CHAPTER 6 

CONFINED EXTENSION TESTS USING 

TRIAXIAL-TYPE TEST DEVICE 

6.1 INTRODUCTION 

One of the primary purposes of this research program was to assess the influence of 

confinement on the tensile load versus strain (i.e., stress-strain) response of geosynthetic 

materials. One of the key steps in making this assessment was to evaluate and develop the 

most appropriate equipment for conducting confined extension tests in the laboratory. To 

this end, Polytechnic University (Polytechnic) participated in a collaborative effort to develop 

alternate and appropriate laboratory testing equipment to conduct confined extension and 

potentially confined creep testing of geosynthetics. The results of the Polytechnic triaxial 

testing program, which focused exclusively on confined extension testing using a modified 

triaxial apparatus (i.e., triaxial-type device), are summarized in this section. In addition, a 

comparison of the two confined extension test results from the testing programs is presented. 

6.2 LABORATORY TESTING EQUIPMENT 

a. Testing Equipment 

To meet the objectives of this research program, it is necessary to compare the response of 

geosynthetic materials under confined and unconfined conditions while test “variables” (Le., 

pretension force, aspect ratio, and strain rate) remain unchanged. Specifically, the stressstrain properties of geosynthetics have been shown to vary with respect to soil confinement, 

pretension force, aspect ratio, and strain rate, and possibly other unknown test variables. 

Therefore, with two or more test variables changing simultaneously in a test, it would be 

difficult to isolate the influence of a specific variable on the test results. As was 

demonstrated previously, any test device developed for conducting the confined extension 

testing should at least meet the following two requirements: (i) provide a constant strain rate 

to the test specimen; and (ii) maintain a constant aspect ratio of the test specimen throughout 

the test. 

97 
On the basis of the results of a literature review and the initial pullout testing program, the 

following two confined extension test devices were identified to have the potential to meet 

these two requirements: 

0 In-Soil Test Apparatus developed by McGown et al. [1982] and modified by WilsonFahmy et al. [1993]; and 

0 Modified Triaxial Apparatus developed by Ling et al. [ 19911 and Wu [ 19911. 

The triaxial-type device used for this program consists of a triaxial (extension) cell and a 

tension loading system. A schematic diagram of this triaxial-type device is shown in figure 

39. A typical test setup using this equipment involves placing a geotextile specimen in a 

vertical orientation inside of a cylindrical soil specimen that is encased in a latex membrane, 

Each end of the geotextile specimen is fixed within a metal clamp. The lower clamp is then 

fit through a slot in the bottom of the triaxial cell and connected to the bottom load cell. The 

bottom load cell is fixed to the platform of the triaxial frame. Similarly, the upper clamp is 

fit through a slot in the cover of the triaxial cell and connected to the upper load cell. The 

upper load cell is connected to the tension loading system. An LVDT is attached to the 

upper clamp to measure test specimen displacement. With reference to figure 39, it is 

explicitly noted that the cylindrical soil specimen is prepared in such a way that its top and 

bottom are in direct contact with the top and bottom of the triaxial cell, respectively. 

Therefore, during the extension testing, the confining soil is constrained in the vertical 

direction while the geotextile moves through the soil. 

The triaxial-type device can accommodate 8-in- (203~mm-) wide and 4-m (102mm-) long 

specimens and can provide up to 22,000 lb (98 kN) of tensile loading capacity on specimens 

confined under a maximum confining stress of 100 psi (690 kPa). 

b. Equipment Calibration 

The triaxial-type test device was calibrated electronically and mechanically. In electronic 

calibration, the electronic data measurement components (i.e., an LVDT and two load cells) 

were calibrated to verify that the loads or displacements applied to the instruments were 

properly conditioned and correctly recorded in the data acquisition computer. In mechanical 

calibration, tests were conducted on the equipment to assess friction losses in the equipment 

and/or effects due to the influence of the equipment and to check reproducibilty of the test 

results. The calibration of the triaxial-type device included the following steps: 

98 
TriaxialCell 1 

TOP 

Upper End Cap 

--EtLVD 

bber O-Ring 

Latex Membrane 

r 

h- Geotextile 

Perforated Plastic 

Glass Mold 

(Note: Not to Scale) 

Figure 39. Schematic diagram of triaxial-type device developed by Polytechnic University, 

99 
l Calibration of an LVDT and two load cells. 

l Calibration of the “triaxial cell effect” on the in-air tensile test results by conducting 

two in-air tensile tests on Geosynthetic PP-15: one with the triaxial cell and the other 

without the triaxial cell. 

l Evaluation of the reproducibility of the test results by conducting duplicate in-air 

tensile tests on Geosynthetics PP-15 and PP-16 under nearly identical test conditions. 

l Evaluation of the friction between the upper clamp and soil. 

The results of the calibration tests are summarized as follows: 

l Both the top and bottom load cells had a precision of f2.2 lb (+ 10 N); the LVDT 

had a precision of f0.0005 in (kO.01 mm). 

l No influence of the triaxial cell on the unconfined extension test results was detected. 

The movement of the upper specimen clamp through the cover of the cell did not 

influence the tension measurements. Loads measured by the two load cells were very 

consistent, as shown in figure 40. 

l Duplicate in-air tensile tests were conducted on Geosynthetics PP-15 and PP- 16. The 

results of two sets of tests indicate that tensile forces varied about 5 percent for 

Geosynthetic PP-15 and 20 percent for Geosynthetic PP-16 for strains up to 10 

percent. 

l Friction developed between the upper clamp and confining soil when the clamp was 

pulled out of the soil. A friction of approximately 25 lb (110 N) was measured when 

the upper clamp alone was confined in the beach sand at confining pressures in the 

range of 2 to 20 psi (14 to 138 kPa). The friction was subtracted from tensile loads 

during reduction of confined extension test data. Little friction was anticipated to 

develop between the lower clamp and soil because the lower clamp is attached to the 

stationary bottom load cell during testing. 

100 
1000 - 

400 - 

200 - 

UNCONFINED TENSILE TESTING ON GEOSYNTHETIC PP- ‘I 5 

SPECIMEN LENGTH: 4 in 

SPECIMEN WIDTH: 8 in 

eeeea FIXED BOTTOM LOAD CELL 

mxaea MOVING UPPER LOAD CELL 

DISPLACEMENT AT UPPER SPECIMEN CLAMP (in) 

1 in = 25.4m 

1 lb = 0.454 Kg 

Figure 40. Comparison of loads measured by top and bottom load cells 

in unconfined wide-width tensile test. 

101 
6.3 TEST PROCEDURE 

A test procedure was developed for conducting the confined extension tests using the triaxialtype device. With reference to figure 39, the step-by-step test procedure is described as 

follows: 

0 Stretch of Membrane: An g-in- (203mm-) diameter latex membrane is stretched to fit 

inside a perforated plastic glass mold. Each end of the membrane is folded back over 

the outside of the mold and fastened with a rubber O-ring. The mold is then placed 

on the lower end cap. 

a Preparation of Geosynthetic Specimen: A geotextile specimen is trimmed from the 

bulk sample and each end of the geotextile specimen is fixed within metal clamps. 

The lower clamp is then fit through the slot in the bottom of the triaxial cell and 

connected to the bottom load cell. The upper clamp is fit through the slot in the 

cover of the triaxial cell and attached to the top load cell. The geotextile is then 

slightly pretensioned to ensure that the geotextile stands vertically inside the mold. 

0 Preparation of Soil Specimen: The beach sand or silty sand is placed within the mold 

around the geotextile specimen in layers. Each layer of soil is compacted to 

approximately 70 to 75 percent relative density. 

l AssembZy of Triuxial Cell: The triaxial cell is placed around the mold containing the 

test specimen. Subsequently, each end of the triaxial membrane is fitted onto the 

lower or upper end cap and fastened with the rubber O-ring. The top of the triaxial 

cell is placed in direct contact with the upper end cap. The top and bottom of the 

triaxial cell is rigidly attached to the loading frame. 

0 Attachment of LVDT: An LVDT is attached to the upper clamp to measure 

displacements of the geotextile specimen. 

l Application of Confining Pressure: An isotropic confining pressure is applied to the 

cylindrical soil specimen by pressurizing the triaxial cell and consolidating the soil 

specimen. 

0 Extension of Geosynthetic Specimen: After application of the confining pressure, the 

upper clamp is pulled at a constant displacement rate, corresponding to an average 

strain rate of 10 percent/min relative to the initial specimen length. 

102 
l Monitoring of Test: Loads and displacements measured by the load cells and LVDT 

are recorded using a computer data acquisition system. Monitoring of the test is 

continued until rupture of the geotextile specimen occurs. 

It should be noted that the extension tests reported in this section were conducted on the 

geotextile specimens having initial dimensions of g-in (203~mm) wide by 4-in (102~mm) 

long. 

6.4 CONFINED EXTENSION TESTING PROGRAM 

a. Test Matrix 

The confined extension testing program consisted of four test series conducted on 

Geosynthetics PP-15 and PP-16 confined in the beach sand and silty sand. Each test series 

consisted of an unconfined tension test and several confined extension t.ests under confining 

pressures ranging from 2 to 20 psi (14 to 138 kPa). At each test confining pressure, two or 

five “identical” tests were conducted, and the average results of the tests were used to assess 

the confined stress-strain properties of the geotextile. A summary of test conditions used for 

conducting these four test series is presented in table 14. 

b. Test Results and Interpretation 

For each confined or unconfined extension test, the directly measured results include: 

e load measured by the top load cell at the upper specimen clamp versus displacement 

measured by the LVDT attached to the upper specimen clamp, referred to as the top 

load versus displacement data; and 

l load measured by the bottom load cell at the lower specimen clamp versus 

displacement measured by the LVDT attached to the upper specimen clamp, referred 

to as the bottom load versus displacement data. 

The results of a confined extension test on Geosynthetic PP-15 confined in the beach sand at 

a confining pressure of 10 psi (69 kPa) is presented in figure 41. This result is typical of the 

test results obtained in the triaxial apparatus. The top load versus displacement data and 

bottom load versus displacement data are graphically represented. It is observed from figure 

41 that there is a significant difference between the two curves. The difference or 

103 
Table 14. Summary of unconfined and confined extension test conditions conducted at Polytechnic University. 

;5 P 

Test Series 

Number 

TX1 

TX2 

TX3 

TX4 

Geosynthetic confining confining Number Test Average Strain 

Material Material Pressure of Tests(‘) SGEen Specimen Rate”) 

(psi) Width Lengjh (%/min) 

(in) (in) 

Geosynthetic PP- 15 In-air 0 2 8 4 10 

in Machine Direction Beach Sand 2 2 8 4 10 

Beach Sand 4 2 8 4 10 

Beach Sand 10 5 8 4 10 

Beach Sand 20 2 8 4 10 

Geosynthetic PP- 15 In-air 0 2 8 4 10 

in Machine Direction Silty Sand 4 2 8 4 10 

Silty Sand 10 2 8 4 10 

Geosynthetic PP- 16 In-air 0 2 8 4 10 

in Machine Direction Beach Sand 2 2 8 4 10 

Beach Sand 4 2 8 4 10 

Beach Sand 10 5 8 4 10 

Beach Sand 20 2 8 4 10 

Geosynthetic PP- 16 In-air 0 2 8 4 10 

in Machine Direction Silty Soil 4 2 8 4 10 

Silty Soil 10 2 8 4 10 

1 in = 25.4 mm 

psi = 6.895 kPa 

Note: (1) Number of tests refers to number of tests conducted at the same confining pressure under nearly identical conditions. 

(2) Average strain rate was defined as total displacement measured at the upper clamp divided by the initial specimen length. 
1200 

1000 

800 

- 

n 

ci 

0 

3 600 

w -I 

ii5 

ifI 

t400 

200 

0 

GEOSYNTHETIC PP-15 CONFINED IN BEACH SAND 

SPECIMEN LENGTH: 4 in 

SPECIMEN WIDTH: 8 in 

CONFINING PRESSURE: 10 psi 

= FIXED BOllOM LOAD CELL 

m MOVING UPPER LOAD CELL 

, 

0.0 0.2 0.4 0.6 0.8 1.0 1.2 

DISPIACEMENT AT UPPER SPECIMEN CLAMP (in) 

1 in = 25.4 mm 

1 lb = 0.454 Kg 

1 psi = 6.89 kPa 

Figure 41. Load versus displacement responses from confined extension test on 

Geosynthetic PP-15 at a normal stress of 10 psi. 

105 
differential load is caused by the friction mobilized between the constrained soil and the 

moving geotextile specimen. The friction response can be readily obtained by plotting 

differential load versus displacement, as shown in figure 42. The friction versus 

displacement curve shown in figure 42 is similar to that of a typical pullout response for a 

geosynthetic material. 

Examining the results of the confined extension tests conducted in the triaxial cell indicates 

the friction developed between the constrained soil and moving geotextile increases with 

increasing confining pressures for a given geosynthetic material. At low confining pressures 

of 2 to 4 psi (14 and 28 kPa), the friction is in the range of 10 and 20 lb (45 to 90 N). 

However, at high confining pressures of 10 and 20 psi (69 and 138 k.Pa), the friction is in 

the range of 200 to 800 lb (890 to 3560 N). 

It is believed that the top load versus displacement response obtained from this type of 

confined extension testing is a coupled response tif geotextile extension and soil-geotextile 

interface friction, At low confining pressures, the friction developed between the constrained 

soil and moving geotextile is relative small, and distribution of tension along the geotextile 

specimen is relatively uniform. For these considerations, tensile forces and strains can be 

calculated directly from the upper load versus displacement data as follows: 

0 divide the displacement at the top by the initial specimen length to obtain the strain; and 

a divide the top load by the initial specimen width to obtain the tensile force (Le., load 

per unit width). 

At high confining pressures, the interface friction becomes a significant component. An 

appropriate interpretation procedure is required to calculate tensile forces and strains of a 

confined geotextile specimen. However, due to the lack of displacement data along the 

length of the geotextile specimen (between the two ends of the geotextile specimen), the 

actual strain distribution cannot be adequately evaluated. At best, an average strain along the 

specimen can be estimated. The authors of this report believe that use of an interpretation procedure to 

define the confined stress-strain properties involves significant assumptions that limit the 

utility of these data, as described previously in the discussion on the pullout test results, For 

the triaxial tests, the tensile forces and strains of the geotextile confined in soil at high 

confining pressures were estimated using the same method that was used for interpreting the 

results of confined extension tests at low confining pressures. 

106 
ow .$ 1000 

P 

z - 

GEOSYNTHETIC PP-15 CONFINED IN BEACH SAND 

SPECIMEN LENGTH: 4 in 

SPECIMEN WIDTH: 8 in 

CONFINING PRESSURE: 10 psi 

cl.2 0.4 0.6 0.8 1.0 1.2 

DlSPlACEMENT AT UPPER SPECIMEN CLAMP (in) 

1 in = 25.4 mm 

1 lb = 0.454 Kg 

1 psi = 6.89 kPa 

Figure 42. Friction versus displacement response from confined extension test on 

Geosynthetic PP-15 at a normal stress of 10 psi. 

107 
Using the tensile force and strain data from each confined or unconfined extension test, the 

following properties were calculated to characterize the confined or unconfined response: (i) 

secant modulus at 5 percent strain; (ii) secant modulus at 10 percent strain; (iii) peak 

strength; and (iv) strain at the peak strength (i.e., failure strain). It is noted that two or five 

confined extension tests were conducted on the same geotextile under nearly identical test 

conditions. An average value of each of these four characterization properties was calculated 

from the results of the duplicate tests. A summary of the average values of these 

characterization properties is presented in table 15. 

