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Investigation of installation damage of some geogridsusing laboratory tests

Huang Ching-Chuan1 and Chiou Shuay-Luen2

1Professor, Department of Civil Engineering, National Cheng Kung University, No. 1, Ta-Hsueh

Road, Tainan, Taiwan 70101, Telephone: +886 6 2757575, Telefax: +886 6 2358542,

E-mail: [email protected] student, Department of Civil Engineering, National Cheng Kung University, No. 1,

Ta-Hsueh Road, Tainan, Taiwan 70101, Telephone: +886 6 2757575, Telefax: +886 6 2358542,

E-mail: [email protected]

Received 7 December 2004, revised 25 September 2005, accepted 19 October 2005

ABSTRACT: A series of laboratory tests simulating installation damage was carried out on four

types of woven geogrid. Relationships between index properties of the geogrids and the loss in

ultimate tensile strength, strain at failure and tensile stiffness of the geogrids are presented. For the

geogrids investigated, the ratio of volume of coating material to the mass of yarn (V-M ratio)

plays a major role in evaluating the loss of ultimate tensile strength: that is, the amount of

ultimate strength loss decreases with an increase in V-M ratio. The V-M ratio also plays a part in

the stress–strain characteristics of the damaged geogrids: for a regularly coated geogrid (PET yarn

+ PVC coating with a relatively low V-M ratio), similar amounts of ultimate strength and strain

losses were found; for a similar geogrid with a relatively high V-M ratio, the amount of ultimate

strain loss was only about 50% of the ultimate strength loss. The experimental results also indicate

that the losses of tensile stiffness at 2% and 5% strains seem to be governed by the types of yarn

and coating material, regardless of their V-M ratio.

KEYWORDS: Geosynthetics, Installation damage, Geogrid, Laboratory tests, Reduction factor,

Ultimate tensile strength, Tensile strain, Tensile stiffness

REFERENCE: Huang, C.-C. & Chiou, S.-L. (2006). Investigation of installation damage of some

geogrids using laboratory tests. Geosynthetics International, 13, No. 1, 23–35

1. INTRODUCTION

Geogrid durability is gaining increasing attention because

of new engineering and environmental applications of

geogrids. The resistance of geogrids to installation damage

has been investigated using full-scale field trials since

1980s. Full-scale field tests have been suggested by the

American Society for Testing and Materials (ASTM 5818)

and the British Standards Institution (BS 8006).

Table 1 summarises the results of various full-scale

trials on the installation damage of geogrids subjected to

compaction. From the results of these trials design guide-

lines have been developed for the use of a reduction

factor, FID, for deriving the design value of ultimate tensile

strength of the geogrid against installation damage:

FID ¼ Tf

Tfd

(1)

where Tf is the ultimate tensile strength of the intact

geogrid, and Tfd is the ultimate tensile strength of the

damaged geogrid.

In the design guidelines of the Federal Highway Admin-

istration (FHWA; Elias 2001), design values of FID are

also suggested according to the above–mentioned full-

scale field tests (see Table 2). In these guidelines the

particle size is taken as a major factor in determining the

design values of FID . The high values of FID (1.30 to

1.85) suggested by FHWA in Table 2 seem to be

supported by the data shown in Table 1. Higher values of

FID were obtained when coarse aggregates were used: FID

¼ 2.17 (Troost and Ploeg 1990); FID ¼ 1.48–1.88 and

1.54–1.81 (Rainey and Barksdale 1993); FID ¼ 2.01 and

1.78 (Muller-Rochholz and Mannsbart 2004); and FID ¼1.81 (Pinho-Lopes et al. 2000, 2002) Smaller values of

FID were obtained by Hufenus et al. (2005): FID ¼ 1.05–

1.10 for a sandy soil with D50 � 0.35 mm and FID ¼1.05–1.56 for coarse aggregates with D50 � 3–6 mm.

This was due to the smaller compaction energy (10 kN

vibratory roller) compared with those used in other full-

scale trials as summarised in Table 1.

