soil-geosynthetic interaction - IGS - International Geosynthetics Society

Technical Paper by M.J. Lopes and M.L. Lopes 

SOIL-GEOSYNTHETIC INTERACTION – INFLUENCE 

OF SOIL PARTICLE SIZE AND GEOSYNTHETIC 

STRUCTURE 

ABSTRACT: This paper reports the results of pullout tests on five different geosynthetics 

embedded in two different granular soils. Soil and geosynthetic properties are 

described and soil-geosynthetic interaction behaviour is studied. Based on the results 

of pullout tests, the influence of soil particle size, geosynthetic structure, and the role 

of geogrid bearing members are discussed. The main conclusion is that the influence 

of soil particle size on soil-geosynthetic interaction is important, but its significance depends 

on several factors. With geogrids, the relative sizes of soil particles and geogrid 

apertures, and the thickness of the geogrid bearing members, determine soil-geogrid 

interface shear resistance. A marked increase in soil-geogrid interface shear resistance 

was observed when the soil contained a significant percentage of particles with sizes 

slightly greater than the thickness of the geogrid bearing members, but smaller than the 

geogrid apertures. Tests, on geogrids in which the bearing members had been cut, show 

a significant decrease in soil-geogrid interface shear resistance. The influence of soil 

particle size is less important for geotextiles and geocomposites. Although the structure 

of geotextiles and geocomposites has an effect on soil-reinforcement interface behaviour, 

mobilised pullout resistance is also affected by the axial tensile stiffness of geotextiles 

and geocomposites. 

KEYWORDS: Pullout test, Geogrid, Geotextile, Geocomposite, Interaction, Soil 

particle size, Geosynthetic structure, Bearing member. 

AUTHORS: M.J. Lopes, Ph.D. candidate, and M.L. Lopes, Assistant Professor, 

Department of Civil Engineering, Geotechnical Division, University of Porto, Rua dos 

Bragas 4099 Porto Codex, Portugal, Telephone: 351/2-2041945, Telefax: 

351/2-2003640, E-mail: lcosta@fe.up.pt. 

PUBLICATION: Geosynthetics International is published by the Industrial Fabrics 

Association International, 1801 County Road B West, Roseville, Minnesota 

55113-4061, USA, Telephone: 1/651-222-2508, Telefax: 1/651-631-9334. 

Geosynthetics International is registered under ISSN 1072-6349. 

DATES: Original manuscript received 5 January 1999, revised version received 3 June 

1999 and accepted 29 June 1999. Discussion open until 1 March 2000. 

REFERENCE: Lopes, M.J. and Lopes, M.L., 1999, “Soil-Geosynthetic Interaction 

- Influence of Soil Particle Size and Geosynthetic Structure”, Geosynthetics 

International, Vol. 6, No. 4, pp. 261-282. 

GEOSYNTHETICS INTERNATIONAL S 1999, VOL. 6, NO. 4 

261

LOPES AND LOPES D Soil-Geosynthetic Interaction 

1 INTRODUCTION 

Pullout tests were used to characterize soil-geosynthetic reinforcement interaction 

with relative soil-geosynthetic reinforcement movement, as the geosynthetic is subjected 

to pullout. 

The test program involved a study of the soil-geosynthetic interaction of two high 

density polyethylene uniaxial geogrids, a polypropylene biaxial geogrid, a polypropylene 

nonwoven spun-bonded geotextile, and a geocomposite comprising a polypropylene 

nonwoven spun-bonded geotextile reinforced in the machine direction with 

polyester yarns. Two different granular soils were used for the pullout tests. 

2 TEST EQUIPMENT 

The pullout tests were performed using the apparatus shown in Figure 1, which is described 

in detail by Lopes and Ladeira (1996). The pullout box is 1.53 m long, 1.00 m 

wide, and 0.80 m deep. The pullout boxtop wall-soil friction wasreduced using a 25mmthick 

neoprene sheet. Tests were performed at a constant displacement rate of 2mm/minute. 

The pullout force, applied by a hydraulic system, was measured using a load cell 

placed in the clamping system (Figure 2) that transmits the force to the reinforcement. 

Vertical stress was applied, normal to the plane of the geosynthetic reinforcement, 

using a platen that was loaded by ten small hydraulic jacks (Figure 1). Tests were run 

at soil constant volume. The displacement along the geosynthetic was measured using 

inextensible wires with one end connected to the geosynthetic and the other end connected 

to linear potentiometers placed outside the pullout box (Figure 1b). The results 

were recorded by an automatic data acquisition system. 

3 MATERIALS 

3.1 Soils 

Two sands, with the particle size distributions shown in Figures 3 and 4, were used 

in the tests. Soil 1 minimum and maximum unit weight values range from 15.5 to 17.9 

kN/m 3 for soil particle diameter values that range from 0.0074 to 2.00 mm (Figure 3). 

