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Publication Number: FHWA-HRT-10-077
Date: July 2013

 

Composite Behavior of Geosynthetic Reinforced Soil Mass

CHAPTER 4. GSGC TESTS

The understanding of GSGC behavior in reinforced soil structures has been lacking. As a result, current design methods have considered the geosynthetic layers simply as added tensile elements and have failed to account for the interaction between soil and geosynthetics. A series of GSGC laboratory tests were designed and conducted to examine the behavior of a GSGC with varying spacing and strength of reinforcement, provide test data for verifying the analytical model for calculating strength properties of a GRS composite as described in chapter 5, and provide test data for calibration of an FE model for a GRS mass. The GSGC tests were conducted at TFHRC in McLean, VA.

4.1 DIMENSIONS OF THE PLANE-STRAIN GSGC TEST SPECIMEN

A soil mass reinforced by layers of geosynthetic reinforcement is not a uniform mass. To investigate the behavior of GSGCs by conducting laboratory tests, it is necessary to determine the proper dimensions of the test specimen so that the test provides an adequate representation of GSGC behavior.

A number of factors were considered prior to determining the test specimen dimensions of the GSGC test, including the following:

Using Plaxis Version 8.2, a series of FE analyses were conducted to examine the effect of specimen dimensions on the resulting global stress-strain and volume change relationships of the composites. The objective of the FE analyses was to determine proper dimensions of a GSGC that will produce load-deformation behavior sufficiently close to that of a large mass of soil-geosynthetic composite, referred to as the reference composite.

Figure 99 shows the typical geometric and loading conditions of the GSGC tests. The reference GSGC is taken as a reinforced soil mass with dimensions of 23 ft (7.0 m) high and 16 ft (4.9 m) wide in a plane-strain condition. Four different dimensions of GSSCs were analyzed with varying specimen heights (23, 6.6, 3.3, and 1.6 ft (7.0, 2.0, 1.0 and 0.5 m), while the width of the test specimen was kept as 0.7 × H. In these analyses, the soil was a dense sand. The sand was reinforced by a medium-strength woven geotextile (Geotex® 4×4) at 0.7 ft (0.2 m) vertical spacing. Table 2 lists the conditions and properties of the soil and reinforcement used in the analyses.

This diagram shows the reference soil-geosynthetic composite used in the generic soil geosynthetic composite (GSGC) tests.
1 m =3.28 ft
Figure 99. Illustration. Typical geometric and loading conditions of a GSGC.

 

Table 2. Conditions and properties of the backfill and reinforcement used in FE analyses.

Element Description
Soil A dense sand where unit weight = 17 kN/m3; cohesion = 5 kPa; angle of internal friction ( Φ ) = 38 degrees; angle of dilation ( Ψ ) = 8 degrees; soil modulus (E50 ) = 40,000 kPa; and Poisson’s ratio = 0.3
Reinforcement Geotex® 4×4 axial stiffness (EA) = 1,000 kN/m; ultimate strength (Tult) = 70 kN/m; and reinforcement spacing = 0.2 m
Confining pressure Constant confining pressures of 0 and 30 kPa

1 kN/m3 = 0.006 kip/ft3
1 kPa = 0.145 psi
1 kN/m = 0.068 kip/ft
1 m = 3.28 ft

The global stress-strain curves obtained from the analyses are shown in figure 100 and figure 101 for confining pressures ( σc ) of 0 and 4.4 psi (0 and 30 kPa), respectively (a confining pressure of 4.4 psi (30 kPa) is representative of the lateral stress at the mid-height of a 23-ft (7.0-m)-high wall). The corresponding global volume change curves are shown in figure 102 and figure 103. The global vertical strain ( εv ) was calculated by figure 104.

This graph shows the global stress-strain curves for generic soil geosynthetic composites (GSGCs) of different dimensions under a confining pressure of 0 psi (0kPa). Sigma subscript v sigma subscript n is on the y-axis from 0 to 290 psi (0 to 2,000 kPa), and global vertical strain is on the x-axis from 0 to 25 percent. There are four lines for specimen dimensions of 22.96 by 16.07 ft (7.0 by 4.9 m), 6.56 by 45.92 ft (2.0 by 14 m),  3.28 by 2.30 ft (1.0 by 0.7 m), and 1.64 by 1.15 ft (0.5 by 0.35 m). All four lines start at the origin and end at 15 percent global vertical strain. The 22.96- by 16.07-ft (7.0- by 4.9-m) line curves up the highest, while the 1.64- by 1.15-ft (0.5- by 0.35-m) line remains lowest and relatively flat.
1 kPa = 0.145 psi
1 m = 3.28 ft

Figure 100. Graph. Global stress-strain curves for GSGCs of different dimensions under a confining pressure of 0 psi (0 kPa).

 

This graph shows the global stress-strain curves obtained for generic soil geosynthetic composites (GSGCs) of different dimensions under a confining pressure of 4.4 psi (30 kPa). Sigma subscript v sigma subscript n is on the y-axis from 0 to 290 psi (0 to 2,000 kPa), and global vertical strain is on the x-axis from 0 to 25 percent. There are four lines for specimen dimensions of 22.96 by 16.07 ft (7.0 by 4.9 m), 6.56 by 45.92 ft (2.0 by 14 m), 3.28 by 2.30 ft (1.0 by 0.7 m), and 1.64 by 1.15 ft (0.5 by 0.35 m). All four lines start at the origin and end at 15 percent global vertical strain. The 22.96- by 16.07-ft (7.0- by 4.9-m) line curves up the highest, while the 1.64- by 1.15-ft (0.5- by 0.35-m) line is lowest, reaching just over 72.5 psi (500 kPa) at about 5 percent vertical strain and remaining relatively flat.
1 kPa = 0.145 psi
1 m = 3.28 ft

Figure 101. Graph. Global stress-strain curves for GSGCs of different dimensions under a confining pressure of 4.4 psi (30 kPa).

 

This graph shows the global volume change curves obtained for generic soil geosynthetic composites (GSGCs) of different dimensions under a confining pressure of 0 psi (0 kPa). Global volumetric strain is on the y-axis from -2 to 6 percent, and global vertical strain is on the x-axis from 0 to 16 percent. There are four lines for specimen dimensions of 22.96 by 16.07 ft (7.0 by 4.9 m), 6.56 by 45.92 ft (2.0 by 14 m), 3.28 by 2.30 ft (1.0 by 0.7 m), and 1.64 by 1.15 ft (0.5 by 0.35 m). All four lines start at the origin and end at about 14.5 percent global vertical strain. Each line dips below 0 percent global volumetric strain. The 22.96- by 16.07-ft (7.0- by 4.9-m) line curves up the highest, while the 1.64- by 1.15-ft (0.5- by 0.35-m) line is lowest, barely going higher than 0 percent global volumetric strain.
1 m = 3.28 ft
Figure 102. Graph. Global volume change curves for GSGCs of different dimensions under a confining pressure of 0 psi (0 kPa).

 

This graph shows the global volume change curves obtained for generic soil geosynthetic composites (GSGCs) of different dimensions under a confining pressure of 4.4 psi (30 kPa). Global volumetric strain is on the y-axis from -1.5 to 2.5 percent, and global vertical strain is on the x-axis from 0 to 16 percent. There are four lines for specimen dimensions of 22.96 by 16.07 ft (7.0 by 4.9 m), 6.56 by 45.92 ft (2.0 by 14 m), 3.28 by 2.30 ft (1.0 by 0.7 m), and 1.64 by 1.15 ft (0.5 by 0.35 m). All four lines start at the origin and end at about 14.5 percent global vertical strain. Each line dips below 0 percent global volumetric strain. The 22.96- by 16.07-ft (7.0- by 4.9-m) line curves up the highest, while the 1.64- by 1.15-ft (0.5- by 0.35-m) m line is lowest, barely going higher than 0 percent global volumetric strain.
1 m = 3.28 ft
Figure 103. Graph. Global volume change curves for GSGCs of different dimensions under a confining pressure of 4.4 psi (30 kPa).

 

Epsilon subscript v equals open parenthesis delta times H divided by H closed parenthesis times 100 percent.
 
Figure 104. Equation. Global vertical strain

Where:

ΔH = Total vertical displacement of the specimen.
H = Initial height of the specimen.

Figure 100 and figure 101 indicate that a composite with a height of 6.6 ft (2.0 m), width of 4.6 ft (1.4 m), and confining pressure of 4.4 psi (30 kPa) yielded stress-strain and volume change relationships that were sufficiently close to those of the reference composite. Specimen sizes with heights of 3.3 and 1.6 ft (1.0 and 0.5 m) appeared too small to provide an adequate representation of the reference composite.

For comparison, additional analyses were conducted on unreinforced soil. Figure 105 and figure 106 show the global stress-strain curves and global volume change curves of the soil masses without any reinforcement for the different specimen dimensions. The results indicate that a specimen height as small as 1.6 ft (0.5 m) will yield nearly the same stress-strain and volume change relationships as the reference soil mass of height 23 ft (7.0 m) when reinforcement is not present.

This graph shows the global stress-strain curves obtained from unreinforced soil under a confining pressure of 4.4 psi (30 kPa). Sigma subscript v sigma subscript n is on the y-axis from 0 to 20.3 psi (0 to 140 kPa), and global vertical strain is on the x-axis from 0 to 6 percent. There are four lines for specimen dimensions of 22.96 by 16.07 ft (7.0 by 4.9 m), 6.56 by 45.92 ft (2.0 by 14 m), 3.28 by 2.30 ft (1.0 by 0.7 m), and 1.64 by 1.15 ft (0.5 by 0.35 m). All four lines start at the origin and end at about 5 percent global vertical strain. The lines match very closely to each other, sloping up quickly to about 1 percent global vertical strain and 17.4 psi (120 kPa) and then leveling off.
1 kPa = 0.145 psi
1 m = 3.28 ft

Figure 105. Graph. Global stress-strain curves of unreinforced soil under a confining pressure of 4.4 psi (30 kPa).