Hufenus et al. (2005) performed a comprehensive study

on the resistance of geosynthetics to installation damage

using 470 test results obtained in 16 field installation

Geosynthetics International, 2006, 13, No. 1

231072-6349 # 2006 Thomas Telford Ltd

Table1.Comparisonoftest

conditionsand

reduction

factors

forinstallation

damageobtained

infull-scale

and

laboratory

tests

Author(date)

Geogridtype

Compactionequipment

Liftthickness

Particletypes

Geogridultim

ate

strength

inmachine

direction(kN/m

)

FID

(2%)

FID

(5%)or

FID

(6%)

FID

Troost

andPloeg

PETyarn(b)

Vibratingplate

compactor

200mm

SW

(well-graded

sand)

150

–FID

(6%)¼

1.04

1.17

(1990)

Dmax:2mm

200

–FID

(6%)¼

1.11

1.16

D50about0.7mm

400

–FID

(6%)¼

0.96

1.09

600

–FID

(6%)¼

0.93

1.08

Dual

Bomag

vibratingroller

200mm

GS

(sandygravel)

150

–FID

(6%)¼

1.05

1.34

(22kN/m

)Gap-graded

200

––

–

Dmax:100mm

400

–FID

(6%)¼

0.86

1.14

D50about0.3mm

600

–FID

(6%)¼

0.91

1.10

GP

(basaltstone)

150

–FID

(6%)¼

1.18

2.17

Dmax:200mm

200

––

–

D50about40mm

400

–FID

(6%)¼

1.11

1.54

600

–FID

(6%)¼

1.06

1.33

PETyarn+

PVC

Vibratingplate

compactor

200mm

SW

(well-graded

sand)

35

–FID

(6%)¼

1.03

1.09

coating(a)

Dmax:2mm

55

–FID

(6%)¼

1.07

1.02

D50about0.7mm

80

–FID

(6%)¼

0.99

1.00

Dual

Bomag

vibratingroller

200mm

GS

(sandygravel)

35

–FID

(6%)¼

0.91

1.15

(22kN/m

)Gap-graded

55

–FID

(6%)¼

1.08

1.03

Dmax:100mm

D50about0.3mm

80

–FID

(6%)¼

1.14

1.02

GP

(basaltstone)

35

–FID

(6%)¼

0.97

1.18

Dmax:200mm

55

–FID

(6%)¼

0.97

1.22

D50about40mm

80

–FID

(6%)¼

1.09

1.03

Rainey

and

PETyarn+

AL

Lightvibratory

roller

orheavy

150mm

or

SG

(gravelly

sand)

32.5

––

1.15–1.29

Barksdale(1993)

coating(b)

vibratory

roller

250mm

Dmax:8mm

D50about0.8mm

109.9

––

1.33–1.37

GP

(crushed

stone)

32.5

––

1.50–2.02

Uniform

-graded

Dmax:50mm

D50about30mm

109.9

––

1.48–1.88

SM

(silty

sand)

32.5

––

1.05

Dmax:20mm

D50about0.2mm

109.9

––

1.13–1.15

PETyarn+

PVC

Lightvibratory

roller

orheavy

150mm

or

SG

(gravelly

sand)

68.3

––

1.07–1.20

coating(a)

vibratory

roller

250mm

Dmax:8mm

94.7

––

1.16–1.22

D50about0.8mm

196.9

––

1.22–1.30

GP

(crushed

stone)

|68.3

––

1.35–1.85

Uniform

-graded

Dmax:50mm

94.7

––

1.26–1.65

D50about30mm

196.9

––

1.54–1.81

SM

(silty

sand)

68.3

––

0.95–1.02

Dmax:20mm

94.7

––

1.14–1.14

D50about0.2mm

196.9

––

1.06–1.09

Sandri

etal.(1993)PETyarn+

Caterpillarsheepsfootroller

or

230mm

GP

(rock

fill

material)

29.2

––

–

AL

coating(b)

100kN

static

smooth

drum

roller

Dmax:75mm

52.5

––

1.08–1.18

D50about3.5mm

93.4

––

1.05

24 Huang and Chiou


124.0

––

–

GP

(slopedrain

material)

29.2

––

1.17

Dmax:75mm

52.5

––

1.11–1.13

D50about3.5mm

93.4

––

1.08–1.11

124.0

––

1.13–1.15

Hsieh

andWu

PETyarn+

PVC

Vibratory

steelwheelcompactor

150mm

GW

(crushed

stone)

60

–FID

(5%)¼

1.08

1.32

(2001)

coating(a)

(43kN/m

)and

Dmax:80mm

100

–FID

(5%)¼

1.70

1.19

300mm

D50about30mm

150

–FID

(5%)¼

1.19

1.18

200

–FID

(5%)¼

0.83

1.20

GC

60

–FID

(5%)¼

1.17

1.10

Dmax:80mm

100

–FID

(5%)¼

1.74

1.09

D50about7mm

150

–FID

(5%)¼

1.28

1.12

200

–FID

(5%)¼

1.04

1.10

GP–GM

60

–FID

(5%)¼

1.09

1.33

Dmax:50mm

|100

–FID

(5%)¼

1.38

1.20

D50about11mm

150

–FID

(5%)¼

1.22

1.17

200

–FID

(5%)¼

1.03

1.21

Pinho-Lopes

etal.

