Geogrid reinforcement of soil has been successfully used for many years in a wide variety of applications. A huge development plan is expected in Iraq. The use of modern techniques like geogrid reinforced earth is expected. It is essential to gain experience in testing methods of geogrids using the available materials produced nationally, in neighboring countries and in developed countries. Some manufacturers do not provide sufficient data on the tensile properties of their products. This paper presents data obtained from a series of laboratory tests performed on various configurations of geogrids. The tests are conducted to determine the physical properties of various seven types of geogrids, these types of geogrids were manufactured in Iraq, Iran, China and Britain. The mechanical properties included peak tensile strength, modulus of elasticity, upper yield strength, lower yield strength, tensile strength, non-proportional extension strength, total extension strength, fracture elongation, elongation at maximum load and total elongation as well as other physical properties such as aperture size, mass per unit area, rib thickness, rib width, junction thickness, roll width, mesh type, standard color and polymer type. The single rib strength test according to ASTM 6637-01 was performed using a computer controlled electronic universal testing machine. The results were compared with some information available from the manufacturers. Good agreement was found between the results obtained from the present tests and those given by manufacturers.

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1. INTRODUCTION

Geosynthetics include exclusively man made polymeric

products such as geotextiles, geogrids, geonets,

geomembranes, geosynthetic clay liners, and geocomposites.

Polypropylene, polyester, polyethylene, polyamide,

polyvinyl choride, and polystyrene are the major polymers

used to manufacture geosynthetics. It is not the properties of

the polymers, but the properties of the final polymeric

products that are of interest to civil and environmental

engineering applications. Geosynthetics are used as part of

the geotechnical, transportation, and environmental facilities.

Geosynthetic products perform five main functions:

separation, reinforcement, filtration, drainage, and

containment (hydraulic barrier). However, in most

applications, geosynthetics typically perform more than one

major function [1].

Geogrids are matrix like materials with large open spaces

called apertures, which are typically 10 to 100mm between

ribs that are called longitudinal and transvers respectively.

The ribs themselves can be manufactured from a number of

different materials, and the rib cross-over joining or

junction-bonding methods can vary. The primary function of

geogrids is clearly reinforcement [2].

Geogrid, is also defined as a geosynthetic formed by a regular

network of integrally connected elements and possess

apertures greater than 6.35 mm (1⁄4 inch) to allow

interlocking with surrounding soil, rock, earth, and other

surrounding materials to primarily function as reinforcement

[3].

Rib for geogrids is the continuous elements of a geogrid

which are either in the machine (MD) or cross-machine

direction (XMD) as manufactured, Junction is the point

where geogrid ribs are interconnected to provide structure

and dimensional stability.

Geogrid is stiff or flexible polymer grid-like sheets with large

apertures used primarily for stabilization and reinforcement

of unstable or week soil. The general types of geogrid are:

1- Unidirectional geogrid.

2- Bidirectional geogrid.

3- Extruded geogrid.

4- Bonded geogrid.

5- Woven geogrid., [2]-[3].

2. EFFECT OF GEOGRID PROPERTIES

The principle requirements of reinforcing materials are

strength and stability (low tendency to creep), durability, ease

of handling, a high coefficient of friction and or adherence

with the soil, together with low cost and ready availability [4].

The selection of fabric for a particular construction

application must necessarily depend upon adequate and

suitable fabric properties and characteristics [5].

Geogrid tests are unique in a number of aspects when

compared with geotextiles. Properties relating to separation,

filtration, drainage, and barrier applications are not included

since geogrids always serve the primary function of

reinforcement [2].

ABSTRACT

Geogrid reinforcement of soil has been successfully used for many years in a wide variety of applications. A huge development

plan is expected in Iraq. The use of modern techniques like geogrid reinforced earth is expected. It is essential to gain

experience in testing methods of geogrids using the available materials produced nationally, in neighboring countries and in

developed countries. Some manufacturers do not provide sufficient data on the tensile properties of their products.