6.5 COMPARISON OF CONFINED EXTENSION TEST EQUIPMENT AND 

RESULTS 

a. Comparison of Test Devices 

The triaxial-type device and the protocol confined. extension/creep test device are similar in 

the following aspects: 

0 capability to provide flexible boundary conditions over a major portion of the soil 

specimen surface; in the extension/creep device, the top and bottom of the soil 

specimen are in contact with air bladders; in the triaxial device, the soil specimen is 

encased in a latex membrane; 

l capability to apply a constant confining pressure to the test specimen; 

l capability to apply a constant strain rate to the test specimen; and 

l potential to maintain an approximately constant aspect ratio for the geosynthetic 

specimen. 

However, there are the following two major differences between the two test devices: 

l The triaxial device applies an isotropic pressure to the entire test specimen while the 

confined/creep device applies a vertical (normal) pressure to the test specimen. It is 

anticipated that the geosynthetic specimen encased in the cylindrical specimen in the 

triaxial device is under compression in all directions. Compression in the direction of 

width (i.e., in-plane compression) may influence the confined response of the geotextile. 

108 
Table 15. Summary of unconfined and confined extension test results conducted at Polytechnic University. 

Test Series Geosynthetic 

Number Material 

Confining 

Material 

confining Number Modulus at Modulus at Peak Strain 

Pressure 

T:(l) 

5% Strain(2) 10% Strength0 at Peakt4) 

(psi) (lblft) Strain(2) (Iblft) (%I 

(lb/ft) 

TX1 

TX2 

Geosynthetic 

PP-15 in 

Machine 

Direction 

Geosynthetic 

PP-15 in 

Machine 

Direction 

In-air 0 2 2,352 1,848 948 65 

Beach Sand 2 2 1,800 1,692 768 44 

Beach Sand 4 2 3,300 2,292 888 51 

Beach Sand 10 5 9,840 6,240 1,008 43 

Beach Sand 20 2 15,840 8,760 996 36 

In-air 0 2 2,352 1,848 948 65 

Silty Sand 4 2 2,700 4,656 888 88 

Silty Sand 10 2 1,572 2,772 756 61 

TX3 

TX4 

Geosynthetic 

PP-16 in 

Machine 

Direction 

Geosynthetic 

PP-16 in Machine 

Direction 

In-air 0 2 2,328 2,076 804 112 

Beach Sand 2 2 4,080 2,640 888 135 

Beach Sand 4 2 1,800 1,344 840 140 

Beach Sand 10 5 2,784 1,800 900 123 

Beach Sand 20 2 7,344 4,572 948 97 

In-air 0 2 2,328 2,076 804 112 

Silty Soil 4 2 1,044 528 444 150 

Silty Soil 10 2 6,144 3,027 1,104 120 

psi = 6.895 kPa 

lblft = 14.59 N/m 

Notes: (1) 

(2) 

(3) 

(4) 

Number of tests refers to number of tests conducted at the same confining pressure under nearly identical conditions. 

Modulus is an average modulus calculated from two or five duplicate tests conducted under the same conditions. 

Peak strength was measured at the upper clamp. 

Strain rate was defined as total displacement measured at the upper clamp divided by the initial specimen length. 
l In the triaxial device, the geotextile moves within the cylindrical soil specimen, which 

is constrained in the vertical direction. A friction is developed at the soil-geosynthetic 

interface, which causes a nonuniform distribution of tension along the specimen 

length. As a result, strain and strain rate are anticipated to decrease from the upper 

to lower end of the test specimen. In the confined extension/creep device, the soil 

tends to move together with the geotextile specimen. The mobilized soil-geosynthetic 

interface friction is relatively small. Therefore, the distribution of tension along the 

geosynthetic specimen is nearly uniform in this device. 

b. Comparison of Test Results 

In the context of the entire research program, there is only one component of the program 

that leads to a direct comparison between the two devices. To this end, a comparison is 

presented of the short-term confined and unconfined extension test results for Geosynthetics 

PP-15 and PP-10 confined in the beach sand and silty sand. Geosynthetics PP-15 and PP-10 

were two nonwoven geotextiles produced by the same manufacturer. On the basis of 

information provided by the manufacturer, the two geotextiles were considered as the same 

material as far as their average properties are concerned. The following summary comments 

reflect this comparison: 

l Unconfined Tensile Strength: In the confined extension/creep device, a peak strength 

of 1,352 lb/ft (lg.,8 kN/m) at a strain of 39 percent for Geosynthetic PP-10 was 

measured; the triaxial device measured a peak strength of 948 lb/ft (13.9 kN/m) at a 

strain of 65 percent for Geosynthetic PP-15. A direct comparison indicates that there 

is a significant difference between the two peak strengths and failure strains of the 

two geotextiles. To understand what caused the difference between the results 

obtained by the two organizations for these unconfined test results, two explanations 

were explored: (i) the difference between the two materials as measured by mass per 

unit area; and (ii) inherent variability of Geosynthetic PP-15. Geosynthetic PP-15 

tested at Polytechnic had a mass per unit area of 8.3 oz/yd* (282 g/m2) while 

Geosynthetic PP-10 tested at GeoSyntec had a mass per unit area of 10.1 oz/yd2 (343 

g/m*). It is expected that Geosynthetic PP-10 would be stronger than Geosynthetic 

PP-15; this is confirmed by the test results. 

Inherent variability of Geosynthetic PP-15 was studied by analyzing a set of in-air test 

data (10 tests) on Geosynthetic PP-15 provided by the manufacturer. The results of 

statistical analysis are as follows: (i) strengths in the machine direction in the range 

110 
from 940 to 1,421 lb/ft (13.7 to 20.7 kN/m) with a mean of 1,043 lb/ft (15.2 kN/m); 

(ii) a calculated standard deviation of 175 lb/ft (2.6 kN/m); and (iii) a calculated 

coefficient of variation of 17 percent. The statistical analysis indicates that 

Geosynthetic PP-15 is highly variable in terms of tensile strengths. The unconfined 

tensile strengths of the two geotextiles measured by the two organizations fall in the 

range of the strength data provided by the manufacturer, yet the differences make a 

direct comparison difficult. 

l Confined Modulus at 5 and IO Percent Strains: Figures 43 and 44 present a summary 

plot of the laboratory-measured moduli at 5 and 10 percent strain for the geotextiles 

confined in the two soil materials. The results are generally consistent and indicate 

that: (i) confinement of each soil significantly improves the modulus; (ii) relative to 

the improved modulus, the higher the confining pressure, the greater the 

improvement; and (iii) under the same confining pressure, the confinement effect of 

the beach sand is greater than that of the &y sand. The triaxial results, however, 

indicate a potential slight reduction in stiffness compared with the in-air stiffness at 

low confining pressures. This may be due to inherent variability in the geotextile 

specimen, as previously described. The improvement in moduli at 5 percent strain 

for the nonwoven geotextiles confined in the beach sand obtained by both techniques 

are also compared with those for similar materials obtained by other researchers,as 

shown in figure 45. 

l Confinement EfSect on Strength: Figure 46 presents a summary plot of the laboratorymeasured peak strength for the confined test specimen. The confined extension creep 

device results indicate that there is consistent improvement in the peak strength as a 

result of soil confinement. The triaxial results indicates essentially no increase in 

peak strength. The internal consistency in both test results indicate that these results 

are likely not the result of inherent sample variability, but rather an effect of the 

specific test conditions (i.e., effect of clamping system, specimen geometry, testing 

equipment, etc.). At this stage, however, it is premature to provide a detailed 

evaluation of the observed response. 

Regardless of the detailed observation described above, the results indicate that: (i) 

soil confinement imposes beneficial effects on the stress-strain response of the 

nonwoven geotextile; (ii) a higher confining pressure results in a greater improvement 

of the confined secant modulus; and (iii) the confinement effect of the beach sand is 

greater than that of the silty sand. 

111 
32000 

GEOSYNTHETICS PP-10 AND PP-15 CONFINED IN 

BEACH SAND. 

