PES COLLEGE OF ENGINEERING, MANDYA-

571401
DEPARTMENT OF CIVIL ENGINEERING

GEOSYNTHETICS-GEOTEXTILES
BY;
Prof. Santhosh Kumar C V[CVS]
B.E, M.Tech[Geo-Technical Engineering]
Assistant Professor
PESCE, Mandya
Email:santhoshcv@pesce.ac.in
 Geosynthetics are man-made materials used to improve soil conditions. The word is
derived from: Geo = earth or soil + Synthetics = man-made
 Geosynthetics are typically made from petrochemical-based polymers (“plastics”)
that are biologically inert and will not decompose from bacterial or fungal action.
 While most are essentially chemical inert, some may be damaged by petrochemicals
and most have some degree of susceptibility to ultraviolet light (sunlight).
 A geosynthetic product comes with several functions, namely reinforcement,
separation, drainage, containment, barrier, the management of surface erosion,
including any other function a geosynthetic material is supposed to have. (some may
perform more than one of these functions simultaneously)
 The use of this material can mostly be observed in the
Civil Engineering profession, transportation, geological
environment, marine, hydraulics, roads, railways, retaining
walls, canals, and other structures that require the need of
this material for certain engineering purposes.
GEOTEXTILE HISTORICAL DEVELOPMENTS
 The usage of geotextiles dates back to thousands of years ago,
 which controlled soil erosion at the time of ancient Romans and was used when the desired soil
was unstable to build the road
 The first recorded usage of geotextile was on the road which was undertaken by the
Department of South Carolina Highways in1926.
 In this project, a heavy cotton geotextile was loaded onto the soil. And then the hot asphalt was
applied to the fabric then a thin layer of sand was poured on the asphalt.
 Research has shown that this fabric has reduced cracking and has prevented the road from
breaking down
 The usage of geotextile has been successful for the past two decades and it has grown rapidly,
due to its excellent performance in structural applications, especially on the roads.
 Today, the world is witnessing thousands of projects where geotextile are used and thousands
of companies and factories are active in the production and installation of geotextiles
throughout Europe, America, Africa and Asia, especially East Asia.
 In figure 2 a geotextiles is used to separate the two layers.
 The separation property is a feature that, along with properties such as flexibility
and porosity, refers to the ability to locate geosynthetics products between two
unmatched materials
 For example, the main cause of road rupture is the injection of adjacent layers into
the pebble and the consequently the decline in the strength of the pebble layer
(Figure 2a).
 When the pebble is placed on the subgrade layer, the underlying layer is mixed by
soil and, over time, the traffic and vibration load, injects the Aggregate layer into
the soil, causing the layer to move upwards.
 Also, in wet places, the traffic causes the weak subgrade soil to pump into the
pebbles and all of these conditions reduce the effective thickness of the pebble layer;
 As a result, the protective layer of the road is damaged and the useful life of the
road decreases, which can be protected by placing a geotextile on a pebble layer
under the subgrade layer.
 GEOSYNTHETICS RECENT DEVELOPMENTS
 Recent developments in geosynthetics: systematic applications of geotextile did not immediately follow
the initial developments that looks play that took place from 1930s to 1960; only when parallel
developments took place in materials technology increasing its availability, capabilities and cost
effectiveness did it's use become popular.
 The polyethylene nets manufactured by Netlon limited UK, were used in Japan for reducing the damage
to embankment caused by seismic activity and rainfall.
 They were used as basal layers to improve embankment stability.
 Further uses of geosynthetics as filter beneath the riprap, separator between the underlying soil, and
subsequently for basic functions such as separation, filter, training and reinforcement were identified to
enable better understanding of the process of its application.
 Use of membranes as impermeable barriers as become the standards for minimizing the effect of
migrating contaminates in contaminated sites, liquid impoundments, water reservoirs com etc.
 The range of Geo synthetic materials available today is very wide.
 Giroud(1986) bakes out several reasons as to why these materials have become successful and
acceptable in professional practices.

 These groups of people contractors, designers and owners are behind the spectacular growth.
 Contractors are interested in quicker, less weather dependent construction materials; reduce volume of
earthworks and capability of handling poor quality soil as well.

 Designers want better reliability, flexibility and control over their design, which are possible with the use
of appropriate choice of geotextile materials.

 Owners expect Cost savings in both construction and maintenance.

 Giroud suggest the following reasons for the wide acceptability of Geosynthetics

1. The membrane like behavior of these materials complements the properties of granular soil. Hence the
soils that are prone to erosion or settlement can be stabilized. The tensile properties of geosynthetics
material become useful in increasing the tensile strength of soil. In addition these materials are
effective as a separator between dissimilar layers of soil.
2. Geotechnical structures such as pavements, foundations and retaining walls use layered construction.
Geosynthetics materials are used as interfaces between layers. This improves the overall performances
3. Geotechnical structures need to be flexible when subjected to differential settlement. Geosynthetic
materials owing to their inherent flexibility or compatible with the behavior of geotechnical structures.
CLASSIFICATIONS BASED ON MATERIAL TYPES:
GEO
 Soil, Rock or other Geotechnical material
SYNTHETIC
 Man made
 Polymeric material

Natural: Coir, jute, hemp etc

Artifical: Polymeric or metallic

 NATURAL GEOTEXTILES: Geotextiles are originally used as natural textiles.

