044
reinforcement, under a sustained average pressure of 15
psi, at 125F) with Test H-l (same conditions as Test
R-2 except under a sustained average pressure of 30 psi).
Test H-l showed larger displacement in both vertical and
lateral direction. Note that the increase in the vertical
displacement approximately proportional to the increase
in the sustained average pressure increasing.
4.3 Long-Term Behavior of the Performance Test
4.3.1 Deformed Shape of Test Specimen and Strain
Distribution along the Geosynthetic
Figure 4.5 shows the relationships of vertical and
lateral displacements at three heights versus elapsed
time of test D-l (the road base with Typar 3301
reinforcement, under a sustained average pressure of 15
psi, at 70F). As to be expected, the displacements at
Points 2 and 3 were larger than those at Point 1. Points
2 and 3 showed very similar lateral creep displacement at
the beginning of the test. Thereafter, however, Point 3
exhibited a larger creep displacement than point 2. The
62


the beginning of the test. Thereafter, however, Point 3
exhibited a larger creep displacement than point 2. The
difference grew larger as time elapsed.
The vertical displacement was fairly close to the
lateral displacement at Point 1. The creep rate at Point
1 was slightly lower than the vertical creep rate.
The lateral deformed shapes of the specimen at
different elapsed times are shown in Figure 4.6. Larger
displacements occurred at 1/4 and 3/4 heights (i.e.,
Points 2 and 3), while smaller displacements occurred at
the top, the bottom, and the mid-height. At t=10 minutes,
the upper part of the specimen was very similar to the
lower part. As time progressed, the lower part showed
more lateral deformation than the upper part. Point 3
experienced the largest creep rate.
Figure 4.7 shows the measured strain distribution
along the length of geotextile of Test D-l at t=10 min.,
4,320 min. and 18,720 min. after releasing the lateral
supports. The strain at the two ends of geotextile was
zero, because there was no restraint at the ends.
The measured strains along the geotextile resembled
a bell shape with an axis of symmetry at the center. The
maximum strains occurred at the center of geosynthetic
63


strain versus time. The maximum measured strain was 2.0%
at t=10 min., and at t=2, 880 min. the maximum strain
increased to 2.8%, then, remained constant for about
1,440 min.(1 day), i.e., at t=4,320 minutes, after that,
the maximum strain decreased at an average rate of 0.005%
per day.
Figure 4.9 shows the relationships between creep
strain rates and elapsed time. It is seen that the creep
rate decreased almost linearly with log(time), and that
the rates of decrease in the vertical direction and
different points in the lateral direction are fairly
similar. The magnitude and rate of creep deformation at
selected elapsed times are listed in Table 4.3.
4.3.2 Loads in Geosynthetic Reinforcement
Loads induced in the geotextile reinforcement are of
i
significant interest in the design of GRS structures. The
conventional approach for determining the loads is to
apply the load-strain relationship of the geotextile ,
which was obtained from "element" load-deformation tests,
to measured or computed strains. However, the load-strain
behavior of geotextiles is affected significantly by,
among other factors, the strain rate. In Test D-l the
64


CTi
c
c

E

o

Q.
W
Q
Elapsed Time, min.
Figure 4.5 : Lateral and Vertical Displacements
Time Relationships of Test D-l
Lateral Disp.
Point 1(9ee Flg.3.5)
Point 2(see Flg.3.5)
Point 3 (9ee Flg.3.5)
Vortical Dl9p.
Versus


Elapsed Time (min.) Lateral Direction Vertical Direction
Point 1 Point 2 Point 3
Displacement Creep Strain Displacement Creep Strain Displacement Creep Strain Displacement Creep Strain
Rate Rate Rate Rate
On.) (%/mln.) (In.) (%/mln.) (In.) (%/mln.) (In.) (%/mln.)
60 0.050 1.0E+01 0.083 1.7E+01 0.093 1.9E+01 0.051 1.0E+01
400 0.064 4.9E-01 0.097 4.9E-01 0.113 7.1E-01 0.071 7.1E-01
1000 0.070 1.2E-01 0.102 1.0E-01 0.118 1.0E-01 0.078 1.4E-01
2000 0.074 4.0E-O2 0.105 3.6E-02 0.122 4.8E-02 0.082 4.8E-02
4000 0.077 1.6E-02 0.108 1.8E-02 0.127 3.0E-02 0.086 2.4E-02
6000 0.078 6.0E-03 0.109 6.0E-03 0.128 6.0E-03 0.088 1.2E-02
8000 0.079 3.0E-03 0.110 6.0E-03 0.129 6.0E-03 0.089 3.0E-03
10000 0.079 3.0E-03 0.111 3.0E-03 0.130 6.0E-03 0.089 3.0E-03
20000 0.080 1.2E-03 0.111 6.0E-04 0.133 3.6E-03 0.090 1.2E-03
Table 4.3 Displacements and Average Creep Strain Rates of Test D-l


+
A
O
+
Figure 4.6: Lateral Deformed Shapds of Test
Different Elapsed Times
1 0 min.
400 min.
4,320 min.
18,720 min.
D-l at
67


Distance from left end of geotextile.in.
10 min. 4320 min. + 18720 min.
Figure 4.7 : Measured Strains along the Length of
Geotextile of Test D-l
at t= 10 min./ 4,320 min., 18,720 min.
68


(Thousands)
Elapsed Time, min.
Figure 4.8: Maximum Strains Versus Time Relationships of
Test D-l
69


Rate of Creep Deformation (%/day)
Lateral Dlsp. (Pt.1)
Lateral Dlsp. (Pt.2)
Lateral Dlsp. (Pt.3)
Vertical Dlsp.
Elapsed Time (min.)
Figure 4.9 : Average Creep Strain Rates in the Vertical
and Lateral Directions Versus Time
Relationships of Tests D-l


strain rate was highly nonlinear, as seen in Figure 4.9.
A different approach, using the isochronous load-strain
curves, was used to determine the loads in the geotextile
reinforcement.
Isochronous load-strain curves were first
established as shown in Figure 4.10. The isochronous
load-strain curve were deduced from the creep curves
shown in Figure 2.9. Using Figure 4.10, the load in
geosynthetic for a certain strain at a given time can be
determined.
Figure 4.11 shows the calculated loads along the
length of geotextile at different elapsed times. The
maximum load occurred at the center of geotextile and
decreased toward to two extremities. This is consistent
with Test U-l in which rupture occurred along the center
line of the geotexile.
Figure 4.12 shows the relationships of loads versus
time at different locations along the geotextile. The
loads decreased at a decreasing rate as time elapsed. The
rate of decrease was nearly the same at all locations.
This decreasing load behavior in the geosynthetic could
be the result of "stress relaxation". Stress relaxation
is a term used to describe a behavior that the load in a
71


li/ni 'nnm
10min
400min
4,320min
18,720min
Strain, %
Figure4.10: Isochronous Load-Strain Curves
72


Load, Ib/ft.
Distance from left end of geotextile,in.
+ 10 min. O 4,320 min.
A 400 min. + 10,720 min.
Figure 4.11 : Loads along the Length of Geotextile at
Different Elapsed Times of Test D-l
73


Load, Ib/ft.
100
90 ?
0 5 10 15 20
(Thousands)
Elapesd Time, min.
+ at center
A at 4 in. from left end
0 at 8 in. from left end
at 10 in. from left end
Figure 4.12 : Maximum Loads in Geotextile Versus Time at
Different Distances from Left End of
Geotextile of Test D-l
74


material, subject to a constant deformation, decreases
with time. Stress relaxation may occur when the rate of
deformation becomes small. In Test D-l, stress relaxation
began at 10 minutes after releasing the lateral supports.
4.3.3 The Role of Reinforcement
Comparison of the lateral and vertical displacements
versus time relationships between Tests S-l and R-l and
between Tests S-2 and R-2 are shown in Figures 4.13 and
4.14, respectively. Test S-l was conducted with the road
base only, under a sustained average pressure of 15 psi,
at 70F while, Test R-l was conducted under the same
conditions as Test S-l except Amoco 2044 reinforcement
was used. Test S-2 and R-2 were conducted under the same
conditions as Tests Test S-l and R-l, respectively,
except the temperature was 125F.
The magnitude of creep deformation in the lateral
and vertical directions of unreinforced tests (Tests S-l
and S-2) were markedly larger thau reinforced soil tests
(Tests R-l and R-2) because the geosynthetic
reinforcement restrained movement in lateral and as a
result the vertical displacement was also reduced. The
reduction of displacements in the lateral direction was
75


Displacement, in.
0.80
Elapsed Time, min.
Figure 4.13 : Lateral and Vertical Displacements
Time Relationships of Tests S-1, R
Lateral Dlsp. S-1
Vertical Dl9p. S-1
Lateral Dl9p. R-1
Vertical Dl9p. R-1
Versus
1


Test S-1 Test R-1
Elapsed Lateral Avg. Incremental Vertical Avg. Incremental Lateral Avg. Incremental Vertical Avg. Incremental
Time Disp. Lateral Creep Disp. Vertical Creep Disp. Lateral Creep Disp. Vertical Creep
Rate Rate Rate Rate
(min.) (In.) (%/day) (In.) (%/day) (In.) (%/day) (In.) (%/day)
60 0.039 7.8E+00 0.031 6.2E+00
400 0.448 1.6E+01 0.174 6.1E+00 0.040 3.5E-02 0.038 2.5E-01
1000 0.542 1.9E+00 0.210 7.2E-01 0.040 0.0E+00 0.042 8.0E-02
10000 0.600 7.7E-02 0.230 2.7E-02 0.040 0.0E+00 0.051 1.2E-02
20000 0.600 O.OE+OO 0.233 3.6E-03 0.040 0.0E+00 0.056 6.0E-03
30000 0.601 1.2E-03 0.237 4.8E-03 0.040 O.OE+OO 0.062 7.2E-03
40000 0.602 1.2E-03 0.241 4.8E-03 0.040 O.OE+OO 0.067 6.0E-03
\
Table 4.4 Displacements and Average Creep Strain Rates of Tests S-1, R-l


Displacement, in.
Lateral Dlsp. S-2
Vertical Olsp. S-2
Lateral Dlsp. R-2
Vertical Dlsp. R-2
Elapsed Time, min.
Figure 4.14 : Lateral and Vertical Displacements Versus
Time Relationships of Tests S-2, R-2


Test S-2 Test R-2
Elapsed Lateral Avg. Incremental Vertical Avg. Incremental Lateral Avg. Incremental Vertical Avg. Incremental
Time Disp. Lateral Creep Disp. Vertical Creep Disp. Lateral Creep . Disp. Vertical Creep
Rate Rate Rate Rate
(min.) (In.) (%/day) (in.) (%/day) (In.) (%/day) (In.) (%/day)
60 0.123 2.5E+01 0.045 9.0E+00 0.042 8.4E+00 0.028 5.6E+00
400 0.160 1.3E+00 0.056 3.9E-01 0.048 2.1E-01 0.030 7.1E-02
1000 0.171 2.2E-01 0.058 4.0E-02 0.049 2.0E-02 0.032 4.0E-02
10000 0.185 1.9E-02 0.066 1.1E-02 0.053 5.3E-03 0.048 1.9E-02
20000 0.187 2.4E-03 0.070 4.8E-03 0.054 1.2E-03 0.053 8.4E-03
30000 0.187 0.0E+00 0.075 6.0E-03 0.055 1.2E-03 0.054 1.2E-03
40000 0.187 0.0E+00 0.075 O.OE+OO 0.055 0.0E+00 0.054 0.0E+00
Table 4.5 Displacements and Average Creep Strain Rates of Tests S-2,
R-2


much larger than that in the vertical direction. The
magnitude of vertical creep displacements occurred
between t=10 min. and t=43,200 min. were 0.144 in. and
0.05 in., for Tests S-l and R-l, respectively. The
lateral creep displacements in the same period of time
were 0.347 in. and 0.008 in. for Tests S-l and R-l,
respectively.
At 70F, the creep rates in both the vertical and
lateral directions of Test S-l were higher than Test R-l
up to t=l,440 min., thereafter, the creep rates were
nearly the same. At 125F, the creep rate of Test S-2.in
the vertical direction was about equal to that of Test R-
2 but significantly higher than Test R-2 in lateral
direction up to t=4,000 minutes, thereafter, the creep
rate of Tests S-2 and R-2 were similar. The creep rates
of Tests S-l, R-l and S-2, R-2 are shown in Tables 4.4
and 4.5, respectively.
Figure 4.15 and 4.16 show the lateral and vertical
displacements versus time relationships of Test C-l (the
clayey soil only, under a sustained average pressure of
15 psi, at 70F) and Test C-2 (under the same conditions
as Test C-l except Amoco 2044 reinforcement was used),
respectively.
80


The test specimen in Test C-l failed at t=17
minutes. The failure occurred due to shear failure. Some
distinct shear bands were visible from the latex membrane
as shown in Figure 4.17. Before failure creep in vertical
and lateral directions occurred at about the same rate,
although the lateral deformation was slightly higher.
With a sheet of reinforcement, Test C-2 exhibited
about 0.1 in. lateral displacement after 40,000 min., at
which time the test was terminated. The creep rate up to
t=40,000 min. was nearly constant in the lateral
direction. In the vertical direction, however, the creep
deformation appeared to be experiencing tertiary creep
from t=10,000 minutes to t=40,000 minutes.
4.3.4 Effect of Geosynthetic Type
Figure 4.18 shows the lateral displacements versus
time relationships of Test R-2 (the road base with Amoco
2044 reinforcement, under a sustained average pressure of
15 psi, at 125 F) and W-l (under the same conditions as
Test R-2 except Amoco 2002 was used) The lateral
displacements of test S-2 (without reinforcement) were
also plotted in the Figure for comparison. The vertical
displacement of Test W-l is not available because the
81


Displacement, in.
Elapsed Time, min.
Lateral disp. a Vertical disp.
Figure 4.15 : Lateral and Vertical Displacements Versus
Time Relationships of Test C-l
82


Displacement, in.
Elapsed Time, min.
Lateral Disp. a Vertical Disp.
Figure 4.16: Lateral and Vertical Displacements Versus
Time Relationships of Test C-2
83


Figure 4.17 : Failure Mode of Test C-l
84


dial gage was found defective. As to be expected, the
magnitude of creep deformation in the lateral direction
was the largest in Test S-2 and the smallest in Test R-2.
The creep rates in the lateral direction of Test W-l were
higher than Test R-2, yet Test W-l and Test S-2 exhibited
similar creep rate. The displacements and creep strain
rates of Tests R-2, W-l, and S-2 are shown in Table 4.6.
Figure 4.19 shows the lateral and vertical
displacements versus time relationships of Test D-l(the
road base with Typar 3301 reinforcement, under a
sustained average vertical pressure of 15 psi, at 70F)
and R-l (under the same conditions as Test D-l except
Amoco 2044 was used as reinforcement). It is to be noted,
as compared with those tests shown in Figure 4.18, these
tests were conducted in ambient temperature.
The magnitude of creep deformation in the vertical
direction of Test D-l were larger than Test R-l but the
creep rates were comparable. The displacements and
average creep strain rates of the two tests in the
vertical direction are shown in Table 4.7.
The magnitudes of creep deformation in the lateral
direction of Test D-l were about the same as Test R-l in
the first 10 minutes and gradually became larger as time
85


Displacement, in.
Elapsed Time, min.
S-2 A R-2 o w-1
Figure 4.18: Lateral Displacements Versus Time
Relationships of Tests S-2, R-2, W-1
86


Test S-2 Test R-2 Test W-1
Elapsed Lateral Avg. Incremental Lateral Avg. Incremental Elapsed Sustained Lateral Avg. Incremental
Time Dlsp. Lateral Creep Dlsp. Lateral Creep Time pressure Dlsp. Lateral Creep
Rate Rate Rate
(min.) (In.) (%/dav) (In.) (%/day) (min.) (psl) (In.) (%/day)
60 0.123 2.5E+01 0.042 8.4E+00 60 15 0.067 1.3E+01
400 0.160 1.3E+O0 0.048 2.1E-01 400 15 0.086 6.7E-01
1000 0.171 2.2E-01 0.048 2.0E-02 1000 15 0.096 2.0E-01
10000 0.185 1.9E-02 0.053 5.3E-03 10000 15 0.114 2.4E-02
20000 0.187 2.4E-03 0.054 1.2E-03 20000 15 0.118 4.BE-03
30000 0.187 0.0E+00 0.055 1.2E-03 30000 15 0.119 1.2E-03
40000 0.187 0.0E+00 0.055 O.OE+OO 34560 15 0.120 2.6E-03
34560 30 0.140
36000 30 0.157 1.4E-01
40000 30 0.159 6.0E-03
R-2,
Table 4.6
Displacements and Average Creep Strain Rates of Tests S-2,
W-l


Displacement, in.
Lateral Dlsp. 0-1
Vertical Dl9p. D-1
Lateral Dlsp. R-1
A Vertloal Dlsp. R-1
Elapsed Time, min.
Figure 4.19: Lateral and Vertical Displacements Versus
Time Relationships of Tests D-l, R-1