This paper presents data obtained from a series of laboratory tests performed on various configurations of geogrids. The tests

are conducted to determine the physical properties of various seven types of geogrids, these types of geogrids were

manufactured in Iraq, Iran, China and Britain. The mechanical properties included peak tensile strength, modulus of elasticity,

upper yield strength, lower yield strength, tensile strength, non-proportional extension strength, total extension strength,

fracture elongation, elongation at maximum load and total elongation as well as other physical properties such as aperture size,

mass per unit area, rib thickness, rib width, junction thickness, roll width, mesh type, standard color and polymer type. The

single rib strength test according to ASTM 6637-01 was performed using a computer controlled electronic universal testing

machine. The results were compared with some information available from the manufacturers. Good agreement was found

between the results obtained from the present tests and those given by manufacturers.

Keywords: geogrid, tensile strength, modulus of elasticity, elongation, polymer type.

MEASUREMENT OF TENSILE PROPERTIES OF GEOGRIDS

Author1 , Author2 and Author 3

Institute, Country

Second International Conference on Geotechnique, Construction Materials and

Environment, Kuala Lumpur, Malaysia, Nov. 19-21, 2012, ISBN: 978-4-9905958-1-4

C3051

Raid R. Al-Omari1and Mohammed K. Fekheraldin2

1Professor, Civil Engineering Department, Nahrain University, Baghdad, Iraq, Email: tosharaid@yahoo.com, Mobile:

00964-7901699487

2Assistant Lecturer, Civil Engineering Department, Kufa University, Kufa, Iraq, Email: Kadum_fekheraldin@yahoo.com,

Mobile: 00964-7811497218

The effective important properties of geogrids may be

concerned in three main properties:

1- Physical properties.

2- Mechanical properties.

3- Endurance properties.

Many of the physical properties of geogrids including the

weight (mass), type of structure, rib dimensions, junction

type, aperture size, and thickness can be measured directly

and are relatively straightforward. Other properties that are of

interest are mass per unit area, which varies over a

tremendous range from 200 to 1000 g/m 2, and percent open

area, which varies from 40 to 95%. The latter suggests that

almost all soils will communicate, or strick-through ,the

plane of geogrids, [2].

The effect of geogrid aperture size on the obtained

enhancement in strength was previously studied. Al-Omari,

et al., (1987) investigated the effect of interlocking

mechanism between soil particles and the aperture of the

mesh using triaxial compression tests. It was concluded that

the strength enhancement in mesh reinforced sand depends on

the mechanism of interlocking which is turn affected by the

ratio of aperture size to particle diameter[ 6].

The mechanical properties of geogrids including the geogrid

stiffness, the peak tensile strength, modulus of elasticity,

upper yield strength, lower yield strength, tensile strength,

non-proportional extension strength, total extension strength,

fracture elongation, elongation at maximum load and total

elongation.

Al-Omari (1991) studied the effect of geogrids of varying

stiffness values embedded in clays of different plasticity

indices and they concluded that the reduction in swell

increased with increasing the geogred stiffness [7]. Also

Al-Omari, (1995) investigated the effect of stiffness of

geogrids using triaxial test on plastic mesh reinforced sand.

The sand density, mesh stiffness and the number of

reinforcing layers were varied and they concluded that there

may be limiting reinforcement stiffness, influenced by the

number of reinforcing layers after which there will be no

further gain in strength [8].

As geogrid are used in critical reinforcement applications,

some of which require long service lifetimes, it is generally

necessary to evaluate selected endurance properties [2].

3. Tensile Properties of Geogrids by the Single or

Multi-Rib Tensile Method

The single or multi-rib tensile test methods cover the

determination of the tensile strength properties of geogrids by

subjecting strips of varying width to tensile loading. Three

alternative procedures are provided to determine the tensile

strength, as follows:

3.1 Method A —Testing a Single Geogrid Rib in Tension

(N or lbf).

In this method, a single, representative rib specimen of a

geogrid is clamped and placed under a tensile force using a

constant rate of extension testing machine. The tensile force

required to fail (rupture) the specimen is recorded. The

ultimate single rib tensile strength (N or lbf) is then

determined based on the average of six single rib tensile tests

[3].

The initial tendency when assessing a geogrid tensile strength

is to pull a single rib in tension until failure and then to note its

behavior. A secondary tendency is to evaluate the in-isolation

junction strength by pulling a longitudinal rib away from its

transverse rib junction. It is important to state "in-isolation"

since there is no normal stress on the junction strength test

must be done with the entire geogrid structure contained

within soil embedment. This is a much more complicated test

and will be covered under anchorage strength from soil

pullout [2].

