ISO/TR 13434:1998
(Main)Geotextiles and geotextile-related products — Guidelines on durability
Geotextiles and geotextile-related products — Guidelines on durability
Géotextiles et produits apparentés — Lignes directrices concernant la durabilité
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TECHNICAL
ISOITR
REPORT
13434
First edition
1998-l 2-l 5
Geotextiles and geotextile-related
products - Guidelines on durability
Gkotextiles et produits apparent& - Lignes directrices concernant
la dura bilit6
Reference number
ISO/TR 13434: 1998(E)
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ISO/TR 13434: 1998(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide federation of national standards bodies (IS0
member bodies). The work of preparing International Standards is normally carried out through IS0 technical
committees, Each member body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, governmental and non-governmental, in
liaison with ISO, also take part in the work. IS0 collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
The main task of technical committees is to prepare International Standards, but in exceptional circumstances a
technical committee may propose the publication of a Technical Report of one of the following types:
- type 1, when the required support cannot be obtained for the publication of an International Standard, despite
repeated efforts;
- type 2, when the subject is still under technical development or where for any other reason there is the future
but not immediate possibility of an agreement on an International Standard;
type 3, when a technical committee has collected data of a different kind from that which is normally published
-
as an International Standard (“state of the art”, for example).
Technical Reports of types 1 and 2 are subject to review within three years of publication, to decide whether they
can be transformed into International Standards. Technical Reports of type 3 do not necessarily have to be
reviewed until data they provide are considered to be no longer valid or useful.
Technical Reports are drafted in accordance with the rules given in the lSO/IEC Directives, Part 3.
Technical Repo rt may be the s ubject of patent
Attention is drawn to the possibility that some of the elements of this
rights. IS0 shall not be held responsible for identifying any or all such patent rights.
ISOTTR 13434, which is a Technical Report of type 3, was prepared by the European Committee for Standardization
(CEN) in collaboration with IS0 Technical Committee TC 38, Textiles, Subcommittee SC 21, Geotextiles, in
accordance with the Agreement on technical cooperation between IS0 and CEN (Vienna Agreement).
Throughout the text of this document, read “ . .this European prestandard.” to mean “.this Technical Report.“.
Annex A of this Technical Report is for information only.
Annex ZZ provides a list of corresponding International and European Standards for which equivalents are not given
in the text.
0 IS0 1998
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic
uding photocopying and mic
or mechanical, incl rofilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 l CH-1211 Geneve 20 l Switzerland
iso @I iso.ch
Internet
Printed in Switzerland
ii
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lSO/TR 13434: 1998(E)
0 IS0
Foreword
This draft CEN Technical Report has been prepared by CEN/TC 189 “Geotextiles and
geotextile-related products” the secretariat of which is held by IBN. It is now submitted to the
CEN/BT for approval.
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This page intentionally left blank
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0 IS0 ISO/TR 13434:1998(E)
1 Scope
This guide is intended to introduce the reader to the basic concepts of geotextiles durability
and its assessment. Consideration of the design parameters, the project conditions and the
geotextile properties leads to the definition of the appropriate tests to be performed for
assessing the durability of the geotextile .
Geotextiles and geotextile-related products (referred to below as geotextiles) are available in a
wide range of compositions appropriate to different applications and environments. The
synthetic polymers used consist mainly of polyamide, polyester, polyethylene and
polypropylene. These materials, when correctly processed and stabilised, are resistant to
chemical and microbiological attack encountered in normal soil environments and for normal
design lives. For such applications only a minimum number of screening or “index” tests are
necessary.
For applications in more severe environments such as soil treated with lime or cement, landfills
or industrial waste, or for applications with particularly long design lives, special tests including
“performance” tests with site-specific parameters may be required.
This guide does not cover products designed to survive for a limited time, such as erosion
control fabric based on natural fibres, nor does it cover geomembranes, nor geotextiles for
asphalt reinforcement. Creep and creep-rupture, which should be taken into consideration for
soil reinforcement applications, are described in outline but the use of the data in reinforced soil
design will be the subject of a separate document.
2 Normative references
ENV 1897 Geotextiles and geotextile related products - Determination of the
compressive creep properties
ENV 12224 Geotextiles and geotextile related products - Determination of the resistance
to weathering
ENV 12225 Geotextiles and geotextile related products - Method for determining the
microbiological resistance by a soil burial test
ENV 12226 Geotextiles and geotextile related products - General tests for evaluation
following durability testing
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ISO/TR 13434:1998(E) 0 IS0
ENV 12447 Geotextiles and geotextile related products - Screening test method for
determining the resistance to hydrolysis
EN IS0 13431 Geotextiles and geotextile related products - Determination of tensile creep
and creep rupture behaviour
EN IS0 13437 Geotextiles and geotextile related products - Method for installing and
extracting samples in soil, and testing specimens in the laboratory
prENV IS0 13438 Geotextiles and geotextile related products - Screening test method for
determining the resistance to oxidation
ENV IS0 12960
Geotextiles and geotextile related products - Screening test method for
determining the resistance to liquids
IS0 10318 Geotextiles - Vocabulary
3 Definitions
3.1 Durability
When a geotextile is used in a civil engineering structure, it is intended to perform a particular
function for a minimum expected time, called the design life. Any application may require one
or more functions from the geotextile. The five functions defined in IS0 10318 are drainage,
filtration, protection, reinforcement and separation. Each function uses one or more properties
of the geotextile, such as tensile strength or water permeability. These are referred to as
functional properties.