 

This graph shows the global volume change curves obtained from unreinforced soil under a confining pressure of 4.4 psi (30 kPa). Global volumetric strain is on the y-axis from -0.4 to 1 percent, and global vertical strain is on the x-axis from 0 to 6 percent. There are four lines for specimen dimensions of 22.96 by 16.07 ft (7.0 by 4.9 m), 6.56 by 45.92 ft (2.0 by 14 m), 3.28 by 2.30 ft (1.0 by 0.7 m), and 1.64 by 1.15 ft (0.5 by 0.35 m). All four lines start at the origin and end at about 5 percent global vertical strain and about 0.8 percent global volumetric strain. The lines match very closely to each other, dropping below 0 percent global volumetric strain before sloping up quickly.
1 m = 3.28 ft
Figure 106. Graph. Global volume change curves of unreinforced soil under a confining pressure of 4.4 psi (30 kPa).

Based on the results of the FE analyses, a specimen height of 6.6 ft (2.0 m) and depth of 4.6 ft (1.4 m) with 0.7-ft (0.2-m) reinforcement spacing was selected for the GSGC tests. The actual specimen dimensions for the GSGC tests are shown in figure 107. Figure 108 and figure 109 show the front and plan views of the GSGC test setup.

This diagram shows the dimensions of the specimen used for the generic soil geosynthetic composite (GSGC) tests. A specimen height of 6.6 ft (2.0 m) and depth of 4.6 ft (1.4 m) with 0.7-ft (0.2-m) reinforcement spacing is shown.
1 m = 3.28 ft
Figure 107. Illustration. Specimen dimensions for the GSGC tests.

 

This schematic shows a detailed front view of the setup for the generic soil geosynthetic composite tests.
1 mm = 0.039 inches
Figure 108. Illustration. Front view of the test setup.

 

This schematic shows a detailed plan view of the setup for the generic soil geosynthetic composite tests.
1 mm = 0.039 inches
Figure 109. Illustration. Plan view of the test setup.

4.2 APPARATUS FOR PLANE-STRAIN TEST

To maintain a plane-strain condition for the GSGC specimens throughout the tests, two major factors were considered: (1) the test bin needed to be sufficiently rigid to have negligible lateral deformation in the longitudinal direction (i.e., the length direction) and (2) the friction between the backfill and the side panels of the test bin needed to be minimized to nearly zero.

4.2.1 Lateral Deformation

Five GSGC masses were tested inside a test bin. The test bin was designed to experience little deformation for a surcharge pressure up to 410 psi (2,800 kPa). The test bin is shown in figure 110.

This photo shows the test bin used for testing the five generic soil geosynthetic composite masses.
 
Figure 110. Photo. Test bin.

4.2.2 Friction

Two transparent Plexiglas® panels were attached inside the steel tubing frame to form the side surfaces of the test bin. To minimize the friction between the Plexiglas® and the backfill in these surfaces, a lubrication layer was created on the inside surfaces of the Plexiglas® panels. The lubrication layer consisted of a 0.02-inch (0.5-mm)-thick latex membrane and an approximately 0.04-inch (1 mm)-thick lubrication agent (Dow Corning® 4 Electrical Insulating Compound NSF 6). This procedure has been used successfully in many plane-strain tests conducted by Tatsuoka and his associates at University of Tokyo and by the lead author of this paper in many large-scale experiments. (See references 64–68.) The friction angle between the lubricant layer and the Plexiglas®, as determined by direct shear test, was less than 1 degree.

4.3 TEST MATERIAL

The backfill and geotextile reinforcement employed in the tests are described in the following sections.

4.3.1 Backfill

The backfill was a crushed diabase from a source near Washington, DC. Before conducting the GSGC tests, a series of laboratory tests was performed to determine the properties of the backfill, including the following:

A summary of some index properties is given in table 3. The grain size distribution of the soil is shown in figure 111. Two gradation tests were performed, and the results agreed well with each other.

Table 3. Summary of index properties of backfill.

Classification Well-Graded Gravel:
Soil Classification A-1a per
AASHTO M-15 and Soil
Classification GW-GM per
ASTM D 2487(69,70)
Maximum dry unit weight 0.15 kip/ft3 (24.1 kN/m3)
Optimum moisture content 5.2 percent
Specific gravity of soil solids 3.03

 

This graph shows the grain size distribution of the soil used in the generic soil geosynthetic composite tests. Grain size is on the x-axis from 3.9 to 0.00039 inches (100 to 0.01 mm), and percent finer is on the y-axis from 0 to 80 percent. Two lines represent the two tests performed. The lines match fairly closely, starting at 0.39 inches (10 mm) and 70 percent and sloping down to less than 0.0039 inches (0.1 mm) and about 15 percent.
1 mm = 0.039 inches
Figure 111. Graph. Grain size distribution of backfill.

Four triaxial tests were conducted at confining pressures of 5, 15, 30, and 70 psi (34, 103, 207, and 482 kPa), and the results were compared with those performed at the University of Colorado Denver on the same soil. The soil specimen was approximately 6 inches (152 mm) in diameter and 12 inches (305 mm) in height. The shapes of a typical specimen before and after failure are shown in figure 112 and figure 113, respectively. Figure 114 and figure 115 present the stress-strain and volume change curves of the tests. The stress-strain curves obtained by Ketchart and Wu are included for comparison and to furnish a more complete set of data.(68) The stress-strain relationships agree well in trend with those by Ketchart and Wu.(68) The Mohr-Coulomb failure envelopes of the backfill are shown in figure 116. For confining pressures between 0 and 30 psi (0 and 103 kPa), the strength parameters are c = 10.3 psi (71.0 kPa) and Φ = 50 degrees. For confining pressures between 30 and 110 psi (103 and 758 kPa), the strength parameters are c = 35.1 psi (242 kPa) and Φ = 38 degrees.

This photo shows a soil specimen used in triaxial tests. The specimen is cylindrical and smooth.
 
Figure 112. Photo. Typical triaxial test specimen before test.

 

This photo shows a soil specimen used in triaxial tests. Compared to the specimen before testing, this specimen is shorter, bulges in the middle, and shows lumps at the surface.
 
Figure 113. Photo. Typical triaxial test specimen after test.

 

This graph shows the stress-strain curves from the triaxial tests. Axial strain is on the x-axis from 0 to 11 percent, and deviatoric stress is on the y-axis from 0 to 600 psi (0 to 4,136.85 kPa). Five lines are shown for 5, 15, 30, 70, 70 (Ketchart), and 110 (Ketchart) psi  (34.45, 103.35, 206.7, 482.3, 482.3 (Ketchart), and 757.9 (Ketchart) kPa. All the lines start at the origin and slope up before leveling off. The 5 psi (34.45 kPa) line remains the lowest, and the 110 psi (Ketchart) (757.9 kPa (Ketchart)) line goes the highest.
1 kPa = 0.145 psi
Figure 114. Graph. Triaxial test results: stress-strain curves of backfill at 0.15 kip/ft3 (24.1 kN/m3) dry density and 5.2 percent moisture.

 

This graph shows the volume change curves from the triaxial tests. Axial strain is on the x-axis from 0 to 4 percent, and volumetric strain is on the y-axis from -0.4 to 0.6 percent. Two lines are shown for 5 and 30 psi (34.45 and 103.35 kPa). Both lines start at the origin, drop below 0 percent volumetric strain, and curve back up. The 5 psi (34.45 kPa) line stays below 0 percent volumetric strain until about 1.25 percent axial strain and then slopes up to about 0.5 percent volumetric strain at about 2.75 percent axial strain. The 30 psi (103.35 kPa) line stays below 0 percent volumetric strain until about 2.75 percent axial strain and then slopes up to about 0.4 percent volumetric strain at about 3.5 percent axial strain.
1 kPa = 0.145 psi
Figure 115. Graph. Triaxial test results: volume change curves of backfill at confining pressures of 5 and 30 psi (34.45 and 103.35 kPa).

 

This graph shows the Mohr-Coulomb failure envelopes of backfill. Shear stress is on the y-axis, and normal stress is on the x-axis.
1 kPa = 0.145 psi
Figure 116. Graph. Mohr-Coulomb failure envelopes of backfill.

4.3.2 Geosynthetics

The geosynthetic used in the experiments was Geotex® 4×4 manufactured by Propex® (formally known as Amoco 2044). This geosynthetic is a woven polypropylene geotextile. Table 4 shows its strength properties as provided by the manufacturer.

Table 4. Summary of Geotex® 4×4 properties.

Property Test Method Machine
Direction (i.e.,
Wrap Direction)
Cross Direction
(i.e., Fill
Direction)
Tensile strength
(grab)
ASTM D4632(71) 0.6 kip
(2.67 kN)
0.5 kip
(2.22 kN)
Wide-width tensile
ultimate strength
ASTM D4595(72) 400 lb/inch
(70 kN/m)
 400 lb/inch
(70 kN/m)
Wide-width strength
at 5 percent strain
ASTM D4595(72) 121 lb/inch
(21 kN/m)
217 lb/inch
(38 kN/m)
Wide-width
ultimate elongation
ASTM D4595(72) 10 percent 10 percent
Puncture ASTM D4833(73) 170 lb (0.8 kN)
Trapezoid tearing
strength
ASTM D4533(74) 250 lb (1.11 kN)

 

Two types of geosynthetics were used for the experiments: a single sheet of Geotex® 4×4 and a double sheet Geotex® 4×4 (by gluing two sheets together using 3M® Super 77 spray adhesive). The double sheet was used to create a geosynthetic that was approximately twice as stiff (and as strong) while maintaining the same interface condition as that of the single-sheet geosynthetic. Geotex® 4×4 geotextile has been used in the construction of hundreds of GRS walls and in many full-scale experiments, including the FHWA GRS pier, Havana Yard Test abutment and pier, Blackhawk preloaded GRS bridge abutment, and National Cooperative Highway Research Program test abutments. (See references 6 and 75–77.)