Elapsed Time Test R-1 Test D-1
Lateral Dlsp. Avg. Incremental Lateral Creep Rate Vertical Dlsp. Avg. Incremental Vertical Creep Rate Lateral Dlsp. Avg. Incremental Lateral Creep Rate Vertical Dlsp. Avg. Incremental Vertical Creep Rate
(min.) (in;) (%/day) (In.) (%/day) (In.) (%/mln.) (In.) (%/day)
60 0.039 7.8E+00 0.031 6.2E+00 0.050 1.0E+01 0.051 1.0E+01
400 0.040 3.5E-02 0.038 2.5E-01 0.064 4.9E-01 0.071 7.1E-01
1000 0.040 0.0E+00 0.042 8.0E-02 0.070 1.2E-01 0.078 1.4E-01
10000 0.040 0.0E+00 0.051 1.2E-02 0.079 1.2E-02 0.089 1.5E-02
20000 0.040 O.OE+OO 0.056 6.0E-03
30000 0.040 O.OE+OO 0.062 7.2E-03
40000 0.040 0.0E+00 0.067 6.0E-03
Table 4.7 Displacements and Average Creep Strain Rates of Tests D-l,
R-l


elapsed. The creep rates in the lateral direction of two
tests were significantly different. The displacements and
average creep strain rates of the two tests in the
lateral direction are also shown in Table 4.7.
4.3.5 Effect of Soil Type
Figure 4.20 shows the lateral and vertical
displacements versus time relationships of Test R-l (the
road base with Amoco 2044 reinforcement, under a
sustained average pressure of 15 psi, at 70F) and Test
C-2 (the clayey soil in otherwise the same conditions as
Test R-l) As to be expected, the magnitude of creep
deformation in the vertical direction of Test C-2 were
much larger than Test R-l. The creep rate in the vertical
direction of Test C-2 was much higher than Test R-l in
the first 100 minutes; however, the creep rates of the
two tests were similar after 100 minutes. The average
creep rate in the vertical direction of Test C-2 was
9.6xl0-3 % per day and 6.0x1 O'3 % per day in Test R-l in
30 days.
Creep deformation in the lateral direction was
negligible in both tests over 43,200 minutes. The tests,
however, were conducted in ambient temperature. The test
90


Displacement, in.
Lateral Dlsp. C-2
Vertical Dlsp. C-2
Lateral Dlsp. R-1
Vertical Dlsp. R-1
Elapsed Time, min.
Figure 4.20: Lateral and Vertical Displacements Versus
Time Relationships of Tests C-2, R-1


Full Text

PAGE 1

LABORATORY LONG-TERM PERFORMANCE TESTS FOR SOIL-GEOSYNTHETIC COMPOSITES by Kanop Ketchart B.Eng, Chulalongkorn University, Thailand, 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 1995

PAGE 2

This thesis for the Master of Science degree by Kanop Ketchart has been approved for the Department of Civil Engineering by T.H. Wu Kevin Rens Date

PAGE 3

Ketchart, Kanop (M.S., Civil Engineering) Laboratory Long-Term Performance Tests for Soil-Geosynthetic Composites Thesis directed by Professor Jonathan T.H. Wu ABSTRACT Creep behavior is of concern in the design of geosynthetic-reinforced soil (GRS) structures because geosynthetics, which are manufactured with various polymers, are generally considered creep-sensitive. In the current design methods for GRS structures, creep is accounted for by performing geosynthetic "element" creep tests in which sustained loads are applied directly to the geosynthetic under confined or unconfined condition. However, field measurement of GRS retaining walls has clearly indicated that the backfill type and density play a very significant role in their long-term performance. In an attempt to investigate the effects of confining soil on the long-term behavior of a soil-geosynthetic composite. Wu and Helwany (1996) developed a long-term iii

PAGE 4

soil-geosynthetic performance test device. They performed two tests using a granular soil and a cohesive soil, and concluded that long-term behavior of a soil-geosynthetic composite is a result of soil-geosynthetic interaction. To properly assess long-term performance of a GRS structure, this interaction behavior must be taken into account. In this study, a modified soil-geosynthetic performance test was devised. The test simulates the predominant deformation behavior of a GRS structure in a "worst" condition by allowing geosynthetic reinforcement and its confining soil to deform in an interactive manner under a sustained surcharge without lateral confinement. A series of performance tests were performed to examine test repeatability and to investigate the effects of soil type, geosynthetic type and sustained load intensity on the behavior of soil-geosynthetic composite. A test was instrumented with strain gages to measure deformation along the length of the geosynthetic. Tests with soil only were also conducted for comparisons with soil-geosynthetic composite. In addition, a loaddeformation test with a weak geosynthetic was conducted iv

PAGE 5

to examine the failure mode of the soil-geosynthetic composites. Many of the tests were conducted at an elevated temperature of 125F. Element test on the geosynthetics indicated that the elevated temperatures typically accelerated creep of the geosynthetic by 100 to 400 folds. A finite element model was employed to analyze one of the performance tests. The analytical results were compared with the measures values. This abstract accurately represents the content of the candidate's thesis. I recommend its publication. Signed T.H. Wu v

PAGE 6

ACKNOWLEDGEMENTS I would like to express my sincerest thanks to Professor Jonathan T.H. Wu for his guidance and encouragement throughout my academic and research program. Special gratitude is also extended to Dr. Sang Ha Lee Yottana Kunatorn and Hsu-Kun Cheng for their helpful assistance. I would also like to thank Robert Barrett, Al Ruckman, Steven Steve and Tammy Harper of the Colorado Department of Transportation. Further thanks are extended to Amoco Fabrics and Fibers Company for providing materials. Finally, I would like to thank my parents and my sister for providing much needed love and support throughout mu study.

PAGE 7

CONTENTS Chapter Page 1. Introduction. . . . . . . . . . . . . . . . . 1 1.1 Problem Statement..... . . . . . . . . . . . 1 1.2 Research Objectives.......................... 5 1. 3 Method of Research. . . . . . . . . . . . . . 6 2. Test Materials and Material Properties ........ 10 2.1 Soils ........................................ 10 2. 2 Geosynthetics............................. . 11 2.3 Acceleration of Geosynthetic Creep at an Elevated Temperature ....... ................ 22 3. Test Apparatus, Test Procedure, and Test Program................................. 27 3.1 Test Apparatus 3.2 Test Procedure 27 34 3.3 Test Instrumentation........................ 36 3.4 Testing Program............................. 40 vii

PAGE 8

4. Test Results and Discussion of Results....... 49 4.1 Verification of Test Method................. 50 4.1.1 Repeatability Test........................ 50 4.1.2 Failure Mode of the Performance Test...... 56 4.2 Behavior Before Releasing Lateral Support... 56 4.3 Long-Term Behavior of the Performance Test.. 62 4.3.1 Deformed Shape of Test Specimen and Strain Distribution along the Geosynthetic...... 62 4.3.2 Loads in Geosynthetic Reinforcement....... 64 4.3.3 The Role of Reinforcement................. 75 4.3.4 Effect of Geosynthetic Type............... 81 4. 3. 5 Effect of Soil Type... . . . . . . . . . . 90 4. 3. 6 Effect of Temperature. . . . . . . . . . . 93 4.3.7 Effect of Sustained Vertical Surcharge... 94 5. Finite Element Analysis of the Performance Test ............................................ 103 5.1 The Finite Element Model .................... 103 5.1.1 Sekiguchi-Ohta Soil Model ................. 104 5.1.2 Generalized Geosynthetic Creep Model ...... 105 5.2 Evaluation of Model Parameters ............... 107 5.2.1 Sekiguchi-Ohta Model Parameters ........... 107 5.2.2 Generalized Geosynthetic Creep Model...... 112 viii

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5.3 Finite Element Simulation of the Performance Test............................................ 112 5.3.1 Finite Element Simulation ................. 112 5.3.2 Results of Finite Element Analysis ......... 115 6. Summary and Conclusions .................. ... 120 6.1 Summary ..................................... 120 6.2 Conclusions................................. 122 Appendixes A. Performance Test Results...... . . . . . . . 127 B. Input Data of Finite Element Analysis....... 139 Bibliography.... . . . . . . . . . . . . . . . 151

PAGE 10

1. INTRODUCTION 1.1 Problem Statement Geosynthetic-reinforced soil (GRS) retaining wall have become increasingly popular in the construction of retaining structure because of its many advantages over conventional reinforced concrete walls, including: ( 1) GRS retaining structures are more flexible, hence more tolerant to foundation settlement. (2) Construction of GRS retaining structure is rapid and requires only "ordinary" construction equipment. ( 3) GRS retaining structures are generally less expensive to construct than their reinforced concrete counterparts. When a geosynthetic is used as reinforcement in a "permanent" retaining structure, acceptable performance of the GRS retaining structure must be satisfied throughout its design life. The creep behavior is of concerned in evaluating the long-term performance of GRS retaining structure because geosynthetic, which are manufactured with various polymers, are generally

PAGE 11

considered creep-sensitive. Some current design methods (e.g., AASHTO, 1992) for GRS retaining structure evaluate the lohg-term creep potential of a GRS retaining structure by performing "element" creep tests on the geosynthetic reinforcement alone (in either a confined or unconfined mode) Other design methods simply apply a safety factor or a creep reduction factor to the ultimate strength of the geosynthetic reinforcement to account for creep. All these design methods tacitly assumed that creep of a GRS retaining structure is due entirely to the geosynthetic and not affected by the surrounding soil. Field measurement of GRS retaining walls has indicated little or no creep when granular backfill is employed. Some examples of well-instrumented, wellmonitored GRS retaining structure are: (1) A 41-ft high geosynthetic-reinforced soil retaining wall constructed in Seattle in 1989 The creep strains in the geotextile 11 months after fill placement were very small (with a maximum creep strain of about 0.13%). The creep rate was 4.5xl0-4% per day after fill placement, and 2. Oxl0-4% per day ten months after fill placement. The rates were approaching zero, 11 months 2

PAGE 12

after placement. The backfill was gravelly sand (Allen, et al., 1992). (2) Forty-six geogrid-reinforced soil retaining walls constructed in Tucson, Arizona in 1984 and 1985 Field measurement showed that despite the in-soil temperature was relatively high (97F), the geogrid reinforcement experienced a maximum strain of approximately 1.0% and was stable with time. The measured creep of the reinforcement in 10-year after construction was negligible (Collin, et al., 1994). (3) An 18-ft high geogrid-reinforced constructed in Algonquin, Illinois A test wall number of instruments were used to monitored the behavior of the test wall. Measured data indicated that the strain/load level remained constant (i.e. no creep) throughout the first five months after construction, and there were no other time-dependent phenomena deteriorating the geogrid performance. The backfill was well-graded sand gravel (Simac, et al., 1990; Bathurst, et al., 1993) However, the creep reduction factors adopted in the current design methods are fairly low, regardless of the backfill type. For example, creep reduction factors ranging from 0.25 to 0.4, depending on the polymer type 3

PAGE 13

of a geosynthetic, were specified in the AASHTO design method. To characterized the soil-geosynthetic composite behavior, Wu (1994) and Wu and Helwany (1996) developed a soil-geosynthetic long-term performance test, in which the stresses applied to the soil are transferred to the geosynthetic in a manner similar to the typical load transfer mechanism in GRS retaining structures, and both the soil and the geosynthetic are allowed to deform in an interactive manner under a constant sustained load. They reported two carefully conducted long-term performance tests, one used a clayey backfill and the other a granular backfill. Using element test on the geosynthetic alone, the maximum strain in the geosynthetic was underestimated by 250% in the clay-backfill test, and over-estimated by 400% in the sand-backfill test. It was noted that creep deformation essentially ceased within 100 minutes after the sand-backfill test began; whereas, the clay-backfill test creep deformation over the entire test period (18 days). Wu and Helwany (1996) indicated that long-term creep of a soil-geosynthetic is a result of soil-geosynthetic interaction. If the confining soil has a tendency to 4

PAGE 14

creep faster tha.n the geosynthetic reinforcement along its axial direction, the geosynthetic will impose a restraining effect on the deformation of the soil through the friction and/or adhesion between the two materials. Conversely, if the geosynthetic reinforcement tends to creep faster than the confining soil, then the confining soil will restrain the reinforcement deformation through the friction/adhesion. This restraining effect is a direct result of soil-reinforcement interaction where redistribution of stresses in the confining soil and changes in axial forces in the reinforcement occur over time in an interactive manner. In this study, a modified soil-geosynthetic longterm performance test was developed. The modified test was simpler to perform, yet represent a "worst" condition by providing no lateral constraint to the soilgeosynthetic composite. 1.2 Research Objectives The objectives of this research were three-fold. The first objective was establish a consistent test procedure for the modified soil-geosynthetic long-term performance test so that long-term soil-geosynthetic interaction 5

PAGE 15

creep behavior can be assessed in a reliable manner. The second objective was to examine the soil-geosynthetic interaction creep behavior for various soils and geosynthetics under different conditions, including accelerated creep at an elevated temperature. The third objective was to analyze the load transfer mechanism in the long-term performance test. 1.3 Method of Research This research was divided into two phases: an experimental phase and an analytical phase. 1.3.1 Experimental Study Long-term performance tests were performed to examine the soil-geosynthetic interactive creep behavior in various conditions of soils, geosynthetics, sustained vertical surcharges, and temperatures. Two types of soil, a road base and a clayey soil with 43% of fines, were employed as backfill for the tests. The road base is a silty sandy gravel(GM). It has been widely used as backfill for construction of road ways and retaining walls. The clayey soil has. a plasticity index of 11 and a higher tendency to deform 6

PAGE 16

with time than the road base. Three types of geosynthetic, Amoco 2044, Amoco 2002, and Typar 3301, were selected as reinforcement for the tests. Amoco 2044 and Amoco 2002 are woven-prolypropylene geotextile with tensile strength of 400 lb/in. and 120 lb/in.,respectively. Amoco 2044 presents a strong reinforcement, while Amoco 2002 presents a weak reinforcement. Typar 3301 is a heat-bonded nonwovenprolypropylene geotextile. Th.is fabric was selected because of its relatively smooth surface which make mounting of strain much easier. The test specimen comprised a cuboid of soil and a layer of geosynthetic reinforcement embedded at the midheight of the soil. The soil-geosynthetic composite was prepared inside the apparatus. The soil was prepared at 2% wet-of-optimum moisture and compacted to 95% relative density for every test conducted in this study. For comparison, tests without geosynthetic (i.e., soil only) were also conducted. Six long-term performance tests were conducted at an elevated temperature of 125F to accelerate creep of the geosynthetics. Tests under ambient temperature were also conducted to examine the effects of temperature on soil-7

PAGE 17

geosynthetic composites. A sustained average vertical pressure of 15 psi was applied to all of the performance tests except one test which was subjected to a sustained pressure of 30 psi. The test under 30 psi pressure was performed to examine the effects pressure intensity on the soil-geosynthetic composites. The lateral and vertical displacements of the soilgeosynthetic composite were monitored by LVDT's (Linear Voltage Displacement Transducers) and mechanical displacement dial gages. In one test, strain gages were installed along the length of the geosynthetic to measure the distribution of axial strain with time. The measured results were also used for verification of a finite element analytical model. 1.3.2 Analytical Study A finite element model developed by Helwany and Wu (1995) was employed to analyze the experimental results. The finite element model incorporated an elastoviscoplastic soil model and a generalized creep model. The generalized creep model was developed by Helwany and Wu(1992) to simulate creep characteristics of 8

PAGE 18

geosynthetics. The elasto-viscoplastic soil model was developed by Sekigushi and Ohta (1977). The finite element model has been verified with the measured behavior by Iizuka and Ohta (1987), Chou (1992) and Helwany and Wu (1995). 9

PAGE 19

2. TEST MATERIALS AND MATERIAL PROPERTIES 2.1 Soils A Road Base and a clayey soil with 43% of fines were selected for the tests. The road base has been widely used as backfill for construction of roadways and retaining walls. The clayey soil represents a natural soil which deforms significantly with time. 2.1.1 The Road Base This soil was classified as A-1-B(O). The grain size distribution curve is shown in Figure 2.1. The material has 76% passing the standard sieve No. 4 and 19% passing No. 200. The specific gravity of the soil solids was 2.67. The maximum dry unit weight of the soil was 134 lb/ft3 and the optimum moisture content was 7.2%. The Road Base was prepared inside the test apparatus by compaction with a 8-pound Proctor hammer. The soil was compacted to 95% relative density and 2% wet-of-optimum moisture content. Three consolidated-drained (CD) triaxial compression tests at confining pressures of 15, 30, 45 psi were 10

PAGE 20

conducted. The test specimen was prepared at a density of 126 lb/ft3 and a moisture content of 8.5%. Each specimen was loaded at a constant deformation rate of 0.3x10-3 in. per hour. The stress-strain relationship is shown in Figure 2.2. The internal friction angle of the road base was 32. 2. 2 The Clayey soil This soil was classified as A-6. The grain size distribution curve is shown in Figure 2.3. The material has 100% passing the standard sieve No. 4 and 43% passing No. 200. The plasticity index and liquid limit were 11 and 26, respectively. The maximum dry unit weight was 120 lb/ft3 and the optimum moisture content was 11%. The clayey soil was prepared inside the test apparatus in the same as that of the road base. 2.2 Geosynthetics 2.2.1 Amoco 2044 AMOCO 2044 is a woven polypropylene geotextile with some of its index properties listed in Table 2.1. The wide width Tensile test with Curtis Sure-Gripe with 16 11

PAGE 21

0 ..: < c c < 0 ... < c.. 100 80 60 40 20 0 0.01 Figure 2.1 v v v J..-v v v 0.1 1. 10 Particle diameter, mm Grain Size Distribution of the Road Base 12

PAGE 22

150 Cii 03=45 psi a. II) 100 "' CD psi ... Cll t) ;:: 0 .! 50 > CD c 03=15 psi 0 10 20 Axial Strain, % Figure 2.2 Consolidated Drained Triaxial Test Results of the Road Base 13

PAGE 23

.: II .5 -c: II u ... II a.. 100 80 60 40 20 0 0.01 Figure 2.3 ..... 1/ / __ v v 0.1 1 10 Particle diameter, mm Grain Size Distribution of the Clayey Soil 14

PAGE 24

inch gage length and 0.5 inch per minute cross head speed was conducted by the manufacturer. The load-deformation relationship is shown in figure 2.4. The element creep tests with 4 inch diameter roller grips and a 8 inch wide specimen were also conducted by the manufacturer. The element creep curves of AMOCO 2044 in the fill direction under 22%, 25%, 30% of the ultimate load are shown in figure 2.5, 2.6, and 2.7, respectively. Each figure shows the creep curves at temperature of 70F, 100F, and 120F. 2.2.2 Amoco 2002 Amoco 2002 is a woven polypropylene geotextile. Creep test data was not available through the manufacturer because the main function of Amoco 2002 was not for reinforcement. The index properties of Amoco 2002 are listed in Table 2.1. 2.2.3 Typer 3301 Typar 3301 is a heat-bonded nonwoven polypropylene geotextile. This geotextile was selected because of easiness for strain gage installation and accuracy for 15