Assessment of the durability of structures using geotextiles requires a study of the effects of
time on the functional properties. The physical structure of the geotextile, the nature of the
polymer used, the manufacturing process, the physical and chemical environment, the
conditions of storage and installation, and the different loads supported by the geotextile are all
parameters which govern the durability. The main task is to understand and assess the
evolution of the functional properties for the entire design life. This problem is quite complex
due to the combination and interaction of numerous parameters present in the soil environment,
and to the lack of well documented experience.
This guide is only intended to cover the durability of the materials; the durability of the
geotechnical structure as a whole should be treated separately.
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0 IS0 ISO/TR 13434:1998(E)
The object of the durability assessment is to provide the design engineer with the necessary
information (generally defined in terms of material reduction or partial safety factors) so that the
expected design life can be achieved with confidence.
3.2 Available and Required Properties
Functional Property
- Available property
..---e
Required property
Safety on Material
I
I
at end of Design Life
: I Safetv
q
a
1
I
I
Needs I
II
:
rrrrl
I
I
I
I 1
0
c
Storage : Install-: Loading : I
Time
I
6
Handling lation :
Anticipated
I
I
Design Life
I
Physical and Chemical Ageing
.
. .
End of Life:
Failure of
the Function
Fig. I: Typica I avai lable and required values of a functional property as a function of
time
It is first necessary to differentiate between the available and required values of a functional
property. Figure 1 is a schematic reresentation of the evolution of the available property of a
material as a function of time, as represented by the upper curve on the graph. The functional
property may be a mechanical property such as tensile strength or a hydraulic property such as
permeability. Along the time axis is indicated the events that happen between manufacture of
the product and the end of product life. The lower curve represents the changes in the required
property during these different and successive events. The shape illustrated applies to
mechanical strength but would not be very different for a hydraulic property. One can see that
after the loading phase, usually by the end of construction, the property required is considered
to be constant and equal to the level defined by the design. In some applications the required
level may change after a certain time, for example in the construction of a wall or increased
water flow in a drain, in which cases the effect of these changes on durability should be
assessed.
In the following sections the two curves are examined in more detail, using as an illustration the
tensile strength of a geotextile in a reinforcement application.
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ISO/TR 13434:1998(E) 0 IS0
3.3 Required Property
During the first period of product life, a minimum strength is needed to resist handling and
transportation loads. Once on site, placing and compaction of the backfill may for a short time
require a strength higher than that required for the design life. After installation and as
construction progresses, the applied loads increase until they reach a peak .
The required tensile strength is estimated by means of empirical calculation methods. As
recognised by most codes, there are uncertainties in the intensities and effects of the applied
loads: weights, surcharges, earth pressure. To cover for these uncertainties, the calculated
loads are multiplied by a first series of partial safety factors (or load factors). The calculated
stresses are then multiplied by a second partial safety factor to cover the relative inadequacy of
the calculation model. This calculation defines the maximum design load deemed to be
The design method and the definition of safety
constant throughout the entire design life.
Reference should be made to the
factors are not the subject of the present document.
appropriate Eurocode.
3.4 Available Property
At any time, the tensile strength required by the design should be smaller than the available
strength. The evolution of the available product property with time is complex, and arises from
various mechanisms. These should be analysed in order to ensure sufficient available strength
at any time, in particular at the end of the anticipated design life.
A new product exhibits a ‘short term’ or ‘initial’ property as defined by a set measurement
standard. Depending on the level of quality control and quality assurance, a reduction factor
may be applied to cover variations in the initial property. During storage and installation, this
property may change due to weathering and mechanical damage.
The extent of the mechanical damage depends on the product, the nature of the materials in
contact with the geotextile, the equipment used and the care provided by the operator.
Installation reduction factors should be considered for each product and typical backfill, based
on systematic tests. A simple reduction factor equal to the ratio of the strengths of undamaged
and damaged material is convenient but may not describe adequately the effect of damage on
long-term strength. Surface scratches or cracks may not significantly alter the short-term
behaviour but could lead to a reduction in long-term rupture life. This is still a subject of
research. Results should be interpreted prudently.
After installation, the operating life of the structure starts. During the operating life the
geotextile is subjected to chemical, biological or physical actions due to the soil, its constituents,
and its air, water and organic content. The typical degradation mechanisms of the polymers
used to manufacture geotextiles will be reviewed in the next section. The reduction in strength
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0 IS0 ISO/TR 13434:1998(E)
may be due to loss of mass, for example due to erosion of the surface, or to chemical
modification, and should be taken into account by specifying reduction factors.
In addition to the effect of the soil and its contents, the time to failure of the geotextile can also
diminish due to the level of the applied load: the greater the applied stress, the shorter the time
to failure. This is a particularly important phenomenon that will be described in 54.1. Thus
there is an interaction between the required property and the available property. There is no
absolute available property curve.
Obtaining the property curve is not an easy task. Temperature plays a major role in all
degradation mechanisms and in mechanical behaviour (creep and rupture). The results of
short-term accelerated tests, often using high temperatures as a means of acceleration and
lasting for one year or less, need to be related to long-term design life. This extrapolation
assumes that the degradation mechanisms are the same at both test and service temperatures
and over the entire design life of the structure.
Precautions should be taken to ensure that no transition, such as a change in the state of the
polymer or of the geotextile, occurs during the design life or in applying accelerated testing,
unless that transition is fully understood and taken into account in the extrapolation.
Failure implies that the geotextile can no longer perform the function for which it is being
applied. For example, if the function is filtration, a greater reduction in mechanical strength may
be acceptable than if the function is reinforcement.