Uniaxial tension tests were performed on both types of geosynthetic to determine the load-deformation behavior using a specimen 12 inches (305 mm) wide and 6 inches (152 mm) long (see figure 117). The stiffness and strength of the two geosynthetics are shown in table 5, and load-deformation curves are shown in figure 118. The stiffness and strength of the double-sheet Geotex® 4×4 were approximately twice as much as those of the single-sheet Geotex® 4×4 with the breakage strain almost the same.

This photo shows the apparatus used to perform uniaxial tests on samples of geosynthetics.
 
Figure 117. Photo. Uniaxial tension test of Geotex® 4×4

 

Table 5. Properties of Geotex® 4×4 in fill direction.

Geosynthetic Wide-Width Tensile Strength per ASTM D4595(72)
Stiffness (kN/m) at
1 Percent Strain
Ultimate Strength (kN/m)
(Percent at Break)
Single-sheet Geotex® 4×4 1,000 70 (12 percent)
Double-sheet Geotex® 4×4 1,960 138 (12 percent)

1 kN/m = 0.069 kip/ft

 

This graph shows the load deformation curves for the two tested geosynthetics, single-sheet and double-sheet. Axial strain is on the x-axis from 0 to 15 percent, and tensile load is on the y-axis from 0 to 10,963.3 lbf/ft (0 to 160 kN/m). The stiffness and strength of the double-sheet geosynthetic is approximately twice as much as the single-sheet geosynthetic.
1 kN/m = 68.52 lbf/ft
Figure 118. Graph. Load deformation curves of the geosynthetics.

4.3.3 Facing Block

Blocks used for the facing of the GSGC mass during specimen preparation were hollow concrete blocks with dimensions of 15.625 by 7.625 by 7.625 inches (397 by 194 by 194 mm) and an average weight of 40 lb/block (18.1 kg/block).

4.4 TEST PROGRAM

The test program comprised five GSGC tests. Their test conditions are shown in table 6. The plate compactor used for the tests (MBW GP1200) had a weight of 120 lb (54 kg), plate dimensions of 12 by 21 inches (305 by 533 mm), centrifugal force of 1,500 lbf (6,700 N), rotation speed of 5,000 vibrations/min, and moving speed of 70 ft/min (21 m/min).

Table 6. Test program for GSGC tests.

Test Designation Geosynthetic Reinforcement Confining Pressure
(kPa)
Wide-Width
Strength of
Reinforcement
(kN/m)
Reinforcement
Spacing, Sv
(m)
Test 1 None 34 None No reinforcement
Test 2 Geotex® 4×4 34 70 0.2
Test 3 Double-sheet Geotex® 4×4 34 140 0.4
Test 4 Geotex® 4×4 34 70 0.4
Test 5 Geotex® 4×4 0 (unconfined) 70 0.2

1 kPa = 0.145 psi
1 kN/m = 0.069 kip/ft
1 m = 3.28 ft

 

4.5 TEST CONDITIONS AND INSTRUMENTATION

4.5.1 Vertical Loading System

The vertical loads were applied to the test specimens by using a 1,000,000-lb- (454,000-kg)-capacity loading frame with a 1,000,000-lb (454,000-kg) hydraulic jack. Loads were measured by load cells and by hydraulic jack pressure gauges. For test 1, two load cells of 100,000 and 300,000 lb (45,400 and 136,200 kg) were used to measure the loads. For tests 2 through 5, a 1,000,000-lb (454,000-kg) load cell was used to measure the loads. A 12-inch (305-mm)-thick concrete pad was placed on top of the specimen before loading. Vertical loads were applied in equal increments with 10 min of elapsed time between increments to allow for equilibrium. The elapsed time also allowed manual recording of displacements of the test specimen. The vertical loads were applied until a failure condition was reached to determine the strength of the composite specimen. The applied pressures on the composite specimens were determined from the applied vertical loads divided by the surface areas of the composite specimens.

4.5.2 Confining Pressure

The confining pressure on the test specimens was applied by vacuuming. The entire surface area of the test specimen was vacuum-sealed with a 0.02-inch (0.5-mm)-thick latex membrane. A prescribed confining pressure of 5 psi (34 kPa) was applied for tests 1 through 4 by connecting the latex membrane to a suction device through two 0.234-inch (6-mm)-diameter flexible plastic tubes. Only test 5 was conducted without confining pressure.

4.5.3 Instrumentation

The specimens were instrumented to monitor their performance during tests. The instruments used include the following:

This illustration shows a front, side, top, and cross section view of the location of linear variable displacement transducers (LVDTs) and digital dial indicators.
 
Figure 119. Illustration. Locations of LVDTs and digital dial indicators.

 

This photo shows a close-up of the strain gauge attachment technique used in the tests. The gauge is mounted on a lightweight nonwoven geotextile, and a microcrystalline wax and rubber coating was used.
 
Figure 120. Photo. Strain gauge on Geotex® 4×4 geotextile before applying protection tape.

 

This photo shows a close-up view of the strain gauge attachment technique used in the tests. The gauge is mounted on a lightweight nonwoven geotextile, and a microcrystalline wax and rubber coating was used. Before placing the reinforcement sheet in the test specimen, tape was used to protect the gauges during compaction.
 
Figure 121. Photo. Strain gauge on Geotex® 4×4 geotextile after applying protection tape.

 

This photo shows a wide view of six strain gauges mounted on the geotextile using tape.
 
Figure 122. Photo. Strain gauges mounted on Geotex® 4×4 geotextile.

Due to the presence of the lightweight geotextile patch, calibration of the strain gauge was needed. The calibration tests were performed to relate the strain obtained from the strain gauge to the actual strain of the reinforcement. Figure 123 and figure 124 show the calibration curves along the fill direction of Geotex® 4×4 geotextile for the single-sheet and double-sheet specimens, respectively.

This graph shows the calibration curve along the full direction for the geotextile specimen for single-sheet Geotex® 4×4. Strain from Instron Machine is on the y-axis from 0 to 6 percent, and strain from strain gauge is on the x-axis from 0 to 5 percent. The graph shows several points clustered closely around a best-fit line showing a direct, linear relationship. The graph indicates that y equals 1.172x and R-squared equals 0.9913.
 
Figure 123. Graph. Calibration curve for single-sheet Geotex® 4×4.

 

This graph shows the calibration curve along the full direction for the geotextile specimen for double-sheet Geotex® 4×4. Strain from Instron Machine is on the y-axis from 0 to 6 percent, and strain from strain gauge is on the x-axis from 0 to 5 percent. The graph shows several points clustered closely around a best-fit line showing a direct, linear relationship. The graph indicates that y equals 1.078x and R-squared equals 0.9986.
 
Figure 124. Graph. Calibration curve for double-sheet Geotex® 4×4.

4.5.4 Preparation of Test Specimen for GSGC Tests

The preparation procedure of a typical composite mass with the dimensions of 6.6 by 4.6 by 3.9 ft (2.0 by 1.4 by 1.2 m) is as follows:

  1. Mark the anticipated location of the GSGC mass on the Plexiglas®

  2.  Apply approximately 0.04-inch (1-mm)-thick lubricating agent (Dow Corning® 4 Electrical Insulating Compound NSF 61) evenly on the inside surfaces of the Plexiglas® (see figure 125).

    This photo shows a worker applying a lubricating agent to the inside surface of Plexiglas® that has been taped to the inside of the test bin.
     
    Figure 125. Photo. Applying grease on Plexiglas® surfaces.

  3. Attach a sheet of membrane (with 2.0-by-2.0-inch (51-by-51-mm) grid system predrawn on membrane) over each Plexiglas® and at the bottom of the specimen (see figure 126). 

    This photo shows a worker using a paint roller to attach at sheet of membrane at the bottom of the Plexiglas® surface inside the test bin.
     
    Figure 126. Photo. Attaching membrane.

     

  4. Lay a course of the facing blocks on the open sides of the specimen (see figure 127). 

    This photo shows a worker laying a row of modular concrete blocks between the walls and along the edge of the test bin.
     
    Figure 127. Photo. Placement of the first course of facing block.

     

  5. Place the backfill in the test bin and compact in 0.7-ft (0.2-m) lifts (see figure 128 and figure 129). If needed, check and adjust the backfill moisture before compaction to achieve the target moisture of 5.2 percent. 

    This photo shows a worker using a hand compactor to compact the first layer of backfill, creating a smooth surface.
     
    Figure 128. Photo. Compacting the first lift of backfill.

     

    This photo shows a large machine releasing backfill into the test bin from above.
     
    Figure 129. Photo. Placing backfill for the second lift.

  6.  Check the water content and dry unit weight of each lift by using a nuclear density gauge (Troxler 3440) by the direct transmission method.

  7.  Place the next layer of geosynthetic reinforcement (with strain gauges already mounted), covering the entire top surface area of compacted fill and the facing blocks (see figure 130).

    This photo shows two workers placing a layer of geosynthetic reinforcement across the top of the compacted fill and facing blocks.
     
    Figure 130. Photo. Placing a reinforcement sheet.

     

  8.  Repeat steps 4 to 8 until the full height of the composite mass is reached.

  9.  Sprinkle a 0.2-inch (5-mm)-thick fine sand layer over the top surface of the completed composite mass to level the surface and protect the membrane from being punctured by gravel in the backfill (see figure 131).