(2000,2002)

Woven

PETyarn

–200mm

Well-graded

aggregates

usedin

road

construction

60

––

–

D50:10mm

55

––

1.81

Residual

soil

ofgranite,

60

––

1.13

D50:0.3

mm

55

––

1.34

Muller-Rochholz

KnittedPETyarn

65kN

roller

compactor

300–500mm

Fourtypes

ofaggregate,

30

1.02(d)

–2.01(d)

andMannsbart

includingcrushed

limestone

50

1.03(d)

–1.78(d)

(2004)

(Dmax

�100mm)andriver

gravel

120

1.12(d)

–1.36(d)

(Dmax

�65mm)

200

1.06(d)

–1.07(d)

Hufenuset

al.

KnittedPETyarn

10kN

vibratory

roller

230mm

Well-graded

sand(0–4mm)

38

––

1.05

(2005)

+PVC

coating

(D50�

0.35mm)

52

––

1.10

160

––

1.10

Well-graded

rounded

gravel

(0–60mm)

38

––

1.32

(D50�

3mm)

52

––

1.10

160

––

1.02

Well-graded

crushed

stone

(0–22mm)

38

––

1.56

(D50�

6mm)

52

––

1.05

160

––

1.13

This

study

PVA

yarn+

PP

coating(c)

Load

intensity

q>5kPaand

q<900kPa

30mm

Sinteredaluminium

dioxide

Particlesize

¼5–10mm

and

19–25mm

60(G

RID

1)

0.98–1.06

FID

(5%)¼

0.99–1.07

0.99–1.14

PETyarn+

PVC

coating(a)

Load

intensity

q>5kPaand

q<900kPa

30mm

Sinteredaluminium

dioxide

Particlesize

¼5–10mm

and

19–25mm

60(G

RID

2)

0.99–1.05

FID

(5%)¼

0.98–1.03

1.03–1.37

60(G

RID

3)

1.00–1.06

FID

(5%)¼

0.99–1.04

0.99–1.16

150(G

RID

4)

0.99–1.04

FID

(5%)¼

0.97–1.03

1.00–1.29

(a) PET

¼polyester,

PVC

¼poly(vinylchloride).

(b) PET

¼polyester,AL

¼acryliclatex.

(c) PVA

¼poly(vinylalcohol),PP¼

polypropylene.

(d) Averagevalueforfourdifferenttypes

ofaggregate.

Investigation of installation damage of some geogrids using laboratory tests 25


damage tests. Values of FID for PVC-coated PET geogrids

suggested by Hufenus et al. (2005) are shown in Table 2.

It can be seen that the main factors controlling the values

of FID are the aggressiveness of aggregates (in terms of

particle size and sharpness) and the compaction energy (in

terms of ground pressure and number of passes). It is also

seen in Table 2 that for compaction using higher ground

pressure (.55 kPa) and coarse aggregates the suggested

range of FID ¼ 1.3–2.1 is larger than that suggested by

FHWA (FID ¼ 1.30–1.85).

Allen and Bathurst (1994) found that the percentage of

tensile stiffness reductions at 2% and 5% strain is

significantly smaller than the percentage of ultimate

strength reduction for damaged geogrids based on full-

scale field compaction tests on flexible geogrids reported

by Troost and Ploeg (1990), Rainey and Barksdale (1993)

and Sandri et al. (1993). It can be seen in Table 1 that the

values of FID(5%) and FID(6%) (reduction factors for tensile

stiffness reduction at 5% and 6% strain) are generally less

than those of FID, with minor exceptions for the tests

performed by Troost and Ploeg (1990). However, in the

case reported by Hsieh and Wu (2001), more than half the

tests gave FID(5%) > FID . This discrepancy is investigated

in detail by using laboratory simulations in the present

study.

Another controversial issue revealed in Table 1 is the

dependence of Tf on the value of FID . In the tests

performed by Troost and Ploeg (1990) and Muller-

Rochholz and Mannsbart (2004) FID decreased with in-

crease in Tf, but the tests by Rainey and Barksdale (1993),

Sandri et al. (1993) and Hsieh and Wu (2001) showed no

such clear dependence. This issue is also investigated in

the present study.

Up to now, both full-scale field tests and laboratory

simulation tests have used commercially available geogrid

products with a range of yarns and coatings. The effect

of the amount and types of yarn and coating material on

the strength loss of geogrids has rarely been studied. In

the geogrid industry it is well known that the cost of the

coating material constitutes a substantial part of the total

cost of flexible geogrids. When geogrids are applied to

harsh environments, such as the ground consisting of

crushed stones or gravelly soils, the use of a coating

layer with enhanced damage resistance to reduce the

design value of FID may be of practical significance. The

present study aims to give an insight into the relation-

ships between the amount (and type) of coating and the

strength loss of woven geogrids via a series of laboratory

installation damage tests.