Partial safety factors are required to describe the various degradation mechanisms (eg light
intensity, chemical concentration). These factors are listed in 7.9.
The testing techniques and the assessment methods for estimating the property curve will be
presented and discussed in later sections.
As described in 7.1, index test methods are
intended to ensure a minimum level of durability and do not constitute a comprehensive
assessment procedure. Where this is needed it will be necessary to carry out further
performance tests more closely related to service conditions. These tests may also include
investigations on samples extracted from sites where the same product has been used for
several years in a similar environment. The procedure is described in prEN IS0 13437. As in
other fields of engineering, confidence in the durability of geotextiles can only be expected to
develop gradually as the technology matures and the results of long-term service experience
accumulate. Examples of experience to date are described in clause 6.
5
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ISO/TR 13434: 1998(E)
0 IS0
3.5 Design Life
The design life is specified on the time axis. It is set by the client and is decided at the design
stage. The codes generally propose several fixed durations according to whether the structure
is meant for short-term use (typically a few years and not exceeding 5 years), temporary use
(around 25 years) or permanent use (50 to >lOO years). The nature of the structure and the
consequences of failure may influence this duration (example: 70 years for a wall, 100 years for
an abutment). Many geotextiles have a temporary function although the structure is
permanent, for example an embankment over a weak soil may require a geotextile
reinforcement until the embankment has settled. At the end of the anticipated design life, the
designer has to ensure a certain safety level (generally also indicated by codes), such that
failure is predicted to be well beyond the design life. The ratio of the predicted available
property to the predicted required property represents the total safety factor for that component.
This can also be expressed in terms of the time to reach failure if the geotextile were to be left
in service after the end of design life. These two representations of safety, the ratio of required
and available property at the design life, and the ratio of the predicted end of life to design life,
should be considered together because in combination they give a better idea of the real level
of safety that exists.
.3.6 End of Life
End of life is the point on the time axis where the available property curve meets the required
property curve. At this point the product is predicted to fail. Residual service may remain either
if the expected loads are overestimated, or if they imply a combination of degradation
mechanisms that may not all have reached their maximum values. Whatever the case, beyond
that point on the graph the possibility of failure is high.
3.7 The durability study
The design and durability assessment of a structure using geotextile can be summarised as
follows:
The design consists of:
l defining the function of the geotextile
l making the inventory of loads and constraints imposed by the application
l defining the design life of the geotextile
l quantifying the required properties of the geotextile (eg strength, permeability)
l defining the quality and quantity of the geotextile material needed
6
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0 IS0
ISO/TR 13434:1998(E)
l making sure that the estimated available properties at the end of the design life are
greater than the required properties; the factor of safety for the material being the
following ratio:
Available properties at the end of design life
factor of safety =
Required properties from loads and constraints
The factor of safety should be greater than unity.
The durability study consists of:
l listing significant environmental factors (see clause 5)
l defining the possible degradation phenomena with regard to the selected materials
and the environment
l estimating the available property as a function of time
l supplying the designer with suitable reduction factors or available properties at the
end of their design life.
Details are given in clause 7.
4 Constituents of Geotextiles
4.1 General
The durability of a geotextile depends upon the basic polymer from which it is made, on any
additives compounded with it, on the polymer microstructure, fibre geometry and fabric layout.
The geotextile should be chemically and biologically resistant if it is to be suitable for long term
applications.
The polymers used to manufacture the geotextiles are generally thermoplastic materials which
may be amorphous or semi-crystalline. An amorphous polymer has a randomly coiled structure
which at the glass transition temperature T, undergoes significant change: from a stiff, glassy,
brittle response to load below the glass transition temperature to a more ductile, rubbery
response above T,. Most polymers used in geotextiles are semi-crystalline, that is they contain
small well-oriented, closely packed crystallites alternating with amorphous material. Since the
change in behaviour only affects the amorphous regions, the glass transition is less marked for
a semicrystalline polymer. At a higher temperature, however, the crystallites melt, which
produces an abrupt change in properties. In civil engineering applications polyesters are used
below their T, while polypropylene and polyethylene are used above T,. Any acceleration of
laboratory tests crossing a transition such as T, should be regarded with caution.
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0 IS0
ISO/TR 13434: 1998(E)
consists of long chain molecules each
Any polymer, whether amorphous or semi-crystalline,
containing many identical chemical units. Each unit may be composed of one or more
monomers, the number of which determines the length of the polymeric chain and resulting
molecular weight. Molecular weight can affect physical properties such as the tensile strength
and modulus, impact strength and heat resistance as well as the durability properties. The
mechanical and physical properties of the plastics are also influenced by the bonds within and
between chains, chain branching, and the degree of crystallinity.
The orientation of polymers by mechanical drawing to form fibres and filaments results in higher
tensile properties and improved durability. As the molecules become more oriented, the fibres
become stronger. The crystallites are retained and the ratio of crystalline regions and
amorphous regions should be properly balanced to produce the physical properties necessary
for fibres used in geotextiles. The increased orientation and associated higher density leads to
higher environmental resistance.
Crystallinity has a strong effect on polymer properties, especially the mechanical properties,
because the tightly packed molecules within the crystallites results in dense regions with high
intermolecular cohesion and resistance to penetration by chemicals. An increase in the degree
of crystallinity leads directly to an increase in rigidity and yield or tensile strength, hardness and
softening point, and to a decrease in chemical permeability. Neighbouring crystallites may be
connected by single molecules running through the amorphous regions, which under tension
become taut and make a significant contribution to the mechanical behaviour. These ‘tie’
molecules are, however, susceptible to chemical attack.