A single rib tension strength test merely uses a constant

rate-of -extension testing machine to pull a single rib to

failure. For unidirectional geogrids, this would most likely be

a longitudinal rib. For bidirectional geogrids, both

longitudinal and transverse ribs require evaluation. By

knowing the repeat pattern of the ribs, equivalent wide-width

strength can be calculated. Alternatively, a number of ribs can

be tested simultaneously to obtain a more statistically

accurate value for the wide-width strength [3].

An in-isolation junction or node strength test can also be

performed. The test method uses a clamping fixture that grips

the transverse ribs of the geogrid immediately adjacent to and

on each side of the longitudinal rib as shown in Fig. 1. The

lower portion of the longitudinal rib is gripped in a standard

clamp, and both clamps are mounted in a tensile testing

machine, where the test specimen is pulled apart. The strength

of the junction, in force units, is obtained [2].

For the laboratory sample, a full roll width swatch is taking

long enough in the machine direction from each roll in the lot

sample. The sample may be taken from the end portion of a

roll provided there is no evidence it is distorted or different

from other portions of the roll. The specimens shall consist of

three (3) junctions or 300 mm in length (12 in.), in order to

establish a minimum specimen length in the direction of the

test (either the machine or cross-machine direction). All

specimens should be free of surface defects, etc., not typical

of the laboratory sample. Take no specimens nearer the

selvage edge along the geogrid than 1⁄10 the width of the

sample. Prepare each finished specimen, as shown in Fig.1, to

contain one rib in the cross-test wide by at least three

junctions (two apertures) long in the direction of the testing,

with the length dimension being designated and accurately

cut parallel to the direction for which the tensile strength is

being measured. The outermost ribs are cut prior to testing to

prevent slippage from occurring within the clamps. For those

cases where the outermost ribs are severed, the test results

shall be based on the unit of width associated with the number

of intact ribs [3].

Figure 1: Test fixture measuring in-isolation junction strength

3.2 Method B—Testing Multiple Geogrid Ribs in

Tension (kN/m or lbf/ft).

A relatively wide specimen is gripped across its entire width

in the clamps of a constant rate of extension type tensile

testing machine operated at a prescribed rate of extension,

applying a uniaxial load to the specimen until the specimen

ruptures. Tensile strength (kN/m or lbf/ft), elongation, and

secant modulus of the test specimen can be calculated from

machine scales, dials, recording charts, or an interfaced

computer [3].

3.3 Method C—Testing Multiple Layers of Multiple

Geogrid Ribs in Tension (kN/m or lbf/ft)

A relatively wide, multiple layered specimen is gripped

across its entire width in the clamps of a constant rate of

extension type tensile testing machine operated at a

prescribed rate of extension, applying a uniaxial load to the

specimen until the specimen ruptures. Tensile strength (kN/m

or lbf/ft), elongation and secant modulus of the test specimen

can be calculated from machine scales, dials recording charts,

or an interfaced computer [3].

4. The used geogrids

With BS 8006, FHWA-SA -96 -071, and independent

certification of product characteristics by the British Board of

Agreement, a sound base for the use of reinforcing products,

whether flexible or stiff, is now available. A range of geogrid

products with varying strength and made in different ways is

now available from which users can select the product best

suited to their purpose. The strength of the geogrids varies

between 20 and 250 kN/m, and they are used in both road

constructions and reinforced slopes. Geogrids can be divided

into two groups [9]:

Stiff geogrids, mostly high density polyethylene (HDPE)

with a monolithic mesh structure.

Flexible geogrids, mostly polyethylene terephthalate (PET)

with poly vinyl chloride (PVC) or acrylic coating with

mechanically connected longitudinal and transverse

elements.

The main design requirements for the use of geogrids in soil

structures result from the geotechnical design. This includes

the calculation of different failure modes resulting in

requirements for: axial tensile design strength of the geogrid

and maximum strain requirements in the geogrid [9].