28000 - 

$ 16000 

mee+~ GeoSyntec: Modulus at 5% strain 

~~~ff3~l Polytechnic: Modulus at 5% strain 

l -*** GeoSyntec: Modulus at 10% strain 

=W-W Polytechnic: Modulus at 10% strain 

0 I I I I I I I I I 

0 

I 

4 8 12 16 20 : 

CONFINING PRESSURE (psi) 

1 lb/ft = 14.59 N/m 

1 psi = 6.89 kPa 

1 

Figure 43. Comparison of GeoSyntec and Polytechnic test results (secant moduli of 

Geosynthetics PP-10 and PP-15 confined in beach sand. 

112 
32000 

28000 

GEOSYNTHETICS PP-10 AND PP-15 CONFINED IN 

SILTY SAND 

0 GeoSyntec: Modulus at 5% strain 

A 24000 

w+em Polytechnic: Modulus at 5% strain 

l MM GeoSyntec: Modulus at 10% strain 

5 

‘*a** Polytechnic: Modulus at 10% strain 

= 20000 

WI 

3 

$ 16000 

I 

l5 12000 

z11 

cn 

8000 

0 

0 4 8 12 16 20 24 

CONFINING PRESSURE (psi) 

1 lb/ft = 14.59 N/m 

1 psi = 6.89 kPa 

Figure 44. Comparison of GeoSyntec and Polytechnic test results (secant moduli of 

Geosynthetics PP-10 and PP-15 confined in silty sand. 

113 
ooooo Christopher et al., 1986 

00000 Christopher et al., 1986 

AAAAA McGown et al., 1984 

00000 Wilson-Fahmy et al., 1993 

-t+t+i- Wilson-Fahmy et al., 1993 

xxxxx wu, 1991 

**I** Boyle, 1995 

***** Boyle, 1995 

- GeoSyntec: Geosynthetic PP-10 in Beach Sand 

=*a** Polytechnic: Geosynthetic PP-15 in Beach Sand 

P / / / / / 

CONFINING PRESSURE (psi) 

1 psi = 6.89 kPa 

Figure 45. Comparison of secant moduli at 5 percent strain for Geosynthetics PP-10 

and PP-15 confined in beach sand obtained by GeoSyntec and 

Polytechnic with data of similar geosynthetic materials reported 

by other researchers. 

114 
3600 

3200 

2800 

n 

-v Cc 

c 2000 

Z 

W 

E 1600 

cn 

0 I I I I I I I I I I I 

0 4 

CONFYhNG 

\ 

Pk2ESSUR1E6 (psi) 

20 : 4 

1 lb/ft = 14.59 N/m 

1 psi = 6.89 kPa 

Figure 46. Comparison of GeoSyntec and Polytechnic test results (peak strengths of 

Geosynthetics PP-10 and PP-15 confined in beach sand and silty sand. 

115 
6.6 SUMMARY COMMENTS AND RECOMMENDATIONS 

The results of the collaborative project provide somewhat comparable results; specifically, 

there is a beneficial effect of confinement on the confined stress-strain behavior of a 

nonwoven geotextile. A detailed comparison of test results indicates that there is a noticeable 

difference between the stress-strain properties of the nonwoven geotextiles obtained by the 

two types of equipment. The difference is likely due to the fact that: (i) the two nonwoven 

geotextiles are highly variable, as suggested by the manufacturer data; and (ii) there are 

significant differences the two test devices. 

It was observed from the test results that the triaxial device works in such a way that a 

potentially significant friction is developed at the soil-geotextile interface at high confining 

pressures. The interface friction causes a nonuniform distribution of tension along the 

geosynthetic specimen similar to the authors’ reported assessment of the pullout test. It is 

difficult to account for the effect of friction on the confined extension properties of 

geosynthetics through an interpretation procedure. The authors believe that it is premature to 

adopt the triaxial-type device for evaluating confined stress-strain properties of geosynthetics 

unless an appropriate procedure is developed to account for the soil-geosynthetic friction 

effect during interpretation and subsequently verified. However, the triaxial device provides 

an alternative for measuring the pullout response of geosynthetics under saturated conditions, 

which cannot be easily simulated in the traditional pullout test device. Soil-geosynthetic 

interaction parameters determined from the triaxial device may have direct applications in 

design and analysis of reinforced soil structures, but additional comparison testing is needed 

prior to adopting this test. 

As indicated previously, the results of the confined extension tests conducted in the modified 

in-soil device were internally consistent. The utilized equipment has been found to be 

appropriate for confined extension tests. As a component of this project, a testing protocol 

for conducting short-term confined extension tests and long-term confined creep tests has 

been developed. At this stage of development, the authors believe that the confined 

extension, also referred to as a confined wide-width device, offers more potential than the 

triaxial-type device. It is recommended that the confined extension testing equipment and the 

testing protocol be utilized to produce, at the very least, a baseline reference for evaluating 

the confined response of geosynthetics. Additional testing is warranted and recommended. 

It is recommended that this additional testing focus on: (i) confined extension for a wide 

range of soil materials; (ii) confined creep at different tensile stress levels; (iii) confined 

creep beyond 1000 hours; (iv) detailed testing of geosynthetics that are used primarily for 

reinforcement; and (v) identifying mechanisms that lead to the understanding of the soil 

confinement effects on the confined response of geosynthetic materials. 

116 
CHAPTER 7 

DEVELOPMENT OF WRITTEN PROTOCOL FOR CONFINED 

EXTENSION/CREEP TESTING 

7.1 OVERVIEW 

The final component of this program is the development of a protocol for conducting 

confined extension and creep tests. The protocol was developed on the basis of chapters 3, 

4, and 5 of this report. The test protocol was written in accordance with the format 

established by the American Society for Testing and Materials (ASTM) for the preparation of 

a standard test method, and is presented in appendix C. 

7.2 DISCUSSION 

Using the confined extension equipment developed and the results of the verification testing 

program, a protocol has been established for conducting confined extension and creep tests. 

The protocol presented in appendix C of this report is essentially a “stand-alone” document. 

Several major factors were considered in the development of this protocol. These factors 

were discussed in the previous sections of this report and are summarized below: 

0 Friction Loss: It was found that the tensile load applied to the front of the 

geosynthetic specimen was not fully transferred to the rear of the geosynthetic 

specimen. The difference between the front and rear loads was mainly caused by the 

mobilized friction between the soil and geosynthetic specimen and specimen clamp. 

The friction loss was minimized by placing steel rollers between the confinement box 

and the supporting table. The overall friction loss should be measured through 

calibration. The friction should be controlled within 2 percent of the anticipated 

maximum load in the confined extension test or the applied creep load in the confined 

creep test in order to achieve a nearly uniform distribution of tensile loads along the 

geosynthetic specimen length. Uniformity should be checked by monitoring the strain 

distribution over the length of a test specimen. 

117 
l Strain Measurement: The tensile strain is to be measured by the use of two tell-tail 

wires connected to the geosynthetic specimen and monitored by electronic 

measurement devices such as LVDTs; however, dial gages could also be used. The 

location of the two tell-tail wires defines the gage length. A gage length of 4 in (102 

mm) should be used for geotextiles. For the geogrids, the gage length should include 

at least two full geogrid apertures but should not be less than 4 in (102 mm) in 

length. In cases where it is necessary to verify the uniformity of the strain 

distribution across the geosynthetic, a minimum of four tell-tails should be mounted 

over the gage length of the test specimen. 

l Pretension Force: In accordance with the procedure established in ASTM D 4595 for 

in-air tensile testing of geosynthetics, a total pretension force equal to 1.25 percent of 

the expected breaking force should be applied to each geosynthetic specimen. 

However, the total pretension force should not be less than 10 lb (45 N) or greater 

than 50 lb (222 N) in any case. The pretension force should be applied to the 

geosynthetic specimen prior to placement of the upper confining soil layer. This 

allows examination of the geosynthetic specimen to assess whether the geosynthetic is 

in uniform contact with the top of the lower confining soil layer. 

l Strain Rate: A constant rate of strain of 10 percent/min should be applied to the 

geosynthetic specimen in the confined extension test. Selection of this constant rate of 

strain is based on the standard loading rate specified in ASTM D 4595. Use of this 

strain rate allows for a direct comparison between the confined and unconfined stressstrain properties of geosynthetics. 

l Aspect Ratio: An aspect ratio of 2: 1 should be used for geotextile specimens. For 

geogrid specimens, a constant aspect ratio cannot be specified for various currently 

available geogrid products. A geogrid specimen should be trimmed in such a way 

that it has a length containing at least two complete apertures in the direction of 

testing (i.e., typically the machine direction) and a width containing at least five ribs 

in the cross-test direction (i.e., typically the cross-machine direction). For any 

geogrid, a minimum width of 6 in (152 mm) is recommended. 

l Initial Loading Rate for Creep Tests: A strain rate of 10 f3 percent/min should be 

used to load each creep test specimen. Selection of this initial loading rate is based 

on the standard loading rate in ASTM D 5262 for conducting unconfined tension 

creep tests of geosynthetics. 

118 
l Confining Soil Thickness: It has been shown that the confined stress-strain curves 

were almost identical for the geotextile specimens when confined in thicknesses of soil 

ranging from 1 to 3 in (25 to 76 mm) and when the geotextile specimens were placed 

at a distance of 2 in (51 mm) away from side walls of the confinement box. For ease 

of the test set-up, a soil thickness of 3 in (76 mm) should be used to assess the fully 

confined response of an g-in- (203-mm-) wide geosynthetic specimen placed within a 

12-in- (305~mm-) wide confinement box. To assess the partially confined response, a 

0.4-in- (41~mm-) thick soil layer should be placed above and below the geosynthetic. 

l Friction Along The Geosynthetic Specimen: It has been shown that the friction along 

the soil-geosynthetic interface cannot be totally eliminated due to the fact that there is 

a significant difference between the failure strains of the confining soil and the 

geosynthetic material. However, the friction along the soil-geosynthetic interface can 

be reduced by imposing low friction boundary conditions to the confining soil similar 

to that which was used by McGown et al. [1982] and Wilson-Fahmy et al. [1993]. 

The proposed test protocol identifies two different test procedures for conducting a 

test. Procedure A consists of a nonlubricated interface between the soil and 

geosynthetic where the test specimen is set up to model a fully confined condition. 

Procedure B consists of a lubricated interface between the soil and geosynthetic to 

model a partially confined condition. The selection of the specific test procedure 

should be based on the designers’ selected design approach. 

7.3 F'UTUREUSE 

As stated, the testing protocol presented in appendix C has been prepared in the format of an 

ASTM standard test method. The protocol in its current state should be offered to the 

ASTM D-35 committee on geosynthetics for consideration as a potential new test method. If 

accepted by the committee, a task group will be formed by ASTM to further review and test 

the method with the hope of eventually approving it as an ASTM standard. 

119 

CHAPTER 8 

CONCLUSIONS AND RECOMMENDATIONS 

8.1 SUMMARY AND CONCLUSIONS 

The objectives of the four-phase research program were to: (i) develop and assess the 

performance of test equipment for evaluating confined stress-strain properties of 

geosynthetics; (ii) establish testing procedures for conducting confined extension and confined 

creep tests on geosynthetics; (iii) verify the performance of the test equipment and confirm 

the validity of the procedures by testing representative geosynthetics; and (iv) develop a 

written protocol for conducting confined extension and confined creep testing. These 

objectives were achieved through the completion of several specific tasks, A brief discussion 

is presented of the most significant conclusions of each task: 

l Literature Review: The literature review identified 12 distinct references in which 

confined extension and/or creep testing equipment and/or test results were described. 

This review indicated that several types of laboratory testing equipment, including the 

pullout device, in-soil test device, and triaxial-type device, have been used to assess 

the confined stress-strain response of geosynthetics. A summary of the test equipment 

and test results reported in the references was presented. The pullout device 

developed by Juran et al. [ 19911, in-soil test device developed by McGown et al. 

[ 19821, and modified triaxial device developed by Ling et al. [1991] were identified 

as having a high potential for measuring a confined response of a geosynthetic that 

can be directly compared to an unconfined response of the geosynthetic in order to 

evaluate the effect of soil confinement. The reported results in these references 

indicate that soil confinement significantly improves the stress-strain properties of 

nonwoven geotextiles but does not significantly affect the stress-strain properties of 

woven geotextiles. 

0 Initial Base-Line Testing: Tests conducted utilizing the pullout device showed that 

there was an effect of soil confinement on the pullout response of various geosynthetic 

products. However, the results from the pullout testing indicate that the confined 

extension pullout test has the following four problems: (i) necking of the nonwoven 

geotextile specimen; (ii) variation of the “mobilized” aspect-ratio during a test; (iii) 

variation of the strain rate along the test specimen; and (iv) arbitrary selection of the 

121 
size of the first element length for interpretation. Because of these problems, it was 

concluded that it would be difficult to “uncouple” the confined stress-strain response 

and provide a measure of the actual confined geosynthetic response. Therefore, the 

pullout test was abandoned in favor of the in-soil apparatus developed by McGown et 

al. [1982], which was anticipated to overcome the problems experienced using the 

pullout testing device. A prototype confined extension testing device, similar to the 

in-soil test apparatus, was subsequently developed. The prototype confined extension 

testing device had an ability to provide: (i) a constant strain rate to a confined 

specimen; and (ii) maintain a constant aspect ratio during testing. 

l Development of Test Equipment: On the basis of the success of the prototype confined 

extension testing device, a test apparatus that could be used for production tests was 

designed, fabricated, and calibrated. The advantages of the test apparatus otherwise 

known as the protocol device fabricated for this project include: (i) ease of the test 

set-up; (ii) well-defined boundary conditions; and (iii) ease of test interpretation. The 

friction along the soil-geosynthetic interface was minimized by placing the entire 

confinement box on steel rollers so that a nearly uniform distribution of tension along 

the specimen length was achieved. Because of this uniform tension distribution, the 

confined stress-strain response of the geosynthetic was readily obtained from the 

measured data and used for a direct comparison with the unconfined response of the 

geosynthetic to evaluate the effect of soil confinement. Tests were conducted under 

constant strain rate and constant tensile load conditions. 

l Verification of Test Equipment: There were five test variables identified in the 

confined extension and confined creep testing program that required verification, 

These variables were: (i) pretension force; (ii) strain rate; (iii) aspect ratio; (iv) initial 

rate of loading for the creep tests; and (v) thickness of the confining soil. The first 

four variables were selected in accordance with ASTM D 4595 (wide-width tensile 

testing of geotextiles) and ASTM D 5262 (unconfined creep testing of geosynthetics). 

The effect of soil thickness on the confined response of geosynthetics was investigated 

through a series of confined extension tests on Geosynthetic PP-10 that was confined 

by various layers of beach sand with thicknesses ranging from 0.4 to 3 in (10 to 76 

mm). The test results indicate that there was little difference when the geosynthetic 

was confined within l-to 3-in- (25- to 76-mm-) thick soil layers. However, the effect 

of soil confinement was reduced when the thickness of the soil layer was reduced to 

0.4 in (10 mm) because cracks developed throughout the thickness of the soil layers, 

A thickness of 3 in (76 mm) was then selected for all production confined extension 

and confined creep tests to provide full confinement. 

122 
l Production Confined Extension and Creep Tests: On the basis of the results of 

verification confined extension and creep tests, production testing was conducted. 

Results based on the following conclusions can be drawn: 

1. Soil confinement significantly improves the moduli and strength of 

Geosynthetic PP-10 (Le., a needle-punched nonwoven geotextile). As the 

confining pressure increases, the moduli and strength of this material similarly 

increases. 

2. Under a constant confining pressure for Geosynthetic PP-10, the confined 

response (Le., modulus and strength) of the geosynthetic specimen in beach 

sand is greater than the response of the geosynthetic specimen in silty sand. 

3. There is a noticeable effect of confinement with respect to the confined 

response for the two woven geotextiles and two geogrids (Geosynthetics PP11, PP-12, PE-13, and PET-14) when confined in the beach sand and in the 

silty sand; the increase in confined moduli at 5 percent strain ranged from 

approximately 5 to 30 percent among Geosynthetics PP- 11, PP-12, PE-13, and 

PET-14 at a normal stress of 20 psi (138 kPa). These increases can be 

considered significant with respect to unconfined moduli of the same materials 

although less significant when compared with the increase of the 5 percent 

moduli for the nonwoven geotextile (Geosynthetic PP-10). 

4. Soil confinement significantly reduced the measured time-dependent total 

strain of Geosynthetic PP-10; the measured total strain reduced in direct 

proportion to the increase at higher confining pressures. 

5. Reduction of measured time-dependent total strains resulting from soil 

confinement for Geosynthetics PP-11, PP-12, PE- 13, and PET- 14 was less 

than that for Geosynthetic PP-10. 

6. Improvement of the confined stress-strain properties for a given geosynthetic 

material is believed to be primarily related to: (i) internal friction between 

fibers or yarns; (ii) alignment of curved fibers or yarns (i.e., tortuosity); and 

(iii) interlocking of soil within openings or apertures, of geosynthetics, 

123 
0 

l 

8.2 

Confined Extension Tests Using a Triaxial-Type Apparatus: The triaxial-type confined 

extension testing device developed at Polytechnic was used for evaluating the confined 

extension responses of Geosynthetic PP-15 and Geosynthetic PP- 16. The results of 

the confined extension tests conducted on Geosynthetic PP-15 are generally consistent 

with those found for Geosynthetic PP-10 at GeoSyntec in that the effect of soil 

confinement is significant and quantifiable. A detailed comparison of test results, 

however, indicates that there is a noticeable difference between the stress-strain 

properties of the nonwoven geotextiles obtained by the two organizations. The 

difference is likely due to the following two facts: (i) the strengths of nonwoven 

geotextiles tested by Polytechnic and GeoSyntec are highly variable, as suggested by 

the manufacturer’s data; and (ii) there are fundamental differences in the test devices. 

The triaxial-type device works in such a way that friction is developed at the soilgeotextile interface, causing a nonuniform distribution of tension along the 

geosynthetic specimen length. The response of the geosynthetic in this device is 

similar to the response in a pullout test. Accordingly, it is difficult to account for the 

effect of friction on the confined stress-strain properties of geosynthetics through an 

interpretation procedure. The authors of this report believe that it is premature to adopt 

the triaxial device for evaluating confined stress-strain properties of geosynthetics. 

Testing Protocol: A written testing protocol has been developed in the format of an 

ASTM standard test method. It is recommended that the testing protocol in its 

current state be offered to the ASTM D-35 committee on geosynthetics for 

consideration as a potential new test method. 

DESIGN IMPLICATIONS 

In the design of geosynthetic-reinforced soil walls and slopes, it is the state-of-practice to use 

the unconfined stress-strain properties of geosynthetic materials to evaluate the short-term 

and long-term stability of the geosynthetic-reinforced structures. The results of this research 

program indicate, that soil confinement imposes beneficial effects on the stress-strain response 

of the nonwoven geotextiles and the other geosynthetic materials tested in the program; 

furthermore, results indicate that the use of unconfined stress-strain properties of these 

geosynthetic materials in the design may be conservative. With specific reference to the 

nonwoven geotextile, the test results indicate that the stiffness is significantly enhanced as a 

result of soil confinement. Use of the unconfined stress-strain properties for the nonwoven 

geotextile in design may be overly conservative. Results of this program indicate that the 

124 
confined response of geosynthetics can be significant in some cases. Therefore, when using 

geosynthetic materials in the design, it is recommended that: 

0 confined extension tests be performed to determine the modulus and peak strength of 

nonwoven geotextiles and other geosynthetic materials; 

0 confined creep tests be performed to determine the long-term strength of the 

nonwoven geotextiles and other geosynthetic materials; 

0 confined extension and/or confined creep tests be performed to obtain serviceability 

values for woven geotextiles and geogrids; and 

0 confined extension and/or confined creep tests be conducted for calibrating 

instrumentation to be used in field monitoring and for assessing input parameters for 

numerical analysis. 

As discussed and supported in this document, the authors believe that the protocol confined 

extension test device is appropriate for assessing the confined properties of geosynthetic 

materials. The testing protocol can be utilized to assess geosynthetic stress-strain 

characteristics under either fully confined or partially confined conditions. The results of this 

study indicate that full confinement provides a larger improvement relative to the unconfined 

response when compared with partial confinement. Depending on the specific design 

condition assessed by the designer, either a fully or partially confined test can be conducted 

using the protocol testing device to obtain parameters to be used in’the design. 

8.3 RECOMMENDATIONS 

The test results from this study regarding the short-term and long-term confined response of 

various geosynthetic materials are encouraging. The test results indicate that soil 

confinement imposes beneficial effects on the stress-strain response of the nonwoven 

geotextile and other geosynthetic materials tested in the program. It is recommended that the 

Federal Highway Administration pursue a more comprehensive study of the confined 

behavior of geosynthetic materials with the use of the protocol confined extension/creep test 

device developed, with the ultimate goal of incorporating the confined stress-strain properties 

into future design procedures. The following recommendations are made to achieve this 

ultimate goal: 

125 
Confined extension tests are recommended to be performed for a wide range of soil 

materials. 

Confined extension tests are recommended to be performed on geosynthetics with the 

use of detailed instrumentation to measure the stiffness (modulus) of the confined 

geosynthetic materials at low strain levels. 

Confined creep tests are recommended to be performed at different tensile stress 

levels, especially at high stress levels to evaluate the confined creep rupture strengths. 

Confined creep tests are recommended to be performed for a duration of 10,000 

hours. 

Detailed tests are recommended to be performed on geosynthetics that are used 

primarily for reinforcement. 

Confined extension and confined creep tests should be conducted under both fully or 

partially confined conditions and the results compared. 

Select geosynthetic materials should be tested using the protocol testing equipment and 

the more complex UCD test device developed by Boyle [1995] and the APSR test 

device developed by Whittle et al. [1993] to assess how the confined extension test 

results relate to the actual response of geosynthetic reinforcement in simulated field 

conditions. 

It should be noted that the protocols developed will likely still result in fairly 

conservative confined creep results, although improved economy will be realized. 

126 
APPENDIX A 

CONFINED EXTENSION TEST RESULTS 

127 
4500 

4000 - 

3500 - 

q 3000 - 

n 

c; 

8 2500 - 

OL 

Lo 2000 - 

5 

G 

z 1500- 

k 

IOOOTEST SERIES NUMBER TIA: GEOSYNTHETIC PP-10 

(MACHINE DIRECTIQN) IN BEACH SAND 

~1888~ IN-AIR 

H-W-H IN BEACH SAND AT IO psi 

- IN BEACH SAND AT 20 psi 

SPECIMEN WIDTH: 8 in 

SPECIMEN LENGTH: 5 in 

GAGE LENGTH: 4 in 

STRAIN RATE: lO%/min 

0 5 10 15 20 25 30 35 40 45 E 3 

STRAIN (w) 

1 in. = 25.4 mm 

= 14.59 N/m 

6.895 kPa 

Figure A-l. Tensile force versus strain response for Geosynthetic PP-10 confined 

in beach sand. 

128 
12000 I 1 TEST SERIES NUMBER T2A: GEOSYNTHEK PP-11 

(CROSS-MACHINE DiRECTIoN) lN BEACH SAND 

10000 - 

B 8000- 

n G 

8 

!i%j 6000- 

IL 

!3 

E 2 4000- 

r 

2000 - 

- IN-AIR 

- IN BEACH SAND AT 10 psi 

- IN BEACH SAND AT 20 psi 

SPECIMEN WIDTH: 8 in 

SPECIMEN LENGTH: 5 in 

GAGE LENGTH: 4 in 

STRAlN RATE: lO%/min 

00 

0 2 4 6 8 10 12 14 16 18 : 0 

STRAIN (w> 

1 in. = 25.4 mm 

= 14.59 N/m 

= 6.895 kPo 

Figure A-2. Tensile force versus strain response for Geosynthetic PP-11 confined 

in beach sand. 

129 
TEST SERIES NUMBER T3A: GEOSYNTHETIC PP-12 

(MACHINE DIRECTION) IN BEACH SAND 

5000 - 

% 4000 - 

G 

8 

g 3000 - 

G 

3 

iz 

z 2000 - 

F 

IOOOM IN-AIR 

- IN BEACH SAND AT 10 psi 

- IN BEACH SAND AT 20 psi 

SPECIMEN WIDTH: 8 in 

SPECIMEN LENGTH: 5 in 

GAGE LENGTH: 4 in 

STRAIN RATE: 1 O%/min 

STRAIN (w) 

1 in. = 25.4 mm 

= 14.59 N/m 

= 6.895 kPa 

Figure A-3. Tensile force versus strain response for Geosynthetic PP-12 confined 

in beach sand. 

130 
8000 

c 7000 

s 

= 6000 

TEST SERIES NUMBER T4A: GEOSYNTHETIC PE-13 

(MACHINE DIRECTION) IN BEACH SAND 

- IN-AIR 

- IN BEACH SAND AT 10 psi 

- IN BEACH SAND AT 20 psi 

SPECIMEN WIDTH: 5 ribs (4.4 in) 

SPECIMEN LENGTH: 2 apertures (13.1 

GAGE LENGTH: 2 a ettures (13.1 in) 

in) 

STRAIN RATE: lO%/!nin 

0 2 4 6 8 10 12 14 1 

STRAIN (w) 

1 in. = 25.4 mm 

= 14.59 N/m 

= 6.895 kPa 

Figure A-4. Tensile force versus strain response for Geosynthetic PE13 confined 

in beach sand. 

131 
11000 1 

10000 

9000 Ii -I 

- 8000- 

c 

> 7000- ;3 

8 6000- 

f5 k 5000- 

Y i7j 4000- 

z 

)- 3000- 

2000 

1000 1 00 

0 2 4 6 8 10 12 14 I 

STRAIN (w) 

TEST SERIES NUMBER T5A: GEOSYNTHETIC Pm-14 

(MACHINE DiREcno~) IN BEACH SAND 

- IN-AIR 

- IN BEACH SAND AT 10 psi 

- IN BEACH SAND AT 20 psi 

6 

1 in. = 25.4 mm 

= 14.59 N/m 

= 6.895 kPa 

Figure A-5. Tensile force versus strain response for Geosynthetic PET-14 

confined in beach sand. 

132 
4500 

4000 

3 

8 2500 

5 

IL 2000 

41 

G 

z 1500 

F 

1000 

500 

0 

TEST SERIES NUMBER TlB: GEOSYNTHETIC PP-10 

(MACHINE ~l~EcnoN) IN sm SAND 

w IN-AIR 

- IN SILTY SAND AT 10 psi 

- IN SILTY SAND AT 20 psi 

SPECIMEN WIDTH: 8 in 

SPECIMEN LENGTH: 5 in 

GAGE LENGTH: 4 in 

STRAIN RATE: 1 Ow/min 

STRAIN (w) 

1 in.-= 25.4 mm _ 

= 14.59 N/m 

6.895 kPa 

Figure A-6. Tensile force versus strain response for Geosynthetic PP-10 confined 

in silty sand. 

133 
10000 - 

5 8000- 

e 

8 

E 6000 - 

kl 

!z 4000- 

F 

2000 - 

TEST SERIES NUMBER T2B: GEOSYNTHETlC PP-11 

(CROSS-MACHINE DIRECTION) IN SILTY SAND 