PAGE 25

Table 2.1 Some Index Properties of Geosynthetics Amoco 2044 Amoco 2002 Typar 3301 Polymer type Polypropylene Polypropylene Polypropylene Manufacturing Woven Woven Non-woven Method Wide width 400 lb/in. 120 lb/in. 35 lb/in. strength (ASTM D-4595) Elongation at 18% 10% 60% break (%) (ASTM D-4595) Grab tensile 600 lb 200 lb 120 lb (ASTM D-4632) Elongation at 20% 15% 60% break (%) (ASTM D-4632) 16

PAGE 26

400 c ::::.. .t:l 300 .s= 'tl 200 'tl "' 0 ...J 100 0 5 10 15 Strain,% Figure 2.4 Load-Deformation Behavior of Amoco 2044 (Courtersy of Rick Valentine, Amoco Fabrics and Fibers Company) 17

PAGE 27

:::.e D c en .... Q) 15 I 1----f I . . I 10 5 0 . ..... .... :. . ..... ... 0.01 0.1 1 10 100 1000 .. 10000 100000 1000000 Elapsed Time, hours 1oF Y 100 F 120 F Figure 2.5 : Creep Curves of Amoco 2044 Geotextile in the Fill Direction at 22% of Ultimate Load (Courtersy of Tom Baker, Amoco Fabrics and Fibers Company)

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";/!. c (J) ..... \.0 15 I . : ; ::: ,, ; .. : I : : : .. :11 I . I : .. : 10 5 0 I ... J ; ... I ...... ... : I . I I 10000 100000 1000000 0.01 0.1 1 10 100 1000 Elapsed Time, hours 70 F Y 100 F 120 F Figure 2.6 : Creep Curves of Amoco 2044 Geotextile in the Fill Direction at 25% of Ultimate Load (Courtersy of Tom Baker, Amoco Fabrics and Fibers Company)

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1\) 0 30 -25 .,__,, _ _____ , , _ .. _, ___ ...... 4-- .:.. . 20 I ::.:1 .... 1 .. : :.::: IIIII ........ 1 .. ---.s 15 .. : _, en 10 5 0 0.01 -----1-..... --- ...... I ----.. ---. 0.1 1 10 100 1000 10000 100000 1000000 Elapsed Time, hours 7oF 100F 120F Figure 2.7 : Creep Curves of Amoco 2044 Geotextile in the Fill Direction at 30% of Ultimate Load (Courtersy of Tom Baker, Amoco Fabrics and .Fibers Company)

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measurement. The index properties of Typar 3301 are shown in Table 2 .1. The load-deformation behavior of Typar 3301 is shown in Figure 2.8. Specimens 30 em in width and 3.75 em in gage length were tested under three conditions: { 1) unconfined {in-isolation), {2) confined by a sand, and {3) confined by a rubber membrane. For the confined tests {i.e. test conditions 2 and 3) an effective normal stress of 11 psi was applied on the geosynthetic. All the tests were conducted at a strain rate of 2% per minute {Wu, 1992) The confined tests were conducted in a manner that the soil-reinforcement interface friction will not be inadvertently mobilized throughout the test. Detailed test procedures and test conditions have been presented by Wu {1991). Since the load-deformation beqavior of the heatbonded geotextile is hardly affected by the confinement, as seen in Figure 2.8, the creep tests were conducted with the geotextile in isolation {unconfined). The specimen size used in the creep tests was 6 in. wide and 1 in. long. Both ends of the test specimen were glued between two sets of thin metal plates to facilitate 21

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application of loads. The sustained loads used in the tests were 96, 140, and 180 lb/ft (approximately 24%, 35%, and 45% of the short-term ultimate strength, respectively) The results of the creep tests are shown in Figure 2.9. 2. 3 Acceleration of Geosynthetic Creep at an Elevated Temperature A Higher temperature tends to accelerate creep in a polymer. Hence, creep tests should be conducted to cover a range of temperatures in the in-service condition of the structure. This does, however, require extensive testing at different temperatures over considerable time periods. In absence of such information, time-shifting techniques may be utilized (with caution) to account for the effect of temperature. Morgan and Ward (1971) have found that the creep curves from element creep test at a certain temperature can be obtained by a simple horizontal shift from creep curve at different test temperature under the same sustained load. A number of element creep tests at different temperatures must be conducted to establish a time shifting factor for a certain change in temperature. 22

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Element creep curves for Amoco 2044 subject to three different sustained loads (at 70F, 100F and 120F), as shown in Figure 2.5, 2.6, and 2.7, were used to determine the time shifting factor as shown in Table 2. 2. The factor varies approximately between 100 to 400 for temperatures changing from 70F to 120F. For instance, a strain of 5% of 70F in the fill direction at 30% of ultimate load was measured at an elapsed time of about 25 hours for Amoco 2044. At 120F, under otherwise identical conditions, the same strain was measured at an elapsed time of only 0 .1 hour, which results in a time shifting factor of 250 (see Figure 2.7). For a strain of 5% in the fill direction at 25% of ultimate load, the measured elapsed time was about 100 hours at 70F. At 120F, under otherwise identical conditions, the same strain was measured at an elapsed time of about 1 hour (see Figure 2.6), which gives a time shifting factor of 100. 23

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... .... ... }60 5 ... "i .. 240 120 Figure 2.8 lh:alfinecl I In-Mrl Ccnfined in SOil Ill psi pn!SSUAI -------_ .... n.-('o c o o o o [ I o o -;:;.; o -10 20 lO 40 50 60 Strtin. \ ol J,; : o] 70 Load.:..Deformation Behavior of Typar 3301 ( Wu, 1992) 24

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..: c: ii .. .. Cl 20 18 18 Sustained Load = 180 lb/ft Sustained Load = 140 lll/ft Sustained Lc!ld = 96 l.b/ft 1 r 12 10 8 6 ..--,.-_, ,, ... ,' .......... --.. --------time. mia.utes ,;, .. / "'" .. ti p Figure 2.9 Creep Behavior of Typar 3301 Geotextile (Wu, 1992) 25

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N c:n Sustained Strain Elapsed Time Time Shifting Factor Load (CW. of Wide Width At 100"F At 120"F 70"F/100"F 70"F/120"F i Tensile Strength) (%) (hours) (hours) (hours) I 22% 4 140 1 4 0.3 100 466.7 5 1200 14 3 85.7 400 6 4000 150 12 26.7 333.3 25% 4 14 0.1 0.016 140 875 5 100 2 1 50 100 6 700 16 6 43.8 116.7 30% 4 4 0 016 0.01 250 400 5 25 0 6 0.1 41.7 250 6 90 3 0.5 30 180 Table 2.2 Time Shifting Factors Due to Elevated Temperatures of Amoco 2044

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3. TEST APPARATUS, TEST PROCEDURE, AND TEST PROGRAM 3.1 Test Apparatus Wu ( 1994) and Wu and Helwany (1996) long-term investigate developed a test to soil-geosynthetic performance long-term interactive behavior of soil-geosynthetic composite. A schematic diagram of the test device is shown in Figure 3.1, in which a reinforced soil unit was placed inside a rigid container with transparent plexiglass side walls. The reinforced soil unit comprised a geosynthetic reinforcement, two_vertical flexible steel plates, and confining soil. The confining soil confined the geosynthetic reinforcement at both top and bottom. The two ends of the geosynthetic reinforcement were securely attached to the two vertical steel plates, each of 1 rnm in thickness, at their mid-height. The transverse direction of the reinforced soil unit was fitted between two lubricated plexiglass side-wall of a rigid container in such a manner that the reinforced soil unit was restrained from movement in the direction to the plexiglass side walls (i.e., in a plane strain 27

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90 em Dimensions: Sand-Backfill Test: L = 81.3 em H = 30.5 em Clay-Backfill Test: L = 45.7 em H = 25.4 em a Geosynthetic Reinforcement b Soil c Steel Plate d Rigid Container with Lubricated Side Walls c f Sustained Load Rigid Plate Figure 3.1 : Schematic Diagram of the Long-Term Soil-Geosynthetic Performance Test Device (Helwany and Wu, 1996) 28

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configuration) On the top surface of the confining soil, another sheet of geosynthetic was used to connect the top edge of the vertical steel plates. Upon the application of a sustained vertical surcharge to the top surface of the reinforced soil unit, the geosynthetic reinforcement and its confining soil will deform in an interactive manner over time. Namely, therewill be an interactive retraining effecting on deformation between the geosynthetic reinforcement and the soil. To maintain plane strain condition throughout the test, the interface between the rigid plexiglass and the soil was minimized to near frictionless. This was accomplished by creating a lubrication layer at the interface of the plexiglass side-wall and the soil. The lubrication layer consists of a 0.02 mm thick membrane and a thin layer of a silicon gre.ase. This procedure was developed by Tatsuoka at the University of Tokyo. The friction angle between the lubrication layer and plexiglass as determined by the direct shear test was less than one degree (Tatsuoka, et al., 1984). In this study, a modified apparatus was developed to simplify sample preparation and load application. A photograph and a schematic diagram of the modified long-29

PAGE 39

term performance test apparatus are shown, respectively, in Figures 3.2 and 3.3. The modified apparatus differs from the original device in five aspects: (a) Dimension of test apparatus The modified test apparatus is 1-ft high, 2-ft wide, and 2-ft long, which was smaller than the original apparatus depicted in Figure 3.1. Test specimen was reduced. to 1-ft high, 1-ft wide, and 2-ft long. The test specimen was prepared at the center of the test apparatus. (b) Moveable Lateral Supporting Panels The longitudinal direction of the test specimen was fitted between two lubricated plexiglass panels. These two lateral supporting panels can be moved horizontally. The movement was controlled by an air cylinder attached to each panel. After the lateral supporting panels were released (i.e., moved away from the soil) the test specimen was free to move in the longitudinal direction in an unconfined condition. This represents a "worst" condition as any lateral confinement will undoubtedly reduce lateral deformation of the soil-geosynthetic composite. (c) Attachment of Geosynthetic The geosynthetic reinforcement at the mid-height as well as at the top surface were simply laid horizontally without attaching 30

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to the vertical plates (not present in the modified apparatus) as in the original apparatus. Such a manner greatly simplifies sample preparation and eliminate possible bucking of the vertical plate. (d) Load Application Mechanism In the modified test, the sustained vertical load was applied with a self-contained loading mechanism which consisted of a rigid frame and a Conbel pneumatic loader. The rigid loading frame was used as the reaction for the load application. To distribute a concentrate load to the top surface of the specimen, rigid plexiglass plates of different sizes were assembled in a pyramid configuration. The moveable supporting panels were released after the sustained vertical load was applied for a given period of time. (e) Measurement of Lateral Deformation The lateral deformation of test specimen was measured by LVDT' s (Linear Voltage Deformation Transducers) at the midheight, where the geosynthetic reinforcement was located. Mechanical displacement dial gage was used to measure the vertical displacement of the specimen. 31

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Legends: A Air Cylinder B Conbel Pneumatic Loading Device C Loading Plate D Lateral Movable Supporting Panel E LVDT Supporting Tube Figure 3.2 The Modified Long-Term Soil-Geosynthetic Performance Test Device 32

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susto.1nea pr-essur-e loo.alng plo. te 12 12 ln. supporting po.nel L VDT supporting tulce o.lr-cylinder(a) Before Releasing Lateral Supporting Panels susto.lnec:J pr-essur-e la. ter-a.l supporting pa.nel L VDT suppor-ting tulcle o.1r-c:yllnaer(b) After Releasing Lateral Supporting Panels Figure 3.3 Schematic Diagram of the Modified Long-Term Soil-Geosynthetic Performance Test Device 33

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3.2 Test Procedure The procedure for the Long-Term Soil-Geosynthetic Performance test can be describedin the following steps: 1. prepare the soil at the desired moisture content (2% wet-of-optimum in this study) and cure the soil overnight in a sealed container inside a high humidity room. 2. apply lubrication layers, each consist of a latex membrane and a thin layer of a silicon grease, on al1 four sides of the plexiglass. 3. restrain movement of the moveable supporting panels with a high air pressure ( 80 psi) through air cylinders. A pair of carpenter's clamps were also used to prevent movement of the supporting panel during soil compaction. This creates a cuboidal volume of 1 ft by 1 ft by 2 ft, within which a sample can be prepared. 4. place a layer of geosyntheti'c (1 ft by 2 ft in size) at the bottom of the test device, and compact the soil in lifts until it reaches the mid-height (i.e., 0.5 ft), and lay a layer of geosynthetic ( 1 ft by 2 ft in size) covering the soil surface. 5. compact soil in lifts over the geosynthetic layer until it reaches 1 ft height, and cover the top surface 34

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with a layer of geosynthetic. 6. remove the carpenter's clamps, and mount the LVDT's and dial indicator, and set the readings to zero. 7. cover the test specimen with a plastic sheet to keep a constant moisture content. 8. apply a sustained vertical load through a loading plate placed on the top surface of the geosynthetic layer (see Figure 3.3(a)). 9. release the moveable supporting panels (the supporting panels are retracted and the lateral confinement is removed) after the sustained vertical load has been applied for a given amount of time (see Figure 3.3(b)), and take a reading of the immediate response.10. take measurement periodically by a data acquisition system. In case of testing at elevated temperature ( 1250F), tests were performed in a heat chamber at constant temperature and humidity (provided by humidifier), as shown in Figure 3. 4. In order to achieve consistent elevated temperature of test specimen, test specimen in test apparatus was placed in the heat chamber for 2 days before load application. 35

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3.3 Test Instrumentation The instruments used in the test are LVDT and mechanical displacement dial gage. With the exception of one test (Test D-1), two LVDT's were used to measure the lateral deformation of test specimen, a dial gage was used to measure the vertical displacement. A typical layout of instrumentation is depicted in Figure 3.5. 3.3.1 Linear Voltage Deformation Transducer (LVDT) Linear Voltage Deformation Transducer (LVDT) was placed in a horizontal position used to measure lateral movement of the soil-geosynthetic composite. The s.tylus of LVDT was set to just touch the mid-height of the composite, where the reinforcement layer was placed. Two LVDT's were employed in each test, one on each side of the composite. Reading of the LVDT's was recorded periodically by an automated data acquisition interfaced with a personal computer. 3.3.2 Mechanical Displacement Dial Gage Mechanical displacement dial gage was used to measure the vertical displacement of the soilgeosynthetic composite. The tip of the dial gage was set 36

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Figure 3.4 The Modified Long-Term Soil-Geosynthetic Performance Test Device at Elevated Temperature 37

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Figure 3.5 I 2 I 1--E =r-t Legend llneo.r val to.ge dlsplo.ceMent tro.nsducer Mecho.nico.L dlsplo.ceMent dial gage Layout of Instrumentation 38

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to touch the top of the loading plate. The accuracy of the dial gage was .001 in. 3.3.3 Strain Gage High-elongation strain gages were used to measure the strain distribution of the Typar geotextile in one of the tests (Test D-1) Two addi tiona! layout of the instruments in such test is depicted in Figure 3.6. A total of 10 strain gages were mounted along the length of geosynthetic on two parallel lines to provide redundancy of the measurement. To avoid inconsistent local stiffening of the geotextile by the adhesive, the strain gage attachment technique developed by Billiard and Wu (1991) was employed by gluing only the two ends of a strain gage to the surface of geotextile with two-ton epoxy. This technique has been used successfully by Wu (1992) and Helwany (1994). Because the soil contained gravel and was moist. A microcrystalline wax material was used to protect the gages from soil moisture. For five of the strain gages, an extensible neoprene rubber patch was used to cover each strain gage (see Figure 3.7) to prevent the expected mechanical damage during compaction. Helwany (1994) 39

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conducted two uniaxial tension tests, one with and the other without the protective cover (wax material plus Neoprene patch), to examine the effect of the protective cover on the extensibility of the geotextile. The results indicated that the protective material had little effect on the extensibility of the geotextile. A uniaxial tension test with two strain gages on a geotextile specimen was performed to obtain the calibration curve. The calibration curves for the two strain gages, as shown in Figure 3.8, are nearly identical. 3.4 Testing Program The testing program was designed to examine the effects of various factors on long-term behavior of soilgeosynthetic composites. These factors included soil type, geosynthetic type, temperature, and sustained vertical surcharge. To demonstrate the validity of the test method, repeatability tests and load-deformation tests were also performed. A summary of these tests is presented in Table 3.1. The test conditions are described briefly as following: 40

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Figure 3.6 9 r--=:1--i 2 f-E 3--l 1 -=:1--i 3 Legend 0 stra.ln ga.ge lrnea.r val ta.ge dlspla.ceMent tra.nsducer ? Mecha.nrca.l dlspla.ceMent dlol goge Layout of Instrumentation of Test D-1 41

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Figure 3.7 Strain Gages Mounted along the Length of Geotextile 42

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20 18 16 !! 14 o_ > 0 12 o, ... c .2 Gl E 0 10 :I 0 o.c 8 .at=0 6 > 4 2 0 0 Figure 3.8 + A 5 10 15 20 Strain, % Calibration Curves for Strain Gages on Typar 3301 Geotextile 43 gage 1 gage 2

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Table 3.1 Test Program Test Soil Reinforcement Temp. Sustained Total Designation Average Elapsed Vertical Time Pressure ("F) (psi) (days) C-1 c.s. None 70 15 30 C-2 c.s. Amoco 2044 70 15 30 D-1 R.B. Typar 3301 70 15 15 H-1 R.B. Amoco 2044 125 30 30 R-1 R.B. Amoco 2044 70 15 30 R-2 R.B. Amoco 2044 125 15 30 R-3 R.B. Amoco 2044 125 15 30 S-1 R.B. None 70 15 30 S-2 R.B. None 125 15 30 U-1 R.B. Amoco 2002 70 failure failure W-1 R.B. Amoco 2002 125 15 30 Note: R.B.= road base C.S.= a clayey soil with 43% of fines and PI=ll 44