2. TEST SET-UP

A hydraulic cyclic loading system with a maximum

capacity of 80 kN and a maximum loading rate of 3 Hz

was used in the present study (Figure 1). Two rigid steel

boxes 300 mm long, 300 mm wide and 150 mm high were

used to contain aggregates and geogrids for the tests.

Figure 2 shows a loading plate, made of a steel plate

200 mm long, 100 mm wide and 50 mm thick placed at

the centre of the rigid box. Figure 3 shows a typical

Table 2. Suggested values of FID

Organisations Type of geogrid Particle types FID

FHWA

(Elias, 2001)

PET yarn + PVC

coating

Backfill

Max. particle size:100 mm

D50 about 30 mm

1.30–1.85

Backfill

Max. particle size: 20 mm

D50 about 0.7 mm

1.10–1.30

Hufenus et al.

(2005)

PET yarn +

PVC coating

Fine-grained soils

(clay, silt, sand)

1.1–1.4(a)

Rounded coarse-grained soil

, 150 mm

1.1–1.5(a)

Angular coarse-grained soil

, 150 mm

1.2–1.8(a)

Fine-grained soils (clay, silt, sand) 1.2–1.7(b)

Rounded coarse-grained soil

, 150 mm

1.2–1.8(b)

Angular coarse-grained soil

, 150 mm

1.3–2.1(b)

*For ground pressure , 55 kPa; multiply by 1.19 when number of passes . 8.(b)For ground pressure . 55 kPa; multiply by 1.19 when number of passes .8.

Figure 1. Servo-controlled cyclic loading system and test box

for simulating installation damage of geogrids

26 Huang and Chiou


example of the relationship of load intensity against time

obtained in the tests. The total time is considerably

shortened in this figure for the sake of simplicity. For all

tests, the load intensities were controlled within �5% of

the desired values. A local displacement transducer was

used to measure the local elongation of the wide geogrid

specimens (Figure 4), modified as follows:

• It covered the full width (200 mm) of the geogrid

specimen, in order to measure the average elongation

induced by all strands of the specimen and hence

eliminate possible errors in strain measurement

caused by non-uniformly damaged strands.

• A gauge length of 200 mm (instead of the conven-

tional 100 mm) was used, so that possible damage

induced by load spread from the 100 mm-wide

loading plate could be measured.

The test medium used was sintered aluminium dioxide. In

order to investigate the effect of particle size on geogrid

damage, two particle sizes were used (Figure 5). Figure 6

shows the particle size distribution curves for the aggre-

gates used in the present study. Particle 4 (P4), with

particle sizes ranging between 5 mm and 10 mm, is

specified in DD ENV ISO 10722-1 as a standard particle

size. The similarity between the chemical composition of

the aggregates used in this study and those specified in

DD ENV ISO 10722-1 is shown in Table 3. The methods

Figure 2. Split test box and loading plate

�

��

��

��

��

��

��

��

�� !

��

��!

� �� "�

Figure 3. Example of load intensity against time. Targeted load intensity is 900 kPa under frequency of 1.0 Hz. For simplicity,

only a duration of 30 s is shown



used to prepare the geogrid specimens and place the

aggregates, geogrids and loading plate were identical to

those specified in DD ENV ISO 10722-1.

3. PROPERTIES OF GEOGRIDS

Figures 7a to 7d show the four types of flexible geogrid

used in this study, and their physical properties are listed

in Table 4:

• GRID 1: poly(vinyl alcohol) (PVA) yarn coated

with regular amount of polypropylene (PP, about

177 g/m2;

• GRID 2: polyester (PET) yarn coated with regular

amount of poly(vinyl chloride) (PVC, about 155

g/m2;

• GRID 3: PET yarn heavily coated with PVC (about

289 g/m2; and

• GRID 4: PET yarn coated with regular amount of

PVC (about 232 g/m2.

��

Figure 4. Modified local strain meter used in this study

� �� "� ��!

��! �#!

$%&��'��(�

� �� "� ��!

Figure 5. Two groups of sintered aluminium dioxide used in this study: (a) Particle 1, 19–25 mm; (b) Particle 4, 5–10 mm

�

��

��

��

��

��

��)�� !

��

�)�*��

��#�

�+��,

)��-!