Soil 2 minimum and maximum unit weight values range from 15.6 to 18.7 kN/m 3 for 

soil particle diameter values that range from 0.0074 to 9.54 mm (Figure 4). The physical 

properties of the two soils are given in Table 1. 

The coefficient of uniformity, C U , coefficient of curvature, C C , and relative density, I D , 

values of Soils and 1 and 2 are calculated using the following expressions, respectively: 

C U = D 60 

(1) 

C C = (D 30 ) 2 

D 10 D 60 

D 10 

(2) 

262 GEOSYNTHETICS INTERNATIONAL S 1999, VOL. 6, NO. 4


(a) 

(b) 

Figure 1. 

view. 

Pullout apparatus: (a) front view showing the hydraulic system; (b) lateral 

Table 1. 

Physical properties of the two types of soil used in the test program. 

Soils 

D min 

(mm) 

D 10 

(mm) 

D 30 

(mm) 

D 50 

(mm) 

D 60 

(mm) 

D max 

(mm) 

C U C C 

γ min 

(kN/m 3 ) 

γ max 

(kN/m 3 ) 

γ (ID = 55%) 

(kN/m 3 ) 

φ* 

(_) 

Soil 1 0.074 0.26 0.32 0.43 0.5 2.00 1.92 0.79 15.0 17.9 16.45 35.7 

Soil 2 0.074 0.44 0.90 1.30 1.6 9.54 3.64 1.15 15.6 18.7 17.15 44.2 

Note: 

* Soil residual internal friction angle (at 38.0 kPa vertical pressure) in direct shear. 


263


Figure 2. 

Geosynthetic clamping system used in the pullout apparatus. 

I D = 

γ max 

γ (ID =55%) 

γ (ID =55%) − γ min 

γ max − γ min 

× 100% 

(3) 

where D 10 , D 30 ,andD 60 are the soil particle diameters corresponding to 10, 30, and 

60% by weight of finer particles passed during sieving (Figures 3 and 4), γ min and γ max 

are the minimum and maximum soil unit weight values, and γ (ID = 55%) is the unit weight 

for soil with a relative density of I D = 55%. 

Both soils were compacted to a relative density, I D = 55%. For I D = 55%, γ = 16.45 

and 17.15 kN/m 3 for Soils 1 and 2, respectively. 

3.2 Geosynthetics 

The following geosynthetics were used in the pullout test program: 

1. two high density polyethylene uniaxial geogrids (Geogrids GG1 and GG2); 

2. a polypropylene biaxial geogrid (Geogrid GG3); 

3. a polypropylene nonwoven spun-bonded geotextile (Geotextile GT1); and 

4. a geocomposite comprising a polypropylene nonwoven spun-bonded geotextile reinforced 

in the machine direction with polyester yarn (Geocomposite GT2). 

The physical properties of Geogrids GG1, GG2, and GG3, Geotextile GT1, and Geocomposite 

GT2 are presented in Table 2 and Figures 5 and 6, Table 3 and Figure 7, and 

Tables 4 and 5, respectively. 



100 

Cumulative fraction passing (%) 

90 

80 

70 

60 

50 

40 

30 

20 

10 

0 

0.05 0.1 0.5 1 5 10 

Particle size (mm) 

Figure 3. 

Soil 1 particle size distribution. 

100 

90 

Cumulative fraction passing (%) 

80 

70 

60 

50 

40 

30 

20 

10 

0 

0.05 0.1 0.5 1 5 10 

Particle size (mm) 

Figure 4. Soil 2 particle size distribution. 


265


t R 

t B 

a L 

a T 

b R 

b B 

18 

Figure 5. 

Geometry of uniaxial Geogrids GG1 and GG2. 

90 

80 

Quality control limit 80 kN/m 

70 

Load (kN/m) 

60 

50 

40 

30 

20 

10 

0 4 8 12 16 

Strain (%) 

Figure 6. 

Tensile behaviour of uniaxial Geogrid GG2. 



Table 2. 

Physical properties of uniaxial Geogrids GG1 and GG2. 

Geogrid 

a L 

(mm) 

a T 

(mm) 

b B 

(mm) 

b R 

(mm) 

t B 

(mm) 

t R 

(mm) 

Tensile strength 

(kN/m) 

Peak strain 

(%) 

GG1 160.0 16.0 16.0 6.0 

GG2 235.0 16.0 16.0 6.0 

2.7 max. 

2.5 min. 

3.7 max. 

3.4 min. 

0.9 55.0 11.5 

1.3 80.0 11.5 

Table 3. 

Physical properties of biaxial Geogrid GG3. 