These textiles are usually used to control soil erosion, mainly due to the above mentioned properties, as the
most appropriate temporary solution.

Some types of famous geotextiles are Coirmat (woven from coconut fiber), Jutmesh (woven from china fibers),
Green furee (a combination of biodegradable and non-biodegradable fibers), RECP (rolled erison control
product), Coirlog (coconut fiber bag tissue), Environmat (spruce wood fiber)
 The properties of natural fibers such as ability to mature fibres to absorb water and
their biodegradability with time give them an edge over synthetic geotextiles for
erosion control purposes.
 The drapability factor due to the flexibility allows them to conform closely to the
terrain.
 Bamboo dowels, due to their high tensile stress can be efficiently to prevent landslides
or slope failure.
 The main challenge while using natural fibers is to prevent them from biodegradation and
attack from micro-organism. This can be done to some extent by coating with polymers,
bitumen etc.
 SYNTHETIC FIBERS /ARTIFICAL FIBRES: These were produced, instead of textiles and natural
fibers mentioned in recent decades which has properties like granular materials and in terms of
mechanical and chemical resistance are at a higher level.
These fibers are made from crude oil derivatives and its main property is the incorruptibility in contrast
of soil degradation factors. Geotextile materials are placed on or in soil to do one of four things:
• Separation/confinement/distribute loads
- Improve level-grade soil situations such as roads, alleys, lane ways
-Improve sloped-grade situations such as banks, hillsides, stream access points
• Reinforce soil
- Soil walls, bridge abutments, box culverts/bridges, and soil arches
• Prevent soil movement while letting water move through the material
- Such as in drainage systems and back fill around water intakes
• Controlling water pressure allowing flow in the plane of the material
- Such as on foundation walls to allow water to move down to perimeter drains
 Metallic reinforcement materials in the form of steel sheets, grids meshes, strips bars,
rods that are capable of sustaining tensile loads and restraining deformations have
been used for many years.

 Steel has been used successfully for a long time in soil for piling and pile lines.

 For using these material as soil reinforcement, information with regard to the tensile
strength behaviour, soil reinforcement friction and durability behaviour is necessary.

 Property such as tensile strength Youngs modulus and stress-strain behaviour can we
obtain by conducting tension tests on reinforcing materials.

 Polymeric Materials majority of geosynthetics is of polymeric origin composed of

polypropylene, polyethylene or polyester fibres; a small percentage of Polyalmide
origin.

 The type of fibres used in the manufacture of geotextile includes monofilament, staple
APPLICATIONS AND POTENTIAL OF GEOSYNTHETICS:

 Soil reinforcement function:

 It ensures improved response of the soil. It increases normal loading and reduces disturbing shear
forces.
 As a result steep slopes can be constructed or an embankment of increased height be built on soft soil ,
which otherwise would not have been possible.
 In payments, geosynthetics, owing to their membrane action which induces tensile forces, control
deformations and significantly improve their performance.
 Separator function :

 Geosynthetics is useful to separate dissimilar soils. A separator helps prevent intermixing of poor in situ
soil with good quality granular materials when the structure is subjected to surface loading.

 It acts as a barrier to migration of particles between 2 dissimilar soils, a requirement in many

applications such as pavements, graded filters, clay covers and liners in landfills etc.

 The separator needs to have sufficient strength to survive ripping, puncturing on impact and must be
durable against chemical attacks
 Filtration function:
 Geosynthetics such as geotextiles allow the moment of liquid across the plane of geotextile while retaining the soil on the
upstream side.
 To achieve this, the material should meet condition of both adequate permeability, requiring an open fabric structure,
and soil retention requiring a small opening size.
 A long term soil to geotextile flow compatibility is also important in that the filter must not clog excessively during its
lifetime.
 The filtration function of geotextile is a major area of importance in many applications such as retaining wall, pavement
and in erosion control measures and landfills
 Drainage function:

 The drainage function of geotextile enables flow in the plane of geotextile.

 Apart from geo textiles that transmit fluids, nowadays there are specific products such as geonets and drainage
composites to meet drainage requirements.

 Other than the ability to direct the flow, geotextile should be able to retain soil.

 Geo synthetic drains have been successful in many cases since they reduce the consolidation time in soft soil.

 Nowadays drainage composites are available which serve dual functions of filtration and drainage which are used in
 Barrier function:
 The barrier function using geomembranes and geotextiles coated with bitumen, rubber bitumen or
other polymer mixes is useful in many applications for minimizing fluid and vapour flow.
 The fluid permeability of materials is very low and is therefore useful in many applications such as
canal lining, liquid impoundments, dams, municipal waste landfills and among others.
 The materials to some extent also prevent the flow of gases and odours that are likely to emanate from
solid waste landfills.
RAW MATERIALS USED FOR MANUFACTURING
GEOSYNTHETIC MATERIALS
 Almost exclusively, the raw materials from which geosynthetics are produced are polymeric.