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3.4.1 Repeatability Tests Two tests were conducted in identical conditions to examine repeatability of the performance test. Tests R-2 and R-3 were conducted with the road base and Amoco 2044 reinforcement. The tests were conducted under a sustained average vertical pressure of 15 psi, and at a constant temperature of 125F. 3.4.2 Failure Mode of the Performance Test In order to investigate failure mode of the performance test, a soil-geosynthetic composite (with the road base and Amoco 2002) was subjected to an increasing applied load at a constant rate of 0.6 in. per minute, using a MTS-810 loading machine, until a failure condition developed. This test was designated as Test U-1. 3.4.3 DefoDmed Shape of Test Specimen and Strain Distribution along the Geosynthetic To' examine strain distribution along the geosynthetic reinforcement and deformed shape of the test specimen, a Test designated as Test D-1 was conducted. 45

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The soil-geosynthetic compositeconsisted of the road base and Typar 3301 reinforcement. Ten strain gages were installed along the length of the geotextile to measure the distribution of strain with time under an average vertical pressure of 15 psi and at ambient temperature. LVDT's were used to measure horizontal displacement of the specimen at Points 1, 2, and 3, as shown in Figure 3.7. The vertical movement was measured by a mechanical displacement dial gage. 3.4.4 Roles of Reinforcement Tests C-1, S-1 were conducted with the clayey soil and the road base only, respectively, under a sustained average vertical pressure of 15 psi at 70F. Comparisons between Test C-2 and C-1, and between R-1 and S-1 were made to assess the role of reinforcement in the long-term performance test. Test C-2 and R-1 were conducted under the same conditions as Tests C-1 and S-1, except that Test C-1 and R-1 are with Amoco. 2044 reinforcement. To investigate the roles of reinforcement at an elevated temperature, Test S-2 was performed with the road base only, under a sustained average vertical pressure of 15 psi at 125F to compare with Test R-2 which was conducted 46

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under the same conditions as Test S-2 except a sheet of Amoco 2044 was incorporated in Test R-2. 3.4.5 Effect of Soil Type To assess the behavior of the performance test with different soil types, the clayey soil and the road base were employed in.Tests C-2 and R-1, respectively. Both tests used Amoco 2044 reinforcement and were conducted under a sustained average pressure of 15 psi at 70F. 3.4.6 Effect of Temperature The creep behavior of the performance test at ambient and elevated temperatures was examined by Tests R-1 and R-2. Test R-1 was conducted at 70F, while Test R-2 was at 125F. Both Tests R-1 and R-2 used the road base and Amoco 2044 reinforcement and both were subjected to a sustained average pressure of 15 psi. 3.4.7 Effect of Geosynthetic Type Amoco 2002 and Amoco 2044 are manufactured by the same method and with the same polymer except that the 47

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same method and with the same polymer except that the ultimate tensile strength of Amoco 2002 is about 3 times lower than Amoco 2044. Test W-1, consisted of the road base and Amoco 2002 reinforcement, were conducted to assess the effect of reinforcement strength by with Test R-2 which was conducted under the. same conditions except with Amoco 2044 reinforcement. The effect of reinforcement type can be also be examined by comparing Tests D-1 and R-1 which were conducted under the same conditions (with the road base under a sustained average pressure of 15 psi at 700F) Typar 3301 and Amoco 2044 were used as reinforcement in Test D-1 and R-1, respectively. 3.4.8 Effect of Sustained Vertical Surcharge Test H-1 was designed to examine the behavior of the performance test under a higher sustained vertical load. An average sustained vertical pressure of 30 psi was applied in Test H-1 which was conducted under the same condition as test R-2 .except for the average sustained vertical pressure. 48

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4. TEST RESULTS AND DISCUSSION OF RESULTS In this research, a number of performance tests were conducted with different soils, geosynthetics, sustained vertical surcharges, and at different temperatures. Lateral and vertical displacements of the soilgeosynthetic composite were recorded periodically throughout each test. The term lateral displacement, unless otherwise specified, is referred to the total lateral displacement on both sides of the test specimen at the mid-height of the soil-geosynthetic composite (i.e. at the location of the reinforcement). The time, t, is referred to the elapsed time after the supporting panels were removed. Strain distributions along geosynthetic with time were measured in one test only (Test D-1). The test data presented in this chapter are tabulated in Appendix A. 49

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4.1 Verification of Test Method 4.1.1 Repeatability tests Figures 4.1 (a) and 4.1 (b) show the lateral and vertical displacements versus time relationships of Tests R-2 and R-3, respectively. The two tests were conducted under the same condition (road base with Amoco 2044 reinforcement, under a sustained average pressure of 15 psi, at 125F) to examine the repeatability of the performance test. Because of the electrical interference of data acquisition system, significant reading scatters of LVDT readings were experienced. To examine the extent of the electrical interference, two LVDT's with their stylus touching a rigid wall (i.e., presumably a zero displacement) were tested in the heat chamber. The readings, as shown in Figure 4.2, are seem to deviate from zero with an accuracy of .4x10-2 in. To accommodate these scatters, curve fittings were performed on the test data to allow comparison of lateral and vertical displacements versus time for Tests R-2 and R-3. Initial vertical displacements at t= 10 min. of 0.018 in. and 0.020 in., and initial lateral displacements of 0.028 in. and 0.013 in. were measured 50

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displacements of 0.028 in. and 0.013 in. were measured for Tests R-2 and R-3 after releasing of lateral supports, respectively. The differences are mostly due to the differences in the degree of restraint of the supporting panels. The magnitudes of creep deformation over 43,200 min. (30 days) and the rates of creep in both directions for Tests R-2 and R-3 were similar. As shown in Table 4.1, the creep deformation in vertical and lateral directions at t=43,200 min. were, respectively/ 0.054 in. and 0.055 in. for Test R-2; and were 0.055 in. and 0.054 in. for Test R-3. The creep rates decreased at fast decreasing rate in both vertical and lateral direction in both tests. The repeatability of the performance test is considered satisfactory. It is of great important to note that, under the elevated temperature condition of which the creep rate accelerated more than 100 folds, the creep deformation was very small and essentially ceased after t=30, 000 minutes. This behavior conferred with those observe in full-scale tests (see section problem statement in Chapter 1) that creep was negligible. 51

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0.20 0.10 c co 0. 00 .,_ __ __,_ ___ _._ ___ __ __,_ __ ___1 0 10 20 30 40 50 (Thousands) Elapsed Time, min R-2 0 R-3 Fiqure4.1(a) Lateral Displacements Versus Time Relationships of Tests R-2, R-3 52

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l. ) l 0.20 0.10 aaoa 0.00 -----...1...----...1...----..l-..---------' 0 10 20 30 40 50 (Thousands) Elapsed Time, min .. R-2 0 R-3 Fiqure4.1(b) Vertical Displacements Versus Time Relationships of Tests R-2, R-3 53

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0.10 0.05 c: ;:. 0.00 I + LVDT No.1 c: CD (.n E $ I 6. LVDT No.2 ol:>o CD u ca c. Cl) c -0.05 -0.10 I I I 0 1000 2000 3000 4000 5000 Elapsed Time (min.) Figure 4.2 Examination of Electrical I-nterference to LVDT

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tn tn TestR-2 Test R-3 Elapsed Lateral Avg. Incremental Vertical Avg. Incremental Lateral Avg. Incremental Vertical Avg. Incremental Time Dlsp. Lateral Creep Dlsp. Vertical Creep Dlsp. Lateral Creep Dlsp. Vertical Creep Rate Rate Rate Rate (min.) nn.l (%/day) (ln.) (%/clay) tln.l (%/day) On.) (%/day) 60 0.042 8.4E+OO 0.028 5.6E+OO 0.025 S.OE+OO 0.028 5.6E+OO X) 0.048 2.1E-01 0.030 7.1E-02 0.034 3.2E-01 0.036 2.8E-01 1000 0.049 2.0E-02 0.032 4.0E-02 0.037 6.0E-02 0.038 4.0E-02 10000 o.o53 5.3E-03 0.046 1.9E-02 0.047 1.3E-02 0.039 1.3E-03 20000 0.054 1.2E-03 0.053 8.4E-03 0.051 4.8E-03 0.045 7.2E-03 30000 0.055 1.2E-03 0.054 1.2E-03 0.052 1.2E-03 0.053 9.6E-03 40000 0.055 O.OE+OO 0.054 O.OE+OO 0.054 2.4E-03 0.055 2.4E-03 Table 4.1 Displacements and Average Creep Strain Rates of Tests R-2, R-3

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4.1.2 Failure Mode of the Performance Test Figure 4.3 shows the applied vertical load versus time curve of Test U-1 (the road base with Amoco 2002 reinforcement) This test was conducted with a metal test apparatus because of the anticipate high load intensity. Part of the curve has to be estimated because the maximum load capacity of the MTS-810 machine was preset at 20 kips. The ultimate load was approximately 24 kips (i.e., an average pressure of 80 psi). As the force in the geotextile reached its ultimate strength, the geosynthetic reinforcement ruptured along the center line, as shown in Figure 4.4, which clearly indicated that the maximum force in reinforcement occurred along the center line of geosynthetic specimen. This behavior also conforms with the anticipated load distribution in the performance test. 4.2 Behaviors Before Releasing Lateral Support After each test specimen was prepared, a sustained vertical load was applied. The transverse movement of the soil-geosynthetic composite was restrained by the side walls of the test device, while the longitudinal movement 56

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30 ... -, U) / \ -20 .:.::: ca 0 ca () .... 10 ID > 0 100 200 Elapsed Time, sec. Figure 4.3: Applied Vertical Load Versus Time Relationships of Test U-1 57 300

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Figure 4.4 Rupture of Amoco 2002 Geotextile, Test U-1 58

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of the composite was restrained by the lateral supporting panels with an air pressure of 80 psi. In addition to vertical displacement, because of the high vertical load, some appreciable (longitudinal) lateral displacements occurred before the lateral supporting panels were released 'due to soil compaction pressure. The measured displacements immediately before releasing the movable supporting panels are presented in Table 4.2. From Table 4.2, the following observations were made: 1. Comparisons of Test S-1 (the road base only, under a sustained average pressure of 15 psi, at 70F), Test R-1 (same as Test S-1 except with Amoco 2044 reinforcement), and Test D-1 (as Test -R-1 except with Typar 3301 reinforcement) indicated-that the geosynthetic reinforcement played a significant role in restraining the lateral movement of the composite, but insignificant in reducing the vertical movement before releasing of the lateral supports. 2. Comparisons of Test C-2 (the clayey soil with Amoco 2044 reinforcement, under a sustained average pressure of 15 psi, at 70F) and Test R-1 (same conditions as Test C-2 except with the road base) 59

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Table 4. 2 Lateral and Vertical Displacements Before Releasing Lateral Supports Test Designation C-1 C-2 D-1 H-1 R-1 R-2 R-3 S-1 S-2 W-1 Note: Soil Reinforcement Temp. Sustained Lateral Vertical Average Disp. Disp. Vertical Pressure (OF) (psi) (in.) (in.) c.s. None 70 15 0.122 0.36 c.s. Amoco 2044 70 15 0.066 0.67 R.B. Typar 3301 70 15 0.138 0.376 R.B. Amoco 2044 125 30 0.24 0. 464 R.B. Amoco 2044 70 15 0.136 0.325 R.B. Amoco 2044 125 15 0.066 0.268 R.B. Amoco 2044 125 15 0.025 0.264 R.B. None 70 15 0.329 0.416 R.B. None. 125 15 0.303 0.257 R.B. Amoco 2002 125 15 0.396 0.238 R.B.= road base C.S.= a clayey soil with 43% of fines and PI=ll 60

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indicated that the clayey soil was more compressible than the road base, thus, Test C-2 exhibited about twice as much vertical displacement than Test R-1. The lateral displacement of Test C-2 was, however, only one half of that occurred in Test R-1. This may be because the. compaction effect in Test C-2 was much smaller. 3. At ambient temperature, Test R-1 (the road base with Amoco 2044 reinforcement, under a sustained average pressure of 15 psi, at 70F) and test D-1 (same condition as Test R-1 except Typar 3301 was.used as reinforcement) exhibited nearly the same lateral and vertical displacements. However, at 125F temperature, Test R-2 (same as R-1 except at 125F) showed six times smaller lateral displacement than Test W-1 (under the same condition as Test R-2 except Amoco 2202 was used as reinforcement), although their vertical displacements were comparable. 4. Test R-1 (the road base with Amoco 2044 reinforcement, under a sustained average pressure of 15 psi, at 70F) showed twice as much lateral displacement as Test R-2 (under the same condition as R-1 except at 125F) The vertical displacement of Test R-1 was only slightly larger than Test R-2. 61

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5. The effect of the sustained load can be assessed by comparing Test R-2 (the road base with Amoco 2 04 4 reinforcement, under a sustained average pressure of 15 psi, at 125F) with Test H-1 (same conditions as Test R-2 except under a sustained average pressure of 30 psi) Test H-1 showed larger displacement in both vertical and lateral direction. Note that the increase in the vertical displacement approximately proportional to the increase in the sustained average pressure increasing. 4.3 Long-Term Behavior of the Performance Test 4.3.1 Deformed Shape of Test Specimen and Strain Distribution along the Geosynthetic Figure 4.5 shows the relationships of vertical and lateral displacements at three heights versus elapsed time of test D-1 (the road base with Typar 3301 reinforcement, under a sustained average pressure of 15 psi, at 70F) As to be expected, the displacements at Points 2 and 3 were larger than those at Point 1. Points 2 and 3 showed very similar lateral creep displacement at the beginning of the test. Thereafter, however, Point 3 exhibited a larger creep displacement than point 2. The 62

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the beginning of the test. Thereafter, however, Point 3 exhibited a larger creep displacement than point 2. The difference grew larger as time elapsed. The vertical displacement was fairly close to the lateral displacement at Point 1. The creep rate at Point 1 was slightly lower than the vertical creep rate. The lateral deformed shapes of the specimen at different elapsed times are shown in Figure 4.6. Larger displacements occurred at 1/4 and 3/4 heights (i.e., Points 2 and 3), while smaller displacements occurred at the top, the bottom, and the mid-height. At t=10 minutes, the upper part of the specimen was very similar to the lower part. As time progressed, the lower part showed more lateral deformation than the upper part. Point 3 experienced the largest creep rate. Figure 4.7 shows the measured strain distribution along the length of geotextile of Test D-1 at t=10 min., 4,320 min. and 18,720 min. after releasing the lateral supports. The strain at the two ends of geotextile was zero, because there was no restraint at the ends. The measured strains along the g_eotextile resembled a bell shape with an axis of symmetry at .the center. The maximum strains occurred at the center of geosynthetic 63

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strain versus time. The maximum measured strain was 2.0% at t=10 min., and at t=2,880 min. the maximum strain increased to 2. 8%, then, remained constant for about 1,440 min. (1 day), i.e., at t=4,320 minutes, after that, the maximum strain decreased at an average rate of 0.005% per day. Figure 4.9 shows the relationships between creep strain rates and elapsed time. It is seen that the creep rate decreased almost linearly with log(time), and that the rates of decrease in the vertical direction and different points in the lateral direction are fairly similar. The magnitude and rate of creep deformation at selected elapsed times are listed in Table 4.3. 4.3.2 Loads in Geosynthetic Reinforcement Loads induced in the geotextile reinforcement are of I significant interest in the design of GRS structures. The conventional approach for determining the loads is to apply the load-strain relationship of the geotextile which was obtained from "element" load-deformation tests, to measured or computed strains. However, the load-strain behavior of geotextiles is affected significantly by, among other factors, the strain rate. In Test D-1 the 64

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c: -c: "' G) 01 E G) u as U) c 0.20 Literal Disp. I Point 1 (see Flg .3.5) D D. Point 2(sae Flg.3.5) [] n_.Q. 0.10 I .. I I<> Point 3 (sea Flg 3.5) 0.00 10 Figure 4.5 I ... Vertical Dlsp. 100 1000 10000 50000 Elapsed Time, min. Lateral and Vertical Displacements Versus Time Relationships of Test D-1

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m m Elapsed Time Lateral DlrecUon Vertical Direction .(min.) Point 1 Point 2 Polnt3 Displacement Creep Strain Displacement Creep Strain Displacement Creep Strain Displacement Creep strain Rate Rate Rate Rate I On.> I ('IL/mln.) ICin.) I C'lfJmln.) Inn.) I ('lfJmln.) ICin.) IC%/mln.) 60 0.050 1.0E+01 0.083 1.7E+01 0.093 1.9E+01 0.051 1.0E+01 400 0.064 4.9E-01 0.097 4.9E-01 0.113 7.1E-01 0.071 7.1E-01 1000 0.070 1.2E-01 0.102 1.0E-01 0.118 1.0E-01 0.078 1.4E-01 2000 0.074 4.8E-02 0.105 3.6E-02 0.122 4.8E-02 0.082 4.8E-02 4000 o.on 1.8E-02 0.108 1.8E-02 0.127 3.0E-02 0.086 2.4E-02 6000 0.078 6.0E-03 0.109 6.0E-03 0.128 6.0E-03 0.088 1.2E-02 8000 0.079 3.0E-03 0.110 6.0E-03 0.129 6.0E-03 0.089 3.0E-03 10000 0.079 3.0E-03 0.111 3.0E-03 0.130 6.0E-03 0.089 3.0E-03 20000 0.080 1.2E-03 0.111 6.0E-04 0.133 3.6E-03 0.090 1.2E-03 Table 4.3 Displacements and Average Creep Strain Rates of Test D-1

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c: 1 2 .............. .............. '\ \ \ \ \ \ 9 r I I IJ / / 1/ / / /1 I / 11 I I I f, 6 + \ T '" \ \ \ ' ........ ' \ \ \ \ 3 + J I I I I I / / / / / ./ / / /------0 ......... 0.00 0.05 0.10 0.15 Displacement, in. 10 min. 400 min. 0 4,320 min. + 18,720 min. 0.20 Figure 4.6: Lateral Deformed Shapes of Test D-1 at Different Elapsed Times 67