Durability may also be influenced by fibre thickness, and the volume to surface ratio. Some
means of degradation, such as oxidation and UV-exposure, are dependent on surface area,
while others such as diffusion and absorption are inversely related to thickness.
4.2 Individual Polymer Types
The polymers used in geotextiles are described below and three of their most important
physical properties are listed in Table 1. The most commonly used are polypropylene and
polyethylene.
Polypropylene (PP) is a thermoplastic long chain polymer. PP is normally used in the isotactic
stereoregular form in which propylene monomers are attached in head-to-tail fashion and the
PP has a semi-
methyl groups are aligned on the same side of the polymer backbone.
crystalline structure which gives to it high stiffness, good tensile properties and resistance to
acids, alkalis and most solvents. It is possible for the tertiary carbon to react with free radicals,
so that stabilisers are added to prevent oxidation during manufacture and generally to improve
long term durability, including weathering.
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0 IS0
lSO/TR 13434:1998(E)
Polyethylene (PE) is one of the simplest organic polymers. It is used in its low density form
(LDPE), which is known for its excellent pliability, ease of processing and good physical
properties, or as high density polyethylene (HDPE) which is more rigid and chemically resistant.
PE can be stabilised to increase its resistance to weathering. Certain grades can be
susceptible to environmental stress cracking.
Polyesters are a group of polymers. The type used most frequently in geotextiles is
polyethylene terephthalate (PET) which is a condensation polymer of a dibasic acid and a
dialcohol. Since it is used below its T,, PET offers good mechanical properties, including a low
creep strain rate, and good chemical resistance to most acids and many solvents. The ester
group, the important polymeric link, can be hydrolysed very slowly in presence of water, and
more rapid attack occurs under highly alkaline conditions. As with other polymers PET is
sensitive to weathering.
Polyvinylchloride (PVC) is the most significant commercial member of the family of vinyl-based
resins. PVC is the most versatile of all plastics because its blending capability with plasticisers
and other additives allows it to take up a great variety of forms. Plasticisers are used in
quantities of up to 35% to create more flexible compounds, the choice of plasticiser being
dictated by the properties desired. Conversely, PVC absorbs certain organic liquids which have
a similar plasticising effect. PVC also tends to become brittle and darken when exposed to.
ultraviolet light or heat-induced degradation.
Polyamides (PA) or nylons are melt processable thermoplastics that contain an amide group as
a recurring part of the chain. PA offers a combination of properties including high strength at
elevated temperatures, ductility, wear and abrasion resistance, low frictional properties, low
permeability by gases and hydrocarbons, and good chemical resistance. Its limitations include
a tendency to absorb moisture, with resulting changes in dimensional and mechanical
properties, and limited resistance to acids and weathering. The PA fibres used in geotextiles
have a T, of 40-60 “C which reduces with moisture content.
Table 1
Typical physical properties for polymers used in geotextiles
HDPE PP PET PA PVC
Density, (g/cm3) 0.95 0.91 1.38 1.12 1.3 to
15 .
Melting temperature, (“C) 130 165 260 220 to
250
Glass transition temperature,
(Z) -100 to -20 to 70 to 80 40 to 60 -25 to
I I I 1 I I 100 I
-70 -12
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ISO/TR 13434:1998(E) 0 IS0
4.3 Manufacturing Processes
Geotextiles and geotextile-related products are manufactured using several different processes.
In this section the main processing technologies for the manufacture of geotextiles, geogrids,
geonets, geocells and geocomposites will be described.
Geotextiles include nonwoven, woven and knitted products. All are made of polymers drawn
into fibres or yarns, which consist of a number of fibres. The different manufacturing processes
lead to geotextile products with a wide range of properties.
For the production of nonwoven geotextiles continuous filaments or staple fibres (cut fibres) are
used. Woven and knitted geotextiles are produced using different types of yarn such as spun
yarns, multifilament yarns, monofilaments and film tapes or split film yarns.
The types of fibres, multifilaments, monofilaments and tapes used in the manufacture of such
geotextiles are produced mainly by a melt spinning process. To produce fibres, multifilaments
and monofilaments the molten polymer is extruded through orifices of a die, cooled, drawn by
stretching and according to the end use:
1) laid on a screen to form a planar structure (continuous filament or spun bonded
nonwoven);
2) processed to staple fibres by crimping and staple cutting or
3) processed to multi- or monofilaments and winding the filaments after drawing and
annealing directly on to spools. In the case of multifilament production this technique is
known as spin drawing.
Spunbonded nonwovens are continuous filament nonwovens and are manufactured in a
continuous process starting with the polymer and proceeding through filament production,
geotextile formation and filament bonding in the same line, finishing with the roll of nonwoven.
Staple fibre nonwovens are manufactured in a two stage process: the first stage consists of
fibre production (extrusion and cutting) and the second stage consists of the formation of the
geotextile, bonding and production of the finished roll.
Woven geotextiles are also produced in a discontinuous process with at least two stages. The
first stage is the production of the yarn, monofilament or multifilament. The second stage is the
weaving either to flat wovens (or simply wovens) or knitted wovens (knits).
Film tapes and split yarns are normally only produced from polypropylene and polyethylene.
These products are made by extruding a film, cutting the film into individual tapes and
stretching them by a uniaxial drawing process. Coarse film tapes are too stiff for further
handling in beaming and weaving, and are therefore fibrillated after the drawing process and
before winding and twisting. These types of yarn are then called split film yarns.