~~~880 IN-AIR 

- IN SILTY SAND AT 10 psi 

- IN SILTY SAND AT 20 psi 

SPECIMEN WIDTH: 8 in 

SPECIMEN LENGTH: 5 in 

GAGE LENGTH: 4 in 

STRAIN RATE: lO%/min 

STRAIN (w) 

1 in. = 25.4 mm 

= 14.59 N/m 

6.895 kPa 

Figure A-7. Tensile force versus strain response for Geosynthetic PP-11 coufined 

in silty sand. 

134 
6000 

5000 

- 

q4000 

4 G 

ow 

5 3000 

L 

w 

1 

g 2000 

2 

1000 

C 

TEST SERIES NUMBER T3l3: GEOSYNTHETIC PP-12 

(MACHINE D~REC~~N) IN BEACH SAND 

w IN-AIR 

- IN SILTY SAND AT 10 psi, 

- IN SILTY SAND AT 20 psi 

SPECIMEN WIDTH: 8 in 

SPECIMEN LENGTH: 5 in 

f?Al!F I FNPTH* A in - 

I I I I I I I I I I I 

4 8 12 16 20 : 

STRAIN (w) 

1 in. = 25.4 mm 

= 14.59 N/ 

6.895 kPa 

4 

n 

Figure A-8. Tensile force versus strain response for Geosynthetic PP-12 confined 

in silty sand. 

135 
10000 

TEST SERIES NUMBER T4B: GEOSYNTHETIC PE-13 

9000 (MACHINE r11~1xnoN) IN slLTy SAND 

8000 

- 

- IN-AIR SILTY SAND AT 10 

IN SILM SAND AT 20 

psi 

- psi 

c 7000 

s 

= 6000 

6 

i? K5000 

3 4000 

z 

P 3000 

2000 

1000 

0 

0 2 4 6 8 IO 12 14 

STRAIN (w) 

1 in. = 25.4 mm _ 

1 Ib/ft =s 14j59kp~/m 

1 psi = . 

Figure A-9. Tensile force versus strain response for Geosynthetic PE13 confined 

in silty sand. 

136 
11000 1 

10000 

9000 

1 

- 8000 

c 

> 7000 5 3 

TEST SERIES NUMBER T5B: GEOSYNTHETIC PET-14 

(MACHINE DIRECTION) IN SILTY SAND 

eeeea IN-AIR 

- IN SlLlY SAND AT 10 psi 

- IN SILTY SAND AT 20 psi 

SPECIMEN WIDTH: 5 ribs (4.8 in) 

SPECIMEN LENGTH: 2 apet-hres (7,7 in) 

‘H: 2 aoertures (7.7 I 

K 8 6000 2 5000 3 i7j 4000 El I- 3000 

2000 

I I I I I I I I I I I I I I 

0 2 4 6 8 10 12 14 ' 

STRAIN (w) 

6 

1 in. = 25.4 mm 

= 14.59 N/m 

6.895 kPa 

Figure A-10. Tensile force versus straiu response for Geosynthetic PET-14 

confined in silty sand. 

137 
APPENDIX B 

CONFINED CREEP TEST RESULTS 

138 
32 

TEST SERIES NUMBER CIA: GEOSYNTHETIC PP-10 

IN MACHINE DIRECTION UNDER 25% OF 

28- ULTlMATE LOAD 

24 

eeeee IN-AIR 

- IN BEACH SAND AT 10 

- IN BEACH SAND AT 20 

psi 

- IN BEACH SAND AT 10 

psi 

psi 

20 

sic 

Z 16 

is I- 

(f) 12 

8 

SPECIMEN WIDTH: 8 in 

SPECIMEN LENGTH: 5 in 

4 

GAGE LENGTH: 4 in 

0 t I I I I llll~ I I I I llll~ I I llllll( I I Illlll~ I lllllr 

10 --2 10 -' 1 

TIME 

IO2 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-l. Strain versus thne response for Geosynthetic PP-10 confined in 

beach sand. 

139 
lo2 

TEST SERIES NUMBER CIA: GEOSYNTHETIC PP-IO 

10 IN MACHINE DIRECTION UNDER 25% OF 

z 

ULTIMATE LOAD 

-5 1 w IN-AIR 

25 - IN BEACH SAND AT 10 psi 

- IN BEACH SAND AT 20 psi 

* IN BEACH SAND AT 10 psi 

SPECIMEN WIDTH: 8 in 

SPECIMEN LENGTH: 5 in 

GAGE LENGTH: 4 in 

lo-’ 1 I I I I llll( I I I I llll( I l I I Ill11 I ‘I I lllll( I I I Ill1 T 

10 -2 IO -' 1 10 IO2 IO3 

TIME (h) 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-2. Incremental strain rate versus time response for Geosynthetic PP-10 

confined in beach sand. 

140 
103g 

TEST SERIES NUMBER CIA: GEOSYNTHETIC PP-IO 

IN MACHINE DIRECTION UNDER 25% 01 

n ULTIMATE LOAD 

c 1n 7 ‘E IU’ w IN-AIR 

-2 

- IN BEi.-. KH SAND AT 10 psi 

- 

4n - IN BEACH si tND AT 20 psi 

IV - IN BEACH SAND AT 10 psi 

P 2 1 

z 10-l 

i55 

6 1p 

a 

2 1o-3 

iii I 

Id lo-$ (1 L 

is 

z 1cr5 4 1” 

SPECIMEN WIDTH: 8 in 

10 -6 ” tSPECIMEN LENGTH: 4 in 5 in 

GAGE LENGTH: 

low7 i 1 

I I I I I -1 I I I I I I I I I 

0 4 8 12 16 20 24 28 : 

TOTAL STRAIN (w) 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-3. Incremental strain rate versus strain response for Geosynthetic 

PP-10 confined in beach sand. 

141 
TEST SERIES NUMBER C2A: GEOSYNTHETIC PP-11 

IN CROSS-MACHINE DIRECTION UNDER 50% OF 

ULTIMATE LOAD 

- IN-AIR 

- IN BEACH SAND AT 10 psi 

- IN BEACH SAND AT 20 psi 

- IN BEACH SAND AT 10 psi 

SPECIMEN WIDTH: 8 in 

SPECIMEN LENGTH: 5 in 

GAGE LENGTH: 4 in 

1 IO 

TIME (h) 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-4. Strain versus time response for Geosynthetic PP-11 confined in 

beach sand. 

142 
1 

TEST SERIES NUMBER C2Az GEOSYNTHErIC PP-11 

IN CROSS-MACHINE DlRECTlON UNDER 50% OF 

ULTlMATE LOAD 

0 

0 

0 

0 

0 

3EACH SAND AT 10 psi 

3EACH SAND AT 20 psi 

- ii BEACH SAND AT 10 psi 

-l- 

-2, 

-3, 

4 

SPECIMEN WIDTH: 8 in 

SPECIMEN LENGTH: 5 in 

GAGE LENGTH: 4 in 

-5 

I I I lllll~ I I I I llll~ I I I I Ill11 I I I I Ill11 I IlllTl 

10 -2 10 -' 1 

TIME 

IO2 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-5. Incremental strain rate versus time response for Geosynthetic PP-11 

confined in beach sand. 

143 
10'3 

TEST SERIES NUMBER C2Az GEOSYNTHEI-IC PP-11 

IN CROSS-MACHINE DIRECTION UNDER 5oW OF 

T 10% ULTIMATE LOAD 

.- 

E 

\ t3eee.a IN-AIR 

-!!s - IN BEACH SAND AT 

1 

10 psi 

E IN BEACH SAND AT 20 psi 

W - IN BEACH SAND AT 10 psi 

Is 

z 10-l-g 

- 

$ lm lo-?? 

SPECIMEN WIDTH; 8 in 

SPECIMEN LENGTH: 5 in 

2 GAGE LENGTH: 4 in 

2 

g 1o-J% 

!z - 

10 -4r 

10 -+ II II II II II II II II 11 1 

0 2 4 6 8 10 12 14 16 18 ; 

TOTAL STRAIN (w ) 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-6. Incremental strain rate versus strain response for Geosynthetic 

PP-11 confined in beach sand. 

144 
32 

TEST SERIES NUMBER C3Az GEOSYNTHETIC PP-12 

IN MACHINE DIRECTION UNDER 50% OF 

U LTI MATE LOAD 

24 w IN-AIR 

- IN BEACH SAND AT 10 psi 

- IN BEACH SAND AT 20 psi 

g20 

z SPECIMEN WIDTH: 8 in 

z SPECIMEN LENGTH: 5 in 

g 16 GAGE LENGTH: 4 in 

10 -2 10 -' 1 

TIME 

IO2 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-7. Strain versus time response for Gosynthetic PP-12 confined in 

beach sand. 

145 
F 10 

.- 

E \ 

25 1 z 

F 

is 

z 10-l-g 

- 

$ 

ix 

a 

10 -2z 

!z 

; lO"z 

P - 

10 -4-g 

TEST SERIES NUMBER C3Az GEOSYNTHEl-IC PP-1 

IN MACHINE DIRECTION UNDER 50% OF 

ULTlMATE LOAD 

k M IN-AIR 

- IN BEACH SAND AT 10 psi 

- IN BEACH SAND AT 20 psi 

SPECIMEN WIDTH: 8 in 

SPECIMEN LENGTH: 5 in 

GAGE LENGTH: 4 in 

2 

IO" 1 I I I Illll~ I I I lllll~ I I I lllll( I I Illlll~ I llllll10 a 10 -’ 1 10 IO2 IO" 

TIME (h) 

1. in = 25.4 mm 

li psi = 6.895 kPa 

Figure B-8. Incremental strain rate versus time response for Geosynthetic PP-12 

confined in beach sand. 

146 
103S 

TEST SERIES NUMBER C3Az GEOSYNTHEl-IC PP-12 

- lop-g 

IN MACHINE DIRECTION UNDER 50% OF 

ULTlMATE LOAD 

.- 

E aeeea IN-AIR 

3 IQ 

- IN BEACH SAND AT 10 psi 

- IN BEACH SAND AT 20 psi 

g 12 SPECIMEN WIDTH: 8 in 

SPECIMEN LENGTH: 5 in 

Z - GAGE LENGTH: 4 in 

$ 

lz 

10 -‘z 

10 -6 I I I I I I I I I I I 

0 4 8 12 16 20 

TOTAL STRAIN (w ) 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-9. Incremental strain rate versus strain response for Geosynthetic 

PP-12 confined in beach sand. 

147 
16 

TEST SERIES NUMBER C4A: GEOSYNTHEI-IC PE-13 

IN MACHINE DIRECTION UNDER 5oW OF 

14 ULTlMATE LOAD 

12 - IN-AIR 

- IN BEACH SAND AT 10 psi 

- IN BEACH SAND AT 20 psi 

2 SPECIMEN WIDTH: 5 ribs (4.4 in) 

SPECIMEN LENGTH: 2 apertures (13.1 

GAGE LENGTH: 1 aperture (6.6 in) 

in) 

1 10 

TIME (h) 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-10. Strain versus time response for Geosynthetic PP-13 confined in 

beach sand. 

148 
lo2 

TEST SERIES NUMBER C4A: GEOSYNTHETIC PE-13 

IN MACHINE DIRECTION UNDER 50% OF 

U LTI MATE LOAD 

eeew~ IN-AIR 

- IN BEACH SAND AT 10 psi 

- IN BEACH SAND AT 20 psi 

z 10-l 

- 

iis 

ii 

d 

10 -2z 

t 

; 1o-3z 

5 

Z - 

lo-+% 

10m5 i I I I I Ill11 I I I I llll~ I I I I Illl~ I I Illlll~ I IllIf l-r 

10 -2 10 -' 1 10 IO2 IO3 

TIME (h) 

SPECIMEN WIDTH: 5 ribs (4.4 in) 

SPECIMEN LENGTH: 2 apertures (13.1 

GAGE LENGTH: 1 aperture (6.6 in) 

in) 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-11. Incremental strain rate versus time response for Geosynthetic PE13 

confiued in beach sand. 