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'#. c ; ... (/) 5 4 3 2 1 0 0 2 4 6 8 10 12 Distance from left end of geotextile,in. 10 min. Figure 4.7 D 4320 min. + 18720 min. Measured Strains along the Length of Geotextile of Test D-1 at t= 10 min., 4,320 min., 18,720 min. 68

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5 4 1-31-: CIS CIJ 2 1 0 5 10 15 20 (Thousands) Elapsed Time, min. Figure 4.8: Maximum Strains Versus Time Relationships of Test D-1 69

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....J 0 >-CG "C *' c: 0 CG E L.. 0 Cl) c c. Cl) Cl) L.. () 0 Cl) CG a: 102 101 10 t 1 o 1 o-2 r 1 o3 1 o4 10 Figure 4.9 I + Lateral Dlsp. (Pt.1) I Lateral Dlsp. (Pt.2) I 0 Lateral Olsp. (Pt.3) I + Vertical Dlsp. 100 1000 10000 100000 Elapsed Time (min.) Average Creep Strain-. Rates in the Vertical and Lateral Directions Time Relationships of Tests D-1

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strain rate was highly nonlinear, as seen in Figure 4.9. A different approach, using the isochronous load-strain curves, was used to determine the loads in the geotextile reinforcement. Isochronous load-strain curves were first established as shown in Figure 4.10. The isochronous load-strain curve were deduced from the creep curves shown in Figure 2. 9. Using Figure 4 .10, the load in geosynthetic for a certain strain at a given time can be determined. Figure 4.11 shows the calculated loads along the length of geotextile at different elapsed times. The maximum load occurred at the center of geotextile and decreased toward to two extremities. This is consistent with Test U-1 in which rupture occurred along the center line of the geotexile. Figure 4.12 shows the relationships of loads versus time at different locations along the geotextile. The loads decreased at a decreasing rate as time elapsed. The rate of decrease was nearly the same at all locations. This decreasing load behavior in the geosynthetic could be the result of "stress relaxation". Stress relaxation is a term used to describe a behavior that the load in a 71

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200 + 10min ... 0 400min :! :I 100 a + 4,320min :I .J 18,720min 0 4 a 12 16 20 Strain, % Fiqure4.10: Isochronous Load-Strain Curves 72

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100 -.Q CIS 0 50 ....J + Figure 4.11 Distance from left end of geotextile,in. 10 min. 0 4,320 min. 400 min. + 18,720 min. Loads along the Length of Geotextile at Different Elapsed of Test D-1 73

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100 90 so 70 60 -.Q "0 50 S 0 40 ..J 30 20 10 0 0 5 10 15 20 (Thousands) Elapesd Time, min. + at ce.nter at 4 in. from left end o at 8 in. from left end 0 at 1 0 in. from left end Figure 4.12 Maximum Loads in Geotextile Versus Time at Different Distances from Left End of Geotextile of Test D-1 74

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material, subject to a constant deformation, decreases with time. Stress relaxation may occur when the rate of deformation becomes small. In Test D-1, stress relaxation began at 10 minutes after releasing the lateral supports. 4.3.3 The Role of Reinforcement Comparison of the lateral and vertical displacements versus time relationships between Tests S-1 and R-1 and between Tests S-2 and R-2 are shown in Figures 4.13 and 4.14, respectively. Test S-1 was conducted with the road base only, under a sustained average pressure of 15.psi, at 70F while, Test R-1 was conducted under the same conditions as Test S-1 except Amoco 2044 reinforcement was used. Test S-2 and R-2 were conducted under the same conditions as Tests Test S-1 and R-1, respectively, except the temperature was 125F. The magnitude of creep deformation in the lateral and vertical directions of unreinforced tests (Tests S-1 and S-2) were markedly larger reinforced soil tests (Tests R-1 and R-2) because the geosynthetic reinforcement restrained movement in lateral and as a result the vertical displacement was also reduced. The reduction of displacements in the lateral direction was 75

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. c: -c: ......J CD 0) E CD 0 lG a. U) 0 0.80 0.60 r Lateral Dlsp. S A Vertical Dlsp. S-1 0.40 I / I 0 Laleral Dlsp. R-1 r / I b. Vertical Dlsp. A-1 0.20 0.00 I I I I"... I I I I"... I I I I II"' I I I I II"' 10 100 1000 10000 100000 Elapsed Time, min. Figure 4.13: Lateral and Vertical Displacements Versus Time Relationships of Tests R-1

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TestS-1 Test R-1 Elapsed L.at8ral Avg. Incremental Veftlcal Avg. Incremental latetal Avg. 11"1Ct8111ental Vertical Avg. liaemenlal Time Dlsp. lateral Creep Dlsp. Vertical Creep Dlsp. Lateral Creep Dlsp V8fttcal Creep Rate Rate Rate Rate Cmln.) Cln.) Cln.) (%1da_y)_ (ln.) jln.}_ ('!Wdlly) 60 0.039 7.8E+OO 0.031 6.2E+OO 400 0.448 1.6E+01 0.174 6.1E+OO 0.040 3.5E-02 0.038 2.5E-01 1000 0.542 1.9E+OO 0.210 7.2E-01 0.040 O.OE+OO 0.042 8.0E-02 10000 0.600 7.7E-02 0.230 2.7E-02 0.040 O.OE+OO 0.051 1.2E-02 20000 0.600 O.OE+OO 0.233 3.6E-03 0.040 O.OE+OO 0.056 &.OE-03 -.1 -.J 30000 0.601 1.2E-03 0.237 4.8E-03 0.040 O.OE+OO 0.062 72E-03 40000 0.602 1.2E-03 0.241 4.8E-03 0.040 O.OE+OO 0.067 &.OE-03 Table 4.4 Displacements and Average Creep Strain Rates of Tests S-1, R-1

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c: c: .....] Cl) CD E Cl) u as c.. Cl) 0 0.30 ..-------------------, 0.20 L I Lateral Dlsp. S-2 I -I Vertical Dlsp. S-2 I 0 Lateral Dlsp. R-2 0.10 L / I 6. Vertical Dlsp. R 0.00 I ' 11 "1 11 "1 ,,., 11 ,J 10 100 1000 10000 100000 Elapsed Time, min. Figure 4.14: Lateral and Vertical Displacements Versus Time Relationships of Tests S-2, R-2

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....,J \0 TestS-2 TestR-2 Elapsed Lateral Avg. lnc:Jemental Vertical Avg. Incremental l..atefal Avg. lnctemental Vertical Avg. lucamenlal I Time Dlsp Lateral Dl&p. Vertical Cr.ep Dl&p. Latecal Creep Dlap. Vertical Creep Rate Rate Rate Rate (min.) (ln.) ('lfJdavl (ln.) (%/day) lln.l 1%/davl (ln.) (%/day) 60 0.123 2 5E+01 0.045 9 .0E+OO 0.042 8.4E+OO 0.028 5.6E+OO 0.160 1.3E+OO 0.056 3 9E-01 0.048 2 1E-01 0.030 7 1E-02 1000 0.171 2.2E-01 0.058 4.0E-02 0.049 2 0E-02 0.032 4.0E-02 10000 0.185 1.9E-02 0.066 1.1E-02 0.053 5 3E-03 0.048 1.9E-02 20000 0.187 2 4E-03 0.070 4 8E-03 0.054 1.2E-03 0.053 8.4E-03 30000 0.187 O .OE+OO 0.075 &.OE-03 0.055 1.2E-03 0.054 1 2E-03 40000 0.187 O .OE+OO 0.075 O .OE+OO 0.055 O.OE+OO 0.054 g.OE+OO Table 4.5 Displacements and Average Creep Strain Rates of Tests S-2, R-2

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much larger than that in the vertical direction. The magnitude of vertical creep displacements occurred between t=10 min. and t=43,200 min. were 0.144 in. and 0.05 in., for Tests S-1 and R-1, respectively. The lateral creep displacements in the same period of time were 0.347 in. and 0.008 in. for Tests S-1 and R-1, respectively. At 70F, the creep rates in both the vertical and lateral directions of Test S-1 were higher than Test R-1 up to t=1, 440 min., thereafter, the creep rates were nearly the same. At 125F, the creep rate of Test S-2.in the vertical direction was about equal to that of Test R-2 but significantly higher than Test R-2 in lateral direction up to t=4,000 minutes, thereafter, the creep rate of Tests S-2 and R-2 were The creep rates of Tests S-1, R-1 and S-2, R-2 are shown in Tables 4.4 and respectively. Figure 4.15 and 4.16 show the lateral and vertical displacements versus time relationships of .Test C-1 (the clayey soil only, under a sustained average pressure of 15 psi, at 70F) and Test C-2 (under the same conditions as Test C-1 except Amoco 2044 reinforcement was used), respectively. 80

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The test specimen in Test C-1 failed at t=17 minutes. The failure occurred due to shear failure. Some distinct shear bands were visible from the latex membrane as shown in Figure 4.17. Before failure creep in vertical and lateral directions occurred at about the same rate, although the lateral deformation was slightly higher. With a sheet of reinforcement, Test C-2 exhibited about 0.1 in. lateral displacement after 40,000 min., at which time the test was terminated. The creep rate up to t=40,000 min. was nearly constant in the lateral direction. In the vertical direction, however, the creep deformation appeared to be experiencing tertiary creep from t=10,000 minutes to t=40,000 minutes. 4.3.4 Effect of Geosynthetic Type Figure 4.18 shows the lateral displacements versus time relationships of Test R-2 (the road base with Amoco 2044 reinforcement, under a sustained average pressure of 15 psi, at 125 F) and W-1 (under the same conditions as Test R-2 except Amoco 2002 was used) The lateral displacements of test S-2 (without reinforcement) were also plotted in the Figure for comparison. The vertical displacement of Test W-1 is not available because the 81

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. c -c CD E 1.00 CD 0 cu Q. fl.l c 0 5 10 15 20 Elapsed Time, min Lateral disp. Vertical disp. Figure4.15: Lateral and Vertical Displacements Versus Time Relationships of Test C-1 82

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. c: c: CD E CD 0 ca c. (1.1 Q 0.20 0.10 0.00 10 100 1000 10000 100000 Elapsed Time, min Lateral Disp. Vertical Disp. Figure 4 .16 : Lateral and Vertical Displacements Versus Time Relationships of Test C-2 83

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Figure 4.17 Failure Mode of Test C-1 84

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dial gage was found defective. As to be expected, the magnitude of creep deformation in the lateral direction was the largest in Test S-2 and the smallest in Test R-2. The creep rates in the lateral direction of Test W-1 were higher than Test R-2, yet Test W-1 and Test S-2 exhibited similar creep rate. The displacements and creep strain rates of Tests R-2, W-1, and S-2 are shown in Table 4.6. Figure 4.19 shows the lateral and vertical displacements versus time relationships of Test D-l(the road base with Typar 3301 reinforcement, under a sustained average vertical pressure of 15 psi, at 70F) and R-1 (under the same conditions as Test D-1 except Amoco 2044 was used as reinforcement) It is to be noted, as compared with those tests shown in Figure 4.18, these tests were conducted in ambient temperature. The magnitude of creep deformation in the vertical direction of Test D-1 were larger than Test R-1 but the creep rates were comparable. The displacements and average creep strain rates of the two tests in the vertical direction are shown in Table 4.7. The magnitudes of creep deformation in the lateral direction of Test D-1 were about the same as Test R-1 in the first 10 minutes and gradually became larger as time 85

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c: c al E al CJ as c. "' c 0.30 0.20 0.10 0.00 10 100 Cl S-2 0 3 t 0 1000 10000 100000 Elapsed Time, min. R-2 0 W-1 Figure 4.18: Lateral Displacements Versus Time Relationships of Tests S-2, R-2, W-1 86

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co .....J Test S-2 Test R-2 TestW-1 Elapsed Lateral Avg. Incremental Lateral Avg. Incremental Elapsed Sustained Lateral Avg. Incremental Time Dlsp. Lateral Creep Dlsp. Lateral Creep Time pressure Clap. Lateral Creep Rate Rate Rate (min.) fln.l (%/day) (ln.) (%/day) lmln.l (DSil (ln.) (%/day) 60 0.123 2.5E+01 0.042 8.4E+OO 60 15 0.087 1.3E+01 400 0.160 1.3E+OO 0.048 2.1 E-01 400 15 0.088 6.7E-01 1000 0.171 2.2E-01 0.049 2.0E-02 1000 15 0.096 2.0E-01 10000 0.185 1.9E-02 0.053 5.3E-03 10000 15 0.114 2.4E-02 20000 0.187 2.4E-03 0.054 1.2E-03 20000 15 0.118 4.BE-03 30000 0.187 O.OE+OO 0.055 1.2E-03 30000 15 0.119 1.2E-03 40000 0.187 O.OE+OO 0.055 O.OE+OO 34560 15 0.120 2.6E-03 34560 30 0.140 36000 30 0.157 1.4E-01 40000 30 0.159 6.0E-03 -Table 4.6 Displacements and Average Creep Strain Rates of Tests S-2, R-2, W-1

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. c::: c::: CD CD CD E CD 0 as a. Cl) 0 0.20 r------------------. I Laleral Dlsp. 0-1 A Verllcal Dlsp. D-1 0.10 I I 0 Laleral Dlsp. A-1 I I 1:1 Verllcal Dlsp. A-1 0.00 10 100 1000 10000 100000 Elapsed Time, min. Figure 4.19 : Lateral and Vertical Versus Time Relationships of Tests D-1, R-1

PAGE 98


PAGE 99

elapsed. The creep rates in the lateral direction of two tests were significantly different. The displacements and average creep strain rates of the two tests in the lateral direction are also shown in Table 4.7. 4.3.5 Effect of Soil Type Figure 4.20 shows the lateral and vertical displacements versus time relationships of Test R-1 (the road base with Amoco 2044 reinforcement, under a sustained average pressure of 15 psi, at 70F) and Test C-2 (the clayey soil in otherwise the same conditions as Test R-1) As to be expected, the magnitude of creep deformation in the vertical direction of Test C-2 were much larger than Test R-1. The creep rate in the vertical direction of Test C-2 was much higher than Test R-1 in the first 100 minutes; however, the creep rates of the two tests were similar after 100 minutes. The average creep rate in the vertical direction of Test C-2 was %per day and %per day in Test R-1 in 30 days. Creep deformation in the lateral direction was negligible in both tests over 43,200 minutes. The tests, however, were conducted in ambient temperature. The test 90

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c c CD \0 E 1-' CD 0 ca a. (I) 0 0.20 .--------------------, I .. Lateral Dlsp. C-2 ... Vertical Dlsp. C-2 0.10 I .. / I 0 Lateral Dlsp. A-1 I I .A I 6 Vertical Dlsp. R-1 0.00 10 100 1000 10000 100000 Elapsed Time, min. Figure 4.20: Lateral and Vertical Displacements Versus Time Relationships of Tests c-2, R-1

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\0 1\) TestC-2 Test R-1 Elapsed Lateral Avg. Incremental Vertical Avg. Incremental Lateral Avg. Incremental Vertical Avg. Incremental Time Dlsp. Lateral Creep Dlsp. Vertical Creep Dlsp. Lateral Creep Dlsp. Vertical Creep Rate Rate Rate Rata lfmln.) I fin.) lf'l6/day) I fin.) lf%/day) lrln.) I {'16/day) I on.) I {'16/day) 60 0.101 2.0E+01 0.114 2.3E+01 0.039 7.BE+OD 0.031 6.2E+OD 400 0.101 O.OE+OD 0.129 5.3E-01 0.040 3.5E-02 0.038 2.5E-01 1000 0.101 O.OE+OD 0.133 B.OE-02 0.040 O.OE+OD 0.042 B.OE-02 10000 0.102 1.3E-03 0.139 B.OE-03 0.040 O.OE+OD 0.051 1.2E-02 20000 0.104 2.4E-03 0.144 B.OE-03 0.040 O.OE+OD 0.056 B.OE-03 30000 0.105 1.2E-03 0.150 7.2E-03 0.040 O.OE+OD 0.062 7.2E-03 40000 0.106 1.2E-03 0.158 9.6E-03 0.040 O.OE+OD 0.067 B.OE-03 Table 4.8 Displacements and Average Creep Strain Rates of Tests C-2, R-1

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period of 43,200 min. (30 days) was relatively short. The displacement and average strain rates in both vertical and lateral directions for Tests C-2 and R-1 are shown in Table 4.8. 4.3.6 Effect of Tempetature Figure 4.21 and 4.22 show the lateral and vertical displacements versus time relationships of Test R-1 (the road base with Amoco 2044 reinforcement, under a sustained average pressure of 15 psi, at 70F) and Test R-2 (under the same condition as Test R-1 except at 125F temperature) The magnitude of creep deformation in the lateral direction of Test R-2 1er.e much larger ;than Test R-1. The creep rate of Test R-2 was higher than Test R-1 up to about 10,000 m'in., beyond which, the creep rate became negligible, as was Test R-1. The magnitudes of creep deformation in the vertical direction of Test R-1 and R-2 were slightly different at the beginning of the tests which was due mostly to different degrees of lateral restraint before releasing the supporting panels. The creep rates in the vertical direction for the two test were somewhat similar. By the --. 93

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conclusion of the tests, however, Test R-2 had reached an equilibrium condition (i.e., creep rate become nearly zero), yet Test R-1 still exhibited continuing creep deformation in the vertical direction with a rate of about 6. Ox10-3% per day. The displacements and average creep strain rates of Test R-1 and R-2 are shown in Table 4. 9. It should be noted that the elevated temperature accelerated the creep rate of the geotextile by more than 100 folds (as discuss in section 2.3), whereas the effect on soil was negligible. Table 4.10 shows the displacements and average strain rates of Tests S-1 and S-2. It is seen that the elevated temperature has little effect on the creep rate of the soil. 4.3.7 Effect of Sustained Vertical Surcharge Figures 4.23, 4.24 show, -respectively, the lateral and vertical displacements versus time relationships for Test R-2 (the road base with Amoco 2044 reinforcement, under a sustained average pressure of 15 psi) and Test H1 (under the same conditions as Test R-2 except at 30 psi 94