    This photo shows a worker crouching on top of the composite mass and using a level to complete the process of compaction.
     
    Figure 131. Photo. Completion of compaction of the composite mass and leveling the top surface with 0.2-inch (5-mm)-thick sand layer.

  10. Place a geosynthetic sheet on top of the composite mass (see figure 132). 

    This photo shows the completed composite mass within the test bin. The modular facing blocks can be seen on the front of the mass, and there is an even layer across the top of the mass.
     
    Figure 132. Photo. Completed composite mass with a geotextile sheet on the top surface.

  11. Glue a sheet of membrane to the top edge of the side membrane sheets (see figure 133). 

    This photo shows the top of the composite mass, where a thin sheet of yellow membrane has been glued to the surface.
     
    Figure 133. Photo. Top surface of the composite mass covered with a sheet of membrane.

  12. Remove all facing blocks and trim off the excess geotextile (see figure 134). 

    This photo shows two workers cutting off excess geotextile from behind the facing blocks.
     
    Figure 134. Photo. Removing facing blocks and trimming off excess geosynthetic reinforcement.

  13. Insert strain gauge cables through the plastic openings that were already attached on the membrane sheets at prescribed locations (see figure 135). 

    This photo shows two workers carefully pulling the strain gauge cables through the membrane sheet and around parts of the test bin.
     
    Figure 135. Photo. Inserting strain gauge cables through the membrane sheet.

  14.  Glue membrane sheets to enclose entire composite mass.

  15. Apply vacuum to the composite mass at a low pressure of 2.0 psi (14 kPa) (see figure 136). 

    This photo shows one side of the test bin, with the completed composite mass and strain gauges visible.
     
    Figure 136. Photo. Vacuuming the composite mass with a low pressure.

  16. Seal the connection between cables and membrane with epoxy to prevent air leaks (see figure 137). The low vacuum pressure allows the epoxy to seal the connection well. 

    This photo shows a worker carefully applying epoxy between the cable and the membrane on the face of the test bin to prevent air leaks during testing.
     
    Figure 137. Photo. Sealing the connection between cable and membrane with epoxy to prevent air leaks.

  17. Raise the vacuum pressure to 4.9 psi (34 kPa) and check air leaks under vacuuming (see figure 138). Measure the specimen dimensions (see table 7 for specimen dimensions of five tests).

    This photo shows a worker holding a tube to his ear to check for air leaks in the membrane.
     
    Figure 138. Photo. Checking air leaks under vacuuming.

 

Table 7. Dimensions of the GSGC specimens before loading.

Test Height,
inches (m)
Width,
inches (m)
Length,
inches (m)
Test 1 76.25 (1.937) 57.00 (1.448) 47.00 (1.194)
Test 2 76.35 (1.939) 54.00 (1.372) 46.75 (1.187)
Test 3 76.35 (1.939) 53.00 (1.346) 46.75 (1.187)
Test 4 76.30 (1.938) 58.75 (1.492) 46.75 (1.187)
Test 5 76.35 (1.939) 49.00 (1.245) 46.75 (1.187)

Figure 139 shows the LVDTs to monitor the lateral movement of a test specimen. The locations of the selected points for the tests are depicted in figure 140. The measured dry unit weights of five tests are shown in figure 141.

This photo shows the linear variable displacement transducers (LVDTs) used on the side of the test specimen to monitor the lateral movement of the specimen.
 
Figure 139. Photo. The LVDTs on an open side of test specimen.

 

This diagram shows the locations selected to measure lateral movement in the test specimen. Tests 1 and 2 are measured at nine points, with three rows of three points each.
1 mm = 0.039 inches
Figure 140. Illustration. Locations of selected points to trace internal movement of tests 1–5.

 

his graph shows the measured dry unit weights of the five tests, labeled test 1 through test 5. Specimen height is on the y-axis from 0 to 6.56 ft (0 to 2 m), and dry unit weight is on the x-axis from 0.09 to 0.18 kip/ft<sup>3</sup> (15 to 30 kN/m<sup>3</sup>). There are five lines, one for each test, and all the points cluster around 0.14 kip/ft<sup>3</sup> (24 kN/m<sup>3</sup>).
1 m = 3.28 ft
1 kN/m3 = 0.006 kip/ft3

Figure 141. Graph. Soil dry unit weight results during specimen preparation.

 

4.6 TEST RESULTS

4.6.1 Test 1—Unreinforced Soil

Test 1 is perhaps the largest plane-strain test for soil with a confining pressure. It was conducted as the baseline for the other four GSGC tests.

The loading sequence of the soil mass was as follows:

The soil mass at failure is shown in figure 142. Figure 143 shows the global vertical stress-strain relationship, and figure 144 shows the volume change relationships of the soil mass. The average lateral displacements on the open faces of the soil mass under different vertical stresses, measured by LVDTs, are presented in figure 145. The internal displacements of the soil at selected points under vertical applied pressures of 28, 45, 90, and 110 psi (190, 310, 620, and 770 kPa) are shown in figure 146. The test 1 results for unreinforced soil are summarized in table 8.

This photo shows a soil mass at failure of test 1.
 
Figure 142. Photo. Soil mass at failure of test 1.

 

This graph shows the global vertical stress/vertical strain relationship for test 1. Applied vertical stress is on the y-axis from 0 to 130.5 psi (0 to 900 kPa), and global vertical strain is on the x-axis from 0 to 6 percent. The line starts at the origin and peaks at about 
3 percent and just below 116 psi (800 kPa).
1 kPa = 0.145 psi
Figure 143. Graph. Test 1 unreinforced soil mass global vertical stress/vertical strain relationship.

 

This graph shows the volume change relationship for test 1. Volumetric strain is on the y-axis from -0.4 to 1.2 percent, and global vertical strain is on the x-axis from 0 to 3.5 percent. The line starts at the origin and dips below 0 percent volumetric strain. It crosses above 0 percent at about 2.25 percent global vertical strain and ends at 3 percent global vertical strain and about 0.9 percent volumetric strain.
 
Figure 144. Graph. Test 1 unreinforced soil mass global volume change strain relationship.

 

The graph shows the average lateral displacements on the open faces of the soil mass under different vertical stresses. Specimen height is on the y-axis from 0 to 6.56 ft (0 to 2 m), and lateral displacement is on the x-axis from 0 to 1.95 inches (0 to 50 mm). Five lines are shown for 39, 58, 87, 101.5, and 111.65 psi (200, 400, 600, 700, and 770 kPa). All five lines start just below 1.64 ft (0.50 m) and end just below 5.74 ft (1.75 m). The lines for 39 and 58 psi (200 and 400 kPa) are fairly straight, with the points staying around less than 0.19 inches (5 mm) for 39 psi (200 kPa) and around more than 0.19 inches (5 mm) for 58 psi (400 kPa). The line for 87 psi (600 kPa) starts at about 0.59 inches (15 mm), curves out to about 0.78 inches (20 mm), and ends back around 0.59 inches (15 mm). The line for 101.5 psi (700 kPa) starts just above 0.78 inches (20 mm), curves out to above 0.98 inches (25 mm), and ends at less than 0.78 inches (20 mm). The 111.65 psi (770 kPa) line starts at about 1.56 inches (40 mm), curves out to above 1.76 inches (45 mm), and ends at about 1.17 inches (30 mm).
1 m = 3.28 ft
1 kPa = 0.145 psi

Figure 145. Graph. Lateral displacements on the open face of test 1.

 

This diagram shows the internal displacements in nine locations within the soil mass. None of the nine points show significant displacement in test 1.
1 N = 0.00022 kip
1 mm = 0.039 inches

Figure 146. Illustration. Internal displacements of test 1.

 

Table 8. GSGC test 1 result summary.

Parameter Measurement
Test condition Geosynthetic reinforcement None
Wide-width strength of reinforcement None
Reinforcement spacing No reinforcement
Confining pressure 34 kPa

Test results

Applied stress at vertical strain of 1 percent 335 kPa
Ultimate applied pressure 770 kPa
Vertical strain at failure 3 percent
Maximum lateral displacement of the open face at failure 47 mm
Stiffness at 1 percent vertical strain (Eat 1%) 33,500 kPa
Stiffness for unloading-reloading (Eur) 87,100 kPa
1 mm = 0.039 inches
1 kPa = 0.145 psi

 

4.6.2 Test 2—GSGC Test (T, Sv )

In the second test, the GSGC mass was reinforced by nine sheets of single-sheet Geotex® 4×4 with spacing of 0.7 ft (0.2 m). The soil layer was compacted at 0.7-ft (0.2-m)-thick lifts. Each reinforcement sheet was mounted with 54 strain gauges.

The failure load in this test was 1,000,000 lb (454,000 kg). All nine reinforcement sheets were ruptured after testing. The composite mass after testing is shown in figure 147. The shear bands of the composite mass after testing are visible through the diagonal lines of the mass (see figure 147 and figure 148). Along the shear bands, the square grids of 2 by 2 inches (51 by 51 mm) were severely distorted after testing (see figure 148). These shear bands correspond exactly with the failure surfaces shown in figure 149.

This photo shows the test 2 composite mass after failure. Two diagonal failure planes are marked, and shear bands of the composite mass are visible through the diagonal lines.
 
Figure 147. Photo. Composite mass at failure of test 2.

 

This photo shows a close-up view of one portion of figure 148, showing the test 2 composite mass after failure. Along the shear bands, the square 2-by-2-inch (50.8-by-50.8-mm) grids are severely distorted.
 
Figure 148. Photo. Close-up of shear bands at failure of area A in figure 147.