Geogrid 

a L 

(mm) 

a T 

(mm) 

b LR 

(mm) 

b TR 

(mm) 

t J 

(mm) 

t LR 

(mm) 

t TR 

(mm) 

MD 

(kN/m) 


XMD 

(kN/m) 

Peak 

strain 

(%) 

GG3 33.0 33.0 2.2 2.5 5.8 2.2 1.4 40.0 40.0 11.5 

Note: 

MD = machine direction, XMD = cross-machine direction. 

Table 4. 

Physical properties of nonwoven Geotextile GT1. 

Geotextile 

Thickness 

Mass per unit area 


Peak strain, MD/XMD 

(mm) 

(g/m 2 ) 

(kN/m) 

(%) 

GT1 6.0 800.0 50.0 65.0 / 57.0 

Note: 


t J 

t TR 

t LR 

a L 

b LR 

a T 

W 

b TR 

Figure 7. 

Geometry of biaxial Geogrid GG3. 


267


Table 5. 

Physical properties of Geocomposite GT2. 

Geocomposite 

Thickness 

(mm) 

Mass per 

unit area 

(g/m 2 ) 


Peak strain 

MD 

XMD 

MD 

XMD 

(kN/m) (kN/m) (%) (%) 

GT2 2.5 600.0 95.0 13.0 12.0 75.0 

Note: 


The geosynthetics can be grouped according to their maximum tensile strength values: 

GG1, GG3, and GT1 have maximum tensile strength values ranging from 40 to 

55 kN/m; and GG2 and GT2 have maximum tensile strength values ranging from 80 

to 95 kN/m. 

4 TEST METHOD 

The soil was poured into the pullout box from a constant height of 0.50 m and placed 

in 0.15 m thick layers. Each layer was levelled and compacted to the required unit 

weight using an electric vibratory hammer. The soil unit weight was controlled with a 

nuclear densimeter. When the soil level reached the pullout slot at the front of the box 

(0.3 m), the reinforcement was laid on the surface of the compacted soil and fixed to 

the clamps outside the box. 

The inextensible wires, used to measure the displacement along the reinforcement, 

were then placed and connected to the linear potentiometers at the back and front of the 

box. Five potentiometers were used in the tests. 

Finally, two 0.15 m thick soil layers were placed, levelled, and compacted, resulting 

in a total soil thickness of 0.60 m with the geosynthetic reinforcement at the middle. 

The geosynthetic specimens were 0.96 m long and 0.33 m wide. The normal stress applied 

at the reinforcement height (i.e. at 0.3 m) was 38.0 kPa, and a displacement rate 

of 2 mm/minute was used. Although 13 tests are reported in Table 6, each one was repeated 

twice and, thus, a total of 39 tests was carried out. 

5 ANALYSIS OF TEST RESULTS 

5.1 Introduction 

Each test was repeated twice to determine a mean value and to ensure repeatability 

of the test results. A high degree of reproducibility was achieved as indicated in Figure 

8, which shows the variation of the measured pullout force with the geogrid front displacement 

for the three tests conducted using Geogrid GG2 specimens under the same 

conditions. For the three tests, the greatest variation of the maximum mobilised pullout 

force was 7% (2% for the other two tests). The test results should be presented in terms 

of the mean maximum pullout force value and the standard deviation. 



Table 6. 

Summary of the pullout test program. 

Test Soil Geosynthetic 

T1 

GG1 

T2 

GG2 

T3 Soil 1 GG3 

T4 

GT1 

T5 

GT2 

T6 

GG1 

T7 

GG2 

T8 

GG3 

T9 Soil 2 GT1 

T10 

GT2 

T11 GG1 * WBM 

T12 GG2 * WBM 

T13 GG3 * WBM 

Note: 

* Tests performed with the geogrid bearing members cut between ribs in the direction of pullout. 

40 

35 

Pullout force (kN/m) 

30 

25 

20 

15 

10 

5 

0 

0 20 40 60 80 100 120 

Front displacement (mm) 

Figure 8. 

Pullout test results for three tests using uniaxial Geogrid GG2. 


269


The data collected from the pullout tests includes the variation of the mobilised pullout 

force with front displacement (i.e. reinforcement elongation, Figure 8), the total displacement 

along the reinforcement, and the displacement from integrated strains along 

the reinforcement. Typically, the latter two types of displacement are measured the moment 

when the maximum pullout force is mobilised. 

The displacement from integrated strains along the reinforcement provides information 

regarding the stress transfer from the soil to the reinforcement and, therefore, the 

mobilisation of shear stresses on the soil-reinforcement interface. Finally, it is possible 

to define the bond coefficient, f, of the soil-reinforcement interfaces, as follows: 

f = 

τ 

σ n tan φ 

(4) 

where: τ and σ n = shear and normal stresses at the soil-reinforcement interface, respectively; 

and φ = internal friction angle of the soil. 