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. c -c Q) E 0.10 Q) 0 as 0 10 100 1000 10000 100000 Elapsed Time, min. 0 R-1 R-2 Figure 4.21: Lateral Displacements Versus Time Relationships of Tests R-1, R-2 95

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0.20 c c E 0.10 0 as Q. en 0 0.00 10 100 1000 10000 100000 Elapsed Time, min. R-1 R-2 Figure 4.22: Vertical Displacements Versus Time Relationships of Tests R-1, R-2 96

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\0 ...,J Test R-1 Test R-2 I Elapsed Lateral Avg. Incremental Vertical Avg. Incremental Lateral Avg. Incremental Vertical Avg. Incremental I Time Dlsp. Lateral Creep Dlsp. Vertical Creep Dlsp. Lateral Creep Dlsp. Vertical Creep Rate Rate Rate Rate (min.) (ln.) (%/day) (ln.) (%/day) (ln.) (%/day) (ln.) ('16/day) 60 0.039 7.8E+OO 0.031 6.2E+OO 0.042 8.4E+OO 0.028 5.6E+OO 400 0.040 3.5E-02 0.038 2.5E-01 0.048 2.1E-01 0.030 7.1E-02 1000 0.040 O.OE+OO 0.042 8.0E-02 0.049 2.0E-02 0.032 4.0E-02 10000 0.040 O.OE+OO 0.051 1.2E-02 0.053 5.3E-03 0.046 1.9E-02 20000 0.040 O.OE+OO 0.056 6.0E-03 0.054 1.2E-03 0.053 8.4E-03 30000 0.040 O.OE+OO 0.062 7.2E-03 0.055 1.2E-03 0.054 1.2E-03 40000 0.040 O.OE+OO 0.067 0.055 -O.OE+OO 0.054 O.OE+OO Table 4.9 Displacements and Average Creep Strain Rates of Tests R-1, R-2

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\0 co Test S-1 TestS-2 Elapsed Lateral Avg. Incremental Vertical Avg. Incremental Lateral Avg. Incremental Vertical Avg. lnentmental I Time Dlsp. Lateral Creep Dlsp. Vertical Creep Dlsp. Lateral Creep Dlsp. VerUcal Creep Rate Rate Rate Rate (min.) (ln.) (%/day) (ln.) (%/day) On.) (%/day) (ln.) C%/davl 60 0.123 2.5E+01 0.045 9 .0E+OO 4100 0.448 1.6E+01 0.174 6.1E+OO 0.160 1.3E+OO 0.056 3.9E-01 1000 0.542 1.9E+OO 0.210 7.2E-01 0.171 2.2E-01 0.056 4.0E-02 10000 0.600 7.7E-02 0.230 2.7E-02 0.185 1.9E-02 0.066 1.1E-02 20000 0.600 O.OE+OO 0.233 3.6E-03 0.187 2.4E-03 0.070 4.8E-03 30000 0.601 1.2E-03 0.237 4.8E-03 0.187 O.OE+OO 0.075 6.0E-03 410000 0.602 1.2E-03 0.241 4.8E-03 0.187 O.OE+OO 0.075 O.OE+OO Table 4.10 Displacements and Average Creep Strain Rates of Tests S-1, S-2

PAGE 108

sustained average pressure) The magnitude of creep deformation in the vertical direction of Test H-1 was higher than Test R-2. The change in vertical displacement with time for the two tests, however, were nearly the same. Due to a difference in the degree of lateral restraint before releasing the lateral supports, the lateral displacement of Test H-1 was smaller than Test R-2 initially. After t=1, 000 min., however, the displacements were larger in Test H-1. The creep rate of test H-1 was much higher than Test R-2. The displacements and creep strain rates of Test R-2 and Test H-1 are shown in Table 4 .11. In Test W-1, the sustained pressure was increased from 15 psi to 30 psi after 20 days, as shown in Figure 4.18. The initial increase in lateral displacement due to additional 15 psi pressure was 0.021 in. which was much smaller than that due to the first 15 psi pressure (0.48 in. at t=10 min.). This is because the soil-geosynthetic composite had been prestressed under 15 psi pressure for 20 days. 99

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. c:: c:: = E 0.10 .= 0 CIS c. en c 10 100 1000 10000 100000 Elapsed Time, min. R-2 0 H-1 Figure 4.23: Vertical Displacements Time Relationships of Tests R-2, H-1 100

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. c c G) E 0.10 G) 0 ca c. en 0 0.00 10 100 1000 10000 100000 Elapsed Time, min. R-2 0 H-1 Figure 4.24: Laiteral Displacements Versus Time Relationships of Tests R-2, H-1 101

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1-' 0 1\) Test R-2 Test H-1 Elapsed lateral Avg. Incremental Vertical Avg. Incremental Lateral Avg. Incremental Vertical Avg. Incremental llme Dlsp. lateral Creep Dlsp. Vertical Creep Dlsp. Lateral Creep Dlsp. Vertical Creep Rate Rate Rate Rate (mln.l Cln.l (41(Jday) (ln.) (Wday) Cln.l (41(Jday) On.) (ll6/day) 60 0.042 8.4E+OO 0.028 5.6E+OO 0.012 2.4E+OO 0.052 1.0E+01 400 0.048 2.1E-01 0.030 7.1E-02 0.043 1.1E+OO 0.058 2.1E-01 1000 0.049 2.0E-02 0 .032 4.0E-02 0.050 1.4E-01 0.061 6.0E-02 10000 0.053 5 3E-03 0.046 1 9E-02 0.065 2.0E-02 0.076 2.0E-02 20000 0.054 1.2E-03 0.053 8.4E-03 0.070 6.0E-03 0.078 2 4E-03 30000 0.055 1.2E-03 0.054 1.2E-03 0.072 2.4E-03 0.080 2.4E-03 40000 0.055 O.OE+OO 0.054 O.OE+OO 0.073 1.2E-03 0.080 O.OE+OO -Table 4.11 Displacements and Average Creep Strain Rates of Tests R-2, H-1

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5. FINITE ELEMENT ANALYSIS OF THE PERFORMANCE TEST In this chapter a finite element model with a timemarching scheme was employed to analyze the behavior of Test D-1. The results of the analyses were compared with the measurement of Test D-1. 5.1 The Finite Element Model A finite element program, DACSAR (Deformation Analysis Considering Stress Anisotropy andReorientation) capable of analyzing long-term soil-geosynthetic interaction, was used by Helwany and Wu (1995) to analyze the original long-term performance test. The finite element model has been shown to give a very good simulation of the tests. In this study, the finite element model was employed to analyze the modified longterm performance test. The finite element model incorporates an elastoviscoplastic soil model and a generalized geosynthetic creep model. The elasto-viscoplastic soil model was developed by Sekiguchi and Ohta (1977) at the University 103

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of Kyoto for simulation of consolidation and creep behavior of soils. The generalized creep model was developed by Helwany and Wu (1992) based on a nonlinear visco-elastic model proposed by Findley, et al. (1976). 5.1.1 Sekiguchi-Ohta Soil Model The Sekiguchi-Ohta model (1977) is an incremental elasto-viscoplastic constitutive model of soils. The model is capable of describing time-independent and timedependant characteristics of normally consolidated and lightly overconsolidated clays. The Sekiguchi-Ohta model is an extension of the model developed by Ohta (1971) based on the dilatancy theory proposed by Shibata (1963) This model reduces to the model proposed by Ohta and Hata (1971) in the case of axisymmetric stress conditions. It further reduces to the original Cam-clay model proposed by Roscoe, Schofield and Thurairajah (1963) under an isotropic stress condition. The Sekiguchi-Ohta model can, therefore, be considered a "generalized" Cam-clay model. The Sekiguchi-Ohta model has been verified using results of laboratory tests, such as K0-triaxial compression/extension tests under different strain rates (Sekiguchi, 1989; Chou, 1992). The model has also been 104

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verified through field tests, such as embankments on soft foundations (Iizuka and Ohta, 1987). Six soil parameters are needed in Sekiguchi-Ohta model, i.e.,A, K, e0 D, a and v .. The parameters A and K are related to the compression index and the swelling index, respectively, e. is void ratio at the preconsolidated state, D is the coefficient of dilatancy as defined by Shibata (1963), a is the coefficient of secondary compression, and v. is the initial volummetric strain rate. Detail description of the soil model can be found in Sekiguchi and Ohta (1977) and Iizuki and Ohta (1987). 5.1.2 Generalized Geosynthetic Creep Model Findley, et al. (1976) represented creep of a nonlinear viscoelastic material by a series of multiple integral. For uniaxial creep, the foll6wing expression results: where e (t) : P: ( 1) total strain applieduniaxial load 105

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kernel functions (time-dependant functions) From Equation (1), the following expressions can be established for three uniaxial tests at constant sustained loads, Pa, Pb, and Pc covering the range of loads of interest. Helwany and Wu (1992) developed a numerical procedure to determine the kernel functions. In the procedure, three measured creep strains (ea, eb and ec) at a selected time are first introduced into Equation (2), and the corresponding kernel functions F11 F21 and E) are determined by solving the three simultaneous equations. This is repeated at different elapsed times to obtain a series of kernel functions. A cubic spline function is then used to the kernel functions with time. Since the values of the kernel functions at any given time can be determined from the cubic spline function, creep strains at any time t under a specified 106

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sustained load P can be readily calculated by Equation (1). Typically, creep curves under three different sustained loads are needed to characterize the creep behavior of a geosynthetic. 5.2 Evaluation of Model Parameters 5.2.1 Sekiguchi-Ohta Model Parameters Iizuka and Ohta ( 1987) developed a flow chart, together with empirical equation, for evaluating of the input parameters of the Sekiguchi-Ohta model, as shown in Figure 5.1. The soil model was developed for simulation of normally consolidated and lightly overconsolidated clays. In this simulate the material. study, however, the model was employed to behaviors of the compacted road base The material parameters for the road base were determined by the following procedure: (1) value was determined from the results of the triaxial test at confining pressures of 15, 30, and 45 psi; (2) M, the critical state parameter, was calculated as: 107

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M 6sin' 3 -sin' (3) the ratio of K/A was calculated by an empirical equation, K M -=1-A 1.75 (4) conduct a series of trial-and-error analyses on an axisymmetric element representing a soil element in a triaxial test until a good fit was obtained. For the road base, it was determined that A= 0.12 and K= 0.024 gave a good agreement with the consolidated drained triaxial test results as shown in Fig 5.2. (5) D, the coefficient of dilatancy, was calculated as: M Small values of creep parameters ex and V0 were assumed for the road base since its creep is known to be negligible. Table 5.1 summarizes the values of the soil parameters used in the analysis. 108

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primitive physical state index s ecial Ill sino"G-IIG-2JlloqPl Krnnrrtt9S91 1121 >.O.'l'C. C2l M &sinf"/(lsinol llll '' l-71>..155 Ill 11"4/1.75 t
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150 TEST tn A FEM 5psi Q. "'-100 tn 0 TEST a3=30psi ) ... en u FEM a3=30psi ... 0 = > 50 0 TEST o-3=45psi ) Cl FEM a3=45psi 0 20 Axial Strain, % Figure 5.2: Consolidated Drained Triaxial Test: Test Results Versus Model Simulation 110

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Table 5.1 Soil parameters for Sekiguchi-Ohta soil model Parameters Value ).. 0.12 K 0.024 M 1.4 D 0.056 eo 0.223 u 0.3 0.004 vo Ol 0.0008 111

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5.2.2 Generalized Geosynthetic Creep Model Typar 3301 was the geotextile used in test D-1. The creeps test results of the geotextile and evaluation of the creep parameters have been presented by Helwany and Wu (1992). A comparison of creep model simulation and creep test results is shown in Figure 5.3. An excellent agreement was noted between the experimental results and the model simulation. 5.3 Finite Element Simulation of the Performance Test 5.3.1 Finite Element Simulation Figure 5.4 depicts the finite element discretization for analysis of Test D-1. Because' of symmetry, only onehalf of the geometry was analyzed. A total of 192 quadrilateral elements with Sekiguchi -Ohta model were used to represent the soil, 12 truss elements with the generalized creep model to represent geosynthetic. The lateral supports, which were used to restrain lateral movement of soil-geosyrtthetic composite during sample preparation and during load application, were simulated by 16 truss elements. These truss elements were connected to the soil elements along the vertical face of 112

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Figure 5.3 Creep Test Results on Reinforcement: Experiment Versus Creep Model (Helwany and Wu, 1992) 113

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6 in 6 in Sustained pressure It l l l l l Loading plate J: "' J: Soil Lateral -... J: Geosynthetic :... -..... -.... -a:: Soil .... -.... t: 1-----6 r-. 1-1-,.. 1 ' 1supports Figure 5.4: Finite Element Discretization 114

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the composite. The removal of the lateral supports was simulated by removing the truss elements from the system. The analysis was carried out with a time-marching procedure. After the sustained vertical load of 15 psi was applied to the top surface, the analysis was continued for a period of 13 days. Input data for the finite element analysis are presented in Appendix B. 5.3.2 Results of Finite Element Analysis Figure 5.5 shows the calculated and measured lateral displacements versus time relationships of the geotextile reinforcement after releasing the lateral supports. A good agreement between the calculated and measured lateral displacements was obtained, although the measured displacement was slightly than the calculated value. The average measure creep rate was 2.4x10-3% per day, while the average calculated creep rate was 1. 6x1 o-3% per day. Figure 5.6 shows the calculated and measured lateral displacements along the side of the soilgeosynthetic composite after 18,720 min. (13 days). The calculated displacements were somewhat lower than the measured values. The calculated lateral displacement at 115

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the mid-height was 0.07 inch,. whereas the measured displacement was 0.11 inch. The deformed shapes of the calculated and measured displacements, however, were similar. Figures 5.7 shows the calculated and the measured distribution of strains alo"ng the geosynthetic at 10, 4,320 and 18,720 minutes. It is seen that finite element simulation was less than satisfactory. The calculated strain did show a maximum value at the center but decreased toward the extremities at a much slower rate than the measured strains. The discrepancies may be caused by the limitation of the soil model in the finite element analysis, which was developed for simulation of normally consolidated or lightly consolidated clays. 116

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c:: -c:: CJ) E CJ) (J as 0.20 0.10 1-n n c. Cl) 1:1 n .... wuul:l -... ... ... --...--0 0.00 0 0 Figure 5.5 5 10 15 20 (Thousands) Elapsed Time, min. Test Results A FEM Lateral Displacements after Releasing of Lateral Supports Versus Time-Test Results Versus FEM 117

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c 12 ..... ..... 9 6 3 ' \ ', \ \ \ \ t T I I I I I I I I I I -r ,. I \ \ \ \ ', \ \ l I J I I I I / / / / ""--:' ... -" 0.00 0.10 0.20 0.30 Didplacement, in. test, 18,720 min FEM, 18,720 min Figure 5.6: Lateral Shapes at 18,720 min.Test Results Versus FEM 118

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5 4 3 ri 2 u; 0 0 5 4 #. 3 ri 2 0 0 5 4 #. 3 =-'! u; 2 Figure 5.7 10 min. test 6. FEM 7 2 4 8 8 10 12 l);slallc:e from lett end af geote:rUie, in 4320 min. test 6. FEM 2 4 8 8 10 12 Dlslallce from lett end af ;eoteXIIIe. In 11720 min. test 6. FEM 8 8 10 12 Dlstanc:e from lett end or ;eotextlle, In Distribution of Strains along the Length of Geotextile: Test Results Versus FEM 119

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6. SUMMARY AND CONCLUSIONS 6.1 Swmnary In this study a modified performance test as well as test procedure for investigation of long-term behavior of soil-geosynthetic composites was developed. The modified test was easier to perform than the test developed by Wu and Helwany (1996) and represented a "worst" condition in the deformation behavior of the soil-geosynthetic composite. In the modified test, a soil-geosynthetic composite was prepared inside the test apparatus in a plane strain condition. A sustained load was applied on the top surface of the soil-geosynthetic composite for a long period of time. The applied load was transferred from the soil to the geosynthetic, which was allowed to deform in an interactive manner with the confining soil. Durihg specimen preparation and during load application, longitudinal movement of the soilgeosynthetic composite was restrained by a pair of plexiglass panels, one on each side of the specimen, 120

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which were released to begin the test. Lateral and vertical movements of the soil-geosynthetic composite were monitored by LVDT's and dial indicators from the instant the lateral support was released. A series of performance tests were performed to examine test repeatability and to investigate the effects of soil type, geosynthetic tYI!Je and sustained load intensity on the behavior of soil-geosynthetic composite. A test was instrumented with strain gages to measure deformation along the length of the geosynthetic. Tests with soil only were also conducted for comparisons with soil-geosynthetic composite. In addition, a loaddeformation test with a weak geosynthetic was conducted to examine the failure mode of the soil-geosynthetic composites. Many of the tests were conducted at an elevated temperature of 125F. Element test on the geosynthetics indicated that the elevated temperatures typically accelerated creep of the geosynthetic by 100 to 400 folds. A finite element model was employed to analyze one of the performance tests. The analytical results were compared with the measured values. 121

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6.2 Conclusions Base on the tests conducted in this study, the following conclusions are advanced: 1) The repeatability of the performance test is considered satisfactory. Other than scatter of test data due to electrical interference, the major discrepancy of the tests occurred immediately after releasing the lateral support, which was due to a difference in the degree of lateral restraint during specimen preparation. 2) A test with Amoco 2002, a weak reinforcement, reached a failure condition with rupture along the centerline of the geotextile which conformed with the anticipated location of maximum force in the reinforcement. 3) A soil-geosynthetic composite, which consisted of a road base and Amoco 2044, subjected to an average vertical pressure of 15 psi, exhibited about 0.03 in. of lateral displacement at the release of the lateral support. In the next 30 days, an additional lateral movement of 0.025 in. occurred in an elevated temperature 122