In this work the stress-strain properties of various types of

geogrids (seven types) manufactured in four different

countries are investigated. The following types of geogrids

have been employed in this work: Netlon CE121and Tensar

SS2, manufactured in Britain , a type of geogrid which

manufactured in Iraq, manufactured in China, SQ12, SQ15

and CE131 manufactured by Pars Mesh Polymer in Iran, Fig .

2 shows the types of geogrids.

Figure 2: The various types of geogrids used in the work

5. Results and Discussions

In the present work a large number of samples (90 samples)

were tested by computer controlled electronic universal

testing machine and this machine give the information as

follow; peak tensile strength, modulus of elasticity, upper

yield strength, lower yield strength, tensile strength,

non-proportional extension strength, total extension strength,

fracture elongation, elongation at maximum load and total

elongation after completing test for each geogrid type. Fig . 3

shows sample test using the computer controlled electronic

universal testing machine and Fig. 4 demonstrates the

information given from this testing machine.

Netlon CE121 Tensar SS2 Iraqi geogrid China geogrid

PMP SQ12 PMP SQ15 PMP CE131

Figure 3: Computer controlled electronic universal testing

machine

Figure 4: Information given after test from computer

controlled electronic universal testing machine

The properties of the geogrids were employed in this work are

as follow

Netlon CE 121

This geogrid was manufactured by the British Company

Netlon ltd. The physical and the presently determined

mechanical properties of this type of geogrid are summarized

in Table 1. The results of single rib test, as determined in the

present work, are shown in Figs. 5a and b.

Table 1: The physical and mechanical properties of Netlon

CE121 geogrid

The Mechanical Properties

Non-proportional extension

strength

Elongation at maximum load

Deformation (mm)

Figure 5a: The load-deformation relationship of

CE121 Netlon geogid

Tensar SS2

This geogrid was manufactured by the British Company

Netlon ltd. The physical and the presently determined

mechanical properties of this type of geogrid are summarized

in Table 2. The results of single rib test, as determined in the

present work, are shown in Figs. 6a, b, c and d.

Table 2: The physical and mechanical properties of Tensar

SS2 geogrids

Longitudinal rib width lw

The Mechanical Properties

Peak Tensile Strength MD/XMD

Upper yield strength MD/XMD

Lower yield strength MD/XMD

Fracture percentage elongation MD/XMD

Percentage elongation at maximum load

MD/XMD

Total percentage elongation MD/XMD

Strain

Figure 6 b: The stress-strain relationship of Tensar SS2

geogrid in XMD direction

Strain

Figure 5b: The stress-strain relationship of CE121 Netlon

geogrid

Deformation (mm)

Figure 6a: The load-deformation relationship of Tensar

SS2 geogrid in XMD direction

Deformation (mm)

Figure 6c: The load-deformation relationship of Tensar SS2

geogrid in MD direction

The results of the present tests reasonably agree with results

provided by the manufactures Tensar specification of geogrid

SS2 in mechanical properties of single rib test. The results

provided by the manufactures are17.5 kN/m and31.5 kN/m

for MD and XMD respectively, while the values from the

single rib test of Tensar SS2 by computer controlled

electronic universal testing machine are 14.4 and 28.2 kN/M

for MD and XMD respectively. The percentages of

agreement are 82.3% and 89.5 for MD and XMD

respectively.

The Iraqi Geogrid

A geogrid product manufactured in Iraq is employed. The

physical and presently determined mechanical properties are

illustrated in Table 3. Fig s . 7a and b demonstrates the

obtained stress-strain and load-deformation relationships.

Table 3: The physical and mechanical properties of Iraqi

geogrid

The Mechanical Properties

Fracture percentage elongation

Percentage elongation at maximum load

Total percentage elongation

The China Geogrid

A geogrid produced in China is employed. The physical

and the presently determined mechanical properties are

illustrated in Table 4. Figs. 8a and b demonstrates the

Strain

Figure 6d: The stress-strain relationship of Tensar SS2 geogrid

in MD direction

Deformation (mm)

Figure 7a: The load-deformation relationship of Iraqi geogrid

Strain

Figure 7b: The stress-strain relationship of Iraqi geogrid

obtained stress-strain and load-deformation

relationships.