The mobilisation of the pullout force with the reinforcement front displacement is 

presented for every case considered. For clarity, the total displacement and the displacement 

from integrated strains at the instant when the maximum pullout force is mobilised 

are presented for only one of the geosynthetics tested in the current study. 

5.2 Influence of Soil Particle Size 

Soil particle size is one of the factors affecting the soil-reinforcement interface behaviour 

in reinforced soil structures and has been studied by Jewell et al. (1984), Palmeira 

and Milligan (1989), Jewell (1990, 1996), Boyle and Holtz (1994), Chen and Chen 

(1994), and Forsman and Slunga (1994). 

Because two different soils are considered in the current study, parameters, such as 

soil unit weight, are distinct and affect the soil-reinforcement interface behaviour. To 

minimize this problem, the two soils were placed in the pullout box with the same relative 

density by adjusting the compaction process. 

Geogrid GG1 exhibits different behaviour when embedded in either Soil 1 or Soil 

2, Figure 9 (Tests T1 and T6 in Table 6). For Geogrid GG1 in Soil 1, the maximum pullout 

force is 40.4 kN/m, mobilised at a front displacement of 106.3 mm. For Geogrid 

GG1 in Soil 2, the maximum pullout force is 38.1kN/m, mobilised at a front displacement 

of 91.0 mm. It is noted that for Soil 2, the geogrid reinforcement fails by tensile 

rupture and not by pullout, which simply means that the pullout resistance is higher than 

the geosynthetic tensile strength. 

This behaviour can be explained by the different relationship between the soil particle 

size and the geogrid aperture size. All Soil 1 particles have an equivalent diameter 

less than 2 mm, while, for Soil 2, 30% of particles are greater than 2 mm in diameter 

with a maximum particle size of 9.54 mm. Soil 1 and 2 particles may penetrate the 

geogrid apertures (16 mm wide) and can mobilize the passive resistance in these members 

because the thickness of the geogrid bearing members ranges from 2.5 and 2.7 mm. 

For Geogrid GG2 (Tests T2 and T7 in Table 6), failure occurs in both soils due to 

a lack of adherence. Geogrid GG2 behaves differently in Soil 2 because its tensile 

strength is greater than that of Geogrid GG1. The failure due to a lack of adherence of 

GG2 when embedded in Soil 2 clarifies the role of soil particle size in the pullout re- 



45 

40 

35 


30 

25 

20 

15 

10 

5 

Geogrid GG1 in Soil 2 


0 

0 50 100 150 200 250 


Figure 9. Pullout test results for uniaxial Geogrid GG1 embedded in Soils 1 and 2. 

sponse of this type of reinforcement. The maximum mobilised pullout force for Geogrid 

GG2 is clearly higher in the tests performed with Soil 2 (Figure 10). In Soil 1, the maximum 

pullout force was 40.4 kN/m at a displacement of 99.3 mm, whereas, for the coarser 

Soil 2, the maximum pullout force is approximately 24% higher at 49.9 kN/m for a 

displacement of 136.8 mm (Figure 10). 

This confirms the importance of soil particle size relative to geogrid aperture size 

and thickness of bearing members. Soil particles smaller than the geogrid aperture size 

can penetrate the geogrid, but are less effective in mobilizing the passive resistance in 

the bearing members as in the case of Soil 1. However, soils with a significant percentage 

of particles larger than the geogrid aperture could lead to a worse situation because 

the particles cannot enter the apertures and would limit the mobilisation of the soil-reinforcement 

interface to skin friction at the contact points between soil particles and the 

planar surface of the reinforcement (Jewell et al. 1984). 

Figure 11 shows the total displacement (Figure 11a) and the displacement from integrated 

strains along the specimen length (Figure 11b) for Geogrid GG2 embedded in 

Soils 1 and 2. Displacements calculated from strains provides information with regard 

to shear stress mobilisation along the reinforcement and, therefore, the process of stress 

transfer from the soil to the reinforcement. The shear stresses mobilised between Geogrid 

GG2 and Soil 2 are clearly higher than those mobilised between Geogrid GG2 and 

Soil 1. This leads to the increase of interface strength as verified for the Geogrid GG1- 

Soil 2 interface. 

In analyzing the test results for biaxial Geogrid GG3 embedded in Soils 1 and 2 (Figure 

12) (Tests T3 and T8 in Table 6), it can be concluded that the influence of soil par- 


271


60 

50 


40 

30 

20 

10 



0 

0 50 100 150 200 



ticle size is not significant. In both cases, the reinforcement fails by tensile rupture with 

an identical maximum pullout force of 31 kN/m, i.e. approximately the tensile strength 

of the geogrid. This result would be expected considering the 33 mm aperture size and 

the 1.4 mm grid thickness relative to the particle sizes of the soils. 