149 
n 

.- 

E 

\ 

25 

P 

s 

1 

1 TEST SERIES NUMBER C4A: GEOSYNTHErlC PE-13 

-I 

10 2x 

IN MACHINE DIRECTION UNDER 50% OF 

ULTlMATE LOAD 

m IN-AIR 

10 E 

- IN BEACH SAND AT IO 

- IN BEACH SAND AT 20 

12 

0 -l0 -3- 

0 -4- 

i SPECIMEN WIDTH: 5 ribs (4.4 in) 

- SPECIMEN LENGTH: 2 apertures (13.1 

- GAGE LENGTH: 1 aperture (6.6 in) 

in) 

0 -5 

I I I I I I I I I I I I r 

0 2 4 6 8 10 12 

TOTAL STRAIN (w) 

psi 

psi 

Ii 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-12. Incremental strain rate versus strain response for Geosynthetic 

PE13 confined in beach sand. 

150 
9 

TEST SERIES NUMBER C5A: GEOSYNTHl3C PET-14 

IN MACHINE DIRECTION UNDER 60% OF 

ULTlMATE LOAD 

eeeee IN-AIR 

- IN BEACH SAND AT 10 psi 

- IN BEACH SAND AT 20 psi 

6 

1 IO 

TIME (h) 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-13. Strain versus time response for Geosynthetic PET-14 confined in 

beach sand. 

151 
1 

TEST SERIES NUMBER C5A: GEOSYNTHETlC Pm-14 

IN MACHINE DIRECTKIN UNDER 6th OF 

IO ULTIMATE LOAD 

eeeee IN-AIR 

1 - IN BEACH SAND AT 10 psi 

- IN BEACH SAND AT 20 psi 

0 -1 SPECIMEN WIDTH: 5 ribs (4.8 in) 

SPECIMEN LENGTH: 2 apertures (7.7 in) 

GAGE LENGTH: 1 aperture (4.0 in) 

0 -2 

1 IO 

TIME (h) 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-14. Incremental strain rate versus time response for Geosynthetic 

PET-14 confined in beach sand. 

152 
TEST SERIES NUMBER C5A: GEOSYNTHEllC PET-14 

IN MACHINE DIRECTION UNDER 60% OF 

ULTIMATE LOAD 

0 IN-AIR 

- IN BEACH SAND AT 10 psi 

- IN BEACH SAND AT 20 psi 

SPECIMEN WIDTH: 5 ribs (4.8 in) 

SPECIMEN LENGTH: 2 apertures (7.7 in) 

GAGE LENGTH: 1 aperture (4.0 In) 

10-y I 1 I 1 I 11 i-1 I 1 I ’ I I I I I ’ 

0123456789' 

TOTAL STRAIN (%) 

0 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-15. Incremental strain rate versus strain response for Geosynthetic 

PET-14 confined in beach sand. 

153 
32 

28 

TEST SERIES NUMBER Cl B: GEOSYNTHErlC PP-10 

IN MACHINE DIRECTION UNDER 25% OF 

ULTlMATE LOAD 

24 

m IN-AIR 

- IN SlLlY SAND AT 10 

- IN SILlY SAND AT 20 

psi 

psi 

20 

2 

Z 16 

i?s 

i.z 

12 

8 

SPECIMEN WIDTH: 8 in 

4 

SPECIMEN LENGTH: 5 in 

GAGE LENGTH: 4 in 

1 10 

TIME (h) 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-16. Strain versus time response for Geosynthetic PP-10 confined in silty 

sand. 

154 
TEST SERIES NUMBER Cl B: GEOSYNTHETIC PP-10 

IN MACHINE DIRECTION UNDER 25% OF 

ULTlMATE LOAD 

E IN-AIR IN SILTY SAND AT IO psi 

- IN SlLrY SAND AT 20 psi 

p 10-l 

$ 

'+ 1o-2 

ii! lo IO4 

s 

- i 

5 lo-$ 

zi 

g lo+ 

-I 

10 -I 

-4 

SPECIMEN WIDTH: 8 in 

SPECIMEN LENGTH: 5 in 

GAGE LENGTH: 4 in 

10m7 i I I 111111~ l I Ill1111 I I I I Illl~ I I I I Illll I IllIn 

I 

IO -2 IO -' 1 10 10 L IO" 

TIME (h) 

1 in = 25,4 mm 

1 psi = 6.895 kPa 

Figure B-17. Incremental strain rate versus time response for Geosynthetic PP-10 

confined in silty sand. 

155 
- il 10” 

TEST SERIES NUMBER Cl B: GEOSYNTHEl-IC PP-10 

IN MACHINE DIRECTION UNDER 25% OF 

ULTIMATE LOAD 

- 

E 

itis 1 

$10-l 

F fl IO" 

d !Ig 1o-s 

ii lo-$ 

f!5 

z 1o-5 

10 -I' 

IO -' 

0 

I 

- IN-AIR 

- IN SILTY SAND AT 

- IN SILTY SAND AT 

SPECIMEN WIDTH: 8 in 

SPECIMEN LENGTH: 5 in 

GAGE LENGTH: 4 in 

IA I I I I I - -1 I I I I I I I 

4 8 12 16 20 24 

TOTAL STRAIN (%) 

10 psi 

20 psi 

1 in = 25,4 mm 

1 psi = 6.895 kPa 

Figure B-18. Incremental strain rate versus strain response for Geosynthetic 

PP-10 confined in silty sand. 

156 
16 

14 

z I2 

Ti E 10 

cweee IN-AIR 

- IN SILTY SAND AT 10 psi 

- IN SILTY SAND AT 20 psi 

cweee IN-AIR 

- IN SILTY SAND AT 10 

- IN SILTY SAND AT 20 

psi 

psi 

SPECIMEN WIDTH: 8 in 

SPECIMEN LENGTH: 5 in 

GAGE LENGTH: 4 in 

SPECIMEN WIDTH: 8 in 

SPECIMEN LENGTH: 5 in 

GAGE LENGTH: 4 in 

6 

4 

2 

T 

10 -2 10 -’ 1 IO IO2 IO3 

TIME (h) 

TEST SERIES NUMBER C2B: GEOSYNTHETIC GEOSYNTHETIC PP-11 

IN CROSS-MACHINE CROSS-MACHINE DIRECTION DIRECTION UNDER 50% OF 

U LTl MATE LOAD 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-19. Strain versus time response for Geosynthetic PP-11 confined in silty 

sand. 

157 
n 

c _- 

10 -'z 

IO -2E 

10 -sz 

10 -4-g 

10 +j-- 

TEST SERIES NUMBER C2B: GEOSYNTHErIC PP-11 

IN CROSS-MACHINE DIRECTION UNDER 5oW OF 

ULlItvlATE LOAD 

v IN-AIR 

- IN SILTY SAND AT 10 psi 

- IN SILTY SAND AT 20 psi 

LENGTH: 5 in 

4GE LENGTH: 4 in 

I I llllll~ I I I I Ill11 I I llllll~ I I Illlll~ I lllllr 

IO -2 10 -' 1 IO IO2 IO= 

TIME (h) 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-20. Incremental strain rate versus time response for Geosynthetic Pk-11 

confined in silty sand. 

158 
102=J 

TEST SERIES NUMBER C2B: GEOSYNTHETIC PP-11 

IN CROSS-MACHINE DIRECTION UNDER 5oW OF 

ULTIMATE LOAD 

eeeea IN-AIR 

W 

I -g 

10 -‘z 

10 -2E 

10 -3z 

10 -4B 

c 

- IN SILTY SAND AT 10 psi 

- IN SILTY SAND AT 20 psi 

SPECIMEN WIDTH: 8 in 

SPECIMEN LENGTH: 5 in 

1 11 &AGE LENGTH: 4. h 

lO”i I 1 I 1 l 1 I 1 l 1 l 1 l 1 l 1 l 1 I 

0 2 4 6 8 10 12 14 16 18 : 

TOTAL STRAIN (w) 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-21. Incremental strain rate versus strain response for Geosynthetic 

PP-11 confined in silty sand. 

159 
TEST SERIES NUMBER C3B: GEOSYNTHFTIC PP-12 

IN MACHINE DIRECTION UNDER 50% OF 

28 ULTIMATE LOAD 

24 

A -i 

CSBBBEI IN-AIR 

- IN SILTY SAND AT 10 psi 

- IN SILTY SAND AT 20 psi P 

24 CSBBBEI IN-AIR 

- IN SILTY SAND AT 10 psi 

x20 

- IN SILTY SAND AT 20 psi 

Z SPECIMEN WIDTH: 8 in 

zz SPECIMEN LENGTH: 5 in 

El6 GAGE LENGTH: 4 in 

a 

6 12 

I8 

IT 

10 -2 IO -' 1 IO 10 2 IO3 

TIME (h) 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-22, Strain versus time response for Geosynthetic PP-12 confined in silty 

sand. 

160 
TEST SERIES NUMBER C3B: GEOSYNTHETIC PP-12 

IN MACHINE DIRECTION UNDER 50% OF 

ULTlMATE LOAD 

w IN-AIR 

- IN SILTY SAND AT 10 psi 

- IN SILTY SAND AT 20 psi 

SPECIMEN WIDTH: 8 in 

SPECIMEN LENGTH: 5 in 

GAGE LENGTH: 4 in 

IO -fl I I I Illll~ I I I I Ill11 I I I I Ill11 I I I IllIll I I Illlr 

10 -2 10 -’ 1 10 IO2 IO" 

TIME (h) 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-23. Incremental strain rate versus time response for Geosynthetic PP-12 

confined in silty sand. 

161 
TEST SERIES NUMBER C3B: GEOSYNTHEIIC PP-12 

- lo"? 

IN MACHINE DIRECTION UNDER 5Qw OF 

ULTlMATE LOAD 

eeeee IN-AIR 

- IN SILTY SAND AT 10 psi 

1 - IN SILTY SAND AT 20 psi 

Z - 

$ 

bi 

10 -' 

d 10-2 

!z 

i!i 

& IO5 

2 - ~ 

SPECIMEN WIDTH: 8 inSPECIMEN LLNGiHi, 5 In 

. 78 GAGE LENGT . 

IO -4-g 

IO -6 I I I I I I I I I I I I I 

0 4 

I 

8 

I 

12 16 20 24 28 Z 

TOTAL STRAIN (w ) 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-24. Incremental strain rate versus strain response for Geosynthetic 

PP-12 confined in silty sand. 

162 
16 

TEST SERIES NUMBER C4B: GEOSYNTHEl-IC PE-13 

14 

IN MACHINE DIRECTION UNDER 50% OF 

ULTlMATE LOAD 

12 OBBBF) IN-AIR 

- IN SILTY SAND AT 10 ps 

- IN SILTY SAND AT 20 ps 

IO A 

8 

z 8 

ii!! 

Li 

6 

2 SPECIMEN WIDTH: 5 ribs (4.4 in) 

SPECIMEN LENGTH: 2 apertures (13.1 

GAGE LENGTH: 1 aperture (6.6 in) 

in) 

0 T 

1 10 IO2 IO3 

TIME (h) 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-25. Strain versus time response for Geosynthetic PE13 coufined in silty 

sand. 

163 
TEST SERIES NUMBER C4B: GEOSYNTHETIC PEIN MACHINE DIRECTION UNDER 50% OF 

‘0 ULTlMATE LOAD 

= IN-AIR 

- IN SILTY SAND AT 10 osi 

0 -l0 -2, 

0 -3, 

a 

0 --+ SPECIMEN WIDTH: 5 ribs (4.4 in) 

SPECIMEN LENGTH: 2 apertures (13.1 

GAGE LENGTH: 1 aperture (6.6 in) 

in) 

813 

I I I I llll~ I I I I Ill11 I I I I llll~ I I Illlll~ I llllll 

10 -2 10 -' 1 IO 

TIME (h) 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-26. Incrernent.al strain rate versus time response for Geosynthetic PE13 

confined in silty sand. 

164 
IO33 

TEST SERIES NUMBER C4B: GEOSYNTHETIC PE-13 

A 102-g IN MACHINE DIRECTION UNDER 50% 0.F 

ULTIMATE LOAD 

.- 

L 0888f) IN-AIR 

- IN SlLlY SAND AT IO psi 

- IN SILTY SAND AT 20 psi 

IP -44 

rl 

J 3 SPECIMEN rk;WyH 5 

SPECIMEN 

2ri~p~~~~en~l 3 ’ , . * ,n) 

- 

10 -5 

GAGE LENGTH: 1 aperture (6.6 in) 

I I I I I I I I I I I I I I I 

0 2 4 TO:AL 8 10 12 14 1 

STRAIN (w) 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-27. Incremental strain rate versus strain response for Geosynthetic 

PE13 confined in silty sand. 

165 
-IN SILTYSANDAT IO ’ 

- IN SILTY S4ND AT 20 ,“:; 

0 ; , , , I,,,,, , , , ,,,,,, , , ,-J- ,,,,, 

IO -2 IO -* 1 

I I I I ir,q I I 

IO 

TIME (h) 

IO 2 

SPECIMEN WIDTH: 5 ribs (4.8 in) 

SPECIMEN LENGTH: 2 apertures (7.7 in) 

GAGE LENGTH: 1 aperture (4.0 in) 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

166 
TEST SERIES NUMBER C5B: GEOSYNTHfllC PET-14 

IN MACHINE DIRECTION UNDER 60% OF 

10 ULTIMATE LOAD 

- IN-AIR 

- IN SILlY SAND AT 10 psi 

- IN SILTY SAND AT 20 psi 

SPECIMEN WIDTH: 5 ribs (4.8 in) 

SPECIMEN LENGTH: 2 apertures (7.7 in) 

GAGE LENGTH: 1 aperture (4.0 in) 

-2, 

-3, 

-4- 

-c -0 I 

I I I I I Ilil~ I I I I Ilil~ I I I I Illl~ I I llllll~ I I I1111 

1o-2 10-l 1 10 lo2 IO" 

TIME (h) 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure B-29. Incremental strain rate versus time response for Geosynthetic 

PET-14 confined in silty sand. 

167 
TEST SERIES NUMBER C5B: GEOSYNTHFTIC PET-14 

IN MACHINE DIRECTION UNDER 60% OF ULTIMATE LOAD 

c)8880 IN-AIR 

- IN SILTY SAND AT 10 psi 

- IN SILTY SAND AT 20 psi 

SPECIMEN WIDTH: 5 ribs (4.8 in) 

SPECIMEN LENGTH: 2 apertures (7.7 in) 

GAGE LENGTH: 1 aperture (4.0 in) 

10-y I I I 1 I 1 I 1-1 1 I I I I I I I I I 

0123456789' 

TOTAL STRAIN (w) 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

D 

Figure B-30. Incremental strain rate versus strain response for Geosynthetic 

PET-14 confined in silty sand. 

168 
APPENDIX C 

PROTOCOL FOR CONFINED 

EXTENSION/CREEP TESTING 

169 
TEST PROTOCOL 

EVALUATING THE CONFINED EXTENSION/CREEP 

BEHAVIOR OF GEOSYNTHETICS FOR 

HIGHWAY APPLICATIONS 

1. Scope 

1.1 This test method is intended for use in determining the confined extension 

and/or confined creep behavior of geosynthetics used in highway applications when subjected 

to a sustained normal stress and tensile stress loading. This test method is applicable for 

geotextiles and geogrids. 

1.2 The test method can be used to measure the tensile force and strain properties 

of a geosynthetic specimen confined and tested at a constant deformation (i.e., strain) rate; 

the test method can also be used to measure the total strain of the geosynthetic test specimen 

tested under a constant sustained tensile load. 

1.3 The test method includes procedures for measuring the extension and creep 

behavior of a geosynthetic under two different confinement conditions. The selection of the 

test procedure should be based on the designer’s selected design approach. Procedure A 

provides full confinement to the soil and the geosynthetic by using a thick soil specimen and 

a nonlubricated interface between the soil and the confining air bladder; Procedure B 

provides partial confinement to the soil and the geosynthetic by using a thin soil specimen 

and a lubricated interface between the soil and the confining air bladder. 