 Polymers are materials of very high molecular weight and are found to have multifarious applications
in the present society.

 The polymers used to manufacture geosynthetics are generally thermoplastics, which may be
amorphous or semi-crystalline.

 Such materials melt on heating and solidify on cooling. The heating and cooling cycles can be applied
several times without affecting the properties.

 Molecular weight can affect physical and mechanical properties, heat resistance and durability
(resistance to chemical and biological attack) properties of geosynthetics.
 The physical and mechanical properties of the polymers are also influenced by the bonds within and
between chains, the chain branching and the degree of crystallinity.
 Polymer fibers have different types such as propylene, polyester, polyethylene, polyamid and other items.
 Polyethylene is the first and oldest polymer used in the production of geotextiles, which was discovered in
1931 in the ICI laboratory.
 Polyamide has the highest record. It has been used since 1935.
 Gradually, polypropylene was also recognized as the primary ingredient in this industry.
 But polyester was in competition with polypropylene and since 1954 it plays a major role in making
geotextiles
Geotextile fiber groups are divided into different polymers as the following:

• Polypropylene (PP) 92% of geotextiles

• Polyester (PET) 5% of geotextiles
• Polyethylene (PE) 2% of geotextiles
• Polyamide (Nylon) 1% of geotextiles.
 There are other powerful polymers in the market, but geotextiles are produced at higher volumes (some
polymers are not available in large volumes) and are economical (very specific polymers are very expensive).
 Among the polymers listed in table 1, the cost versus performance of polyester is today more optimal, while
polypropylene and polyethylene have more chemical resistance.
 Polyethylene: Polyethylene (PE) can be produced in a highly crystalline form, which is an extremely
important characteristics in fibre-forming polymer. Three main groups of polyethylene are
available, viz.,

LDPE — low density polyethylene (density 920—930 kg/m 3)

LLDPE — linear low density polyethylene (density 925—945 kg/m 3)

HDPE — high density polyethylene (density 940—960 kg/m 3)

 Polypropylene (PP):
 Polypropylene (PP) is a crystalline thermoplastic produced by polymerizing propylene monomers in the
presence of a stereo-specific catalyst system.
 The primary reason for PP usage in geotextile manufacturing is its low cost.
 For non-critical structures, PP provides an excellent, cost-effective raw material.
 It has excellent chemical and pH range resistance because of its semi crystalline structure.
 Additives and stabilizers (such as carbon black) must be added to give PP ultraviolet (UV) light
resistance during processing.

 Polyester: Polyester (PETP) is made by polymerizing ethylene glycol with dimethyl terephthalate or with
terephthalic acid.

 All these three materials are derivatives of petroleum. Polyster is produced discontinuously in two reactors, in
series or in a continuous process using more reactors in series.

 Polyester is increasingly being used to manufacture reinforcing geosynthetics such as geogrids because of high
strength and resistance to creep.

 Chemical resistance of polyester is generally excellent, with the exception of very high pH environments. It is
inherently stable to UV light.

 Polyamide: There are two most important types of polyamide (PA).

 The first one is an aliphatic polyamide obtained by polymerisation of the petroleum derivatives-caprolactam.
Aliphatic polyamides are composed of chains which do not contain ring-shaped rigid structures.

 The other type is also an aliphatic polyamide. It is obtained by the polymerisation of a salt of adipic acid and
hexamethylenediamine and both of them are petroleum products.

 They are manufactured in the form of thread or tape which are cut into granules.
 Polyvinylchloride, Ethylenecopolymer Bitumen: , Chlorinated Polyethylene are some
of other raw materials, apart from the raw materials explained above there are other
polymers also available with less market value.
MANUFACTURING PROCESS OF
GEOSYNTHETIC MATERIALS
 If fibres are twisted or spun together they are known as Yarn
 Monofilament fibers are created by extruding Molten polymers
through an apparatus known as spinnaret, containing several
small diameter holes
 The excluded polymer strings are then cooled and stretched to
align the polymer and give the fiber increased strength
 The staple fibres are then spun into longer fibers known as staple
yarn
 Slitfilm fibers are manufactured by extruding a continuous sheet
of polymers and cutting them into fibers by knives or air jets
THE EXTRUSION PROCESS