Table 4: The physical and mechanical properties of China

geogrid

The Mechanical Properties

Fracture percentage elongation

Percentage elongation at maximum

load

Total percentage elongation

PMP SQ12

This geogrid is manufactured by the Iranian company

Pars Mesh Polymer. The physical and the presently

determined mechanical properties of this geogrid are

summarized in the Table 5. The results of single rib test,

as determined in the present research are shown in Figs.

9a and b.

Table 5: The physical and mechanical properties of SQ12

geogrids

Longitudinal rib width lw

The Mechanical Properties

Fracture percentage elongation

Percentage elongation at

maximum load

Total percentage elongation

Deformation (mm)

Figure 8a: The load-deformation relationship of China

geogrid

Strain

Figure 8b: The stress-strain relationship of China geogrid

.

PMP SQ15

This geogrid is manufactured by the Iranian company Pars

Mesh Polymer. The physical and the presently determined

mechanical properties of this geogrid are summarized in

Table 6. The results of single rib, as determined in the present

tests are shown in Figs. 10 a and b.

Table 6: The physical and mechanical properties of SQ15

geogrids

Longitudinal rib width lw

The Mechanical Properties

Fracture percentage elongation

Percentage elongation at maximum load

Total percentage elongation

Deformation (mm)

Figure 9a: The load-deformation relationship of SQ12

geogrid

Strain

Figure 9b: The stress-strain relationship of SQ12 geogrid

Deformation (mm)

Figure 10a: The load-deformation relationship of SQ15

geogrid

Strain

Figure 10b: The stress-strain relationship of SQ15 geogrid

PMP CE131

This geogrid is manufactured by the Iranian company Pars

Mesh Polymer. The physical and the presently determined

mechanical properties of this geogrid are summarized in

Table 7. The results of single rib test, as determined in the

present research are shown in Figs. 11 a and b.

Table 7: The physical and mechanical properties of CE131

geogrids

Longitudinal rib width lw

The Mechanical Properties

Fracture percentage elongation

Percentage elongation at maximum load

Total percentage elongation

6. Discussion of test resuls

This study was carried out to investigate and analysis the

parameters that govern the behavior of geogrids. The results

of various geogrids are summarized in Table 8.

Table 8: Results of various geogrids

Peak tensile

strength

MD/XMD(kN/m )

Modulus

of

elasticity

MD/XMD

(GPa)

Rib

Thickness

MD/XMD

(mm)

Mass

per

unit

area

(g/m2 )

Deformation (mm)

Figure 11a: The load-deformation relationship of CE131

geogrid

Strain

Figure 11b: The stress-strain relationship of CE131 geogrid

7. CONCLUSION

Based on this experimental study the following conclusions

may be drawn:

1- The geogrids Netlon CE121 and Tensar SS2 have

tensile strength and elastic modulus higher than

other geogrids made by different manufactures.

2- The tensile strength and elastic modulus are not

dependent on the density of materials but dependent

on type of polymer used and method of manufacture.

3- The dimensional properties such as rib thickness,

junction thickness, longitudinal and transverse rib

width of geogrid play important role in the

mechanical properties such as tensile and elastic

modulus.

4- The effect of tensile strength (stiffness) is more

significant than elastic modulus when geogrids are

used as reinforcement in the soil.

.

8. ACKNOWLEDGMENTS

The experimental part of the work was conducted in the

laboratory of Materials Engineering Department in College of

Engineering of Kufa University. Special thanks are presented

to Dr. Ali Sabaa Hummoud, the chairman of materials

engineering department and deepest wishes to Miss. Batool

Hatim, responsible on laboratory of materials engineering.

9. REFERENCES

[1] Hoe I. Ling, "Civil and Environmental Applications

of Geosynthetics," Reinforced Soil Engineering.

Advances in Research and Practice, 4th ed. vol. 1, Hoe I.

Ling, Dov Leshchinsky and Fumio Tatsuoka, Ed.

Library of Congress Cataloging: Publisher's , 200 3, pp.

14– 31.

[2] Roberrt M. Koerner, Designing with Geosynthetics,

Library of Congress Cataloging: Publisher's , 2005, Ch. 3.

[3] ASTM D6637-01 -2009 , "Standard Test Method for

Determining Tensile Properties of Geogrids by the Single

or Multi-Rib Tensile Method".