1.4 The test method also provides guidance on the calculation and presentation of 

test data. In the extension test, data are used to calculate tensile strength, strain, tensile 

modulus (i.e., initial tensile modulus, offset tensile modulus, and secant tensile modulus), 

and force versus strain curves. In the creep test, data are used to calculate total strain, 

incremental strain rate, total strain versus time curves, incremental strain rate versus time 

curves, and incremental strain rate versus total strain curves. 

1.5 The values stated in SI units are to be regarded as the standard. The values 

given in parentheses are for information only. Within this protocol, the use of the term 

strain is considered as standard. 

170 
1.6 This test protocol may involve hazardous materials and equipment. This test 

protocol does not address all of the health and safety problems associated with its use when 

hazardous materials are involved. It is the responsibility of the user of this test protocol to 

establish appropriate health and safety practices and determine the applicability of regulatory 

limitations prior to use. 

2. Referenced Documents 

2.1 ASTM Standards: 

D 123 

D 653 

D 1776 

D 1909 

D 2435 

D 2990 

D 4354 

D 4439 

D 4595 

D 5262 

E6 

Terminology Relating to Textile Materials 

Standard Terminology Relating to Soil, Rock, and Contained 

Fluids 

Practice for Conditioning Textiles for Testing 

Table of Commercial Moisture Regains for Textile Fibers 

Standard Test Method for One-Dimensional Consolidation 

Properties of Soils 

Test Methods for Tensile, Compressive, and Flexural Creep and 

Creep Rupture of Plastics 

Practice for Sampling of Geotextiles for Testing 

Terminology for Geosynthetics 

Test Method for Tensile Properties of Geotextiles by the Wide 

Width Strip Method 

Standard Test Method for Evaluating the Unconfined Tension 

Creep Behavior of Geosynthetics 

Terminology Relating to Methods of Mechanical Testing 

171 
3. Terminology 

3.1 Definitions - For definitions of other terms used in this standard, refer to 

Terminology D 123, D 653, D 4439, and E 6. 

3.2 Descriptions of Terms Specific to This Standard: 

3.2.1 atmosphere for testing geosynthetics, n. - air maintained at a relative humidity 

between 50 to 70 percent and temperature of 21 O +2”C (70” f4 OF). 

3.2.2 confined extension tensile test, n. - an extension test in which a geosynthetic 

material is stretched in one direction while under confinement to determine the force versus 

strain characteristics, the tensile strength, tensile modulus (i.e., initial, offset, and/or secant), 

and the total strain. 

3.2.3 creep, n. - the time-dependent increase in accumulated strain in a material 

resulting from an applied constant force while under confinement (i.e., a confined creep 

test). 

3.2.4 creep strain, n. - the total strain (i.e., extension divided by gage length) at any 

given time produced by the applied tensile load during a confined creep test. 

3.2.5 corresponding force, n. - the force associated with a specific strain on the 

force per unit width strain curve. 

3.2.6 design load, n. - the load at which the geosynthetic is required to operate in 

order to perform its intended function. 

3.2.7 extension, n. - the change in the initial gage length of the geosynthetic 

specimen during the confined extension or confined creep test. 

3.2.8 failure, n. - the point during a confined extension or confined creep test at 

which a material ceases to be functionally capable of its intended use. 

3.2.9 gage length, n. - the initial length of the portion of the specimen over which 

strain (or creep strain) is to be measured. 

172 
3.2.10 geogrid, n. - a geosynthetic formed by a regular network of integrally 

connected elements with apertures greater than 6.35 mm (l/4 in) to allow interlocking with 

surrounding soil, rock, earth, and other materials to function primarily as reinforcement. 

3.2.11 geosynthetic, n. - a planar product manufactured from polymeric material 

used with soil, rock, earth, or other geotechnical engineering-related material as an integral 

part of a man-made project, structure, or system. 

3.2.12 geotextile, n. - a permeable geosynthetic comprised solely of textiles. Current 

manufacturing techniques produce nonwoven geotextiles, knitted (nontubular) geotextiles, and 

woven geotextiles. 

3.2.13 initial tensile modulus, n. - the ratio of the change in tensile force per unit 

width to a change in strain for the initial portion of a force per unit width strain curve. 

3.2.14 ofSset tensile modulus, n. - the ratio of the change in force per unit width to a 

change in strain below the proportional limit point and above the tangent point on the force 

per unit strain curve. 

3 -2.15 proportional limit, n. - the greatest stress that a material is capable of 

sustaining without any deviation from linear proportionality of stress to strain (Hooke’s 

Law). 

3.2.16 rate of creep, n. - the slope of the creep versus time curve at a given time. 

3.2.17 secant tensile modulus, n. - the ratio of the change in force per unit width to 

a change in strain between two points on a force per unit width strain curve. One of the two 

points will be the origin (or the offset of the origin). The second point will be the point on 

the curve corresponding to a specified strain. 

3.2.18 strain, n. - the total extension divided by the gage length produced by the 

applied tensile load during a confined extension or confined creep test. (Syn. total strain) 

3.2.19 tangent point, n. - the first point of the force versus strain curve at which a 

major increase in slope occurs. The tangent point is determined by extending the line on the 

force versus strain curve where Hooke’s Law is valid (see proportional limit) to the zero 

force axis. The point where the force versus strain curve first touches this line is the tangent 

point. 

173 
3.2.20 tensile creep rupture strength, n. - for geosynthetics, the force per unit width 

that will produce failure by rupture in a confined creep test in a given time in a specified 

constant environment. 

3.2.21 tensile creep strain, n. - the total strain at any given time during a confined 

creep test. 

3.2.22 tensile modulus, n. - the ratio of the change in tensile force per unit width to 

a corresponding change in strain. 

3.2.23 tensile strength, n. - the maximum resistance to deformation developed for a 

specific material when subjected to tension by an external force. Tensile strength of 

geosynthetics is the characteristic of a sample as distinct from a specimen and is expressed in 

force per unit width. 

3.2.24 wide-width strip tensile test, n. - for geosynthetics, a tensile test in which the 

entire width of a 200~mm (8.0-in) wide geosynthetic specimen incorporating a gage length of 

100 mm (4.0 in) is gripped in the clamps. 

4. Summary of Test Method 

4.1 Both ends of a relatively wide geosynthetic specimen are gripped across the 

entire specimen width in clamps. The specimen is placed in a confinement box between 

layers of a specified soil. Confining pressures are applied at the boundaries of soil to 

provide normal stress to the geosynthetic specimen. 

4.2 For both the confined extension and confined creep test, the thickness of soil 

adjacent to the geosynthetic can be controlled to provide either partial or full confinement to 

the geosynthetic. 

4.3 For a confined extension test, a constant rate of extension (CRE) type tensile 

testing machine is operated at a prescribed rate of extension to apply a tensile force to the 

confined geosynthetic specimen until the specimen ruptures, Tensile strength, strain, and 

initial, offset, and secant tensile modulus of the test specimen can be calculated from 

machine scales, dials, recording charts, or an interfaced computer. 

174 
4.4 For a confined creep test, the tension creep behavior of a confined 

geosynthetic specimen is measured by applying an initial load in one step and sustaining the 

load for the duration of the test. The total strain and creep strain of the test specimen as a 

function of time are measured while maintaining a specified confining stress and sustained 

tensile load. 

5. Significance and Use 

5.1 This test method is developed for use in the determination of tensile force and 

strain properties or creep properties that may occur in geosynthetics while under confined 

conditions. 

5.1.1 The test data can be used in conjunction with interpretive methods to evaluate 

tensile force versus strain and the creep strain at design loads. 

5.2 This test method is not intended for routine acceptance testing of 

geosynthetics. This test method should be used to characterize geosynthetics intended for use 

in reinforcement applications in which the confined stress-strain and creep behavior of the 

geosynthetic are of concern. Test Method D 4595 for the determination of the wide-width 

strip tensile properties of geotextiles should be used for the acceptance testing of commercial 

shipments of geosynthetics. 

5.3 The determination of the confined extension tensile force versus strain 

properties of geosynthetics under a confining stress provides design parameters for soil 

reinforcement applications. Example applications include reinforced embankments over soft 

subgrades, reinforced soil retaining walls, and reinforced slopes. 

5.4 Most geotextiles and geogrids can be tested by this test method. Some 

modification of clamping techniques may be necessary for certain geosynthetics depending on 

the structure of the geosynthetic. Special clamping adaption may be necessary for highstrength geosynthetics (i . e . , tensile strength greater than approximately 100 kN/m (600 

lbf/in)) or geosynthetics made from glass fibers to prevent them from slipping in the clamps 

or being damaged as a result of being gripped in the clamps. Specimen clamping may be 

modified at the discretion of the individual laboratory provided that a representative tensile 

strength is obtained. In any event, the procedure described in section 11 of this test method 

for obtaining confined extension/confined creep behavior must be maintained. 

175 
6. Apparatus 

6.1 Test Setup - The confined extension and/or confined creep test setup is similar 

to that described in ASTM D 4595 and ASTM D 5262 for unconfined testing, respectively. 

For confined testing, the specimen is placed within a horizontally aligned containment box 

that incorporates the use of two air pressure bladders such that normal stress can be applied 

to the test specimen from above and below the geosynthetic. Figure 1 shows the horizontal 

orientation of the test setup. 

6.1.1 For Procedure A, the setup consists of the geosynthetic test specimen mounted 

in suitable grips within the containment box, with a layer of soil having an approximate 

thickness of 75 -mm (3 -in) on both sides. The air bladders that are fitted to receive 

compressed air at a specified sustained pressure are contained within the confinement box, 

above and below the soil layers. The two air bladders interface directly onto the soil 

surfaces as shown in figure 2A. 

6.1.2 For Procedure B, the setup consists of the geosynthetic test specimen mounted 

in suitable grips within the containment box, with a thin layer of soil having an approximate 

thickness of 10 -mm (0.4 -in) on both sides. Covering each soil layer are two layers of thin 

lubricated latex membranes and a relatively thick rubber rub-sheet. Each of the two air 

bladders interface directly onto each of the rub-sheets, as shown in Figure 2B. Depending 

on the design of the air bladder systems, rigid spacers may be required, as discussed in note 

. 

1. 

Note 1 - It should be noted that rigid spacers may be required to be placed between 

the air bladder systems and soil confining layers, depending on the design of the air 

bladder systems and the selected test procedure (i.e., Procedure A or Procedure B), in 

order to fill the containment box to the proper level. 

6.2 Containment BOX - An open rigid box is used as the containment box. It is 

constructed of 13-mm- (O-50-in-) thick steel plates, consisting of two smooth parallel sides, 

front and back walls containing horizontal split adjustable doors at their center line (Le., 

mid-section of the wall), and a removable bottom and top plate. The internal dimensions of 

the containment box should have minimum dimensions of 430 mm (17 in) long by 305 mm 

(12 in) wide by 150 mm (6 in) deep. The air bladder systems used to provide the confining 

stress should be designed to be incorporated into the top and bottom of the containment box. 

176 
LVDTs 

Confinement Box 

Rear Load Cell 

\- ^_ 

Upper Air 

7 -7 

Bladder Front Load Cell Air Cylinder 

\ 

1 in = 25.4 mm 

Supporting 

Table 

Steel 

Roller Roller 

+ 42” 

Figure 1. Test setup configuration. 
1 in - 25.4 mm 

Figure 2A. Cross-section for Procedure A with full confinement to the soil and the 

geosynthetic by using a thick soil specimen and a nonlubricated 

interface between the soil and the confining air bladder. 

Figure 2B. Cross-section for Procedure B with partial confinement to the soil and the 

geosynthetic by using a thin soil specimen and a lubricated 

interface between the soil and the confining air bladder. 

178 
6.3 Rigid Supporting Table - A rigid supporting table consisting of a reaction 

frame with a smooth and polished tabletop should be constructed of structural steel tubing 

and a minimum 13-mm- (0.5-in-) thick steel plate rigidly attached to the frame to form the 

table. The overall minimum plan dimensions of the supporting table should be 1065 mm (42 

in) in length and 710 mm (28 in) in width. The structural frame should incorporate the 

tensile loading system and a very low friction bearing surface. As presented in this 

document, the table allows two 25-mm- (l-in-) diameter steel rollers to be placed between 

the bottom of the containment box and the polished surface of the tabletop. This setup is 

required to allow the containment box to move together with the geosynthetic specimen in the 

horizontal direction during the confined extension and confined creep tests. Other means of 

providing very low friction are acceptable, but are not required by this standard. 

6.4 Test Grips - The test grips must be smooth-surfaced thin steel plates measuring 

200~mm (&O-in) wide and of a length to extend out of each side of the containment box. 

The test specimen is held within these grips by a resin/epoxy to allow full and uniform 

tension to be applied during the test. The resin/epoxy should exit the grips within the 

containment box to leave, for geotextiles a minimum loo-mm- (4.0-in-) long gage length of 

test specimen or, for geogrids, a minimum of two complete apertures of the test specimen 

exposed for stress application. 

6.5 Normal Pressure Loading System - To maintain a uniform normal stress, a 

flexible pneumatic diaphragm loading device (air bladder) that is continuous over the entire 

containment box should be used. Air pressure within the upper and lower air bladders is 

used to simulate the normal stresses anticipated in the field. The magnitude of this pressure 

must be agreed upon by the parties using the test results. Air pressure in equal amounts 

above and below the specimen is applied before the testing tension force is applied. The 

normal pressure loading system should have an operating capacity of up to 345 Wa (50 psi). 

Note 2 - It is generally recognized that there can be a reduction of confining pressure 

applied to the specimen because of side wall friction for thick soil specimens, This 

reduction from side wall friction can be on the order of 5 to 10 percent of the applied 

normal pressure. It is believed that the effect of side wall friction on the soilgeosynthetic interface is minimized by maintaining a minimum distance of 50 -mm 

(2 -in) between the geosynthetic specimen and the side walls of the containment box. 

By maintaining this minimum distance, the confining pressure transmitted to the 

geosynthetic specimen in a confined extension or confined creep test is expected to be 

the same as the air pressure applied to the air bladders. 

179 
6.6 Tensile Loading System - The tension force is to be applied to the grips exiting 

the containment box. As shown in figure 1, a horizontally deployed test setup uses a loading 

system consisting of a “moving grip” and a “fixed grip.” A large-capacity hydraulic cylinder 

incorporating an electronic load cell is mounted on the front of the supporting table and 

placed in line with the center line of the horizontal containment box. This hydraulic cylinder 

is used to load the moving grip. The fixed grip is attached to the rear of the supporting table 

through the use of a second electronic load cell placed in line with the center line of the 

horizontal containment box. For a confined extension test, a constant rate of strain can be 

achieved by manually adjusting the rate of fluid flow into the hydraulic cylinder. For a 

confined creep test, a constant load can be maintained by applying a constant pressure into 

the hydraulic cylinder. The tensile loading system should have an operating capacity of at 

least 45 kN (10,000 lbf). Testing can be conducted using air or hydraulic fluid, although 

higher system capacity is generally available for tests conducted using hydraulic fluid. 

Note 3 - Even if specimens of the proper aspect ratio are used for testing, the tensile 

load applied to the front of the geosynthetic specimen may not be fully transferred to 

the rear of the geosynthetic specimen. The difference between the front and rear 

loads is mainly caused by the mobilized friction between the soil and geosynthetic 

specimen and the specimen clamp, as well as friction developing between the 

supporting table, steel rollers, and the containment box. The use of Procedure B can 

help to reduce the mobilized friction between the soil and geosynthetic specimen. 

The overall friction loss should be measured through calibration, and the total friction 

should be controlled to within 2 percent of the anticipated maximum load in the 

confined extension test or the applied creep load in the confined creep test. 