 Almost all geosynthetic manufacturing starts with an extrusion process,

whether this is the extrusion of fibres to be made into geotextiles or sheet
to be made into membrane or grids.
 The extrusion of plastics is a high-volume manufacturing process in
which raw plastic is melted and formed into a continuous profile.
 In the extrusion of plastics, the raw compound material is commonly in
the form of pellets (small beads, often called resin) that are gravity fed
from a top mounted hopper into the barrel of the extruder.
 Additives such as colorants and UV inhibitors (in either liquid or pellet
form) are often used and can be mixed into the resin prior to arriving at
the hopper
 At the end of the extruder the polymer passes through a die, and is
then extruded into the required shape.
 The extrusion technique is very versatile and can be adapted to
produce a wide range of products, merely by using the appropriate
dies.
 Extrusion is a process used to create objects of a fixed cross-sectional
profile. A material is pushed through a die of the desired cross-section.
 Materials are often drawn to impart strength through molecular
orientation.
 This process is particular relevant in the manufacture are high
strength fibres and filaments, and in the drawing process used in the
manufacture of high strength grids.
 WOVEN & NON-WOVEN GEOTEXTILES
 The fibres or yarns are formed into geotextiles using either Woven or non woven (spun
bonded) methods.
 Woven geotextiles are formed using traditional weaving methods and weave types.
 Common terminology associated with geotextile includes machine direction, cross
mission direction, wrap and weft.
 The machine direction refers to the direction in the plane of fabric parallel to the
direction of manufacture, and conversely.
 The cross machine direction refers to the direction in the plane of fabric direction in the
plane of fabric perpendicular to the direction of manufacture.
 The mission direction is also known as wrap since wrap Yarns are those that are placed
lengthwise on the weaving Loom &
 The cross machine direction is known as weft since weft Yarns are woven in between
and perpendicular to the warp yarns.
Weaving can be summarized as a repeat of three primary actions:
- Shedding:
- Picking:
- Beating-up:
The elements that are used to weave a geotextile may be produced
in a variety of ways:
- Slit Film Tape
- Extruded Flat Tape
- Multifilament Yarn
- Tape Yarn
- Monofilament
- Combination Weave
 Extruded Flat Tape
 The tape is drawn off the extruder by a bank of rollers which rotate at differing speeds to apply tension.
This tension orientates the molecules in the polymer to impart strength.
 The drawing process will reduce the thickness of the tape so that it can be woven into a relatively strong
fabric.
 Slit Film Tape
 It is similar to an extruded film tape with the principal difference being that rather than being directly
extruded from a tape, a sheet is produced and then slit down into narrow strips.
 The same drawing process is used to impart strength into the weaving element.
 It is common place to fibrillate the tape by adding spall nicks.
 This fibrillation process can allow for a tighter weave and a higher strength finished fabric.
 Tape Yarn
 A yarn uses a slit film tape which is then wound into a yarn to allow for the production of heavier, stronger
woven geotextiles.
 The fibrillation process allows for the tape to be twisted and spun into a yarn which provides a much
stronger weaving element.
 Monofilament
 The term monofilament could encompass flat tapes, it generally refers to extruded elements with a
circular cross section. The manufacturing process is basically the same as that which is used to
produce an extruded flat tape except the die head is shaped differently.
 The finished fabric would have a very different structure to that of a tape, normally with differing
filter properties
 Multifilament
 It uses similar technology to that which is used to produce a fiber for a nonwoven geotextiles, except
rather than lay the fibres down randomly the fibres are spun into a yarn and used in the weaving
process.
 As with a fibre manufacturing process, the elements are drawn to impart strength into the weaving
element
 Combination Weave
 The weaving process is such that the warp and weft yarns do not necessarily need to be the same type
of weaving element.
 It is therefore possible to manufacture woven geotextiles which combine different combinations
 NON-WOVEN GEOTEXTILES
 To obtain non woven geotextile the fibres are place and oriented on a moving conveyor belt.
 The fibres are bonded by needle punching, melt bonding or resin bonding
 The needle punching process consists of pushing numerous barbed needles through the fiber web
 The fibres are thus mechanically interlocked into a stable configuration
 The melt bonding process consists of melting and pressurizing fibres together at the crossover
points.
 In resin bonding and acrylic resin is applied to the fiber web to form the geotextile
 Most nonwoven experts agree that four major elements characterize a nonwoven structure.
- Fibre: the building block of the fabric structure (see durability of geotextiles)
- Web Formation: how fibres are assembled
- Bonding system: the means for holding the structure together
- Finishing treatment: the additional chemical/mechanical or thermal treatments
 WEB FORMATION
In this web formation process fibres or filaments are either deposited onto a forming surface to form a web or are condensed in to a
web and fed to a conveyor surface.
The formation of a web involves converting staple (cut) fibres or filaments into a web assembly which is the precursor to the finished
fabric.
The structure and composition of this web formation will have a strong influence on the dimensions, structure and properties of this
finished fabric.
Geotextile web-formation is split into two principal methods, these are:
- Dry Laid/Carded(divided) Webs
- Polymer Laid/Spunlaid Webs
 DRY LAID/CARDED WEBS
In dry-laid web formation, staple (cut) fibres are carded (combed) and then cross lapped (folded) and then bonded in a subsequent
stage.
Fibres, which are normally supplied in dense-packed bakes, are usually opened prior to carding.
 POLYMER LAID WEBS
Polymer laid, spun laid or spun melt nonwoven geotextiles are manufactured using an extrusion spinning process whereby the
filaments are directly collected to form a web.
The principal factor in the manufacture of a spunbonded fabric is the control of four simultaneous, integrated operations: filament
extrusion, drawing, lay down and bonding.
 WEB BONDING METHODS