In Figure 13, the influence of the soil particle size on the pullout behaviour of the nonwoven 

Geotextile GT1 (Tests T4 and T9 in Table 6) is presented in terms of the variation 

of pullout force with front displacement. Due to its higher extensibility and interaction 

mechanism, which involves mobilisation of skin friction over its surface, a geotextile 

behaves differently than a geogrid. The maximum pullout forces are lower than those 

for Geogrid GG1, but the corresponding front displacement is larger (Table 7). 

Figure 14 shows the variation of the mobilised pullout force with the front displacement 

of Geocomposite GT2 embedded in Soils 1 and 2 (Tests T5 and T10 in Table 6). 

The type of soil appears to have a slightly greater influence on the interface shear 

strength when Geocomposite GT2 is used instead of Geotextile GT1. The maximum 

pullout forces on Geocomposite GT2, for a front displacement of approximately 100 

mm, are approximately 40 and 49 kN/m for Soils 1 and 2, respectively. 

The observed behaviour could be the result of the significantly lower deformability 

of Geocomposite GT2 in the longitudinal direction (test direction, Table 5) when 

compared with that of the nonwoven Geotextile GT1 (Tables 4 and 5) and from the wider 

particle size distribution of Soil 2 when compared to that of Soil 1 (Figures 3 and 4, 

respectively). 



(a) 

140 

120 



Total displacement (mm) 

100 

80 

60 

40 

20 

(b) 

Displacement from integrated strains (mm) 

0 

1 2 3 4 5 6 

Geogrid bearing member counted from front of specimen 

80 

70 



60 

50 

40 

30 

20 

10 

0 

1 2 3 4 5 6 


Figure 11. Pullout test results for uniaxial Geogrid GG2 embedded in Soils 1 and 2: 

(a) total displacement; (b) displacement from integrated strains along the specimen length. 


273


35 

30 


25 

20 

15 

10 

5 

0 



0 10 20 30 40 50 60 70 


Figure 12. Pullout test results for biaxial Geogrid GG3 embedded in Soils 1 and 2. 

16 

14 


12 

10 

8 

6 

4 

2 

0 

Geotextile GT1 in Soil 2 


0 50 100 150 200 


Figure 13. Pullout test results for Geotextile GT1 embedded in Soils 1 and 2. 



Table 7. Maximum pullout force, F max , and corresponding front displacement, u max ,for 

Geogrid GG1 and Geotextile GT1. 

Soil 1 Soil 2 

Geosynthetic 


Peak strain 

(kN/m) (%) 

F max u max F max u max 

(kN/m) (mm) (kN/m) (mm) 

GT1 50.0 65.0 / 57.0 14.2 * 161.3 12.3 * 199.8 

GG1 55.0 11.5 40.4 106.3 38.1 * 91.0 

Note: 

* Failure occurs by lack of tensile strength. 

60 

50 


40 

30 

20 

10 

Geocomposite GT2 in Soil 2 


0 

0 20 40 60 80 100 120 


Figure 14. Pullout test results for Geocomposite GT2 embedded in Soils 1 and 2. 

The higher stiffness of Geocomposite GT2 results in an increase of interface shear 

strength when the effective contact area between the soil and the reinforcement increases, 

which occurs with wider soil particle size distributions. 

For Soils 1 and 2, Geocomposite GT2 fails due to a lack of tensile strength in the 

unconfined area of the sleeve, essentially because polyester yarns are damaged during 

the reinforcement clamping procedure, which induces local strength reductions. (A 

0.20 m long steel sleeve was used inside the pullout box to reduce the frictional effect 

of the front wall boundary (Lopes and Ladeira 1996, Figure 1).) 

Based on the presented test results thus far, it was expected that Geocomposite GT2 

would exhibit a higher pullout strength than those recorded in the current study. 


275


It can be concluded, from the test results analysed in Section 5.2, that soil particle 

size significantly influences the soil-geosynthetic interaction mechanism, particularly 

for geogrids, with respect to reinforcement aperture dimensions, structure, and stiffness. 

5.3 Influence of Geosynthetic Structure 

Based on the tensile strength of the tested geosynthetics, the following two sets of 

geosynthetics were chosen in order to analyse the influence of geosynthetic structure 

on soil-geosynthetic interface shear resistance: (i) Set 1, comprising Geogrid GG2 and 

Geocomposite GT2; and (ii) Set 2, comprising Geogrid GG1, Geogrid GG3, and Geotextile 

GT1. Sets 1 and 2 used Soils 1 and 2. 