.%� )�� /��#��

�0'1�0

"1�021�0

�1�0'1��0

��

"1�021��0

�1�02��

��

��)��23��!�2��2��

��)��"��3�"��!�2��

��)��"3��!�2��2��

��)��3�2��!�2��"��

Figure 6. Particle size distribution curves for two groups of

aggregate used in this study

Table 3. Chemical components of sintered aluminium diox-

ide used in the standard test and this study

DD ENV ISO 0722-1 This study

Component % Component %

Al2O3 94.0 Al2O3 95.0

TiO2 3.2 TiO2 2.8

Fe2O3 1 Fe2O3 0.5

SiO2 1 SiO2 0.6

C 0 C 0.2

28 Huang and Chiou


GRID 4 has a higher nominal ultimate strength (Tf ) of

about 150 kN/m in the machine direction (MD) than

GRID 1, GRID 2 and GRID 3, which have a nominal Tf¼ 60 kN/m in that direction. Although GRID 4 has a

greater mass of PVC coating than GRID 2, the ratio

between the volume of coating and the mass of yarn (V-M

ratio) is slightly lower than that for GRID 2, as shown in

Table 4. Therefore the coating for GRID 4 is also

classified as ‘regular’, as for GRID 2. It can be seen in

Table 4 that GRID 4 has the highest mass per unit area

(554 g/m2), and GRID 1 has the greatest thickness of

strands (2.45 mm) and junction (2.55 mm) among the

geogrids with Tf ¼ 60 kN/m. These values are even

greater than those for GRID 3, which has been classified

as heavily coated. This is attributable to their different

coating material and processes. PP has a smaller density

(r ¼ 900 kg/m3) than PVC (r ¼ 1300 kg/m3). Therefore

the volume of PP for a unit area of geogrid is greater than

that of PVC when equal weights of them are used.

Furthermore, GRID 1 is produced by pre-coating the PVA

yarn with PP before the weaving and heat-melting pro-

cesses, whereas GRID 4 is manufactured by dipping the

woven PET yarn in the heat-melted PVC.

Figure 8 shows the results of wide-width tensile test

results for all types of geogrid tested in this study. It can

be seen that five tests were performed for each geogrid,

and there are consistent ultimate tensile strength, strains at

breakage, and tensile stiffness at 2% and 5% for each

geogrid, with small variations.

4. TEST RESULTS AND DISCUSSION

Figure 9 shows a typical example of the relationship of

percentage of ultimate strength reduction (PSR) to cyclic

load intensity q for GRID 1 using Particle 1 (P1),

frequency F ¼ 1.0 Hz and loading cycles N ¼ 200. For

each average value, as denoted by a solid mark in this and

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Figure 7. Geogrids used in this study: (a) GRID 1 (60/30 kN/m), PVA yarn + PP regular coating; (b) GRID 2 (60/30 kN/m), PET

yarn + PVC regular coating; (c) GRID 3 (60/30 kN/m), PET yarn + PVC heavy coating; (d) GRID 4 (150/30 kN/m), PET yarn +

PVC regular coating

Table 4. Physical properties of woven geogrid used in this study

Unit Geogrid type

GRID 1 GRID 2 GRID 3 GRID 4

Wide-width tensile strength, Tf (kN/m) 60 3 30 60 3 30 60 3 30 150 3 30

Mass of yarn (g/m2) 156 167 178 327

Mass of coating (g/m2) 177 155 289 231

Volume of coating material cm3/m2 197 119 222 178

Volume of coating/Mass of yarn (V-M ratio) (cm3/g) 1.26 0.71 1.24 0.54

Nominal thickness (under surcharge of 2 kPa) (mm) 2.4 1.5 2.1 1.9

Rib thickness (mm) Machine 1.9 1.1 1.4 1.3

Cross-machine 1.2 0.7 1.4 1.1

Thickness of junction (mm) 2.5 1.4 2.1 1.7

Rib width (mm) Machine 3.1 5.8 5.8 9.4

Cross-machine 5.2 3.8 4.9 3.2

Aperture size (mm) 22 3 21 23 3 28 24 3 27 20 3 22

Number of strands/m 40 35 35 35

Material PVA+PP PET+PVC



all subsequent figures, five tests were performed under

identical test conditions.

Figures 10a to 10d show PSR against q for GRIDs 1, 2,

3 and 4, respectively. Figure 10a shows that for GRID 1

PSR increases with the increase in q when P1 (19–

25 mm) is used. However, this is not true for the tests

using P4 (5–10 mm). The extremely small values of PSR

for P4 suggest that the use of a smaller particle size (P4)

in the standard test (DD ENV ISO 10722-1) may under-

estimate the damage of GRID 1 when the site is

dominated by larger particles. A similar conclusion has

been drawn by Schroer et al. (2000) based on a compara-

tive study on a PVC-coated woven PET geogrid with Tf�78 kN/m using laboratory damage simulation tests as

used in this study and an on-site simulation test suggested

by Watts and Brady (1994).