 Nonwoven binding methods can be mechanical, chemical or thermal. bond The method and degree of bonding is the
principal factor in the determination of the fabrics mechanical properties and filtration properties.
 In a mechanical binding process a fibrous web is manipulated mechanically so that entanglement (a complicated or
compromising ) of the constituent fibres occurs and is carried out to such an extent that fabric integrity results from the
interlocking.
 The major bonding in systems of these types is friction.
 There are a number of specific processes involved in providing sufficient mechanical interlocking of fibres to adequately
bond a nonwoven structure including the following:
- Fibre entanglement via water jets
- Needle punching
- Stitch-Bonding
 The vast majority of mechanically bonded geotextiles that are commercially produced are manufactured using a needle
punching process.
 The needle punching process involves the use of barbed needles which penetrated the fibrous web driving and facilitate the
entanglement process. As this process continues, generally from both sides, the web consolidates and becomes highly
densified.
 Geotextiles that are bonded using this process alone are usually characterised by their high strength and high elongation at
break.
 It should be noted that additional finishing treatments that follow this process can significantly alter the properties of the
fabric.
 THERMALLY BONDED
 Thermal bonding requires the presence of a thermoplastic component whereby heat is applied
until the component becomes viscous or melts.
 The component may be present in the form of a homofill fibre, powder, film, hot-melt or as a
sheath part of a bi-component fibre.
 The polymer will flow by surface tension and capillary action to the fibre to fibre crossover
point where the bonding regions are formed and then fixed by subsequent cooling.
 CALENDARING
 Thermal calendaring is a process whereby the nonwoven web is passed continuously between
two heated cylinders, often under pressure.
 Both cylinders are usually heated to a point that exceeds that of the melting point of the
material.
 Calendars are extensively used for finishing of nonwovens as well as thermal boning.
Normally, after calendaring the fabric is passed over cooling rollers.
 GEOTEXTILES (GT):
 Geotextiles are defined as “any permeable textile used with foundation soil, rock, earth, or any other
geotechnical engineering-related material as an integral part of a human-made project, structure, or
system”.
 They are typically the most used geosynthetic material for agriculture purposes.
 These are fabric or cloth-like materials that are classified based on the method used to place the threads
or yarns in the fabric: either woven or non-woven.
 Geotextiles typically come in rolls up to approximately 5.6m (18 ft) wide and 50 to 150m (160 to 500 ft)
long.
 Flexible, textile-like fabrics
 Majority are made from polypropylene fibers
 Woven (slit film, monofilament or multifilament)
 Nonwoven (needle punched or heat/chemical bonded)
 Characterized by an open and porous structure (with controlled permeability)
 Mechanical and Hydraulic properties vary widely
 Very versatile in their primary function (except as liquid barrier)
 GEOGRIDS (GG):
 These are open grid-like materials of integrally connected polymers, as shown in Figure below.
 They are used primarily for soil reinforcement.
 Their strength can be greater than the more common geotextiles.
 Geogrids have a low strain and stretch only about 2 to 5% under load.
 Where practicable they would likely be used in heavy load or high demand agricultural
situations.
 stiff or flexible polymer grid-like sheets
 structure allows for soil “strike-through”
 bidirectional – equal strength in both directions
 unidirectional – main strength in machine direction
 focuses entirely on reinforcement applications,
 e.g.,walls, steep slopes, base and foundation reinforcement
 GEOCELLS (GC):
 Whereas geotextiles and geogrids are ‘flat’ materials, geocells or geowebs
have ‘depth’, as shown in Figure 5, below.
 They are typically formed from polyethylene sheets and expand out like an
accordion when opened up to use.
 They are meant to contain soil, gravel or other fill material within their
maze of cells or pockets and may be porous to allow water movement.
 They are used on slopes with soft subgrades and in erosion control in
channels.
 They may be used over top of a geotextile or geogrid.
 While they come in compact bundles when collapsed, they typically cover an
area 2.5m (8 ft) wide by 6 to 12m (20 to 40 ft) long when expanded
 GEONETS (GN):
 This includes LDPE and HDPE nets and has
functions similar to geogrids.
 all are made from high density polyethylene
 results in parallel sets of ribs as a integral unit
 biplanar – flow is equal in all directions
 triplanar – flow much greater in machine direction
 function is always in-plane drainage
 surfaces must be covered; usually with GTs
 GEOMEMBRANES (GM):
 Whereas geotextiles, geogrids and geocells are usually porous to allow water to filter through
them, geomembranes are polymer sheets used to control fluid movement. T
 These materials have very low permeability and would be used for lining ponds, pits etc to
control leachate.
 They may be used over top of a geotextile.
 impermeable sheets (10-11 to 10-13 cm/s)
 function is always containment
 represents a barrier to liquids and gases
 Many types: HDPE, LLDPE, FPP, PVC, EPDM, etc.
 manufactured rolls are field seamed
 new applications in hydraulics and private development
 GEOSYNTHETIC CLAY LINERS(GCL):
 function is always containment
 common product is bentonite between 2-GTs
 internally reinforced by needle punched or
stitching
 bentoniteproduct bonded to GM is also
available many other variations exist
 competitive with compacted clay liners (CCLs)
 beneath a GM; one has a composite liner
 GEOPIPE (GP):
 Its really buried plastic pipe!
 function is always drainage
 HDPE and PVC most common
 can be smooth walled or corrugated
 corrugated HDPE growth is enormous
 Geofoam (GF):
 lightweight fill on soft or sensitive soils
 relieves lateral pressure on walls
 Also used for insulation of frost-sensitive soils
 woven geotextile are formed using traditional weaving methods
and view types
 GEOCOMPOSITES (GCM):
 hybrid systems of any or all
 array of available products
 GT/GM; GT/GG; GT/GN; etc.
 considerable ongoing innovation
 primary function depends on final product
  PROPERTIES OF GEOSYNTHETICS:
PARAMETERS THAT INDICATE THE PROPERTIES OF GEOSYNTHETICS