Figure 15 shows the variation of pullout force with displacement for Geogrid GG2 

and Geocomposite GT2 (Tests T7 and T10 in Table 6). It can be seen that, although having 

similar tensile strength and peak strain values (Tables 2 and 5, respectively), both 

geosynthetics exhibit different pullout behaviour. While Geogrid GG2 mobilises pullout 

forces upon commencement of a test, Geocomposite GT2 exhibits a more ductile 

response. For Geocomposite GT2 and small front displacement values, the pullout 

force is approximately zero, only starting to increase at a front displacement of approximately 

10 mm when the strong polyester yarns become effective. The maximum pull- 

60 

50 


40 

30 

20 

10 



0 

0 50 100 150 200 


Figure 15. Pullout test results for Geocomposite GT2 and uniaxial Geogrid GG2 in Soil 2. 



out force recorded for both Geogrid GG2 and Geocomposite GT2 is similar; however, 

Geocomposite GT2 fails by tensile rupture outside the pullout box, suggesting that its 

true pullout resistance is higher than that observed during the test. 

Figure 16 shows the variation of pullout force with displacement for Set 2 geosynthetics 

comprising Geogrid GG1, Geogrid GG3, and Geotextile GT1 (Tests T1, T3, and 

T4 in Table 6, respectively). Although their tensile strength values are in the same range 

(Tables 2, 3, and 4, respectively), these three geosynthetics exhibit different pullout behaviour. 

The uniaxial Geogrid GG1, being the more resistant and less extensible geosynthetic, 

fails by lack of adherence at a maximum pullout force of 40.4 kN/m and 

displacement of 106.3 mm. The potentially high pullout resistance of Geogrid GG3, 

having a lower tensile strength than Geogrid GG1, leads to failure by tensile rupture. 

The pullout behaviour of Geotextile GT1 is completely different from that observed 

for Geogrids GG1 and GG3. Although Geotextile GT1 has a similar tensile strength to 

Geogrid GG1, it is the most extensible. The extensibility of Geotextile GT1 does not 

allow the mobilisation of pullout forces, as in less extensible materials such as geogrids, 

and has a maximum measured pullout force of 14.2 kN/m at a displacement of 160.0 

mm (Figure 16). 

45 

40 

35 


30 

25 

20 

15 

10 

5 

0 

0 

50 100 150 200 250 





Figure 16. Pullout test results for Geotextile GT1 and uniaxial Geogrid GG1 and biaxial 

Geogrid GG3 in Soil 1. 


277


5.4 Influence of Geogrid Bearing Members 

The following are interaction mechanisms that can be mobilised in soil-geogrid interfaces 

during pullout: (i) skin friction over the planar geogrid surface; (ii) soil-soil 

friction through the geogrid apertures; and (iii) passive resistance of the geogrid bearing 

members. 

To assess the contribution of the third mechanism, three pullout tests were performed 

(Tests T11, T12, and T13 in Table 6) with the geogrid bearing members cut between 

ribs in the direction of pullout. The tests were carried out using Soil 2, and the 

results are compared with those of intact geogrids tested in similar conditions. 

Figure 17 shows the variation of pullout force with displacement for Geogrid GG1 

and Geogrid GG1 without bearing members, GG1 WBM (Tests T6 and T11 in Table 6, 

respectively). It can be seen that the maximum recorded pullout force reduces by 

approximately 27% for specimens tested without bearing members. This behaviour emphasizes 

the importance of the passive resistance mobilised on the geogrid bearing 

members. It should be noted that Geogrid GG1 failed due to tensile rupture and not lack 

of adherence, as did Geogrid GG1 WBM , because of the increase in interface shear resistance 

resulting from mobilisation of passive resistance on the geogrid bearing members. 

40 

35 


30 

25 

20 

15 

10 

5 


Geogrid GG1 WBM in Soil 2 

0 

0 50 100 150 


Figure 17. Pullout test results for uniaxial Geogrid GG1 and uniaxial Geogrid GG1 

without bearing members, GG1 WBM . 



It should also be noted that, if GG1 did not fail by tensile rupture, the difference between 

the results would be greater. 

The variation of the pullout force with the front displacement of Geogrid GG2 and 

Geogrid GG2 without bearing members, GG2 WBM , is presented in Figure 18 (Tests T7 

and T12 in Table 6, respectively). The decrease of soil-geogrid interface shear resistance 

observed for Geogrid GG2 WBM is approximately 25%, and both geogrid specimens 

failed due to a lack of adherence. The measured decrease of interface shear resistance 

for Geogrids GG2 and GG2 WBM is smaller than that for Geogrids GG1 and GG1 WBM , 

which may be caused by the reduction of the soil particle size-to-width ratio of the Geogrids 

GG1 and GG1 WBM bearing members. 

Figure 19 shows the variation of the pullout force with displacement for Geogrid 

GG3 and Geogrid GG3 without bearing members, GG3 WBM (Tests T8 and T13 in Table 

6, respectively). The influence of the bearing members on the pullout behaviour of the 

biaxial geogrids is less significant than that of the uniaxial geogrids (Figures 17 and 18). 