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environment of 125F. The creep deformation decreased with time at a decreasing rate. The lateral deformation essentially ceased at 30,000 minutes after release of lateral support. Similar deformation behavior was measured in the vertical direction. 4) A soil-geosynthetic comp0site with a clayey soil and Amoco 2044, subjected to an average vertical pressure of 15 psi, also exhibited negligible creep in the lateral direction over the testing period of 30 days in ambient temperature. Creep deformation in the vertical direction, however, was significant and continueto increase at the end of the test. It is to be noted that the clayey soil without a reinforcement in otherwise the same test conditions failed within 17 minutes after released of the lateral support. 5) With the use of Amoco 2002 (a weaker reinforcement), the soil-geosynthetic composite, which employed the road base, subjected to 15 psi average vertical pressure 123

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and 125F temperature, exhibited about 0.05 in. at the release of the lateral support. Over the next 20 days, the lateral displacement increased by 0.06 in., which was more than two times as much as the composite with Amoco 2044 reinforcement. 6) At an average vertical pressure of 30 psi, the soil-geosynthetic composite, which employed the road base and Amoco 2044.reinforcement in a 125F environment, exhibited about 0.01 in. lateral displacement at the release of the lateral support. The lateral displacement increased by 0.06 in. in the next 30 days, which is more than twice the increase in lateral displacement with 15 psi pressure (0.025 in. increase in lateral displacement). The vertical displacements at the release of the lateral support were about 0.018 in. and 0.035 in. under 15 psi and 30 psi, respectively. The increase in vertical displacements over the next 30 days were about the same under 15 psi and 30 psi (about 0.04 in.) 124

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7) In the test which the strains along the geosynthetic reinforcement were measured, the soil-geosynthetic composite comprising the road base and Typar 3301 reinforcement, and subjected to an average vertical pressure of 15 psi and 70F temperature. The maximum strain occurred at the center of the reinforcement, and decreased, in a fashion, to zero at the two extremities. The maximum strain was 2.0% at the release of the lateral support. The maximum strain increased to 2.8% after 2 days and remained constant for about 1 day then decreased at an average rate of 0.005% per day. The maximum lateral displacement of the soil-geosynthetic occurred near the quarter point, i.e., at 3 in. above the base. The rate of lateral deformation was also the highest at the quarter point. Using isochronous load-strain curves, the forces along the length of the reinforcement can readily be determined. The loads decreased, as a result of stress relaxation, soon after the lateral support was released. The decrease 125

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of loads occurred at a decreasing rate. The rate of decrease was about the same along the length of the reinforcement. 8) The agreement between the finite element analysis and measured test results was fairly good in terms of the magnitude of creep deformation and rate of creep in the lateral direction. The strains obtained from the finite element analysis were markedly different from the measured value. The discrepancy was attributed to the inability of the soil model for simulation of compacted soil. The above conclusions regarding the long-term soil-geosynthetic performance test were drawn from limited number of tests. Further study is needed to confirm these observations. 126

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APPENDIX A PERFORMANCE TEST RESULTS 127

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TEST: REINFORCEMNENT: SOIL: TEMPERATURE: SUSTAINED VERTICAL LOAD: DATE: Elapsed time left side (min.) (in.) 0 0.000 5 0.113 0 0.000 1 0.070 2 0.078 3 0.087 4 0.100 5 0.105 6 0.114 7 0.124 9 0.151 10 0.167 11 0.191 12 0.228 13 0.271 14 0.314 15 0.351 16 0.383 17 0.452 18 0.890 128 C-1 None Clayey Soil 70 F 15 psi 07/07/95 Displacement Horizontal riqht side (in.) o.ooo 0.009 0.000 0.033 0.049 0.059 0.064 0.074 0.082 0.083 0.097 0.107 0.117 0.127 0.140 0.155 0.173 0.192 0.260 0.679 Vertical Total (in.) (in.) 0.000 0.000 0.122 0.360 0.000 o.ooo 0.103 0.053 0.127 0.076 0.146 0.102 0.164 0.113 0.179 0.132 0.196 0.142 0.207 0.159 0.248 0.174 0.274 0.199 0.308 0.227 0.355 0.257 0.411 0.295 0.469 0.335 0.524 0.365 0.575 o. 403 o. 712 0.520 1. 569 1.293

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TEST: REINFORCEMNENT: SOIL: TEMPERATURE: SUSTAINED VERTICAL LOAD: DATE: Elapsed time left side (min.) (in.) 0 0.000 10 0.024 0 0.000 10 0.055 60 0.055 400 0.056 1440 0.055 4320 0.057 5760 0.057 7200 0.055 11520 0.055 14400 0.058 15840 0.057 17280 0.055 18720 0.056 21600 0.056 24480 0.056 25920 0.055 27360 0.057 28800 0.056 30240 0.056 33120 0.055 34560 0.056 37440 0.055 129. C-2 Amoco 2044 Clayey Soil 70 F 15 psi 10/06/95 Displacement Horizontal right side (in.) 0.000 0.042 0.000 0.044 0.046 0.045 0.045 0.046 0.048 0.049 0.048 0.046 0.047 0.046 0.047 0.045 0.048 0.047 0.049 0.050 0.048 0.049 0.048 0.052 Vertical Total (in.) (in.) 0.000 0.000 0.066 0.670 0.000 O.OOQ 0.099 0.038 0.101 0.114 0.101 0.129 0.100 0.134 0.103 0.136 0.105 0.138 0.104 0.140 0.103 0.140 0.104 0.142 0.104 0.143 0.101 0.145 0.103 0.145 0.101 0.145 0.104 0.147 0.102 0.148 0.106 0.150 0.106 0.151 0.104 0.152 0.104 0.152 0.104 0.152 0.107 0.157

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TEST: REINFORCEMNENT: SOIL: TEMPERATURE: SUSTAINED VERTICAL LOAD: DATE: Elapsed time Point 1 (min.) (in.) 0 0.000 10 0.138 0 0.000 5 0.027 10 0.034 60 0.050 400 0.064 1440 0.072 2880 0.073 4320 0.079 5760 0.079 7200 0.078 8640 0.078 11520 0.076 12960 0.076 17280 0.082 18720 0.082 130 D-1 Typar 3301 Road Base 70 F 15 psi 09/06/95 Displacement Total Horizontal Point 2 Point 3 (in.) (in.) 0.000 0.000 0.192 0.175 0.000 0.000 0. 063 0.055 0.066 0.065 0.083 0.093 0.097 0.113 0.103 0.121 0.110 0.134 0.112 0.134 0.108 0.131 0.115 0.129 0.106 0.131 0.112 0.131 0.109 0.132 0.114 0.134 0.113 0.134 Vertical (in.) 0.000 0.376 0.000 0.031 0.036 0.051 0.071 0.080 0.080 0.085 0.085 0.088 0.089 0.091 0.091 0.0915 0.0922

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TEST: REINFORCEMNENT: SOIL: TEMPERATURE: SUSTAINED VERTICAL LOAD: DATE: Elapsed time left side (min.) (in.) 0 0.000 10 0.114 0 0.000 10 0.004 60 0.006 400 0.031 1440 0.036 2880 0.039 4320 0.040 7200 0.041 8640 0.044 10080 0.039 11520 0.044 12960 0.045 17280 0.045 18720 0.042 20160 0.050 24480 0.047 27360 0.050 28800 0.048 31680 0.048 34560 0.047 36000 0.048 37440 0.047 38880 0.047 40320 0.048 41760 0.047 131 H-1 .Amoco 2044 Road Base 125 F 30 psi 09/27/95 Displacement Horizontal right side (in.) 0.000 0.126 0.000 0.005 0.007 0.012 0.015 0.015 0.019 0.017 0.020 0.017 0.018 0.020 0.023 0.021 0.023 0.020 0.026 0.026 0.026 0.026 0.025 0.024 0.023 0.022 0. 026 Vertical Total (in.) (in.) 0.000 0.000 0.240 0.470 0.000 0.000 0.009 0.034 0.013 0.052 0.043 0.058 0.051 0.062 0.054 0.067 0.059 0.069 0.058 0.074 0.064 0.075 0.056 0.077 0.062 0.077 0.065 0.077 0.068 0.077 0.063 0.077 0.073 0.078 0.067 0.080 0.076 0.080 0.074 0.080 0.074 0.080 0.073 0.080 0.073 0.079 0.071 0.081 0.070 0.080 0.070 0.080 0.073 0.080

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TEST: REINFORCEMNENT: SOIL: TEM:PERATURE: SUSTAINED VERTICAL LOAD: DATE: Elapsed time left side (min.) (in.) 0 0.000 10 0.052 0 0.000 10 0.014 60 0.017 400 0.019 1440 0.021 4320 0.020 5760 0.018 7200 0.020 11520 0.018 14400 0.023 15840 0.018 17280 0.021 18720 0.021 21600 0.022 24480 0.022 25920 0.019 30240 0.021 33120 0.025 37440 0.020 132 R-1 Amoco 2044 Road Base 70 F 15 psi 10/06/95 DisJ>lacernent Horizontal riqht side (in.) 0.000 0.084 0.000 0.016 0.022 0.021 0.021 0.022 0.021 0.018 0.018 0.021 0.019 0.017 0.018 0.019 0.016 0.021 0.017 0.018 0.020 Vertical Total (in.) (in.) 0.000 0.000 0.136 0.325 0.000 0.000 0.030 0.018 0.039 0.031 0.040 0.038 0.042 0.045 0.042 0.049 0.039 0.049 0.038 0.050 0.036 0.053 0.044 0.054 0.037 0.055 0.038 0.055 0.039 0.056 0.041 0.058 0.038 0.060 0.040 0.060 0.038 0.061 0.043 0.064 0.040 0.066

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TEST: REINFORCEMNENT: SOIL: TEMPERATURE: SUSTAINED VERTICAL LOAD: DATE: Elapsed time left side (min.) (in.) 0 0.000 10 0.036 0 0.000 10 0.012 60 0.016 400 0.019 1440 0.020 2880 0.020 4320 0.020 7200 0.020 8640 0.021 10080 0.019 11520 0.020 12960 0.020 17280 0.023 18720 0.024 20160 0.022 24480 0.022 27360 0.024 28800 0.023 31680 0.026 34560 36000 0.024 37440 o. 026 38880 0. 026 40320 0. 026 41760 0.024 133 R-2 Amoco 2044 Road Base 125 F 15 psi 09/27/95. Displacement Horizontal riqht side (in.) 0.000 0.030 0.000 0.016 0.025 0.029 0.029 0.034 0.031 0.032 0.033 0.034 0.029 0.032 0.030 0.030 0.033 0.030 0.034 0.033 0.032 0.033 0.031 0.030 0.028 0.030 0.032 Vertical Total (in.) (in.) 0.000 0.000 0.066 0.262 0.000 0.000 0.028 0.018 0.041 0.025 0.048 0.031 0.049 0.033 0.054 0.037 0.051 0.040 0.052 0.045 0.054 0.045 0.053 0.047 0.049 0.048 0.052 0.048 0.053 0.050 0.054 0.051 0.055 0.051 0.052 0.052 0.058 0.053 0.056 0.053 0.058 0.054 0.056 0.054 0.055 0.054 0.056 0.055 0.054 0.054 0.056 0.054 0.056 0.054

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TEST: REINFORCEMNENT: SOIL: TEMPERATURE: SUSTAINED VERTICAL LOAD: DATE: Elapsed time left side (min.) (in.) 0 0.000 10 0.016 0 0.000 10 0.007 60 0.016 400 0.018 1440 0.020 5760 0.021 7200 0.019 10080 0.019 12960 0.020 14400 0.030 17280 0.028 18720 0.030 20160 0.030 21600 0.031 23040 0.028 24480 0.030 28800 0.030 30240 0.028 31680 0.029 34560 0.029 37440 0.028 134 R-3 Amoco 2044 Road Base 125 F 15 psi 08/09/95 Displacement Horizontal right side (in.) 0.000 0.009 0.000 0.006 0.009 0.016 0.019 0.025 0.023 0.023 0.023 0.021 o. 026 0.029 0.027 0.021 0.024 0.024 0.024 0.022 0.021 0.021 0.023 Vertical Total (in.) (in.) 0.000 0.000 0.025 0.264 0.000 0.000 0.013 0.020 0.025 0.028 .034 0.030 0.039 0.038 0.046 0.038 0.042 0.039 0.042 0.039 0.043 0.040 0.051 0.041 0.054 0.043 0.059 0.044 0.057 0.045 0.052 0.046 0.052 0.047 0.054 0.049 0.054 0.052 0.050 0.053 0.050 0.053 0.050 0.055 0.051 0.055

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TEST: REINFORCEMNENT: SOIL: TEMPERATURE: SUSTAINED VERTICAL LOAD: DATE: Elapsed time left side (min.) (in.) 0 0.000 10 0.164 0 0.000 10 0.120 400 0.189 1440 0.231 4320 0.235 5760 0.234 7200 0.234 11520 0.235 14400 0.236 15840 0.239 17280 0.237 18720 0.238 21600 0.237 24480 0.236 25920 0.235 27360 0.237 28800 0.236 30240 0.236 37440 0.238 38880 0.236 41760 0.237 44640 0.238 135 S-1 None Road Base 70 F 15 psi 10/06/95 Displacement Horizontal right side (in.) 0.000 0.264 0.000 0.135 0.259 0.349 0.359 0.364 0.360 0.362 0.362 0.363 0.365 0.362 0.365 0.362 0.365 0.364 0.361 0.367 0.362 0.364 0.365 0.364 Vertical Total (in.) (in.) 0.000 0.000 0.428 0.416 o.ooo 0.000 0.255 0.098 0.448 0.174 0.580 0.220 0.594 0.227 0.598 0.228 0.594 0.229 0.597 0.231 0.598 0.231 0.602 0.232 0.602 0.232 0.600 0.233 0.602 0.234 0.598 0.235 0.600 0.236 0.601 0.236 0.597 0.236 0.603 0.237 0.600 0.240 0.600 0.241 0.602 0.242 0.602 0.2422

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TEST: REINFORCEMNENT: SOIL: TEMPERATURE: SUSTAINED VERTICAL LOAD: DATE: Elapsed time left side (min.) (in.) 0 0.000 10 0.124 0 0.000 10 0.038 60 0.061 400 0.080 1440 0.089 2880 0.086 4320 5760 7200 8640 10080 0.095 11520 0.097 12960 0.099 17280 0.100 20160 0.096 21600 0.094 23040 0.094 24480 0.096 30240 0.097 33120 0.093 34560 0.089 36000 0.092 38880 0.092 43200 0.088 136 S-2 None Road Base 125 F 15 psi 08/09/95 Displacement Horizontal right side (in.) 0.000 0.179 0.000 0.041 0.062 0.080 0.085 0.083 0.091 0.090 0.088 0.089 0.090 0.093 0.092 0.091 0.089 0.087 o.b86 0.086 0.088 0.091 0.096 0.098 0.095 0.097 Vertical Total (in.) (in.) 0.000 0.000 0.303 0.300 0.000 0.000 0.078 0.032 0.123 0.045 0.160 0.056 0.174 0.059 0.169 0.065 0.183 0.065 0.180 0.066 0.177 0.066 0.177 0.066 0.186 0.067 0.190 0.067 0.190 0.067 0.192 0.069 0.185 0.070 0.181 0.071 0.180 0.072 0.182 0.072 0.185 0.075 0.184 0.075 0.185 0.075 0.190 0.075 0.186 0.075 0.185 0.075

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TEST: REINFORCEMENT: SOIL: TEMPERATURE: Elapsed Time (sec.) 0.00 10.44 20.87 30.26 40.70 50.09 60.53 70.96 80.36 90.79 100.19 110.62 111.66 112.71 113.75 190.98 192.02 193.06 194.11 195.15 196.19 197.24 198.28 199.33 200.37 Vertical Load (kips) 0.00 2.73 4.93 6.85 8.88 10.62 12.43 14.17 15.63 17.12 18.37 19.64 19.76 19.87 20.00 20.00 19.41 18.83 18.39 18.14 17.88 17.32 17.02 16.87 16.71 137 U-1 Amoco 2002 Road Base 70 F Equivalent Vertical Pressure (osi) 0.00 9.49 17.12 23.77 30.82 36.86 43.17 49.20 54.25 59.44 63.78 68.19 68.60 69.00 69.44 69.44 67.41 65.38 63.85 63.00 62.09 60.15 59.10 58.56 58.02

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TEST: REINFORCEMNENT: SOIL: TEMPERATURE: SUSTAINED VERTICAL LOAD: DATE: Elapsed time left side (min.) (in.) 0 0.000 10 0 0.000 10 400 1440 0.051 2880 0.055 4320 0.055 8640 0.056 10080 0.059 11520 0.056 14400 15840 18720 21600 23040 25920 27360 30240 34560 34560 30 psi 36000 38880 40320 43200 138 W-1 Amoco 2002 Road Base 125 F 15 psi after 20 days increase to 30 psi 08/15/95 Displacement Horizontal riqht side Total (in.) (in.) o.ooo 0.000 0.020 0.040 0.000 0.000 0.024 0.048 0.043 0.085 0.050 0.101 0.055 0.109 0.055 0.109 0.053 0.109 0.058 0.117 0.054 0.110 0.056 0.111 0.058 0.115 0.058 0.116 0.058 0.116 0.061 0.122 0.060 0.120 0.061 0.122 0.055 0.110 0.060 0.119 0.070 0.140 0.078 0.157 0.081 0.162 0.080 0.160 0.079 0.158