TYPE OF PROPERTY PARAMETERS

PHYSICAL Thickness, specific gravity, mass per unit area, porosity, apparent
opening size.
CHEMICAL Polymer type, filler material, carbon black percentage, plasticizer and
additive details, manufacturing process for fiber and geosynthetics.
MECHANICAL Tensile strength, compressibility, elongation, tear/impact/ puncture
resistance, burst strength, seam strength, fatigue resistance, interface
friction with soil, anchorage in soil.
HYDRAULIC Permittivity (cross-plane permeability), transmissivity (in-plane
permeability), clogging potential.
ENDURANCE Installation damage potential - tear/impact/puncture resistance,
abrasion resistance, creep
DEGRADATION Resistance to ultra-violet radiation, temperature, oxidation, aging,
chemical and biological reactions.
 PROPERTIES OF GEOSYNTHETICS:
 The various properties of geosynthetic have been classified as physical properties,
mechanical properties, hydraulic properties, endurance (durability) properties and
degradation properties.
 Physical properties are the fundamental properties, which describe the material
itself.
 Mechanical properties define the strength of the product and then its interaction
with some other materials like soil or stones and so on.
 Hydraulic properties describe the pattern of flow of water through geosynthetic.
 The endurance properties reflect the how the geosynthetics will last when used in
soil.
 Degradation properties indicate that how the geosynthetics will degrade with time
when subjected to ultraviolet rays or some absurd environment.
 PHYSICAL PROPERTIES :
The physical properties which are of prime interest are as follows:
(i) Specific gravity
(ii) Mass per unit area (weight)
(iii) Thickness
(iv) Stiffness

Some more physical properties which are important for geogrids and geonets
 Type of structure
 Junction type
 Aperture size and shape
 Rib dimensions
 Planar angles made by intersecting ribs and vertical angles made at the junction point.
1 SPECIFIC GRAVITY:
 The specific gravity of a polymer, from which the geosynthetic is manufactured, is expressed
as a ratio of the weight of a given volume of material (without any voids) to weight of an equal
volume of distilled de-aired water at a temperature of 27 degree centigrade as per the relevant
Indian standard.
 The specific gravity of a base polymer is an important property since it can assist in
identifying the base polymer of the geosynthetics.
 It also helps in calculating strength–weight and cost–weight ratios.
 In case of polyethylene (PE), specific gravity, or more correctly density, is an important
property, since it forms the basis upon which PE is classified as very low, low, medium or high
density. T
 Typical values of specific gravity of commonly used polymeric materials are given as follows.
 It is to be noted that the specific gravity of some of the polymers [polypropylene (PP) and
(PE)] is less than 1.0, which is a drawback when working with geosynthetics in under water
applications; that is, some of them may float.
2 MASS PER UNIT AREA ( UNIT WEIGHT)
 The mass per unit area is determined by cutting a minimum of 10 specimens, each at least 100
mm square, and then weighing them on an accurate scale. Usually given in units of gram per
square metre (g/m2).
 It is determined by weighing square or circular test specimens of known dimensions
(generally area not less than 100 cm2).
 Linear dimensions should be measured without any tension in the specimen.
 For commonly used geo-synthetics, it varies in order of 100 to 1000 g/m2.
 Unit weight of geo-textiles< Unit weight of geomembranes may have substantially larger
values of mass per unit area, even up to several thousands of grams per square metre.
 It should be measured to the accuracy nearest to 0.01 % of total specimen weight.
 Since fabric cost and mechanical properties such as tensile strength, tear strength, puncture
strength, etc., are directly related to mass per unit area, therefore it is an important property.
 It can be used for the quality control of the delivered geotextile
3 THICKNESS:
 The thickness of a geosynthetic is the distance between its upper and lower surfaces, measured
normal to the surfaces.
 Since the thickness of the geotextile especially non-woven geotextile varies with pressure therefore a
compressive pressure of 2 kPa is applied at the time of thickness measurement.
 It is measured by using a thickness-testing instrument to an accuracy of at least 0.01 mm.
 Normally the thickness of geotextiles should be determined by measuring one layer only.
 In cases where two or more layers are used in contact with each other in an application, a test may be
made with a specific number of layers instead of one.
 The typical thickness of the woven geotextiles varies from 0.25 to 1 mm whereas; the nonwoven
geotextiles especially of the needle punch variety are much thicker 1 mm to more than 10 mm.
 Some of them are as thick as 30 mm especially when
they are used as cushions.
 The change in thickness of non-woven geotextile with
application of pressure is called its compressibility.
4 STIFFNESS

 The stiffness or flexural rigidity of a geosynthetic is its ability to resist flexure

(bending) under its own weight.