Figure 10b shows test results for GRID 2 obtained

under identical test conditions to those shown in Figure

10a. The values of PSR increase with increase in q, and

are significantly greater than those shown in Figure 10a.

An important factor contributing to this difference is the

volume of coating material, as indicated in Table 4.

Although similar masses of coating material are used for

GRID 1 and GRID 2, their volumes are significantly

different, because PP and PVC have somewhat different

densities, as mentioned in Section 3. The PSR–q relation-

ships for GRID 3 (Figure 10c) are similar to those for

GRID 1. This is attributable to their similar volumes of

coating material, as indicated in Table 4.

These observations suggest that GRID 1 can be referred

to as heavily coated in terms of the volume of coating

material, although it has a relatively small weight of

coating material. It is conceivable that the thickness of the

coating layer is a function of the volume of the coating

material applied and the diameter of the bundle of the

yarns. Therefore the ratio of the volume of coating to the

mass of yarn (V-M ratio) for a unit area of geogrid may be

used as a quantitative indicator of the geogrid’s robustness

against installation damage. To verify this conclusion, all

the data shown in Figures 10a to 10d are summarised in

Figure 11. For a given loading condition, most of the

values of PSR tend to decrease with an increase in V-M

ratio, except a minor portion of the points for GRID 2

using a large particle (P1). A relatively large degree of

variation in PSR when using P1 as the test medium may

account for this discrepancy. More tests in the future using

geogrid specimens under carefully controlled coating

processes are necessary to clarify this issue.

Figure 12a shows the relationship of PLR (percentage

of ultimate strain reduction) to PSR for GRID 1 obtained

using various test conditions. The values of PLR are

smaller than those of PSR. This is different from the

results reported by Allen and Bathurst (1994). They

summarised the data obtained in full-scale installation

damage tests on flexible geogrids by Troost and Ploeg

(1990), Rainey and Barksdale (1993) and Sandri et al.

(1993), and found similar percentages of ultimate strength

and strain losses for the exhumed PET woven geogrids.

The difference between the PLR–PSR relationships be-

tween GRID 1 in this study and those reported by Allen

and Bathurst (1994) may reflect differences in the types of

yarn used for the geogrids. In this figure and subsequent

figures, instead of averaged values for five identical tests,

all individual test results are presented in order to show

the possible uncertainties of the damage evaluation. In all

the cases investigated, a linear regression line is used to

show the approximate trend of the data. We shall focus on

the slope of these regression lines. The intercept with the

y-axis will not be discussed because it is relatively small,

and is possibly induced and/or affected by the inevitable

experimental errors.

Figures 12b and 12c show, respectively, the percentage

of strength (or stiffness) reduction at 2% tensile strain,

PSR(2%), and at 5% tensile strain, PSR(5%), against PSR

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Figure 8. Stress–strain curves for geogrids obtained in wide-

width tensile tests

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Figure 9. Typical example of averaged and original test

results of in-lab installation damage tests

30 Huang and Chiou


for GRID 1. Similar to that shown in Figure 12a, the

geogrid is subjected to some degree of damage, but the

PLR and the degree of damage are less than those for

PSR. In addition, the scattering of data points is greater

than that shown in Figure 12a, indicating that a greater

degree of uncertainty may be associated with the evalua-

tion of PSR(2%) and PSR(5%) than with that of PSR.

Figures 13a to 13c show the test results for GRID 2.

The test conditions are the same as those shown in Figures

12a to 12c. The differences between Figure 12 and Figure

13 reflect the differing physical properties between GRID

1 and GRID 2, which include the type of polymeric yarn,

the type and quantity of coating material, and the coating

method.

Figure 13a shows that, for GRID 2, PLR is approxi-

mately equal to PSR. This is different from GRID 1 as

shown in Figure 12a. Figures 13b and 13c show smaller

decreases in tensile strength (or modulus) at 2% and 5%

strains, compared with those shown in Figures 12b and

12c for GRID 1.

Figures 14a to 14c show test results similar to those

shown in Figures 13a to 13c, except that GRID 3 is used.