 

This figure shows the test 2 composite mass removed from the test bin. The mass is deformed, and two clear failure planes are marked, making a “Y” shape on one side of the mass.
 
Figure 149. Photo. Failure planes of the composite mass after testing in test 2.

The measured data from test 2 were as follows:

his figure shows the global vertical stress-vertical strain relationship of the test 2 composite mass up to and after failure. Applied vertical stress is on the y-axis from 0 to 435 psi (0 to 3,000 kPa), and global vertical strain is on the x-axis from 0 to 9 percent. The line starts at the origin, slopes up to a peak at about 391.5 psi (2,700 kPa) and 7 percent, and then slopes back down.
1 kPa = 0.145 psi
Figure 150. Graph. Test 2 reinforced soil mass global vertical stress-vertical strain relationship.

 

This figure shows the global volume change strain relationship of the test 2 composite mass up to and after failure. Volumetric strain is on the y-axis from -1.8 to 0 percent, and global vertical strain is on the x-axis from 0 to 7 percent. The graph starts at the origin and ends at about 6.5 percent global vertical strain and -1.6 percent volumetric strain.
 
Figure 151. Graph. Test 2 reinforced soil mass global volume change strain relationship.

 

This graph shows the lateral displacement profiles on the open face of the composite under different applied vertical pressures. Specimen height is on the y-axis from 0 to 6.56 ft (0 to 2 m), and lateral displacement is on the x-axis from 0 to 2.73 inches (0 to 70 mm). There are 12 lines showing the displacements at applied pressures ranging from 29 to 391.5 psi (200 to 2,700 kPa).
1 m = 3.28 ft
1 mm = 0.039 inches
1 kPa = 0.145 psi

Figure 152. Graph. Lateral displacements on the open face of test 2.

 

This diagram shows the internal displacements in nine locations within the composite mass. Most of the points are displaced significantly more than they were in the test 1 mass.
1 mm = 0.039 inches
1 kPa = 0.145 psi

Figure 153. Illustration. Internal displacements of test 2.

 

This diagram shows the location of the strain gauges on the nine geosynthetic sheets in test 2. The gauges appear evenly spaced on each reinforcement layer.
1 mm = 0.039 inches
Figure 154. Illustration. Locations of strain gauges on geosynthetic sheets in test 2.

 

This graph shows reinforcement strain distributions in the test 2 composite mass. Strain is on the y-axis from 0 to 2.5 percent, and distance from the edge of the composite mass is on the x-axis from 0 to 1.97 ft (0 to 0.6 m). The graph shows seven lines for applied pressures ranging from 29 to 217.5 psi (200 to 1,500 kPa). The locations of the maximum strain in reinforcement are different between layers. In layer 1, the lines peak just before 0.98 ft (0.3 m) from the edge of the composite mass.
1 m = 3.28 ft
1 kPa = 0.145 psi

Figure 155. Graph. Reinforcement strain distribution of the composite mass in layer 1 of test 2 0.7 ft (0.2 m) from the base.

 

This graph shows reinforcement strain distributions in the test 2 composite mass. Strain is on the y-axis from 0 to 3 percent, and distance from the edge of the composite mass is on the x-axis from 0 to 1.97 ft (0 to 0.6 m). The graph shows seven lines for applied pressures ranging from 29 to 217.5 psi (200 to 1,500 kPa). The locations of the maximum strain in reinforcement are different between layers. In layer 2, the lines peak just before 0.98 ft (0.3 m) from the edge of the composite mass.
1 m = 3.28 ft
1 kPa = 0.145 psi

Figure 156. Graph. Reinforcement strain distribution of the composite mass in layer 2 of test 2 1.3 ft (0.4 m) from the base.

 

This graph shows reinforcement strain distributions in the test 2 composite mass. Strain is on the y-axis from 0 to 4.5 percent, and distance from the edge of the composite mass is on the x-axis from 0 to 1.97 ft (0 to 0.6 m). The graph shows seven lines for applied pressures ranging from 29 to 217.5 psi (200 to 1,500 kPa). The locations of the maximum strain in reinforcement are different between layers. In layer 3, the lines peak just before 0.98 ft (0.3 m) from the edge of the composite mass.
1 m = 3.28 ft
1 kPa = 0.145 psi

Figure 157. Graph. Reinforcement strain distribution of the composite mass in layer 3 of test 2 2 ft (0.6 m) from the base.

 

This graph shows reinforcement strain distributions in the test 2 composite mass. Strain is on the y-axis from 0 to 3.5 percent, and distance from the edge of the composite mass is on the x-axis from 0 to 1.97 ft (0 to 0.6 m). The graph shows five lines for applied pressures ranging from 29 to 145 psi (200 to 1,000 kPa). The locations of the maximum strain in reinforcement are different between layers. In layer 4, the lines peak just before 1.64 ft (0.5 m) from the edge of the composite mass.
1 m = 3.28 ft
1 kPa = 0.145 psi

Figure 158. Graph. Reinforcement strain distribution of the composite mass in layer 4 of test 2 2.6 ft (0.8 m) from the base.

 

This graph shows reinforcement strain distributions in the test 2 composite mass. Strain is on the y-axis from 0 to 3 percent, and distance from the edge of the composite mass is on the x-axis from 0 to 1.97 ft (0 to 0.6 m). The graph shows five lines for applied pressures ranging from 29 to 145 psi (200 to 1,000 kPa). The locations of the maximum strain in reinforcement are different between layers. In layer 5, the lines peak at about 2.30 ft (0.7 m) from the edge of the composite mass.
1 m = 3.28 ft
1 kPa = 0.145 psi

Figure 159. Graph. Reinforcement strain distribution of the composite mass in layer 5 of test 2 3.3 ft (1.0 m) from the base.

 

This graph shows reinforcement strain distributions in the test 2 composite mass. Strain is on the y-axis from 0 to 3 percent, and distance from the edge of the composite mass is on the x-axis from 0 to 1.97 ft (0 to 0.6 m). The graph shows five lines for applied pressures ranging from 29 to 145 psi (200 to 1,000 kPa). The maximum strain in reinforcement are different between layers. In layer 6, the lines peak just before 0.98 ft (0.3 m) from the edge of the composite mass.
1 m = 3.28 ft
1 kPa = 0.145 psi

Figure 160. Graph. Reinforcement strain distribution of the composite mass in layer 6 of test 2 3.9 ft (1.2 m) from the base.

 

This graph shows reinforcement strain distributions in the test 2 composite mass. Strain is on the y-axis from 0 to 4 percent, and distance from the edge of the composite mass is on the x-axis from 0 to 1.97 ft (0 to 0.6 m). The graph shows six lines for applied pressures ranging from 29 to 181.25 psi (200 to 1,250 kPa). The locations of the maximum strain in reinforcement are different between layers. In layer 7, the lines peak just before 1.64 ft (0.5 m) from the edge of the composite mass.
1 m = 3.28 ft
1 kPa = 0.145 psi

Figure 161. Graph. Reinforcement strain distribution of the composite mass in layer 7 of test 2 4.6 ft (1.4 m) from the base.

 

This graph shows reinforcement strain distributions in the test 2 composite mass. Strain is on the y-axis from 0 to 3 percent, and distance from the edge of the composite mass is on the x-axis from 0 to 1.97 ft (0 to 0.6 m). The graph shows six lines for applied pressures ranging from 29 to 181.25 psi (200 to 1,250 kPa). The locations of the maximum strain in reinforcement are different between layers. In layer 8, the lines peak just before 0.98 ft (0.3 m) from the edge of the composite mass.
1 m = 3.28 ft
1 kPa = 0.145 psi

Figure 162. Graph. Reinforcement strain distribution of the composite mass in layer 8 of test 2 5.2 ft (1.6 m) from the base.

 

This graph shows reinforcement strain distributions in the test 2 composite mass. Strain is on the y-axis from 0 to 1.6 percent, and distance from the edge of the composite mass is on the x-axis from 0 to 1.97 ft (0 to 0.6 m). The graph shows four lines for applied pressures ranging from 29 to 116 psi (200 to 800 kPa). The locations of the maximum strain in reinforcement are different between layers. In layer 9, the lines peak just before 0.98 ft (0.3 m) from the edge of the composite mass.
1 m = 3.28 ft
1 kPa = 0.145 psi

Figure 163. Graph. Reinforcement strain distribution of the composite mass in layer 9 of test 2 5.9 ft (1.8 m) from the base.

 

This photo shows all of the geosynthetic reinforcement layers from the test 2 composite mass. Clear rupture lines can be seen, which highlight the location of maximum strain.
 
Figure 164. Photo. Aerial view of the reinforcement sheets exhumed from the composite mass after test 2 (numbers indicate sheet number).

 

This diagram, which was created with information from figure 165, shows the rupture lines in each layer of geosynthetic reinforcement. The rupture lines create two diagonal paths that come together in a “Y” shape.
1 mm = 0.039 inches
Figure 165. Illustration. Locations of rupture lines of reinforcement in test 2 based on figure 164.

The results of test 2 are summarized in table 9.

Table 9 . GSGC test 2 results summary.

Parameter Measurement
Test condition Geosynthetic reinforcement Geotex® 4×4
Wide-width strength of reinforcement 70 kN/m
Reinforcement spacing 0.2 m
Confining pressure 34 kPa

Test results

Ultimate applied pressure 2,700 kPa
Vertical strain at failure 6.5 percent
Maximum lateral displacement of the open face at failure 60 mm
Stiffness at 1 percent vertical strain (Eat 1%) 61,600 kPa
Maximum strain in reinforcement at ruptured 12 percent
Maximum measured strain in reinforcement 4.0 percent
1 kN/m = 0.069 kip/ft
1 m = 3.28 ft
1 kPa = 0.145 psi
1 mm = 0.039 inches

 

4.6.3 Test 3—GSGC Test (2T, 2Sv )

In this test, the GSGC mass was reinforced by four double sheets of Geotex® 4×4 at a 1.31-ft (0.4-m) spacing. The strength and stiffness of the double-sheet reinforcement were nearly doubled compared to those of the single-sheet reinforcement used in test 2. The GSGC mass after testing is shown in figure 166.