10
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0 IS0 ISO/TR 13434:1998(E)
The drawing process is very important in the production of the different types of polymeric
fibres, filaments and tapes. During this process the polymeric chains become aligned along the
filament or tape length and their crystallinity, mechanical properties and durability all increase.
The mechanical properties of the product depend upon the details of the manufacturing
process.
Bonding of nonwoven geotextiles formed from either continuous filaments or from staple fibres
is done mechanically by needle punching with felting needles, by thermal (cohesive) bonding
using heat with or without pressure (cal
...
TECHNICAL ISO/TR
REPORT 13434
First edition
1998-12-15
Geotextiles and geotextile-related
products — Guidelines on durability
Géotextiles et produits apparentés — Lignes directrices concernant
la durabilité
A
Reference number
ISO/TR 13434:1998(E)
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ISO/TR 13434:1998(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO
member bodies). The work of preparing International Standards is normally carried out through ISO technical
committees. Each member body interested in a subject for which a technical committee has been established has
the right to be represented on that committee. International organizations, governmental and non-governmental, in
liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
The main task of technical committees is to prepare International Standards, but in exceptional circumstances a
technical committee may propose the publication of a Technical Report of one of the following types:
type 1, when the required support cannot be obtained for the publication of an International Standard, despite
repeated efforts;
type 2, when the subject is still under technical development or where for any other reason there is the future
but not immediate possibility of an agreement on an International Standard;
type 3, when a technical committee has collected data of a different kind from that which is normally published
as an International Standard (“state of the art”, for example).
Technical Reports of types 1 and 2 are subject to review within three years of publication, to decide whether they
can be transformed into International Standards. Technical Reports of type 3 do not necessarily have to be
reviewed until data they provide are considered to be no longer valid or useful.
Technical Reports are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.
Attention is drawn to the possibility that some of the elements of this Technical Report may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO/TR 13434, which is a Technical Report of type 3, was prepared by the European Committee for Standardization
(CEN) in collaboration with ISO Technical Committee TC 38, Textiles, Subcommittee SC 21, Geotextiles, in
accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
Throughout the text of this document, read “.this European prestandard.” to mean “.this Technical Report.”.
Annex A of this Technical Report is for information only.
Annex ZZ provides a list of corresponding International and European Standards for which equivalents are not given
in the text.
© ISO 1998
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic
or mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 • CH-1211 Genève 20 • Switzerland
Internet iso@iso.ch
Printed in Switzerland
ii
---------------------- Page: 2 ----------------------
© ISO ISO/TR 13434:1998(E)
Foreword
This draft CEN Technical Report has been prepared by CEN/TC 189 "Geotextiles and
geotextile-related products" the secretariat of which is held by IBN. It is now submitted to the
CEN/BT for approval.
iii
---------------------- Page: 3 ----------------------
© ISO ISO/TR 13434:1998(E)
1 Scope
This guide is intended to introduce the reader to the basic concepts of geotextiles durability
and its assessment. Consideration of the design parameters, the project conditions and the
geotextile properties leads to the definition of the appropriate tests to be performed for
assessing the durability of the geotextile .
Geotextiles and geotextile-related products (referred to below as geotextiles) are available in a
wide range of compositions appropriate to different applications and environments. The
synthetic polymers used consist mainly of polyamide, polyester, polyethylene and
polypropylene. These materials, when correctly processed and stabilised, are resistant to
chemical and microbiological attack encountered in normal soil environments and for normal
design lives. For such applications only a minimum number of screening or "index" tests are
necessary.
For applications in more severe environments such as soil treated with lime or cement, landfills
or industrial waste, or for applications with particularly long design lives, special tests including
"performance" tests with site-specific parameters may be required.
This guide does not cover products designed to survive for a limited time, such as erosion
control fabric based on natural fibres, nor does it cover geomembranes, nor geotextiles for
asphalt reinforcement. Creep and creep-rupture, which should be taken into consideration for
soil reinforcement applications, are described in outline but the use of the data in reinforced soil
design will be the subject of a separate document.
2 Normative references
ENV 1897 Geotextiles and geotextile related products - Determination of the
compressive creep properties
ENV 12224 Geotextiles and geotextile related products - Determination of the resistance
to weathering
ENV 12225 Geotextiles and geotextile related products - Method for determining the
microbiological resistance by a soil burial test
ENV 12226 Geotextiles and geotextile related products - General tests for evaluation
following durability testing
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ISO/TR 13434:1998(E) © ISO
ENV 12447 Geotextiles and geotextile related products - Screening test method for
determining the resistance to hydrolysis
EN ISO 13431 Geotextiles and geotextile related products - Determination of tensile creep
and creep rupture behaviour
EN ISO 13437 Geotextiles and geotextile related products - Method for installing and
extracting samples in soil, and testing specimens in the laboratory
prENV ISO 13438 Geotextiles and geotextile related products - Screening test method for
determining the resistance to oxidation
ENV ISO 12960 Geotextiles and geotextile related products - Screening test method for
determining the resistance to liquids
ISO 10318 Geotextiles - Vocabulary
3 Definitions
3.1 Durability
When a geotextile is used in a civil engineering structure, it is intended to perform a particular
function for a minimum expected time, called the design life. Any application may require one
or more functions from the geotextile. The five functions defined in ISO 10318 are drainage,
filtration, protection, reinforcement and separation. Each function uses one or more properties
of the geotextile, such as tensile strength or water permeability. These are referred to as
functional properties.