6.7 Extension Measurement - Extension of the geosynthetic specimen is measured 

at the moving grip and at several locations along the gage length of the confined portion of 

the geosynthetic specimen. Extensometers are preferred for the measurement of strain in 

geosynthetics when confined in soil. One such device utilizes tell-tail wires attached to the 

specimen and to externally mounted extensometers. The wires are protected from the 

influence of normal stress by a small-diameter tube surrounding the wire, which runs from a 

location on the test specimen to the extensometer mounted outside of the containment box. 

Whenever possible, other means of measuring strain should be calibrated against 

extensometers (see appendix Xl). In any case, the device chosen shall be capable of 

measuring deformations to an accuracy of at least +O. 03 mm ( fO.001 in). The means of 

measuring strain should be indicated clearly in the report. 

180 
6.8 Vibration Control - Confined creep tests are sensitive to shock and vibration. 

The location of the apparatus, test equipment, and mounting shall be designed so that the 

specimen is isolated from vibration. 

6.9 Time Measurement - The accuracy of the time measuring device shall be f I 

percent of the elapsed time of each creep measurement load increment. 

6.10 Temperature Control - The temperature in the containment box, especially that 

close to the gage length of the specimen, shall be maintained within +2”C (+4”F) of the 

targeted value by a suitable automatic device and shall be stated in the report. 

6.11 Temperature Measurements - Temperature measurements shall be recorded at 

frequent intervals, or recorded continuously, in order to ensure an accurate determination of 

the average test temperature and compliance with 6.10. 

6.12 Environmental Control - The test environment shall be maintained constant 

throughout the test. Safety precautions should be taken to avoid personal contact during the 

test. The area should be isolated adequately and fenced such ,mat only the test operator has 

access to the test station. 

6.13 Soil Preparation Equipment - Use equipment as necessary for the placement of 

soils at desired conditions. This may include compaction devices such as vibratory or 

“jumping-jack” type compaction or hand compaction hammers. Soil containers or hoppers, 

leveling tools, and soil placement/removal tools may be required. 

6.14 Miscellaneous Equipment - Measurement and trimming equipment as necessary 

for geosynthetic preparation, a timing device, and soil property testing equipment are 

necessary for testing, but are considered to be routine components of a geosynthetic testing 

laboratory. 

7. Sampling 

7.1 Lot Sample - For the lot sample, rolls of geosynthetics should be obtained as 

directed in an applicable material specification, or as agreed upon between the purchaser and 

the supplier. 

181 
7.2 Laboratory Sample - For the laboratory sample, a full-width swatch 

approximately l-m- (40-in-) long in the machine direction should be obtained from each roll 

in the lot sample. The sample may be taken from the end portion of a roll, provided there is 

no evidence that it is distorted or different from other portions of the roll. In general, and 

particularly in cases of dispute, it is recommended that a sample be obtained that will exclude 

material from the outer wrap of the roll or the inner wrap around the core. 

7.3 Test Specimens: 

7.3.1 Geotextiles - For tests in the machine and cross-machine directions, 

respectively, the number of specimens as directed in section 9.1 should be taken from each 

sample. The specimens should be taken along a diagonal across the width of the sample, 

with no specimens closer than l/10 the width of the roll or 150- mm (6- in) from the edge of 

the sample, whichever is smaller. 

7.3.2 Geogrids - For tests in the machine and cross-machine directions, 

respectively, the number of specimens as directed in section 9.1 should be taken from each 

sample. The specimens should be taken at random locations from the laboratory sample. 

Machine direction samples should be obtained from locations independent from the crossmachine samples. The test specimens should exclude the outermost longitudinal and 

transverse ribs. No specimens should be taken closer to the edge than l/10 the width of the 

roll or 150 mm (6 in) from the edge, whichever is smaller. 

8. Test Specimen Preparation 

8.1 Test Specimen Preparation: 

8.1.1 Geotextiles - An aspect ratio of 2: 1 should be used for all geotextile 

specimens. Prepare each finished specimen to 200~mm (8.0-in) wide by at least 200-mm 

(8.0-in-) long, with the length dimension being designated and accurately cut parallel to the 

direction for which the confined extension or confined creep behavior is being measured. 

Draw two parallel lines near the center of each specimen length that are separated by 100 

mm (4.0 in) and that extend the full width of the specimen. These lines should be exactly 

perpendicular to the length of the specimen. 

8.1.1-l The length of the specimen depends on the type of clamps being used. The 

specimen must be long enough to extend through the full length of both clamps, as 

182 
determined for the direction of the test. When specimen integrity is not affected, the 

specimen may be cut initially to the finished width. 

8.1.2 Geogrids - Prepare each finished specimen to contain a width of at least five 

ribs in the cross-test direction (i.e., typically the cross-machine direction) by a length of at 

least two complete apertures in the direction of testing (i.e., typically the machine direction), 

with the length dimension being designated and accurately cut parallel to the direction for 

which the confined extension or confined creep behavior is being measured, 

8.1.3 This test method may not be suitable for some woven geotextiles or geogrids 

that exhibit breaking strengths in excess of 100 kN/m (600 lbf/in), due to clamping and 

equipment limitations. In such cases, 100~mm- (4.0-in-) wide specimens may be substituted 

for 200~mm- (8.0-in-) wide geotextile specimens. For geogrids, a minimum of three ribs in 

the cross-test direction may be substituted for the five ribs in the cross-test direction to 

ensure proper load distribution. 

9. Number of Tests 

9.1 Confined Extension Tests - Unless otherwise agreed upon, confined extension 

tests shall be conducted at normal stress levels as specified by the designer. Three different 

normal stress levels are recommended for characterization of the interaction of the 

geosynthetic material and the confining soil. 

9.2 Confined Creep Tests - To evaluate design creep strains, it is recommended 

that a minimum of two different normal stress conditions be evaluated to cover the range of 

normal stresses anticipated in the design. For each normal stress condition, applied tensile 

loads shall be selected at intervals of approximately 10 to 20 percent of the maximum load 

per unit width, that is, 20, 30, 40 and 60 percent, as determined by applicable ASTM test 

methods. 

Note 4 - To properly characterize the confined behavior of a geosynthetic involves 

identification of the load levels at which there is no creep (no increase in strain with 

the log of time), low to moderate creep (linear increase in strain with the log of time), 

and high creep (exponential increase in strain with log of time). Therefore, a 

minimum of three tests are recommended for each normal stress. 

183 
10. Conditioning and Testing Atmosphere 

10.1 The specimens should be brought to moisture equilibrium in the atmosphere 

for testing geosynthetics. Equilibrium is considered to have been reached when the increase 

in mass of the specimen, in successive weighing, made at intervals of not less than 2 hours, 

does not exceed 0.1 percent of the mass measured at the previous time period. 

Note 5 - Geosynthetic materials are frequently not weighed to determine when 

moisture equilibrium has been reached. While such a procedure cannot be accepted 

in cases of dispute, in routine testing, it may be sufficient to expose the material to 

the standard atmosphere for testing for a reasonable time period before the specimens 

are tested. A period of 24 hours has been found acceptable in most cases. However, 

certain fibers may exhibit slow moisture equilibrium rates from the as-received wet 

side. When this is known, a preconditioning cycle, as prescribed in ASTM D 1776, 

may be agreed upon between contractual parties. 

11. Procedure 

11.1 Adequately conditioned specimens should be tested. Test are conducted at a 

temperature of 21’ +2”C (70” +4”F) and relative humidity of 50 to 75 percent. 

11.2 Procedure A or Procedure B should be selected on the basis of the designer’s 

design approach. The test setup is then constructed as discussed in section 6.1. 

11.3 The amount of soil should be determined to achieve the desired dry unit 

weight of the soil when placed in the lower half of the containment box above the lower air 

bladder system. The selected soil material is then compacted into the lower half of the 

confinement box to form the lower confining layer. The soil should be compacted by hand 

tamping or by some other means to the desired unit weight under the specified moisture 

condition. The upper surface of the lower confining layer should be placed so that it is level 

with the center line of the loading harness, (i.e., the hydraulic cylinder and the rear load 

cell). 

11.4 A test specimen should be obtained as described in section 8. The end of each 

geosynthetic specimen should be cast in a low-temperature curing epoxy, resin which should 

be reinforced using layers of impregnated nonwoven geotextile to facilitate clamping of each 

184 
geosynthetic. The epoxy resin should be prepared by mixing the components of the resin 

compound and curing agent as directed by the manufacturer. During the curing period, 

typically 24 -hours, each end of the specimen should be confined between smooth steel plates 

under a minimum normal stress of 1 kPa (0.15 psi) to ensure a uniform casting that 

facilitates clamping. 

11.5 After preparation of the geosynthetic specimen, the test specimen is then 

placed on top of the lower confining soil layer. The two cast ends of the geosynthetic 

specimen are then connected to the front moving grip through a clevis and the rear fixed grip 

through a clevis on the tensile loading system as shown in figure 1, 

11.6 At least two in-soil extension monitoring devices (typically tell-tail wires 

attached to extensometers) should be used to monitor displacement of the geosynthetic 

specimen within the containment box. When only two tell-tail wires are used, they should be 

connected to the two ends of the geosynthetic specimen gage length. The tell-tail wire gages 

can be attached by hooking the wire to a glued-on tab or by tying them directly onto the 

specimen. Care should be taken to ensure that any slack in the wire is eliminated and that 

the geosynthetic specimen is not damaged. The other end of each wire can then be 

connected to the extensometer mounted to the rear of the supporting table outside the 

containment box. See appendix X. 1 for information about extensometers. 

Note 6 - It is recommended that additional in-soil extension monitoring devices be 

used during testing to confirm that there is uniform strain distribution along the gage 

length of the confined portion of the geosynthetic specimen. 

11.7 A pretension force should be applied to the geosynthetic specimen to eliminate 

slack within the geosynthetic specimen. The amount of pretension force is preselected for 

each test in accordance with the procedure established in ASTM D 4595 for in-air tensile 

testing of geosynthetics. A total pretension force equal to 1.25 percent of the expected 

breaking force should be applied to each geosynthetic specimen. However, the total 

pretension force should not be less than 45 N (10 lb) or greater than 222 N (50 lb) in any 

case. The pretension force should be applied to the geosynthetic specimen prior to placement 

of the upper confining soil layer. This allows examination of the geosynthetic specimen to 

assess whether the geosynthetic is in uniform contact with the top of the lower confining soil 

layer. 

185 
11.8 Additional soil should now be placed above the geosynthetic in the upper half 

of the containment box and compacted by hand tamping or by some other means to form the 

upper confining layer above the geosynthetic specimen. The soil should be compacted to the 

same unit weight and at the same specified moisture content as the lower confining soil layer. 

11.9 The test setup is completed with the installation of the upper lubricated 

interface if Procedure B is used, upper air bladder system, and top plate (see note 1). 

11.10 A normal stress is then applied to the test specimen by pressurizing the upper 

and lower air bladder loading systems. The desired predetermined source pressure should be 

applied simultaneously through the lower and upper air bladders. 

11.11 For a confined extension test, the geosynthetic specimen should be loaded 

under a constant rate of strain of 10 percent/min as measured on the front specimen clamp. 

The selection of this constant rate of strain is based on the standard loading rate specified in 

ASTM D 4595 for conducting unconfined wide-width strip tension tests on geosynthetics. 

For a confined creep test, a load should be applied to the test specimen at an initial loading 

strain rate of 10 percent/min until the selected test load is achieved. Selection of this initial 

loading rate is based on the standard loading rate in ASTM D 5262 for conducting 

unconfined tension creep tests on geosynthetics. The variation of the applied constant load 

should be within & 1 percent of the desired load to be applied to the test specimen throughout 

the duration of the test. Readings should be taken regularly and, at a minimum at the same 

time the extension of the test specimen is measured, as discussed in section 11.11.1. 

11.11.1 During the confined creep test, the extension of the specimen should be 

measured in accordance with the following approximate time schedule: 1, 2, 6, 10, and 30 

min; and 1, 2, 5, 10, 30, 100, 200, 500, and 1000 hours, For creep tests longer than 1000 

hours, extension readings should be recorded every 500 hours until testing is complete. 

Note 7 - In design, it is generally accepted that creep data should not be extrapolated 

for time periods beyond one order of magnitude of the test time. In many cases, a 

test period of 1000 hours may not reflect the long-term creep behavior of the material 

accurately, as this reflects an extrapolation limit of approximately 10,000 hours or 

approximately 14 months. For such cases, creep tests should be conducted for more 

than 10,000 hours. 

11.11.2 Test results should be plotted on a graph as discussed in section 12.2. 

Results should be plotted regularly during the test. Readings should be recorded more 

186 
frequently if discontinuities in the creep strain versus log of time plot are suspected or 

encountered. To avoid such discontinuities, the use of automatic monitoring and measuring 

equipment is recommended. 

11.12 The test should be terminated when the specimen ruptures or at the end of the 

agreed upon time period. If the specimen ruptures, the type of failure, the location, and time 

to failure should be recorded. 

12. Calculations 

12.1 Confined Extension Tests: 

12.1.1 Tensile Strength - Calculate the tensile strength of individual specimens by 

reading the maximum force per unit width to cause a specimen to rupture from the testing 

instrument. Tensile strength is expressed in N/m (lbf/ft) of width, using Eq 1, as follows: 

af = F,/W, (1) 

where: 

af = tensile strength, N/m (lbf/ft) of width, 

Ff = observed breaking force, N (lbf’), and 

WS = initial specimen width, m (ft). 

2: 

12.1.1.1 For geogrids, the equivalent tensile strength is determined by the use of Eq 

a = (F/N,) x N, (2) 

where: 

a = equivalent tensile strength, N/m (lbf/ft) of width, 

F = observed breaking force, N (lbf), 

Nr = number of ribs tested, and 

w = number of ribs per unit width. 

12.1.2 Strain - Calculate the strain of individual specimens, expressed as the percentage 

increase in length, relative to the initial nominal gage length of the specimen, using Eq 3, as 

follows: 

E = (AL x 100)/L, (3) 

187 
where: 

E = strain, %, 

Lg = initial nominal gage length, mm (in), and 

AL = the unit change in length (extension) of the gaged portion of the specimen 

from zero force to the corresponding measured force, mm (in). 

12.1.3 Tensile Modulus: 

12.1.3.1 Initial Tensile Modulus - Calculate the initial tensile modulus using the initial 

straight portion of the force versus strain curve by drawing a line tangent to this curve. At 

any point on this tangent line, measure the slope by measuring the change in force and the 

corresponding change in strain. Calculate initial tensile modulus in N/m (lbf/ft) of width 

using Eq 4 (See appendix X2 and figure X2. l), as follows: 

Ji = (F X lOO)/(e X W,) (4) 

where: 

Ji = initial tensile modulus, N/m (lbf/ft) of width, 

F = determined force on the drawn tangent line, N (lbf), 

E = corresponding strain with respect to the drawn tangent 

line and determined force, %, and 

w, = initial specimen width, m (ft). 

12.1.3.2 Ofsset Tensile Modulus - Calculate the offset tensile modulus by determining the 

location where modulus is to be assessed and drawing a line tangent to the force versus strain 

curve between the tangent point and the proportional limit and through the zero force axis. 

Measure the force and the corresponding strain with respect to the force axis. Calculate 

offset tensile modulus in N/m (lbf/ft) of width using Eq 5 (See appendix X2 and X3 and 

figures X2.1 and X3. l), as follows: 

J, = (F x loo)& x W,) (5) 

where: 

J, = 

F = 

E = 

w,= 

offset tensile modulus, N/m (lbf/ft) of width, 

determined force on the drawn tangent line, N (Ibf), 

corresponding strain with respect to the drawn tangent 

line and determined force, %, and 

initial specimen width, m (ft). 