The differences between Figure 14 and Figure 13 reflect

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Figure 10. PSR against cyclic load intensity q for: (a) GRID 1; (b) GRID 2; (c) GRID 3; (d) GRID 4

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Figure 11. PSR against V-M ratio for all tests performed in

this study



the different physical properties between GRID 3 and

GRID 2, i.e. the difference in the volume of coating (or

V-M ratio). Figure 14a shows that the values of PSR for

GRID 3 are generally less than those for GRID 2 shown

in Figure 13a. Figure 14a also shows that the values of

PLR are smaller than those of PSR when P1 is used. In

general, the results shown in Figures 13a and 14a reveal

the merit of using a greater volume of PVC coating in

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Figure 12. Characteristics of damaged geogrid (GRID 1) expressed by: (a) PLR against PSR; (b) PSR(2%) against PSR;

(c) PSR(5%) against PSR

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32 Huang and Chiou


reducing the degree of damage (in terms of PLR and

PSR). Figures 14b and 14c show that the tendencies of the

relationships between PSR(2%) and PSR, and between

PSR(5%) and PSR, are very similar to those shown in

Figures 13b and 13c. The relationship between PSR(2%)

(or PSR(5%)) and PSR seems to be insusceptible to the

change in the volume of coating (or the V-M ratio) when

we compare Figures 13b and 13c with Figures 14b and

14c.

Figures 15a to 15c show the test results for GRID 4.

The stress–strain characteristics of the damaged GRID 4

are similar to those of GRID 2 (Figure 13), which

indicates that the stress–strain characteristics of damaged

geogrids can be closely related to the V-M ratio rather

than the volume of coating when geogrids with different

values of Tf are compared.

Figure 16 summarises the slope (a:1 ¼ V:H) of the

regression lines shown in Figures 12 to 15. The following

two points can be inferred:

• Similar values of a for the PLR–PSR relationship

can be obtained for GRID 1 and GRID 3, which

have similarly large V-M ratios.

• GRID 2, GRID 3 and GRID 4 have similar values of

a for the PSR(2%) –PSR and PSR(5%) –PSR relation-

ships despite their largely different V-M ratios. This

indicates that the characteristics of PSR(2%) and

PSR(5%) may be controlled uniquely by the yarn and

coating used (PET yarn + PVC coating, in this case)

rather than by the V-M ratios. This is supported by

the observation for GRID 1 (PVA yarn + PP coating),

for which the a values for PSR(2%) and PSR(5%) are

substantially higher than those for GRID 2, GRID 3

and GRID 4 (PET yarn + PVC coating).

Suggested values of FID(5%) for the various geogrids

obtained in the present study are summarised in Table 1.

The values of FID(5%) for the ranges of load intensity and

particle size used in the present study fall within a narrow

range. When we comparing the values of FID(5%) for GRID

2 and GRID 4, no clear dependence of FID and FID(5%) on

the value of Tf can be detected.

Note, however, that the V-M ratio has been used

throughout this study, where all types of yarn have similar

values of r (¼ 1.3 g/cm3). When comparing yarns with

various r values, the ratio of volume of yarn to volume of

coating (V-V ratio) may be of more physical significance.

This issue is beyond the scope of the present study.

5. CONCLUSIONS

The present study comprised a series of laboratory cyclic

loading tests to simulate installation damage on four types

of woven geogrid. The following conclusions can be

drawn:

• The ratio of volume of coating material to mass of

yarn ratio (V-M ratio) has a major influence on the

ultimate strength loss of flexible geogrids. The extent

of ultimate tensile strength loss decreases with

increase in the V-M ratio of the geogrid regardless of

the different types of yarn and coating material used.

• The characteristics of ultimate strain loss (i.e. the

PLR–PSR relationships) are also governed by the

V-M ratio of the geogrid, regardless of the types of

yarn and coating material used. Test results show

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Figure 16. Characteristics of damaged geogrids illustrated by

using a values for slope of regression lines



that, for the geogrids using higher V-M ratios (GRID

1 and GRID 3), the loss of ultimate strain (PLR) is

about 45–57% of the loss of ultimate strength

(PSR); for those using lower V-M ratios (GRID 2

and GRID 4), the ratios between PLR and PSR are

approximately 1.0 (or 0.9–1.1).

• For the woven geogrids made of PET yarn and PVC

coating, the losses of tensile stiffness (or strength) at

2% and 5% strains are less than 50% of the loss of

ultimate strength, regardless of their different V-M

ratios. For the geogrid made of PVA yarn and PP

coating (GRID 1), the tensile stiffness losses at 2%

and 5% strains are less than the ultimate strength

loss. In the case of stiffness losses at 2% and 5%

strains, the types of yarn and coating material seem

to play a major role while the V-M ratio plays a

minor one.

• No clear dependence of FID, FID(2%) and FID(5%) on

the ultimate strength of geogrids (Tf ) has been

detected for similar types of geogrid (namely GRID

2 and GRID 4) having a similar V-M ratio.