This photo shows the test 3 composite mass after failure. The mass is slightly deformed, and one diagonal failure plane is marked.
 
Figure 166. Photo. Composite mass after testing of test 3.

The measured data of test 3 were as follows:

This graph shows the global stress-strain relationship of the test 3 composite mass up to and after failure. Applied vertical stress is on the y-axis from 0 to 290 psi(0 to 2,000 kPa), and global vertical strain is on the x-axis from 0 to 8 percent. The line starts at the origin, slopes up to a peak at about 253.75 psi (1,750 kPa) and 6 percent, and then slopes back down.
1kPa = 0.145 psi
Figure 167. Graph. Global stress-strain relationship of test 3.

 

This graph shows the lateral displacement profiles on the open face of the composite under different vertical pressures. Specimen height is on the y-axis from 0 to 6.56 ft (0 to 2 m), and lateral displacement is on the x-axis from 0 to 2.34 inches (0 to 60 mm). There are eight lines showing the displacements at applied pressures ranging from 29 to 253.75 psi (200 to 1,750 kPa).
1 m = 3.28 ft
1 mm = 0.039 inches
1 kPa = 0.145 psi

Figure 168. Graph. Lateral displacements on the open face of test 3.

 

This diagram shows the internal displacements in 11 locations within the composite mass. Most of the points are displaced significantly more than they were in the test 1 mass.
1 mm = 0.039 inches
1 kPa = 0.145 psi

Figure 169. Illustration. Internal displacements of test 3.

 

This diagram shows the location of the strain gauges on four geosynthetic sheets in test 4. The gauges appear evenly spaced on each reinforcement layer.
1 mm= 0.039 inches
Figure 170. Illustration. Location of strain gauges on geosynthetic sheets in test 3.

 

This graph shows reinforcement strain distributions in the test 3 composite mass. Strain is on the y-axis from 0 to 4.5 percent, and distance from the edge of the composite mass is on the x-axis from 0 to 1.97 ft (0 to 0.6 m). The graph shows six lines for applied pressures ranging from 29 to 181.25 psi (200 to 1,250 kPa). In layer 1, the lines peak just before 0.98 ft (0.3 m) from the edge of the composite mass.
1 m = 3.28 ft
1 kPa = 0.145 psi

Figure 171. Graph. Reinforcement strain distribution of the composite mass in layer 1 of test 3 1.3 ft (0.4 m) from the base.

 

This graph shows reinforcement strain distributions in the test 3 composite mass. Strain is on the y-axis from 0 to 4.5 percent, and distance from the edge of the composite mass is on the x-axis from 0 to 1.97 ft (0 to 0.6 m). The graph shows five lines for applied pressures ranging from 29 and 145 psi (200 to 1,000 kPa). In layer 2, the lines peak just before 1.64 ft (0.5 m) from the edge of the composite mass.
1 m = 3.28 ft
1 kPa = 0.145 psi

Figure 172. Graph. Reinforcement strain distribution of the composite mass in layer 2 of test 3 2.6 ft (0.8 m) from the base.

 

This graph shows reinforcement strain distributions in the test 3 composite mass. Strain is on the y-axis from 0 to 4.5 percent, and distance from the edge of the composite mass is on the x-axis from 0 to 1.97 ft (0 to 0.6 m). The graph shows five lines for applied pressures ranging from 29 to 145 psi (200 to 1,000 kPa). In layer 3, the lines peak just before 0.98 ft (0.3 m) from the edge of the composite mass and stay relatively steady through 2.30 ft (0.7 m) from the composite mass.
1 m = 3.28 ft
1 kPa = 0.145 psi

Figure 173. Graph. Reinforcement strain distribution of the composite mass in layer 3 of test 3 3.9 ft (1.2 m) from the base.

 

This graph shows reinforcement strain distributions in the test 3 composite mass. Strain is on the y-axis from 0 to 4.5 percent, and distance from the edge of the composite mass is on the x-axis from 0 to 1.97 ft (0 to 0.6 m). The graph shows five lines for applied pressures ranging from 29 to 145 psi (200 to 1,000 kPa). In layer 4, the lines peak just before 0.98 ft (0.3 m) from the edge of the composite mass and stay relatively steady through 2.30 ft (0.7 m) from the composite mass.
1 m = 3.28 ft
1 kPa = 0.145 psi

Figure 174. Graph. Reinforcement strain distribution of the composite mass in layer 4 of test 3 5.2 ft (1.6 m) from the base.

 

This photo shows all four of the geosynthetic reinforcement layers from the test 3 composite mass. Sheets 1 through 4 are shown, with sheet 4 at the top and sheet 1 at the bottom. Clear rupture lines can be seen, which highlight the location of maximum strain.This photo shows all four of the geosynthetic reinforcement layers from the test 3 composite mass. Sheets 1 through 4 are shown, with sheet 4 at the top and sheet 1 at the bottom. Clear rupture lines can be seen, which highlight the location of maximum strain.
 
Figure 175. Photo. Aerial view of the reinforcement sheets exhumed from the composite mass after test 3 (numbers indicate sheet number).

 

This diagram, which was created with information from figure 176, shows the rupture lines in each layer of geosynthetic reinforcement. There are four sheets, with sheet 1 at the top and sheet 4 at the bottom. There is even spacing between the sheets. The rupture lines create a diagonal path through sheets 1–3.
1 mm = 0.039 inches
Figure 176. Illustration. Locations of rupture lines of reinforcement in test 3 based on figure 175.

The results of test 2 are summarized in table 10.

Table 10. Test 3 result summary.

Parameter Measurement
Test conditions Geosynthetic reinforcement Geotex® 4×4
Wide-width strength of reinforcement 140 kN/m
Reinforcement spacing 0.4 m
Confining pressure 34 kPa
Test results Ultimate applied pressure 1,750 kPa
Vertical strain at failure 6.1 percent
Maximum lateral displacement of the open face at failure 54 mm
Stiffness at 1 percent vertical strain (Eat 1%) 48,900 kPa
Maximum strain in reinforcement at rupture 12 percent
Maximum measured strain in reinforcement 4.0 percent
1 kN/m = 0.069 kip/ft
1 m = 3.28 ft
1 mm = 0.039 inches
1 kPa = 0.145 psi

 

4.6.4 Test 4—GSGC Test (T, 2Sv )

The reinforcement used in this test was a single sheet of Geotex® 4×4 at spacing of 1.3 ft (0.4 m). The composite mass after testing is shown in figure 177 and figure 178. The failure surfaces can be seen clearly in the figures.

This figure shows one side of the test 4 composite mass after it was removed from the test bin. The mass shows two clear, diagonal failure planes, making a “V” shape on the side of the mass.
 
Figure 177. Photo. Front view of failure planes of the composite mass after test 4.

 

This figure shows one side of the test 4 composite mass after it was removed from the test bin. The mass shows two clear, diagonal failure planes, making a “V” shape on the side of the mass.
 
Figure 178. Photo. Back view of failure planes of the composite mass after test 4.

The measured data for test 4 are as follows:

This graph shows the global stress-strain relationship of the test 4 composite mass up to and after failure. Applied vertical stress is on the y-axis from 0 to 203 psi (0 to 1,400 kPa), and global vertical strain is on the x-axis from 0 to 7 percent. The line starts at the origin, slopes up to a peak at about 188.5 psi (1,300 kPa) and 4 percent, and then slopes back down.
1 kPa = 0.145 psi
Figure 179. Graph. Global stress-strain relationship of test 4.

 

This graph shows the lateral displacement profiles on the open face of the composite under different vertical pressures. Specimen height is on the y-axis from 0 to 6.56 ft (0 to 2 m), and lateral displacement is on the x-axis from 0 to 2.34 inches (0 to 60 mm). There are seven lines showing the displacements at applied pressures ranging from 29 to 188.5 psi (200 to 1,300 kPa).
1 m = 3.28 ft
1 mm = 0.029 inches
1 kPa = 0.145 psi

Figure 180. Graph. Lateral displacements on the open face of test 4.

 

This diagram shows the internal displacements in 11 locations within the composite mass. Most of the points are displaced more than they were in the test 1 mass.
1 mm = 0.039 inches
1 kPa = 0.145 psi

Figure 181. Illustration. Internal displacements of test 4.

 

This diagram shows the location of the strain gauges on the four geosynthetic sheets in test 4. There are four sheets, with sheet 4 on the top and sheet 1 on the bottom. The gauges appear evenly spaced on each reinforcement layer, and there is even spacing between each sheet.
1 mm = 0.039 inches
Figure 182. Illustration. Locations of strain gauges on geosynthetic sheets in test 4.

 

This graph shows reinforcement strain distributions in the test 4 composite mass. Strain is on the y-axis from 0 to 1.8 percent, and distance from the edge of the composite mass is on the x-axis from 0 to 2.30 ft (0 to 0.7 m). The graph shows seven lines for applied pressures ranging from 29 to 116 psi (200 to 800 kPa). The lines peak at about 1.80 ft (0.55 m) from the edge of the composite mass and remain relatively steady through 2.30 ft (0.7 m).
1 m = 3.28 ft
1 kPa = 0.145 psi

Figure 183. Graph. Reinforcement strain distribution of the composite mass in layer 1 of test 4 1.3 ft (0.4 m) from the base.