 It can be measured by its capacity to form a cantilever beam without exceeding

a certain amount of downward bending under its own weight

 In the commonly used test, known as the single cantilever test, the geosynthetic
specimen (25 mm wide strip) is placed on a horizontal platform with a weight
placed on it.

 The value is expressed in gm-cm units.

 The stiffness of a geosynthetic indicates the feasibility of providing a suitable

working surface for installation.

 When placing a geotextile on extremely soft soils, a high stiffness is desirable.

 The stiffness of geosynthetics can also have some effects on their performance
when they are used in the mitigation of soil erosion of hill slopes.
 MECHANICAL PROPERTIES:
Mechanical properties are important in those applications where a geosynthetic is required to perform a structural role
under applied loads or where it is required to survive installation damage and localized stresses.

The mechanical properties which are of prime interest are as follows:

(i) Compressibility

(ii) Tensile Strength

(iii) Fatigue Strength

(iv) Burst Strength

(v) Tear Strength

(vi) Impact Tests

(vii) Puncture Tests

(viii) Friction Behaviour

(ix) Pullout (Anchorage) Tests

1 COMPRESSIBILITY
 The compressibility of a geotextile is the rate of decrease of thickness due to increased
stresses.
 It is determined by observing the change in thickness of geotextile at varying applied
normal stresses.
 Woven and nonwoven heat bonded geotextiles have very low compressibility and is of
little direct consequence as far as design is concerned.
 However, compressibility is more important for nonwoven needle punched geotextile,
because they are often used to convey liquid within the plane of their structure.
 The more a fabric compresses under load, the lower its transmissivity.
 Figure 3 illustrates the compressibility of several geotextile types, where the influence
of normal stress on thickness is clearly seen.
 The nonwoven needle-punched geotextiles are the most
compressible, and this in turn is directly related to their
mass per unit area.
2 TENSILE STRENGTH
 The single most property of a geotextile is its tensile strength.
 Invariably all geotextile applications rely on this property either as the primary function (as in
reinforcement application) or as secondary function (as in separation, filtration or drainage).
 It is defined as the maximum tensile stress that the test specimen can sustain at the point of
failure.
 It is defined as the maximum load that can be applied per unit length along the edge of the
geosynthetic in its plane.
 Tensile properties of a geosynthetic are studied using a tensile strength test in which the
geosynthetic specimen is loaded and the corresponding stress-strain curve is obtained.
 Tensile strength is usually determined by the wide-width strip tensile test.
 A 200-mmwide geosynthetic strip with a gauge length of
100 mm is used for this purpose (Figure 4).
 The entire width of a 200-mm wide geosynthetic specimen is
gripped in the jaws of a tensile strength testing machine and
it is stretched in one direction at a prescribed constant rate of
extension until the specimen ruptures (breaks).
 During the extension process, both load and deformations are measured.
 Stress is calculated as force divided by width of specimen and the strain is calculated as
deformation divided by original specimen length.
The test provides following four parameters:
1. Maximum tensile stress (referred to as the geotextile’s strength)
2. Strain at failure (generally referred to as maximum elongation or simply elongation
3. Toughness (property of a geosynthetic by virtue of which it can absorb energy i.e. work done
per unit volume before failure, usually taken as the area under the stress-strain curve)
4. Modulus of elasticity (which is the slope of the initial portion of the stress-strain curve)
 As far as the test specimen size [length, width, aspect ratio (length to width ratio)] is
concerned, there are several specimen sizes (Figure 6) used for testing purpose.
 As per the specimen sizes, the tests are known as grab test, narrow strip test, wide-width
test and very wide-width test
 The grab tensile test is used to determine the strength of the geosynthetic in a specific
width, together with the additional strength contributed by adjacent geosynthetic or other
 The geotextile specimen dimensions are 100 mm wide and 200 mm long, but the jaws of the clamps grip
only the central 25 mm of the test specimen.
 A continually increasing load is applied longitudinally to the specimen and the test is carried to rupture.
 It is not clear how the force is distributed across the width of the specimen.
 This test simulates the field situation as shown in Figure 7.
 It is difficult to relate grab tensile strength to wide-width strip tensile strength in a simple manner
without direct correlation tests.
 Therefore, the grab tensile test is useful as a quality control or acceptance test for geotextiles.
 Almost all geotextile manufacturers and geotextile specifications use this value.
3 FATIGUE STRENGTH
 In the field, the loads are sometimes applied repeatedly as in case of wave loading on the offshore
structures, seismic loading, and railroad loading.
 Here the strength of geotextile may go on reducing with time, which is called fatigue strength.
 Thus, the fatigue strength may be defined as the ability of a geotextile to withstand repetitive loading
before undergoing failure.
 Fatigue strength is determined through conducting wide strip tensile test by applying a
predetermined load (less than the failure load) and then reducing it to zero.
 The load is again applied and then relaxed.
 This cycling is repeated till failure takes place.
 The resulting cyclic stress – strain response is used
to calculate the cyclic modulus.
 As expected, lower the stress level, the larger the number
of cycles required before failure.
4 TEAR STRENGTH
 If the geotextile is defective (having a small cut) either because of manufacturing process
or because of some rupture that takes place during the construction process, this cut
propagates while the geotextile is subjected to tension.