Assessment of the durability of structures using geotextiles requires a study of the effects of
time on the functional properties. The physical structure of the geotextile, the nature of the
polymer used, the manufacturing process, the physical and chemical environment, the
conditions of storage and installation, and the different loads supported by the geotextile are all
parameters which govern the durability. The main task is to understand and assess the
evolution of the functional properties for the entire design life. This problem is quite complex
due to the combination and interaction of numerous parameters present in the soil environment,
and to the lack of well documented experience.
This guide is only intended to cover the durability of the materials; the durability of the
geotechnical structure as a whole should be treated separately.
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The object of the durability assessment is to provide the design engineer with the necessary
information (generally defined in terms of material reduction or partial safety factors) so that the
expected design life can be achieved with confidence.
3.2 Available and Required Properties
Fig. 1: Typical available and required values of a functional property as a function of
time
It is first necessary to differentiate between the available and required values of a functional
property. Figure 1 is a schematic reresentation of the evolution of the available property of a
material as a function of time, as represented by the upper curve on the graph. The functional
property may be a mechanical property such as tensile strength or a hydraulic property such as
permeability. Along the time axis is indicated the events that happen between manufacture of
the product and the end of product life. The lower curve represents the changes in the required
property during these different and successive events. The shape illustrated applies to
mechanical strength but would not be very different for a hydraulic property. One can see that
after the loading phase, usually by the end of construction, the property required is considered
to be constant and equal to the level defined by the design. In some applications the required
level may change after a certain time, for example in the construction of a wall or increased
water flow in a drain, in which cases the effect of these changes on durability should be
assessed.
In the following sections the two curves are examined in more detail, using as an illustration the
tensile strength of a geotextile in a reinforcement application.
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3.3 Required Property
During the first period of product life, a minimum strength is needed to resist handling and
transportation loads. Once on site, placing and compaction of the backfill may for a short time
require a strength higher than that required for the design life. After installation and as
construction progresses, the applied loads increase until they reach a peak .
The required tensile strength is estimated by means of empirical calculation methods. As
recognised by most codes, there are uncertainties in the intensities and effects of the applied
loads: weights, surcharges, earth pressure. To cover for these uncertainties, the calculated
loads are multiplied by a first series of partial safety factors (or load factors). The calculated
stresses are then multiplied by a second partial safety factor to cover the relative inadequacy of
the calculation model. This calculation defines the maximum design load deemed to be
constant throughout the entire design life. The design method and the definition of safety
factors are not the subject of the present document. Reference should be made to the
appropriate Eurocode.
3.4 Available Property
At any time, the tensile strength required by the design should be smaller than the available
strength. The evolution of the available product property with time is complex, and arises from
various mechanisms. These should be analysed in order to ensure sufficient available strength
at any time, in particular at the end of the anticipated design life.
A new product exhibits a 'short term' or 'initial' property as defined by a set measurement
standard. Depending on the level of quality control and quality assurance, a reduction factor
may be applied to cover variations in the initial property. During storage and installation, this
property may change due to weathering and mechanical damage.
The extent of the mechanical damage depends on the product, the nature of the materials in
contact with the geotextile, the equipment used and the care provided by the operator.
Installation reduction factors should be considered for each product and typical backfill, based
on systematic tests. A simple reduction factor equal to the ratio of the strengths of undamaged
and damaged material is convenient but may not describe adequately the effect of damage on
long-term strength. Surface scratches or cracks may not significantly alter the short-term
behaviour but could lead to a reduction in long-term rupture life. This is still a subject of
research. Results should be interpreted prudently.
After installation, the operating life of the structure starts. During the operating life the
geotextile is subjected to chemical, biological or physical actions due to the soil, its constituents,
and its air, water and organic content. The typical degradation mechanisms of the polymers
used to manufacture geotextiles will be reviewed in the next section. The reduction in strength
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may be due to loss of mass, for example due to erosion of the surface, or to chemical
modification, and should be taken into account by specifying reduction factors.
In addition to the effect of the soil and its contents, the time to failure of the geotextile can also
diminish due to the level of the applied load: the greater the applied stress, the shorter the time
to failure. This is a particularly important phenomenon that will be described in 5.4.1. Thus
there is an interaction between the required property and the available property. There is no
absolute available property curve.
Obtaining the property curve is not an easy task. Temperature plays a major role in all
degradation mechanisms and in mechanical behaviour (creep and rupture). The results of
short-term accelerated tests, often using high temperatures as a means of acceleration and
lasting for one year or less, need to be related to long-term design life. This extrapolation
assumes that the degradation mechanisms are the same at both test and service temperatures
and over the entire design life of the structure.
Precautions should be taken to ensure that no transition, such as a change in the state of the
polymer or of the geotextile, occurs during the design life or in applying accelerated testing,
unless that transition is fully understood and taken into account in the extrapolation.
Failure implies that the geotextile can no longer perform the function for which it is being
applied. For example, if the function is filtration, a greater reduction in mechanical strength may
be acceptable than if the function is reinforcement.
Partial safety factors are required to describe the various degradation mechanisms (eg light
intensity, chemical concentration). These factors are listed in 7.9.
The testing techniques and the assessment methods for estimating the property curve will be
presented and discussed in later sections. As described in 7.1, index test methods are
intended to ensure a minimum level of durability and do not constitute a comprehensive
assessment procedure. Where this is needed it will be necessary to carry out further
performance tests more closely related to service conditions. These tests may also include
investigations on samples extracted from sites where the same product has been used for
several years in a similar environment. The procedure is described in prEN ISO 13437. As in
other fields of engineering, confidence in the durability of geotextiles can only be expected to
develop gradually as the technology matures and the results of long-term service experience
accumulate. Examples of experience to date are described in clause 6.