 

This graph shows reinforcement strain distributions in the test 4 composite mass. Strain is on the y-axis from 0 to 2 percent, and distance from the edge of the composite mass is on the x-axis from 0 to 2.30 ft (0 to 0.7 m). The graph shows six lines for applied pressures ranging from 29 to 87 psi (200 to 600 kPa). The lines peak at about 1.80 ft (0.55 m) from the edge of the composite mass.
1 m = 3.28 ft
1 kPa = 0.145 psi

Figure 184. Graph. Reinforcement strain distribution of the composite mass in layer 2 of test 4 2.6 ft (0.8 m) from the base.

 

This graph shows reinforcement strain distributions in the test 4 composite mass. Strain is on the y-axis from 0 to 1 percent, and distance from the edge of the composite mass is on the x-axis from 0 to 2.30 ft (0 to 0.7 m). The graph shows four lines for applied pressures ranging from 29 to 58 psi (200 to 400 kPa). The lines peak at about 1.80 ft (0.55 m) from the edge of the composite mass.
1 m = 3.28 ft
1 kPa = 0.145 psi

Figure 185. Graph. Reinforcement strain distribution of the composite mass in layer 3 of test 4 3.9 ft (1.2 m) from the base.

 

This graph shows reinforcement strain distributions in the test 4 composite mass. Strain is on the y-axis from 0 to 1.8 percent, and distance from the edge of the composite mass is on the x-axis from 0 to 2.30 ft (0 to 0.7 m). The graph shows five lines for applied pressures ranging from 29 to 72.5 psi (200 to 500 kPa). In layer 4, the lines peak at about 1.15 ft (0.35 m) from the edge of the composite mass.
1 m = 3.28 ft
1 kPa = 0.145 psi

Figure 186. Graph. Reinforcement strain distribution of the composite mass in layer 4 of test 4 5.2 ft (1.6 m) from the base.

 

This photo shows all four geosynthetic reinforcement layers from the test 4 composite mass. Four sheets are shown, with sheet 1 on the right side and sheet 4 on the left side. Clear rupture lines can be seen, which highlight the location of maximum strain.
 
Figure 187. Photo. Aerial view of the reinforcement sheets exhumed from the composite mass after test 4 (numbers indicate sheet number).

 

This diagram, which was created with information from figure 188, shows the rupture lines in each of the four layers of geosynthetic reinforcement. Four sheets are shown, with sheet 1 at the top and sheet 4 at the bottom. The sheets are evenly spaced. The rupture lines create a diagonal path through layers 1–3.
1 mm = 0.039 inches
Figure 188. Illustration. Locations of rupture lines of reinforcement in test 4 based on figure 187.

 

The test 4 results are summarized in table 11.

Table 11. GSGC test 4 result summary.

Parameter Measurement
Test conditions Geosynthetic reinforcement Geotex® 4×4
Wide-width strength of reinforcement 70 kN/m
Reinforcement spacing 0.4 m
Confining pressure 34 kPa
Test results Ultimate applied pressure 1,300 kPa
Vertical strain at failure 4.0 percent
Maximum lateral displacement of the open face at failure 53 mm
Stiffness at 1 percent vertical strain (Eat 1%) 46,600 kPa
Maximum strain in reinforcement at rupture 12 percent
Maximum measured strain in reinforcement 2.0 percent
1 kN/m = 0.069 kip/ft
1 m = 3.28 ft
1 mm = 0.039 inches
1 kPa = 0.145 psi

4.6.5 Test 5—GSGC Test (Unconfined with T, Sv )

The configuration of this test was the same as test 2. The reinforcement was single-sheet Geotex® 4×4 at a spacing of 0.6 ft (0.2 m). Confining pressure was not applied for this test. Without applying confining pressure, the soil on the open faces fell off continuously with increasing applied pressure. The composite mass and failure surfaces after testing are shown in figure 189 through figure 191.

This figure shows the test 5 composite mass after it was removed from the test bin. The mass shows a clear, diagonal failure plane on one side of the mass.
 
Figure 189. Photo. Composite mass at failure of test 5.

 

This figure shows the front side of the test 5 composite mass after it was removed from the test bin. The mass shows a clear, diagonal failure plane on the side of the mass.
 
Figure 190. Photo. Front view of failure planes of the composite mass after test 5.

 

This figure shows the back side of the test 5 composite mass after it was removed from the test bin. The mass shows a clear, diagonal failure plane on the side of the mass.
 
Figure 191. Photo. Back view of failure planes of the composite mass after test 5.

 

The measured data of test 5 are as follows:

This graph shows the global stress-strain relationship of the test 5 composite mass up to and after failure. Applied vertical stress is on the y-axis from 0 to 319 psi(0 to 2,200 kPa), and global vertical strain is on the x-axis from 0 to 8 percent. The line starts at the origin, slopes up to a peak at about 275.5 psi (1,900 kPa) and 6 percent, and then slopes back down.
1 kPa = 0.145 psi
Figure 192. Graph. Global stress-strain relationship of test 5.

 

This graph shows the lateral displacement profiles on the open face of the composite under different vertical pressures. Specimen height is on the y-axis from 0 to 6.56 ft (0 to 2 m), and lateral displacement is on the x-axis from 0 to 1.56 inches (0 to 40 mm). There are four lines showing the displacements at applied pressures ranging from 29 to 217.5 psi (200 to 1,500 kPa).
1 m = 3.28 ft
1 mm = 0.039 inches
1 kPa = 0.145 psi

Figure 193. Graph. Lateral displacements on the open face of test 5.

 

This diagram shows the internal displacements in 11 locations within the composite mass. Most of the points are displaced significantly more than they were in the test 1 mass.
1 mm = 0.039 inches
1 kPa = 0.145 psi

Figure 194. Illustration. Internal displacements of test 5.

 

This diagram shows the location of the strain gauges on the nine geosynthetic sheets in test 5. Sheet 9 is located at the top, while sheet 1 is located at the bottom. There is even spacing between the sheets. The gauges appear evenly spaced on reinforcement layers 2, 4, 6, and 8. There are no gauges on the other layers.
1 mm = 0.039 inches
Figure 195. Illustration. Locations of strain gauges on geosynthetic sheets in test 5.

 

This figure shows reinforcement strain distributions in the test 5 composite mass. Strain is on the y-axis from 0 to 3.5 percent, and distance from the edge of the composite mass is on the x-axis from 0 to 1.97 ft (0 to 0.6 m). The graph shows seven lines for applied pressures ranging from 14.5 to 108.75 psi (100 to 750 kPa). The lines peak just after 1.31 ft (0.4 m) from the edge of the composite mass.
1 m = 3.28 ft
1 kPa = 0.145 psi

Figure 196. Graph. Reinforcement strain distribution of the composite mass in layer 1 of test 5 1.3 ft (0.4 m) from the base.

 

This figure shows reinforcement strain distributions in the test 5 composite mass. Strain is on the y-axis from 0 to 3 percent, and distance from the edge of the composite mass is on the x-axis from 0 to 1.97 ft (0 to 0.6 m). The graph shows seven lines for applied pressures ranging from 14.5 to 108.75 psi (100 to 750 kPa). The lines slope significantly upward, leading to a point just after 1.31 ft (0.4 m) from the edge of the composite mass, and then increase slightly to 2.13 ft (0.65 m).
1 m = 3.28 ft
1 kPa = 0.145 psi

Figure 197. Graph. Reinforcement strain distribution of the composite mass in layer 2 of test 5 2.6 ft (0.8 m) from the base.

 

This figure shows reinforcement strain distributions in the test 5 composite mass. Strain is on the y-axis from 0 to 1.2 percent, and distance from the edge of the composite mass is on the x-axis from 0 to 1.97 ft (0 to 0.6 m). The graph shows five lines for applied pressures ranging from 14.5 to 76.13 psi (100 to 525 kPa). The lines peak just after 6.56 ft (0.2 m) from the edge of the composite mass and slope down very slightly through 2.13 ft (0.65 m).
1 m = 3.28 ft
1 kPa = 0.145 psi

Figure 198. Graph. Reinforcement strain distribution of the composite mass in layer 3 of test 5 3.9 ft (1.2 m) from the base.

 

This photo shows eight geosynthetic reinforcement layers from the test 5 composite mass, with sheet 1 on the left and sheet 8 on the right. Clear rupture lines can be seen, which highlight the location of maximum strain.
 
Figure 199. Photo. Aerial view of the reinforcement sheets exhumed from the composite mass after test 5 (numbers indicate sheet number).

 

This diagram, which was created with information from figure 200, shows the rupture lines in each layer of geosynthetic reinforcement. There are 9 sheets, with sheet 1 at the top and sheet 9 at the bottom. The sheets are evenly spaced. The rupture lines create a diagonal path through layers 1–8. The bottom layer (layer 9) did not rupture.
1 mm = 0.039 inches
Figure 200. Illustration. Locations of rupture lines of reinforcement in test 5 based on figure 199.

The test results of test 5 are summarized in table 12.

Table 12. GSGC test 5 result summary.

Parameter Measurement
Test conditions Geosynthetic reinforcement Geotex® 4×4
Wide-width strength of reinforcement 70 kN/m
Reinforcement spacing 0.2 m
Confining pressure 0
Test results Ultimate applied pressure 1,900 kPa
Vertical strain at failure 6.0 percent
Maximum lateral displacement of the open face at failure Not measured
Stiffness at 1 percent vertical strain (Eat 1%) 52,900 kPa
Maximum strain in reinforcement at rupture 12 percent
Maximum measured strain in reinforcement 3.2 percent
1 kN/m = 0.069 kip/ft
1 m = 3.28 ft
1 kPa = 0.145 psi

 

4.7 DISCUSSION OF THE RESULTS

The results of the GSGC tests are discussed in terms of the following:

4.7.1 Effects of Geosynthetic Inclusion (Comparison Between Tests 1 and 2)

Table 13 shows the result comparisons between an unreinforced soil mass (test 1) and a soil mass reinforced by Geotex® 4×4 at a 0.7-ft (0.2-m) spacing (test 2). The reinforced soil was much stronger than the unreinforced soil. The ultimate applied pressure for the GSGC mass was about 3.5 times as large as the strength of the soil mass without reinforcement. The stiffness of the unreinforced soil mass was 50 percent of that for the reinforced soil mass. In addition, the reinforced soil mass was much more ductile than the unreinforced soil mass. The global vertical strain was 6.5 percent at failure for test 2, whereas it was only 3.0 percent for test 1.