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APPENDIX B INPUT DATA OF FINITE ELEMENT ANALYSIS 139

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lb in min Modified LongTerm SoilGeosynthetic Performance Test 0 0 0 0 0 0 0 0 0 1 1 1 0 0 0 0 0 0 0 0 0 0.0361. 0 0 0 1 0.042 0.800 1.40 0.3 1000 1000. 20.00 0.56 0.966 1.0 004 0008 0.12 .6500 0.0 0 2 0.042 0.800 1.40 0 3 1000 1000. 20.00 0.56 0 882 1.0 .004 .0008 0.12 .6500 0.0 0 3 0.042 0.800 1.40 0.3 1000. 1000. 20.00 0.560 0.798 1.0 .004 .0008 0.12 .6500 0.0 0 4 0.042 0.800 1.40 0.3 1000 1000 20.00 0.560 0.714 1.0 004 .0008 0.12 .6500 0.0 0 5 0 042 0.800 1.40 0.3 1000 1000 20.00 0 560 0.630 1.0 .004 .0008 0.12 6500 0.0 0 6 0.042 0.800 1.40 0.3 1000. 1000. 20.00 0.560 0.546 1.0 004 .0008 0.12 .6500 0.0 0 7 0.042 0 800 1.40 0.3 1000 1000. 20 00 0 560 0.462 1.0 .004 0008 0 12 .6500 0 0 0 8 0 042 0.800 1.40 0.3 1000. 1000. 20 00 0.560 0.378 1.0 004 .0008 0.12 .6500 0.0 0 9 0.042 0.800 1.40 0.3 1000. 1000. 20.00 0.560 0.294 1.0 004 .0008 0 .12 .6500 0 0 0 10 0 042 0.800 1.40 0 3 1000 1000. 20.00 0.560 0 210 1.0 004 .0008 0 .12 6500 0 0 0 11 0.042 0.800 1.40 0 3 1000. 1000 20.00 0 560 0.126 1.0 .004 .0008 0 12 .6500 0.0 140

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0 12 0.042 0.800 1.40 0.3 1000. 1000. 20.00 0.560 0.042 1.0 .004 .0008 0.12 .6500 0.0 3 13 150. 1.0 3 14 50. 1.0 2 16 450000. 1.7 2.0 E 6 15 37570. 0.011 50 7.996 11.70. 15.0 1.0 0.0000 2.6000 2.8500 4.4000 0.1000 2.6417 2.9246 4.5412 0.2000 2.6840 3.0012 4.6869 0.3000 2.7270 3.0798 4.8372 0.4000 2.7707 3.1604 4.9925 o.5ooo 2.8151 3.2432 5.1526 0.6000 2.8603 3.3281 5.3180 0.7000 2.9061 3.4153 5.4886 0.8000 2.9527 3.5047 5.6647 0.9000 3.0000 3.5965 5.8465 1.0000 3.0481 3.6907 6.0341 .1.1000 3.0970 3.7874 6.2277 1.2000 3.1466 3.8865 6.4275 1.3000 3.1970 3.9883 6.6337 1.4000 3.2483 4.0928 6.8466 1.5000 3.3004 4.2000 7.0663 1.6000 3.3533 4.3099 7.2930 1.7000 3.4070 4.4228 7.5270 1.8000 3.4616 4.5386 7.7685 1.9000 3.5171 4.6575 8.0178 2.0000 3.5735 4.7795 8.2750 2.1000 3.6307 4.9046 8.5406 2.2000 3.6889 5.0331 8.8146 2.3000 3.7481 5.1649 9.0974 2.4000. 3.8081 5.3001 9.3893 2.5000 3.8692 5.4389 9.6906 2.6000 3.9312 5.5814 10.0015 2.7000 3.9942 5.7276 10.3224 2.8000 4.0582 5.8775 10.6536 2.9000 4.1233 6.0315 10.9955 141

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3 0000 4.1894 6.1894 11.3483 3.1000 4.2565 6 3515 11.7124 3.2000 4.3248 6.5178 12 0882 3.3000 4.3941 6.6885 12.4761 3.4000 4.4645 6.8637 12. 8764 3.5000 4 5361 7.0434 13. 2895 3.6000 4.6088 7.2279 13. 7159 3.7000 4.6827 7.4172 14.1560 3.8000 4.7577 7.6114 14. 6103 3 9000 4.8340 7 8108 15. 0790 4.0000 4 9115 8.0153 15.5629 4 1000 4.9902 8 2252 16 0622 4.2000 5.0702 8.4406 16.5776 4 3000 5.1514 8 6617 17. 1095 4.4000 5.2340 8 8885 17. 6585 4.5000 5.3179 9 1213 18. 2251 4.6000 5.4031 9.3601 18.8099 4 7000 5.4897 9 6053 19.4134 4.8000 5.5777 9.8568 20 0363 4 9000 5.6671 10. 1149 20.6792 5 0000 5.7580 10.3798 21.3427 39 0 0001. 1. 2. 3 4 5. 6 7. 8. 9 10. 1440 2880 4320 5760. 7200 142

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8640. I0080. 11520. 12960. 14400. 15840. I7280. 18720 20160. 2I600. 23040. 24480. 25920. 27360. 28800. 30240. 31680. 33120. 34560. 36000. 37440. 38880. 40320. 12 I93 85 97 I94 86 98 I95 87 99 196 88 IOO 197 89 101 198 90 102 199 91 _103 200 92 104 201 93 105 202 94 106 203 95 I07 204 96 I08 I I I 1 1 0 1 1.0 1 1 0.0 0 0 13 6.0 0.0 143

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14 7.0 0 0 15 o:o 1.0 27 6.0 1.0 28 7.0 1.0 29 0.0 2.0 41 6.0 2.0 42 7.0 2.0 43 0. 0 3 0 55 6.0 3.0 56 7.0 3 0 57 0 0 4.0 69 6 0 4.0 70 7.0 4 0 71 0.0 4 5 83 6.0 4.5 84 7.0 4.5 85 0.0 5.0 97 6.0 5.0 98 7.0 5.0 99 0. 0 5 5 111 6.0 5 5 112 7.0 5.5 113 0 0 6.0 125 6 0 6 0 126 7 0 6.0 127 0.0 6.5 139 6 0 6.5 140 7.0 6.5 141 0 0 7.0 153 6.0 7.0 154 7.0 7.0 155 0. 0 7.5 167 6.0 7.5 168 7 0 7.5 169 0.0 8.0 181 6.0 8.0 182 7.0 8.0 183 0 0 9 0 195 6.0 9.0 196 7.0 9 0 197 0.0 10.0 209 6.0 10.0 210 7 0 10.0 211 0.0 11.0 223 6.0 11.0 224 7.0 11.0 225 0.0 12.0 237 6.0 12.0 E 238 7.0 12.0 1 1 2 16 15" 1 12 13 15 16 30 29 2 24 25 29 30 44 43 3 36 37 43 44 58 57 4 48 49 57 58 72 71 5 60 144

PAGE 154

61 71 72 86 85 5 72 73 85 86 100 99 6 84 85 99 100 114 113 6 96 97 113 114 128 127 7 108 109 127 128 142 141 7 120 121 141 142 156 155 8 132 133 155 156 170 169 8 144 145 169 170 184 183 9 156 157 183 184 198 197 10 168 169 197 198 212 211 11 180 181 211 212 226 225 12 192 193 113 114 15 204 205 13 14 13 205 206 27 28 13 206 207 41 42 13 207 208 55 56 13 208 209 69 70 14 209 210 83 84 14 210 211 97 98 14 211 212 Ill 112 14 212 213 139 140 14 213 214 153 154 14 214 215 167 168 14 215 216 181 182 14 216 217 195 196 13 217 218 209 210 13 218 219 223 224 13 219 220 237 238 13 220 221 125 126 14 221 E 222 225 226 16 232 1 13 1 1 15 1 0 29 1 0 43 1 0 57 1 0 71 1 0 85 1 0 99 1 0 145

PAGE 155

113 1 0 127 1 0 141 1 0 155 1 0 169 1 0 183 1 0 197 1 0 211 1 0 225 1 0 1 14 1 1 28 1 1 42 1 1 56 1 1 70 1 1 84 1 1 98 1 1 112 1 1 126 1 1 140 1 1 154 1 1 168 1 1 182 1 1 196 1 1 210 1 1 224 1 1 E 238 1 1 1 12 1 181 192 3 222 232 2 222 232 1 222 232 3 222 232 4 13 0 4 25 0 4 37 0 4 49 0 4 61 0 4 73 0. 4 146

PAGE 156

85 0 4 97 0 4 109 0 4 121 0 4 133 0 4 145 0 4 157 0 4 169 0 4 181 o 4 12 0 2 24 0 2 36 0 2 48 0 2 60 0 2 72 0 2 84 0 2 96 0 2 108 0 2 120 0 2 132 0 2 144 0 2 156 0 2 168 0 2 180 0 2 E 192 0 2 2 0 0 0 0 1 1 0.05 1 1 225 -0.195 1 226 235 -0.39 E 1 236 -0.195 3 0 0 0 0 1 0 0.05 1 1 225 -0.195 1 226 235 -0.39 E 1 236 -0.195 4 0 0 0 0 1 0 0.05 1 1 225 -0.195 1 226 235 -0.39 E 1 236 -0.195 5 0 0 0 0 1 0 0.05 1 147

PAGE 157

1 225 -0 .195 1 226 235 -0.39 E 1 236 -0.195 6 0 0 0 0 1 0 0.05 1 1 225 -0.195 1 226 235 -0.39 E 1 236 -0.195 7 0 0 0 0 1 0 0.05 1 1 225 -0.195 1 226 235 -0 39 E 1 236 -0.195 8 0 0 0 0 1 0 0.05 1 1 225 -0.195 1 226 235 -0.39 E 1 236 -0.195 9 0 0 0 0 1 0 0.05 1 1 225 -0 195 1 226 235 -0.39 E 1 236 -0 .195 10 0 0 0 0 1 0 0.05 1 1 225 -0 195 1 226 235 -0 39 E 1 236 -0.195 11 0 0 0 0 1 0 0 .05 1 1 225 -0.195 1 226 235 -0.39 E 1 236 -0.195 12 0 0 0 0 1 0 0.05 1 1 225 -0.195 1 226 235 -0.39 E 1 236 -0 .195 13 0 0 0 0 1 0 0.05 1 I 225 -0.195 1 226 235 -0.39 E 1 236 -0.195 14 0.0 0 0 1 0 0.05 1 1 225 -0.195 1 226 235 -0.39 148

PAGE 158

E 1 236 -0 .195 15 0 0 0 0 1 0 0.05 1 1 225 -0.195 1 226 235 -0.39 E 1 236 -0.195 16 0 0 0 0 1 0 0.05 1 1 225 -0 .195 1 226 235 -0.39 E 1 236 -0.195 17 0 0 0 0 1 0 0.05 1 1 225 -0 .195 1 226 235 -0 39 E 1 236 -0.195 18 0 0 0 0 1 0 0.05 1 1 225 -0.195 1 226 235 -0.39 E 1 236 -0.195 19 0 0 0 0 1 0 0.05 1 1 225 -0 .195 1 226 235 -0.39 E 1 236 -0.195 20 0 0 0 0 1 0 0.05 1 1 225 -0 .195 1 226 235 -0.39 E I 236 -0 .195 21 0 0 0 0 1 1 0.05 1 1 225 -0.195 1 226 235 -0.39 E 1 236 -0 .195 22 0 0 0 0 0 0 5.0 1 23 0 0 0 0 0 1 5.0 1 24 0 1 0 0 0 1 0.05 1 -205 -206 -207 -208 -209 -210 149

PAGE 159

-211 -212 -213 -214 -215 -216 -217 -218 -219 -220 E -221 25 0 0 0 0 0 1 10.0 1 26 0 0 0 0 0 1 100. 1 27 0 0 0 0 0 1 1440 1 28 0 0 0 0 0 1 1440 1 29 oo 0 0 0 1 1440. 1 30 0 0 0 0 0 1 1440. 1 31 0 0 0 0 0 1 1440 1 32 0 0 0 0 0 1 1440 1 33 0 0 0 0 0 1 1440. 1 34 0 0 0 0 0 1 1440. 1 35 0 0 0 0 0 1 1440 1 36 0 0 0 0 0 1 1440. 1 37 0 0 0 0 0 1 1440. 1 38 0 0 0 0 0 1 1440 I E 39 0 0 0 0 0 1 1440. 1 150

PAGE 160

BIBLIOGRAPHY AASHTO Standard Specifications for Highway Bridges, 15th edition (1992), AASHTO subcommittee on Bridges and Structure. Allen, T.M., Christopher, B.R., and Holtz, R.D. (1992) "Performance of a 12.6 m High Geotextile Wall in Seattle, Washington," International Symposium on Geosynthetic-Reinforced Soil Retaining Walls, Balkema Publishers, Natherlands, pp. 81-.100. Bathurst, R.J., Simac, M.R., Christopher, B.R., and Bonczkiewicz (1993),"A Data Base of Result from a Geosynthetic Reinforced Modular Block Soil Retaining Wall," International Symposium: Soil Reinforcement: Full Scale Experiment of the 80's, Paris, France, pp. 341-365. Billiard, J.W. and Wu, J.T.H. (1991), "Load Test of a Large-Scale Geotextile-Reinforced Retaining Wall," Proceedings of Geosynthetics 1991 Conference, Atlanta, Georgia, pp. 537-548. 151

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Chou, N.N.S. (1992), "Performance of Geosynthetic Reinforced Soil Walls," Ph.D. Thesis, Department of Civil Engineering, University o! Colorado, Denver, CO, USA. Collins, J.G., Bright, D.G., and Berg, R.R. (1994), "Performance Summary of the Tanque Verde Project Geogrid Reinforced Soil Retaining Walls," Proceedings, Earth Retaining Session, ASCE National Convention, Atlanta, GA., 1994. Findley, Lai and Onaran (1976), '"Creep and Relaxation of Nonlinear Viscoelastic Materials," North-Holland series in Applied Mathemetics and Mechanics, Vol. 18, North-Holland Publishing Company. Helwany, M.B. and Wu, J.T.H. (1995), "A Numerical Model for Analyzing Long-Term Performance of Geosynthetic Reinforced Soil Structures," Geosynthetics International, Vol. 2, No. 2, pp. 429-453. Helwany, M.B. (1994), A Deep Patch Technique for Landslide Repair," Report No. CTI-UCD-2-94, Colorado 152

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Transportation Institute. Helwany, M.B. and Wu, J.T.H. (1992), "A Generalized Creep Model for Geosynthetics," Earth Reinforcement Practice, Ochiai, H., Hayashi, S. and tani, J., Eds., Balkema, 1992, Proceedings of the International Symposium on Earth Reinforcement Practice, Fukuoka, Kyushu, Japan, Vol. 1, Nov 1992, pp. 79-84. Iizuka, A. and Ohta, H. (1987), "A Determination Procedure of Input Parameters in Elasto-Viscoplastic Finite Element Analysis," Soils and Foundations, Vol. 27, No. 3, pp. 71-87. Morgan, C.J. and Ward, I.M. (1971), "The Temperature Dependence of Nonlinear Creep and Recovery in Oriented Polypropylene," J. Mech. Phy. Solids, Vol. 19, pp. 165-178. Ohta, H. (1971), "Analysis of Deformation of Soils Based on the Theory of Plasticity and its Application to Settlement of Embankments," Doctor of Engineering Thesis, Kyoto University, Japan. 153

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Ohta, H. and Hata, s. (1971),"A Theoretical Study of the Stress-Strain Relations for Clays," Soils and Foundations, Vol. 11, No. 3, pp. 65-90. Roscoe, K.H., Schofield, A.N. and Thurairajah, A. (1963),"Yielding of Clays in State Wetter Than Critical," Geotechnique, Vol. 13, No. 3, pp. 211-240. Sekiguchi, H. (1989),"Theory of Undrained Creep Rupture of Normally Consolidated Clay Based on ElastoI Viscoplasticity," Soils and Foundations, Vol. 24, No. 1, pp. 129-147. Sekiguchi, H. and Ohta, H (1977),"Induced Anisotropy and Time Dependency in Clays," Proceedings of the 9th International Conference on Soil Mechanics and Foundation Engineering, Special Session 9, Vol. 3, Tokyo, Japan, pp. 542-544. Shibata, T. (1963),"0n the Volume Changes of.Normally Consolidated Clays," Annuals of Disaster Prevention Research Institute, Kyoto University, No. 6, pp. 128-134. (in Japanese). 154

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Simac, M.R., Christopher, B.R., and Bonczkiewicz, C. (1990),"Instrumented Field Performance of a 6 m Geogrid Soil Wall," Proceedings of the Forth International Conference on Geotextiles, Geomembranes and Related Products, The Hague, Vol. 1, pp. 53-59. Tatsuoka, F., Molenkamp, F., Torii, T. and Hino, T. (1984),"Behavior of Lubrication Layers of Platens in Element Tests," Soils and Foundations, Vol. 24, No. 1, pp. 113-128. Wu, J.T.H. and Helwany, S.M.B. (1996),"A Performance Test for Assessment of Long-Term Creep Behavior of Soil-Geosynthetic Composites," Geosynthetic International, Journal of International Geotextile Society, Vol. 3, No. 1. Wu, J.T.H. (1994),"long-Terni Creep Behavior," Discussion, International Symposium on Recent Case Histories of Permanent Geosynthetic-Reinforced Soil I Retaining Walls, Tokyo, Japan, 1992, A.A. Balkema Publishers, Natherlands, pp. 343-344. 155

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Wu, J.T.H. (1992a),"Predicting Performance of the Denver Walls: General Report," Geosynthetic-Reinforced I Soil Retaining Walls, Denver, CO, Balkema publisher, pp. 3-20. Wu, J.T.H. (1992b),"Construction and Instrumentation of the Denver Walls," Geosynthetic-Reinforced Soil Retaining Walls, Denver, CO, Balkema publisher, pp. 21-30. Wu, J.T.H. (1991),"Measuring Inherent load Extension Properties of Geotextiles for Design of Reinforced Structure," ASTM Geotechnical Testing Journal, Vol. 14, No. 2, pp. 157-165. 156