However, until tensile rupture failure occurs in both Geogrid GG3 and GG3 WBM specimens, 

the recorded pullout force is lower for specimens without bearing members 

(GG3 WBM ) with a maximum difference of approximately 13%. Failure by tensile rupture 

likely masks the effect of the geogrid bearing members on pullout resistance. 

60 

50 


40 

30 

20 

10 



0 

0 50 100 150 200 250 



without bearing members, GG2 WBM , in Soil 2. 


279


35 

30 


25 

20 

15 

10 

5 Geogrid GG3 in Soil 2 


0 

0 20 40 60 80 100 


Figure 19. Pullout test results for biaxial Geogrid GG3 and biaxial Geogrid GG3 without 

bearing members, GG3 WBM , in Soil 2. 

6 CONCLUSIONS 

The current study considers the influence of soil particle size, geosynthetic structure, 

and geogrid bearing members on pullout behaviour. The following are the most 

significant conclusions of this study: 

S Soil particle size hasan important influence onsoil-geosynthetic interface behaviour. 

S For geogrids, the relative dimensions of the soil particles, geogrid apertures, and the 

thickness of the bearing members determine the soil-geosynthetic interface shear 

strength. 

S An increase of soil-geogrid shear resistance exceeding 20% was observed when the 

soil contained a significant percentage of particle sizes slightly greater than the geogrid 

bearing member thickness, but less than the geogrid aperture size. 

S The influence of soil particle size is less significant for nonwoven geotextiles, which 

is likely due to their high extensibility. 

S Geocomposite interface shear strength increases slightly when the soil particle size 

range increases. 



S Cutting the geogrid bearing members leads to a significant decrease in the soil-geogrid 

interface shear resistance, thus, clarifying the important role of the mobilisation 

of passive resistance on transverse geogrid members. 

S At a given displacement, geosynthetics with greater axial tensile stiffness mobilise 

greater pullout resistance than geosynthetics with lower axial tensile stiffness. 

ACKNOWLEDGMENTS 

The authors are grateful for the financial support of Program PRAXISXXI and FED- 

ER, Research Project 3/3.1/CEG/2598/95. 

REFERENCES 

Boyle, S.R. and Holtz, R.D., 1994, “Deformation Characteristics of Geosynthetic-Reinforced 

Structures”, Proceedings of the Fifth International Conference on Geotextiles, 

Geomembranes and Related Products, Vol. 1, Singapore, September 1994, pp. 

361-364. 

Chen, R.-H. and Chen, C.-C., 1994, “Investigation of Pull-Out Resistance of Geogrids”, 

Proceedings of the Fifth International Conference on Geotextiles, Geomembranes 

and Related Products, Vol. 1, Singapore, September 1994, pp. 461-464. 

Forsman, J. and Slunga, E., 1994, “The Interface Friction and Anchor Capacity of Synthetic 

Georeinforcements”, Proceedings of the Fifth International Conference on 

Geotextiles, Geomembranes and Related Products, Vol. 1, Singapore, September 

1994, pp. 405-410. 

Jewell, R.A., 1990, “Reinforced Bond Capacity”, Geotechnique, Vol. 40, No. 3, pp. 

513-518. 

Jewell, R.A., 1996, “Soil Reinforcement with Geotextiles”, CIRIA and Thomas Telford, 

London, United Kingdom, 332 p. 

Jewell, R.A., Milligan, G.W.E., Sarsby, R.W. and DuBois, D., 1984, “Interaction Between 

Reinforcement and Geogrids”, Polymer Grid Reinforcement, Thomas Telford, 

1985, Proceedings of a conference held in London, UK, March 1984, pp. 18-30. 

Lopes, M.L. and Ladeira, M., 1996, “Role of the Specimen Geometry, Soil Height, and 

Sleeve Length on the Pull-Out Behaviour of Geogrids”, Geosynthetics International, 

Vol. 3, No. 6, pp. 701-719. 

Palmeira, E.M. and Milligan, G.W.E., 1989, “Scale and Other Factors Affecting the Results 

of Pull-Out Tests of Grids Buried in Sand”, Geotechnique, Vol. 39, No. 3, pp. 

511-524. 