ACKNOWLEDGEMENTS

The authors acknowledge the financial support from the

National Science Council under contract nos. NSC

92-2211-E-006-039 and NSC 92-2622-E-006-116-CC3.

Financial support from the Gold-Joint Industry Co. Ltd

under the contract No. 92S28 and from Newmark En-

gineering Co. under the contract No. 92S29 are also

acknowledged.

NOTATIONS

Basic SI units are shown in parentheses:

a coefficient representing slope of fitted line

(dimensionless)

D50 average particle size (m)

Dmax maximum particle size (m)

F frequency

FID(5%) reduction factor for tensile stiffness reduction

at 5% strain (dimensionless)

FID(6%) reduction factors for tensile stiffness

reduction at 6% strain (dimensionless)

N loading cycles

PLR percentage of ultimate strain reduction

(dimensionless)

PSR percentage of ultimate strength reduction

(dimensionless)

PSR(2%) percentage of tensile strength (and/or

stiffness) reduction at 2% strain

(dimensionless)

PSR(5%) percentage of tensile strength (and/or

stiffness) reduction at 5% strain

(dimensionless)

q cyclic load intensity (N/m2)

Tf ultimate tensile strength of intact geogrids

(N/m)

Tfd ultimate tensile strength of damaged geogrids

(N/m)

r density (kg/m3)

ABBREVIATIONS

AL acrylic latex

GRID 1 geogrid type 1 used in present study




P1 aggregates of sintered dioxide (19–25 mm)

P4 aggregates of sintered dioxide (5–10 mm)

PET polyester

PP polypropylene

PVA poly(vinyl alcohol)

PVC poly(vinyl chloride)

V:H slope of fitted line

REFERENCES

Allen, T. M. & Bathurst, R. J. (1994). Characterization of geosynthetic

load–strain behavior after installation damage. Geosynthetics

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ASTM D 5818. Construction Damage Practice for Obtaining Samples of

Geosynthetics from a Test Section for Assessment of Installation

Damage. ASTM International, West Conshohocken, PA, USA.

BS 8006. Code of Practice for Strengthened Reinforced Soils and Other

Fills. British Standards Institution, London, UK.

DD ENV ISO 10722-1. Geotextiles and Geotextile-Related Products.

Procedure for Simulating Damage During Installation, Part 1:

Installation in Granular Materials.

Elias, V. (2001). Corrosion/Degradation of Soil Reinforcement for

Mechanically Stabilized Earth Walls and Reinforced Soil Slopes,

Report No. FHWA-NHI-00-044, Federal Highway Administration,

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Hsieh, C. W. & Wu, J. H. (2001). Installation survivability of flexible

geogrids in various pavement subgrade materials. Transportation

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under cyclic load. Proceedings of the Third Asian Regional

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B., Yoo, C. & Jeon, H. Y., Editors, pp. 535–542.

Hufenus, R., Ruegger, R., Flum, D. & Sterba, I. J. (2005). Strength

reduction factors due to installation damage of reinforcing

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Muller-Rochholz, J. and Mannsbart, G. (2004). Installation stress testing:

results and interpretation. Proceedings of the Third European

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Pinho-Lopes, M., Recker, C., Muller-Rochholz, J. & Lopes, M. L.

(2000). Installation damage and creep of geosynthetics and their

combined effect-experimental analysis. Proceedings of the Second

European Geosynthetics Conference, Eurogeo 2, Bologna, Italy, pp.

895–897.

Pinho-Lopes, M., Recker, C., Lopes, M. L. & Muller-Rochholz, J.

(2002). Experimental analysis of the combined effect of installation

damage and creep of geosynthetics-new results. Proceedings of the

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Delmas, Gourc and Girard, Editors, Swets & Zeitlinger, pp. 1539–

1544.

Rainey, T. & Barksdale, B. (1993). Construction induced reduction in

tensile strength of polymer geogrids. Proceedings of Geosynthetics

’93, IFAI, Vancouver, Canada, Vol. 2, pp. 729–742.

Sandri, D., Martin, J. S., Vann, C. W., Ferrer, M. & Zeppenfeldt, I.

(1993). Installation damage testing of four polyester geogrids in

34 Huang and Chiou


three soil types. Proceedings of Geosynthetics’93, IFAI, Vancouver,

Canada, Vol. 2, pp. 743–755.

Schroer, S., Thornton, J. S., Muller-Rochholz, J. and Recker, C. (2000).

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351–355.

Troost, G. H. & Ploeg, N. A. (1990). Influence of weaving structure and

coating on the degree of mechanical damage of reinforcing mats

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The Editors welcome discussion on all papers published in Geosynthetics International. Please email your contribution to

[email protected] by 15 August 2006.



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