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3.5 Design Life
The design life is specified on the time axis. It is set by the client and is decided at the design
stage. The codes generally propose several fixed durations according to whether the structure
is meant for short-term use (typically a few years and not exceeding 5 years), temporary use
(around 25 years) or permanent use (50 to >100 years). The nature of the structure and the
consequences of failure may influence this duration (example: 70 years for a wall, 100 years for
an abutment). Many geotextiles have a temporary function although the structure is
permanent, for example an embankment over a weak soil may require a geotextile
reinforcement until the embankment has settled. At the end of the anticipated design life, the
designer has to ensure a certain safety level (generally also indicated by codes), such that
failure is predicted to be well beyond the design life. The ratio of the predicted available
property to the predicted required property represents the total safety factor for that component.
This can also be expressed in terms of the time to reach failure if the geotextile were to be left
in service after the end of design life. These two representations of safety, the ratio of required
and available property at the design life, and the ratio of the predicted end of life to design life,
should be considered together because in combination they give a better idea of the real level
of safety that exists.
3.6 End of Life
End of life is the point on the time axis where the available property curve meets the required
property curve. At this point the product is predicted to fail. Residual service may remain either
if the expected loads are overestimated, or if they imply a combination of degradation
mechanisms that may not all have reached their maximum values. Whatever the case, beyond
that point on the graph the possibility of failure is high.
3.7 The durability study
The design and durability assessment of a structure using geotextile can be summarised as
follows:
The design consists of:
• defining the function of the geotextile
• making the inventory of loads and constraints imposed by the application
• defining the design life of the geotextile
• quantifying the required properties of the geotextile (eg strength, permeability)
• defining the quality and quantity of the geotextile material needed
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• making sure that the estimated available properties at the end of the design life are
greater than the required properties; the factor of safety for the material being the
following ratio:
Available properties at the end of design life
factor of safety =
Required properties from loads and constraints
The factor of safety should be greater than unity.
The durability study consists of:
• listing significant environmental factors (see clause 5)
• defining the possible degradation phenomena with regard to the selected materials
and the environment
• estimating the available property as a function of time
•
supplying the designer with suitable reduction factors or available properties at the
end of their design life.
Details are given in clause 7.
4 Constituents of Geotextiles
4.1 General
The durability of a geotextile depends upon the basic polymer from which it is made, on any
additives compounded with it, on the polymer microstructure, fibre geometry and fabric layout.
The geotextile should be chemically and biologically resistant if it is to be suitable for long term
applications.
The polymers used to manufacture the geotextiles are generally thermoplastic materials which
may be amorphous or semi-crystalline. An amorphous polymer has a randomly coiled structure
which at the glass transition temperature T undergoes significant change: from a stiff, glassy,
g
brittle response to load below the glass transition temperature to a more ductile, rubbery
response above T . Most polymers used in geotextiles are semi-crystalline, that is they contain
g
small well-oriented, closely packed crystallites alternating with amorphous material. Since the
change in behaviour only affects the amorphous regions, the glass transition is less marked for
a semicrystalline polymer. At a higher temperature, however, the crystallites melt, which
produces an abrupt change in properties. In civil engineering applications polyesters are used
below their T while polypropylene and polyethylene are used above T . Any acceleration of
g g
laboratory tests crossing a transition such as T should be regarded with caution.
g
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Any polymer, whether amorphous or semi-crystalline, consists of long chain molecules each
containing many identical chemical units. Each unit may be composed of one or more
monomers, the number of which determines the length of the polymeric chain and resulting
molecular weight. Molecular weight can affect physical properties such as the tensile strength
and modulus, impact strength and heat resistance as well as the durability properties. The
mechanical and physical properties of the plastics are also influenced by the bonds within and
between chains, chain branching, and the degree of crystallinity.
The orientation of polymers by mechanical drawing to form fibres and filaments results in higher
tensile properties and improved durability. As the molecules become more oriented, the fibres
become stronger. The crystallites are retained and the ratio of crystalline regions and
amorphous regions should be properly balanced to produce the physical properties necessary
for fibres used in geotextiles. The increased orientation and associated higher density leads to
higher environmental resistance.
Crystallinity has a strong effect on polymer properties, especially the mechanical properties,
because the tightly packed molecules within the crystallites results in dense regions with high
intermolecular cohesion and resistance to penetration by chemicals. An increase in the degree
of crystallinity leads directly to an increase in rigidity and yield or tensile strength, hardness and
softening point, and to a decrease in chemical permeability. Neighbouring crystallites may be
connected by single molecules running through the amorphous regions, which under tension
become taut and make a significant contribution to the mechanical behaviour. These 'tie'
molecules are, however, susceptible to chemical attack.
Durability may also be influenced by fibre thickness, and the volume to surface ratio. Some
means of degradation, such as oxidation and UV-exposure, are dependent on surface area,
while others such as diffusion and absorption are inversely related to thickness.
4.2 Individual Polymer Types
The polymers used in geotextiles are described below and three of their most important
physical properties are listed in Table 1. The most commonly used are polypropylene and
polyethylene.
Polypropylene (PP) is a thermoplastic long chain polymer. PP is normally used in the isotactic
stereoregular form in which propylene monomers are attached in head-to-tail fashion and the
methyl groups are aligned on the same side of the polymer backbone. PP has a semi-
crystalline structure which gives to it high stiffness, good tensile properties and resistance to
acids, alkalis and most solvents. It is possible for the tertiary carbon to react with free radicals,
so that stabilisers are added to prevent oxidation during manufacture and generally to improve
long term durability, including weathering.