[4] Colin JFP Jones, Earth Reinforcement and Soil Structure,

British Library Cataloguing: Publisher's, 1985, Ch. 5.

[5] Roberrt M. Koerner and Joseph P. Welsh, Construction

and Geotechnical Engineering Using Synthetic Fabrics,

Library of Congress Cataloging: Publisher's, 1980, Ch. 4.

[6] Al-Omari, R.R, AL-Dobaissi, H.H. and Al -Wadood,

B.A."Inextensible geomesh included in sand and clay" .In

Proceedings, International Symposium on Prediction and

Performance in Geotechnical Engineering, Calgary, 1987,

pp. 155-160.

[7] Al-Omari, R.R. & Hamodi F. J. "Swelling Resistant

Geogrid- A new Approach for the Treatment of Expansive

Soils" J. of Geotextiles and Geomembranes, 1991, , pp.

295-317.

[8] Al-Omari, R.R., Nazhat, Y.N. & AL-Dobaissi, H.H.

"Effect of Stiffness and Amount of Reinforcement on

Strength of Sand" J. of Engineering Geology, 1995, pp.

363- 367.

[9] Voskamp W." Performance Properties of Geogrids"

Reinforced Soil Engineering. Advances in Research and

Practice, 4th ed. vol. 1, Hoe I. Ling, Dov Leshchinsky and

Fumio Tatsuoka, Ed. Library of Congress Cataloging:

Publisher's, 2003, pp. 32-48.

ResearchGate has not been able to resolve any citations for this publication.

High-quality geosynthetics of high-stiffness materials are being increasingly used in developing countries although they are not always readily available. An alternative approach in some situations is to use a larger amount of low-stiffness reinforcement. Triaxial tests have been performed on plastic mesh reinforced sand. The sand density, mesh stiffness and the number of reinforcing layers were varied. From these tests it was concluded that there may be a limiting reinforcement stiffness, influenced by the number of reinforcing layers after which there will he no further gain in strength. The density of sand reinforced using plastic mesh is found not to control strongly the strength. The results also revealed that the use of multiple layers of low-quality material can be more effective than the use of fewer layers of high-stiffness reinforcement.

  • RR ALOMARI
  • Faris J. Hamodi

The art of soil reinforcement has so far been restricted to the problem of 'strengthening' cohesionless materials. The present work is aimed at exploring the feasibility of using tensile geogrids for the purpose of controlling the swell of plastic soils. Swelling tests using an enlarged oedometer revealed promising results. The reinforcements were cylindrical geogrids of varying stiffness values embedded in clays of different plasticity indices. The reduction in swell increased with increasing the geogrid stiffness, apparently due to a strong 'interference' bond restricting the relative movement between clay and the grid. A footings model test confirmed the effectiveness of the proposed technique.

Civil and Environmental Applications of Geosynthetics

  • I Hoe
  • Ling

Hoe I. Ling, "Civil and Environmental Applications of Geosynthetics," Reinforced Soil Engineering.

Designing with Geosynthetics, Library of Congress Cataloging: Publisher's

  • M Roberrt
  • Koerner

Roberrt M. Koerner, Designing with Geosynthetics, Library of Congress Cataloging: Publisher's, 2005, Ch. 3.

  • Jfp Colin
  • Jones

Colin JFP Jones, Earth Reinforcement and Soil Structure, British Library Cataloguing: Publisher's, 1985, Ch. 5.

Inextensible geomesh included in sand and clay

  • R R Al-Omari
  • H H Al-Dobaissi
  • B A Al-Wadood

Al-Omari, R.R, AL-Dobaissi, H.H. and Al-Wadood, B.A."Inextensible geomesh included in sand and clay".In Proceedings, International Symposium on Prediction and Performance in Geotechnical Engineering, Calgary, 1987, pp. 155-160.

Performance Properties of Geogrids

  • W Voskamp

Voskamp W." Performance Properties of Geogrids" Reinforced Soil Engineering. Advances in Research and Practice, 4th ed. vol. 1, Hoe I. Ling, Dov Leshchinsky and Fumio Tatsuoka, Ed. Library of Congress Cataloging: Publisher's, 2003, pp. 32-48.