 

Table 13. Comparison between test 1 and test 2.

Parameter Test 1 Test 2 (T, Sv )
Geosynthetic reinforcement None Geotex® 4×4
Wide-width strength of reinforcement None Tf = 70 kN/m
Reinforcement spacing No reinforcement Sv = 0.2 m
Confining pressure 34 kPa 34 kPa
Ultimate applied pressure 770 kPa 2,700 kPa
Vertical strain at failure 3 percent 6.5 percent
Maximum lateral displacement of the open face at failure 47 mm 60 mm
Stiffness at 1 percent vertical strain (Eat 1%) 33,500 kPa 61,600 kPa
Stiffness for unloading-reloading (Eur) 87,100 kPa Not applied
1 kN/m = 0.069 kip/ft
1 m = 3.28 ft.
1 kPa = 0.145 psi
1 mm = 0.039 inches

 

4.7.2 Relationship Between Reinforcement Spacing and Reinforcement Strength (Comparison Between Tests 2 and 3)

Comparing the results of tests 2 and 3 demonstrates the relationship between reinforcement spacing and reinforcement strength (see table 14). As noted in section 2.1, the current design methods are based on the concept that reinforcement spacing and reinforcement strength play an equal role in the performance of a GRS mass. In other words, a GRS wall with reinforcement strength Tf at spacing Sv will behave the same as the one with reinforcement strength of 2 × Tf at spacing 2 × Sv. The results of tests 2 and 3 demonstrate that this assumption is incorrect. Even with the same Tf / Sv ratio (7.3 kip/ft2 (350 kN/m2)) in tests 2 and 3, the stiffness and strength of test 2 (with Tf and Sv = 0.7 ft (0.2 m)) was much higher than that of test 3 (with 2Tf and Sv = 1.3 ft (0.4 m)). The strength of the composite mass in test 3 was only 65 percent of the strength in test 2. These results suggest that reinforcement spacing plays a more important role than strength of reinforcement in a reinforced soil mass.

Table 14. Comparison between test 2 and test 3 with the same Tf /Sv

Parameter Test 2 (T, Sv ) Test 3 (2T, 2Sv )
Wide-width strength of reinforcement (Tf) 70 kN/m 140 kN/m
Reinforcement spacing (Sv ) 0.2 m 0.4 m
Tf /Sv 350 kPa 350 kPa
Confining pressure 34 kPa 34 kPa
Ultimate applied pressure 2,700 kPa 1,750 kPa
Vertical strain at failure 6.5 percent 6.1 percent
Maximum lateral displacement of the open face at failure 60 mm 54 mm
1 kN/m = 0.069 kip/ft
1 m = 3.28 ft.
1 kPa = 0.145 psi
1 mm = 0.039 inches

 

4.7.3 Effects of Reinforcement Spacing (Comparison Between Tests 2 and 4)

The effects of reinforcement spacing can be seen by comparing the results of tests 2 and 4 (see table 15). All test conditions in the two tests were the same except the reinforcement spacing. The spacing was 1.3 ft (0.4 m) in test 4 and 0.65 ft (0.2 m) in test 2. The results demonstrate the importance of reinforcement spacing on the behavior of a GRS mass. With reinforcement spacing of 0.7 ft (0.2 m), the strength of the GRS mass was about twice as high as the one with the 1.3-ft (0.4-m) spacing. The corresponding increase in stiffness at 1 percent strain was about 30 percent. The GRS mass at the 0.7-ft (0.2‑m) spacing also exhibited significantly higher ductility than at the 1.3-ft (0.4‑m) spacing.

Table 15. Comparison between test 2 and test 4.

Parameter Test 2 (T, Sv ) Test 4 (T, 2Sv )
Wide-width strength of reinforcement (Tf ) 70 kN/m 70 kN/m
Reinforcement spacing (Sv ) 0.2 m 0.4 m
Tf /Sv 350 kPa 175 kPa
Confining pressure 34 kPa 34 kPa
Ultimate applied pressure 2,700 kPa 1,300 kPa
Vertical strain at failure 6.5 percent 4.0 percent
Maximum lateral displacement of the open face at failure 60 mm 53 mm
Stiffness at 1 percent vertical strain (Eat 1% ) 61,600 kPa 46,600 kPa
1 kN/m = 0.069 kip/ft
1 m = 3.28 ft.
1 kPa = 0.145 psi
1 mm = 0.039 inches

4.7.4 Effects of Reinforcement Strength (Comparison Between Tests 3 and 4)

The effects of reinforcement strength can be seen by comparing the results of tests 3 and 4 (see table 16). All test conditions in the two tests were identical except that reinforcement strength in test 3 was almost twice as high as that in test 4. The results indicate that the increase in strength of the GRS mass due to doubling the reinforcement strength was about 35 percent. This increase was much smaller than doubling the reinforcement spacing, where the increase in strength of the GRS mass was over 100 percent. The increase in stiffness at 1 percent strain due to doubling the reinforcement strength was only about 5 percent, compared to about a 30 percent increase due to doubling the reinforcement spacing.

Table 16. Comparison between test 3 and test 4.

Parameter Test 3 (T, Sv ) Test 4 (T, 2Sv )
Wide-width strength of reinforcement (Tf ) 140 kN/m 70 kN/m
Reinforcement spacing (Sv ) 0.4 m 0.4 m
Tf /Sv 350 kPa 175 kPa
Confining pressure 34 kPa 34 kPa
Ultimate applied pressure 1,750 kPa 1,300 kPa
Vertical strain at failure 6.1 percent 4.0 percent
Maximum lateral displacement of the open face at failure 54 mm 53 mm
Stiffness at 1 percent vertical strain (Eat 1%) 48,900 kPa 46,600 kPa
1 kN/m = 0.069 kip/ft
1 m = 3.28 ft.
1 kPa = 0.145 psi
1 mm = 0.039 inches

4.7.5 Effects of Confining Pressure (Comparison Between Tests 2 and 5)

The effects of confining pressure can be seen by comparing the test results of tests 2 and 5 (see table 17). All test conditions in the two tests were identical except that the confining pressure in test 2 was 4.9 psi (34 kPa) and test 5 was conducted without confinement. The results indicate that the increase in strength due to the confining pressure was about 40 percent. The increase in stiffness at 1 percent strain due to the confining pressure was about 15 percent.

Table 17. Comparison between test 2 and test 5.

Parameter Test 2 (T, Sv ) Test 5 (T, Sv )
Wide-width strength of reinforcement (Tf ) 70 kN/m 70 kN/m
Reinforcement spacing (Sv ) 0.2 m 0.2 m
Tf /Sv 350 kPa 350 kPa
Confining pressure 34 kPa 0
Ultimate applied pressure 2.700 kPa 1,900 kPa
Vertical strain at failure 6.5 percent 6.0 percent
Maximum lateral displacement of the open face at failure 60 mm Not measured
Stiffness at 1 percent vertical strain (Eat 1%) 61.600 kPa 52,900 kPa
1 kN/m = 0.069 kip/ft
1 m = 3.28 ft.
1 kPa = 0.145 psi
1 mm = 0.039 inches

 

4.7.6 Composite Strength Properties

Table 18 shows a comparison of the composite strength properties of the five GSGC tests as obtained from the measured data and calculated from Schlosser and Long’s method by assuming the friction angle remains the same as unreinforced soil (i.e., the same Φ value as in test 1).(25) The apparent cohesion, cR, from Schlosser and Long’s method is calculated as shown in figure 201.(25)

Table 18. Comparison of strength properties of five GSGC tests.

Parameter Test 1
(unreinforced)
Test 2
(T, Sv )
Test 3
(2T, 2Sv )
Test 4
(T, 2Sv )
Test 5
(T, Sv )
Wide-width strength of reinforcement, Tf (kN/m)   70 140 70 70
Reinforcement spacing, Sv (m)   0.2 0.4 0.4 0.2
Tf /Sv (kPa)   350 350 175 350
Confining pressure (kPa) 34 34 34 34 0
Apparent cohesion, cR, (kPa) by Schlosser and Long’s method   550 550 310 550
Ultimate applied pressure (kPa) from measured data 770 2,700 1,750 1,300 1,900
Ultimate applied pressure (kPa) by Schlosser and Long’s method   3,250 3,250 1,930 3,030
Difference in ultimate pressure between measured data and Schlosser and Long’s method (percent)   20 86 48 59
1 kN/m = 0.069 kip/ft
1 m = 3.28 ft.
1 kPa = 0.145 psi
Note: Blank cells indicate parameters for which there were no measurements.

 

c subscript R equals T subscript f divided by 2 times S subscript v times the square root of K subscript p end square root plus c.
 
Figure 201. Equation. Apparent cohesion from Schlosser and Long.(25)

Where:

c = Cohesion of the backfill.
Tf = Strength of reinforcement.
Sv = Reinforcement spacing.
Kp = Coefficient of passive Earth pressure.

The values calculated from Schlosser and Long’s method were higher than the measured values by 20 to 86 percent.

 

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