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Polyethylene (PE) is one of the simplest organic polymers. It is used in its low density form
(LDPE), which is known for its excellent pliability, ease of processing and good physical
properties, or as high density polyethylene (HDPE) which is more rigid and chemically resistant.
PE can be stabilised to increase its resistance to weathering. Certain grades can be
susceptible to environmental stress cracking.
Polyesters are a group of polymers. The type used most frequently in geotextiles is
polyethylene terephthalate (PET) which is a condensation polymer of a dibasic acid and a
dialcohol. Since it is used below its T , PET offers good mechanical properties, including a low
g
creep strain rate, and good chemical resistance to most acids and many solvents. The ester
group, the important polymeric link, can be hydrolysed very slowly in presence of water, and
more rapid attack occurs under highly alkaline conditions. As with other polymers PET is
sensitive to weathering.
Polyvinylchloride (PVC) is the most significant commercial member of the family of vinyl-based
resins. PVC is the most versatile of all plastics because its blending capability with plasticisers
and other additives allows it to take up a great variety of forms. Plasticisers are used in
quantities of up to 35% to create more flexible compounds, the choice of plasticiser being
dictated by the properties desired. Conversely, PVC absorbs certain organic liquids which have
a similar plasticising effect. PVC also tends to become brittle and darken when exposed to
ultraviolet light or heat-induced degradation.
Polyamides (PA) or nylons are melt processable thermoplastics that contain an amide group as
a recurring part of the chain. PA offers a combination of properties including high strength at
elevated temperatures, ductility, wear and abrasion resistance, low frictional properties, low
permeability by gases and hydrocarbons, and good chemical resistance. Its limitations include
a tendency to absorb moisture, with resulting changes in dimensional and mechanical
properties, and limited resistance to acids and weathering. The PA fibres used in geotextiles
have a T of 40-60 °C which reduces with moisture content.
g
Table 1
Typical physical properties for polymers used in geotextiles
HDPE PP PET PA PVC
3
Density, (g/cm ) 0.95 0.91 1.38 1.12 1.3 to
1.5
Melting temperature, (ºC) 130 165 260 220 to
250
Glass transition temperature, (ºC) -100 to -20 to 70 to 80 40 to 60 -25 to
-70 -12 100
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4.3 Manufacturing Processes
Geotextiles and geotextile-related products are manufactured using several different processes.
In this section the main processing technologies for the manufacture of geotextiles, geogrids,
geonets, geocells and geocomposites will be described.
Geotextiles include nonwoven, woven and knitted products. All are made of polymers drawn
into fibres or yarns, which consist of a number of fibres. The different manufacturing processes
lead to geotextile products with a wide range of properties.
For the production of nonwoven geotextiles continuous filaments or staple fibres (cut fibres) are
used. Woven and knitted geotextiles are produced using different types of yarn such as spun
yarns, multifilament yarns, monofilaments and film tapes or split film yarns.
The types of fibres, multifilaments, monofilaments and tapes used in the manufacture of such
geotextiles are produced mainly by a melt spinning process. To produce fibres, multifilaments
and monofilaments the molten polymer is extruded through orifices of a die, cooled, drawn by
stretching and according to the end use:
1) laid on a screen to form a planar structure (continuous filament or spun bonded
nonwoven);
2) processed to staple fibres by crimping and staple cutting or
3) processed to multi- or monofilaments and winding the filaments after drawing and
annealing directly on to spools. In the case of multifilament production this technique is
known as spin drawing.
Spunbonded nonwovens are continuous filament nonwovens and are manufactured in a
continuous process starting with the polymer and proceeding through filament production,
geotextile formation and filament bonding in the same line, finishing with the roll of nonwoven.
Staple fibre nonwovens are manufactured in a two stage process: the first stage consists of
fibre production (extrusion and cutting) and the second stage consists of the formation of the
geotextile, bonding and production of the finished roll.
Woven geotextiles are also produced in a discontinuous process with at least two stages. The
first stage is the production of the yarn, monofilament or multifilament. The second stage is the
weaving either to flat wovens (or simply wovens) or knitted wovens (knits).
Film tapes and split yarns are normally only produced from polypropylene and polyethylene.
These products are made by extruding a film, cutting the film into individual tapes and
stretching them by a uniaxial drawing process. Coarse film tapes are too stiff for further
handling in beaming and weaving, and are therefore fibrillated after the drawing process and
before winding and twisting. These types of yarn are then called split film yarns.
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The drawing process is very important in the production of the different types of polymeric
fibres, filaments and tapes. During this process the polymeric chains become aligned along the
filament or tape length and their crystallinity, mechanical properties and durability all increase.
The mechanical properties of the product depend upon the details of the manufacturing
process.
Bonding of nonwoven geotextiles formed from either continuous filaments or from staple fibres
is done mechanically by needle punching with felting needles, by thermal (cohesive) bonding
using heat with or without pressure (calendering), by chemical (adhesive) bonding, or by a
combination of these processes.
The physical structure and properties of the nonwoven products are linked to the bonding
system. For example heat bonded wovens and nonwovens (tape film wovens) are thin
products in which the fibres are oriented in a two-dimensional structure. Needle punched
nonwovens have a three-dimensional structure, the configuration of which may be fixed by a
final thermal bonding stage.
The structure of the fabric will contribute to the durability properties, for example thick fibres
and tapes are less susceptible to weathering. The stabilisation systems applied to improve the
properties are therefore adjusted to suit either a nonwoven geotextile of fine
...
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