281


NOTATIONS 

Basic SI units are given in parentheses. 

a L = distance between uniaxial geogrid bearing members, or longitudinal 

distance between biaxial geogrid ribs (m) 

a T = aperture width of uniaxial geogrids, or transverse distance between 

biaxial geogrid ribs (m) 

b LR = width of biaxial geogrid longitudinal ribs (m) 

b R = width of uniaxial geogrid bearing members (m) 

b TR = width of biaxial geogrid transverse ribs (m) 

C C = coefficient of curvature of soil (dimensionless) 

C U = coefficient of uniformity of soil (dimensionless) 

D max = maximum soil particle diameter (m) 

D min = minimum soil particle diameter (m) 

D 10 = soil particle diameter corresponding to 10% by weight of finer particles 

(m) 


(m) 


(m) 


(m) 

f = bond coefficient (dimensionless) 

F max = maximum pullout force (N/m) 

I D = relative density of soil (%) 

t B = thickness of uniaxial geogrid bearing members (m) 

t R = thickness of uniaxial geogrid ribs (m) 

t J = thickness of biaxial geogrid junctions (m) 

t LR = thickness of biaxial geogrid longitudinal ribs (m) 

t TR = thickness of biaxial geogrid transverse ribs (m) 

u max = front displacement for the maximum pullout force (m) 

φ = internal friction angle of soil (_) 

γ = unit weight of soil (N/m 3 ) 

γ max = maximum unit weight of soil (N/m 3 ) 

γ(ID = 55%) = unit weight of soil at relative density of 55% (N/m 3 ) 

γ = unit weight of soil (N/m 3 ) 

σ n = normal stress (N/m 2 ) 

τ = shear stress (N/m 2 ) 


Errata 

SOIL-GEOSYNTHETIC INTERACTION – 

INFLUENCE OF SOIL PARTICLE SIZE AND 

GEOSYNTHETIC STRUCTURE 

TECHNICAL PAPER FOR ERRATA: Lopes, M.J. and Lopes, M.L., 1999, 

“Soil-Geosynthetic Interaction - Influence of Soil Particle Size and Geosynthetic 

Structure”, Geosynthetics International, Vol. 6, No. 4, pp. 261-282. 

PUBLICATION: Geosynthetics International is published by the Industrial Fabrics 

Association International, 1801 County Road B West, Roseville, Minnesota 

55113-4061, USA, Telephone: 1/651-222-2508, Telefax: 1/651-631-9334. 

Geosynthetics International is registered under ISSN 1072-6349. 

REFERENCE FOR ERRATA: Lopes, M.J. and Lopes, M.L., 1999, “Errata for 

‘Soil-Geosynthetic Interaction - Influence of Soil Particle Size and Geosynthetic 

Structure’”, Geosynthetics International, Vol. 6, No. 5, pp. 449-453. 

Due to a software malfunction during final printing, several errors were incurred to 

the authors paper, which appeared in Geosynthetics International, Vol. 6, No. 4, pp. 

261-282. The Editors sincerely regret this error and any inconveniences this may have 

caused the authors and the readership. 

ERRATUM FOR SECTION: 

5.1 Introduction 

The x-axis label for Figure 8 on page 269 in Section 5.1 did not print correctly. The corrected 

Figure 8 is on page 450 of the current Errata. 

ERRATA FOR SECTION: 

5.2 Influence of Soil Particle Size 

The x-axes labels for Figures 10, 11, and 12 on pages 272, 273, and 274, respectively, 

in Section 5.2 did not print correctly. The corrected figures are on pages 450, 451, and 

452 of the current Errata. 


449

ERRATA D Soil-Geosynthetic Interaction 

40 

35 


30 

25 

20 

15 

10 

5 

0 

0 20 40 60 80 100 120 


Figure 8. 

Pullout test results for three tests using uniaxial Geogrid GG2. 

60 

50 


40 

30 

20 

10 



0 

0 50 100 150 200 





(a) 

140 

120 



Total displacement (mm) 

100 

80 

60 

40 

20 

(b) 

Displacement from integrated strains (mm) 

0 

1 2 3 4 5 6 


80 

70 



60 

50 

40 

30 

20 

10 

0 

1 2 3 4 5 6 


Figure 11. Pullout test results for uniaxial Geogrid GG2 embedded in Soils 1 and 2: 

(a) total displacement; (b) displacement from integrated strains along the specimen length. 


451


35 

30 


25 

20 

15 

10 

5 

0 



0 10 20 30 40 50 60 70 


Figure 12. Pullout test results for biaxial Geogrid GG3 embedded in Soils 1 and 2. 


5.3 Influence of Geosynthetic Structure 

The x-axis label for Figure 16 on page 277 in Section 5.3 did not print correctly. The 

corrected Figure 16 is on page 453 of the current Errata. 


5.4 Influence of Geogrid Bearing Members 

The x-axis label for Figure 17 on page 278 in Section 5.4 did not print correctly. The 

corrected Figure 17 is on page 453 of the current Errata. 




45 

40 

35 

30 

25 

20 

15 

10 

5 

0 

0 




50 100 150 200 250 


Figure 16. Pullout test results for Geotextile GT1 and uniaxial Geogrid GG1 and biaxial 

Geogrid GG3 in Soil 1. 

40 

35 


30 

25 

20 

15 

10 

5 



0 

0 50 100 150 



without bearing members, GG1 WBM . 


453

soil-geosynthetic interaction - IGS - International Geosynthetics Society

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