188 
12.1.3.3 Secant Tensile Modulus - Calculate the secant tensile modulus by determining 

the force for a specified strain, e2, and label that point on the force versus strain curve as P2. 

It is typical to report secant modulus for 2, 5, and/or 10 percent strain. Accordingly, P2 

would be located on the force versus strain curve at either 2, 5, and/or 10 percent strain, 

Likewise, label a second point, PI at a specified strain, el, usually 0 percent strain. Draw a 

straight line (secant) through points PI and P2 intersecting the zero force axis. The typical 

values are 0 and 10 percent strain for points PI and Pz, respectively, although other values 

may be used when required in an applicable material specification. The secant tensile 

modulus is calculated in N/m (lbf/ft) of width using Eq 6 (See appendix X4 and figure 

X4.1), as follows: 

Js = (F x lOO)/(e x W,) 

where: 

J, = secant tensile modulus, N/m (lbf/ft) between specified strains 

per m (ft) of width, 

F = determined force on the constructed line, N (lbf), 

E = corresponding strain with respect to the constructed 

line and determined force, % , and 

w, = initial specimen width, m (ft). 

(6) 

12.1.4 Force Versus Strain Curve - The standard confined extension curve is a graph of 

the force versus strain as measured on the geosynthetic while under a specified confining 

stress. A typical plot is presented in figure 3 and should be provided in the report if 

requested. 

12.2 Confined Creep Tests: 

12.2.1 Creep Curves - There are three standard confined creep curves, a graph of total 

strain versus log of time, a graph of log of incremental strain rate versus log of time, and a 

graph of log of incremental strain rate versus total strain. Typical plots of these three curves 

are presented in figures 4, 5, and 6. The data are prepared by use of the following 

calculations: 

12.2.1-l Time - Elapsed time intervals are converted to hours and converted to the log of 

time (in hours). 

12.2.1.2 Total Strain - The accumulated total strain at each interval is calculated (to the 

nearest 0.03 mm (0.001 in) of extension) using Eq 3. 

189 
12.2.1.3 Incremental Strain Rate - The incremental strain rate at each time interval is 

calculated as the change in strain, E, with respect to time between two successive monitoring 

periods. 

12.2.2 The data are then plotted as: (i) percent total strain as ordinate versus log of time 

as abscissa, (ii) log of incremental strain rate as ordinate versus log of time as abscissa and 

(iii) log of incremental strain rate as ordinate versus total strain as abscissa, see figures 4, 5, 

and 6). If several loads are used for testing, each plot shall be labeled clearly with the 

appropriate loading or force per unit width, expressed in N/m (lb/ft). 

4500 

4000 - 

3500 - 

A 

< 3000 - 

la 

ci 

w 2500 - 

2 

0 

h 2000 - 

W 

.-I 

G E 1500- 

1000 - 

500 - 

- IN-AIR 

- IN BEACH SAND AT 10 psi 

- IN BEACH SAND AT 20 psi 

SPECIMEN WIDTH: 8 in 

SPECIMEN LENGTH: 5 in 

GAGE LENGTH: 4 in. 

STRAIN RATE: 1 O%/min 

0 5 10 15 20 25 30 35 40 45 50 

STRAIN (w) 

1 in = 25.4 mm 

1 Ib/ft = 14.59 N/m 

1 psi = 6.89 kPa 

Figure 3. Typical force versus strain response for a geosynthetic material during 

confined extension testing. 

190 
18 

16 

6 

r 

10 -z 10 -' 1 10 IO = IO3 

TIME (h) 

- IN-AIR 

- IN BEACH SAND AT IO psi 

- IN BEACH SAND AT 20 psi 

- IN BEACH SAND AT 10 psi 

SPECIMEN WIDTH: 8 in 

SPECIMEN LENGTH: 5 in 

GAGE LENGTH: 4 in 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure 4. Typical total strain versus log of time response for a geosynthetic 

material during confined creep testing. 

191 
1 

10 

k 

0888fl IN-AIR 

- IN BEACH SAND AT 10 psi 

1 - IN BEACH SAND AT 20 psi 

- IN BEACH SAND AT 10 wi 

SPECIMEN WIDTH: 8 in 

O4 

SPECIMEN LENGTH: 5 in 

GAGE LENGTH: 4 in 

0 -3 

I rIrllll( I I I I lllll I I I I Ill11 

,,, ,h 

I IIII 1 

10 -z IO -' 1 10 IO2 IO" 

TIME (h) 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure 5. Typical log of incremental strain rate versus log of time response for 

a geosynthetic material during confined creep testing. 

192 
lop-\ 

cteetn, IN-AIR 

- IN E 

- IN BEACF 

- IN BEACH SA 

3EACH SAND AT 10 psi 

I SAND AT 20 psi 

ND;AT 10 psi 

SPECIMEN WIDTH: 8 in 

SPECIMEN LENGTH: 5 in 

GAGE LENGTH: 4 in 

lo-51 I 1 I 1 I 1 I 1 I (1 1 1 1 1 I 1 I 1 

0 2 4 6 8 IO 12 14 16 18 : 

TOTAL STRAIN (5%) 

1 in = 25.4 mm 

1 psi = 6.895 kPa 

Figure 6. Typical log of incremental strain rate versus total strain response for 

a geosynthetic material during confined creep testing. 

193 
13. Report 

13.1 Confined Extension Tests: The report should include the following information: 

13.1.1 Description of test apparatus. 

13.1.2 Test conditions, including which test procedure was used. 

13.1.3 Any departures from standard procedure. 

13.1.4 Notation that the specimens were tested as directed in this test method. 

Description of the material tested, including all pertinent information required for complete 

identification of the specimen. 

13.1.5 Dimensions of the test specimen. 

13.1.6 Identification of and description of soil, including soil classification, water 

content, unit weight, grain size, and other identifying information if available. 

13.1.7 All basic data including normal stresses, tensile strength, initial tensile modulus, 

offset tensile modulus, and/or secant tensile modulus, strain at rupture, and, if requested, 

include a force versus strain curve for each test. 

13.1.8 Description of the geosynthetic specimen conditions before and after testing. 

13.2 Confined Creep Tests: The report should include the following information: 

13.2.1 Description of test apparatus. 

13.2.2 Test conditions, including which test procedure was used. 

13.2.3 Any departures from standard procedure. 

13.2.4 Notation that the specimens were tested as directed in this test method. 

Description of the material tested, including all pertinent information required for complete 

identification of the specimen. 

194 
13.2.5 Dimensions of the test specimen. 

13.2.6 Identification of and description of soil, including soil classification, water 

content, unit weight, grain size, and other identifying information if available. 

13.2.7 Dates of the confined creep tests. 

13.2.8 For each test, plot of total strain in percent versus log of time in hours, log of 

incremental strain rate in percent/min versus log of time in hours, and log of incremental 

strain rate in percent/min versus total strain in percent under a given normal stress and creep 

load per unit width and as a percent of ultimate load as determined in appropriate ASTM test 

methods. 

13.2.9 Description of the geosynthetic specimen conditions before and after testing. 

14. Precision and Bias 

14.1 Precision - The precision of the procedure in this test protocol is being 

established. 

14.2 Bias - This test has no bias because the confined extension and creep behavior of 

geosynthetics are defined in terms of this test method. 

15. Key Words 

15.1 Geogrid; geosynthetics; geotextile; confined extension; confined creep; 

performance test. 

195 
APPENDIXES 

(Nonmandatory Information) 

Xl. EXTENSOMETERS 

Xl, 1 Three types of extensometers have been used successfully in testing 

geosynthetics .

Xl. 1.1 Direct reading extensometers are mounted directly on the geosynthetic. 

These extensometers typically consist of linear variable-differential transformers (LVDTs) 

units that read strain directly as the material extends. These units place an additional force 

(weight) on the material undergoing testing and may result in alteration of the force versus 

strain results. The user should determine that this additional force is or is not significant for 

the material being tested. This type of extensometer cannot typically be used during confined 

testing. 

Xl. 1.2 Semi-remote reading extensometers use clamps that are mounted directly 

on the geosynthetic. Wires, pulley systems, or other physical devices connect the clamps to 

LVDT units. This type of extensometer are appropriate for confined testing, but provisions 

must be provided to protect the wires, etc., from influences due to confinement. 

Xl. 1.3 Remote extensometers use clamps or markers that are mounted directly on 

the geosynthetic and sensing units that are mounted independently both of the geosynthetic 

and the clamps or markers. These sensing units use electromagnetic radiation, such as light, 

to sense the distance between the markers. These type extensometers may be inappropriate 

due to confinement. 

Xl.2 Users must bear in mind that clamps, markers, or other physical 

attachments can damage materials undergoing testing. This damage can cause premature 

failure in geosynthetics. It is of paramount importance to design and use clamps, markers, 

or other attachments in a manner that will not alter the test results by damaging the material 

undergoing testing. 

X2. INITIAL GEOSYNTHETIC TENSILE MODULUS 

X2.1 In a typical force versus strain curve (figure X2. l), there is usually a toe 

region AC that represents take up of slack, alignment, or seating of the specimen. For some 

196 
geosynthetics, this portion can represent a significant part of the strain characteristic of the 

specimen. This region is considered when determining the initial geosynthetic modulus. 

X2.1.1 The initial geosynthetic tensile modulus can be determined by dividing the 

force at any point along the straight-line projection of the force versus strain curve (i.e., line 

AG or its extension) by the strain at the same point (measured from point A, defined as zero, 

strain). 

Figure X2.1. Material with Hookean region. 

X3. OFFSET GEOSYNTHETIC TENSILE MODULUS 

X3.1 In the case of a geosynthetic exhibiting a region of Hookean (linear) 

behavior (figure X2.1) after the nonlinear initial region, a continuation of the linear region of 

the curve is constructed through the zero-force axis. This intersection point B is the zero 

strain point from which strain is measured. 

X3.1.1 The offset geosynthetic tensile modulus can be determined by dividing the 

force at any point along the line BD (or its extension) by the strain at the same point 

(measured from point B, defined as zero strain). The point where line BD first touches the 

force versus strain curve is the tangent point (i.e., point C). 

197 
X3.2 In the case of a geosynthetic that does not exhibit any linear region (figure 

X3. l), a line is constructed tangent to the point on the force versus strain curve exhibiting 

the maximum slope (i.e., point H). This is extended to intersect the zero force axis at point 

B’. This intersection point B’ is the zero strain point from which strain is measured. 

X3.2.1 The offset geosynthetic tensile modulus can be determined by dividing the 

force at any point along line Bk’ (or its extension) by the strain at the same point (measured 

from point B’, defined as zero strain). 

Figure X3.1. Material with no Hookean region. 

X4. SECANT GEOSYNTHETIC TENSILE MODULUS 

X4.1 In a typical force versus strain curve (figure X4. l), a straight line is 

constructed through the zero force axis, usually at zero strain point A’ and a second 

point usually at 10 percent strain, point M’. Point A” is the zero strain point from which 

strain is measured. 

X4.1.1 The secant geosynthetic tensile modulus at the selected strain level can be 

determined by dividing the force at any point along the line A”M’ (or its extension) by the 

strain at the same point (measured from point A’, defined as zero strain). 

198 
X4.1.2 Figure X4.1 also presents a straight line constructed through any two 

specified points where a secant modulus is to be calculated, point Q” and point R”, other than 

zero and 10 percent strain. In this case, the line is extended through the zero force axis at 

point B’. This intersection is the zero strain point from which strain is measured. The 

secant geosynthetic tensile modulus can be determined by dividing the force at any point 

along line Q”R” (or its extension) by the strain at the same point (measured from point B”, 

defined as zero strain). If this latter method is used, for example to account for zero-force 

offset due to removal of slack, etc., in the geosynthetic, the specified means for defining 

point Q” and R’ should be identified in the testing report. 

A- II- cFigure X4.1. Construction line for secant modulus. 

199 
REFERENCES 

Boyle, S. R. (1995), “Unit Cell Test on Reinforced Cohesionless Soils,” Proceedings of 

Geosynthetics’9.5, Nashville, Vol. 3, Feb, pp. 1221-1234. 

Boyle, S. R. (1995), “Deformation Prediction of GeoSynthetic Reinforced Soil Retaining 

Walls,” Ph.D Dissertation, University of Washington, June, pp. 391. 

Christopher, B. R., Holtz, R. D., and Bell, W. D. (1986), “New Tests for Determining the 

In-Soil Stress-Strain Properties of Geotextiles, ” Proceedings of 3rd International Conference 

on Geotextiles, Vol. 3, Vienna, pp. 683-688. 

Fabian, K. J. and Fourie, A. B. (1988),“Clay Geotextile Interaction in In-Soil Tests,” 

Proceedings of Symposium on Theory and Practice of Earth Reinforcement, Fukuoka, Japan, 

Ott, pp. 81-86. 

Fock, G. and McGown, A. (1987), “The Creep Behavior of A Needle Punched 

Polypropylene Geotextile, ” 9th Southeast Asian Geotechnical Conference, Bangkok, 

Thailand, Dee, pp. 101-112. 

Holtz, R. D. (1977), “Laboratory Studies of Reinforced Earth Using a Woven Polyester 

Fabric, ” International Conference on the Use of Fabrics in Geotechnics, Paris, Vol 2, pp. 

149-154. 

Juran, I., Farrag, K. H., and Richmond, L. (1991),“Short and Long Term Performance of 

Polymeric Geogrids, ” Proceedings of Geosynthetics ‘91, Vol. 2, Atlanta, Feb, pp. 587-599. 

Leshchinsky, D. and Field, D. A. (1987), “In-Soil Load Elongation, Tensile Strength and 

Interface Friction of Nonwoven Geotextile, ” Proceedings of Geosynthetics’ 87, New 

Orleans, pp. 238-249. 

Ling, H. I., Wu, J. T. H., and Tatsuoka, F. (1991), “Effectiveness of In-Membrane Test in 

Simulating Strength and Deformation Characteristics of a Nonwoven Geotextile Under 

Operational Conditions, ” Proceedings of Geosynthetics ‘91 Conference, Atlanta, Feb, Vol. 2, 

pp. 601-614. 

200 
McGown, A., Andrawes, K. Z., and Kabir, M. H. (1982), “Load-Extension Testing of 

Geotextiles Confined In-Soils, ” Proceedings of Znd International Conference on Geotextiles, 

Las Vegas, pp. 793-798. 

McGown, A., Andrawes, K. Z., Yeo, K., and DuBois, D. (1984), “The Load-Strain-Time 

Behavior of Tenser Geogrids, ” Polymer Grid Reinforcement, Thomas Telford 1985, 

Proceedings of a conference held in London, UK, March Paper No. 1.2, pp. 11-17. 

Myles, B. and Carswell, I. G., (1986), “Tensile Testing of Geotextiles,” Third International 

Conference on Geotextiles, ” Vienna, Austria, pp. 713-718. 

Whittle, A. J., Larson, D. G., Germaine, J. T., and Abramento, M. (1993), “A New Device 

for Evaluating Load-Transfer in Geosynthetic Reinforced Soils, ” ASTM STP 1190, pp. l- 15. 

Wilson-Fahmy, R. F., Koerner, R. M., and Fleck, J. A. (1993), “Unconfined and Confined 

Wide-Width Tension Testing of Geosynthetics,” ASTM STP 1190, pp. 49-63. 

Wu, J. T. H. (1991), “Measuring Inherent Load-Extension Properties of Geotextiles for 

Design of Reinforced Structures, ” Geotechnical Testing Journal, Vol. 14, No. 2, Jan, 

pp. 157-165. 

Wu, J. T. H. and Tatsuoka, F. (1992), Discussion of “Laboratory Model Study on 

Geosynthetic Reinforced Retaining Wall, ” Journal of Geotechnical Engineering, ASCE, Vol. 

118, March, pp. 496-501. 

201