 Thus, the ability of a geotextile to withstand the stresses causing propagation of tear in it
is called its tearing strength.

 The tear strength of geotextile is determined by trapezoidal tear test.

 A rectangular specimen of size 200 mm × 76 mm is taken and an outline of an isosceles

trapezoid is marked on it as shown in Figure 13(a).

 An initial small cut of 15 mm is given on 25 mm side along the width of the specimen.

 The non-parallel sides of the trapezoid marked on the specimen are clamped in parallel
jaws of a tensile testing machine.
 The separation of the jaws is continuously increased at a rate of 300 mm per minute.

 The initial tear goes one widening and at some point, the entire width of specimen is cut.

 The load actually stresses the individual yarns gripped in the clamps rather than stressing the entire
fabric.

 During propagation of tear, the force developed is also recorded.

 The tearing strength, which is the maximum value of the tearing force, is obtained from the force-
extension curve (Fig. 13b).

 The failure pattern in tear is different in nonwoven geotextiles from that in woven geotextiles.
5 PUNCTURE TEST
 There is a need for an assessment of geotextiles resistance to objects such as stones,
ballast, stumps etc. under static condition.

 Thus, the puncture strength is the ability of geotextile to withstand the localized
stresses generated by penetrating or puncturing objects e.g. aggregate etc.

 Puncture strength is determined by a penetrating steel rod of 8 mm in diameter.

 The geotextile specimen is firmly clamped in an empty cylinder of 45 mm inside

diameter and the rod is pushed through it via a compression testing machine at a
prescribed rate.

 Resistance to puncture is measured in force units.

6 Bursting strength
 It is measured by the bursting test (multi-axial tensile test) using the
apparatus shown in Figure 16.
 This test is performed by applying a normal pressure, usually by air
pressure against a geosynthetic specimen clamped properly.
 Sometimes an inflatable (too much expandable) rubber
membrane is also used below the geotextile.
 The normal stress against the geosynthetic at
failure gives the value of the bursting strength.
 This test is more important in case of geomembranes
7 FRICTION BEHAVIOUR
 In direct shear test, the shear resistance between a geosynthetic and a soil
is determined by placing the geosynthetic and soil within a direct shear
box, about 300 mm square in plan, divided into upper and lower halves
(Fig. 17).
 The force required to cause sliding between the fabric and soil is
determined for different normal stresses and the shear strength
parameters are obtained.
 The test is useful for quality control and may
be used to compare different geotextiles.
 However, for reinforced soil applications the
proposed fill material should be used in the test.
8 PULLOUT OR ANCHORAGE STRENGTH
 Inthe pullout test, a geosynthetic specimen, embedded between two
layers of soil in a rigid box, is subjected to a horizontal force,
keeping the normal stress applied to the upper layer of soil constant
and uniform.
 Figure 18 depicts the general test arrangement of the pullout test.
 The force required to pull the geosynthetic out
of the soil is recorded.
 Pullout
resistance is calculated by dividing
the maximum load by the test specimen width.
 HYDRAULIC PROPERTIES
The hydraulic properties of geosynthetics influence their ability to
function as filters and drains.
i. Porosity,
ii. Percent open area,
iii. Apparent opening size,
iv. Permittivity and
v. Transmissivity
These are the most important hydraulic properties of geosynthetics,
mainly of geotextiles, geonets and many drainage geocomposites,
which are commonly used in filtration and drainage applications.
1 POROSITY
 The voids or holes in a geosynthetic are called pores or openings.
 The porosity of a geotextile is the ratio of void volume (volume of void
spaces) to the total volume of the geosynthetic, usually expressed as a
percentage.
 It is related to the ability of liquid to flow through or within the geotextile
but is rarely measured directly. Indeed it is calculated from other
properties of the geotextile:
2 PERCENT OPEN AREA (POA)
 Percent open area of a geotextile is defined as the ratio of the total area of its
openings to the total area of the specimen.
 This property is applicable only for woven geotextiles, and even then only for
woven monofilament geotextiles.
 It is to be noted that a higher POA generally indicates a greater number of
openings per unit area in the geotextile.
 For filter applications of a geotextiles, its POA should be higher to avoid any
clogging phenomenon to occur throughout the design life of the particular
application.
 A convenient way to measure the open area is to project a light through the
geotextile onto a large poster sized piece of a cardboard background that is
crosshatched like graph paper.
 Here the squares are counted and summed up for the open area.
3 APPARENT OPENING SIZE [ASTM D4751]
 A.O.S. is an important parameter in assessing a
geotextile's soil filtration capability. Spherical solid glass
beads are dry sieved through a geotextile for a specified
time and at a specified frequency of vibration.
 The amount of beads retained by the geotextile sample is
then measured.
 The test is carried out on a range of sizes of glass beads.
The apparent opening size is the pore size at which 90%
of the glass beads are retained on and within the fabric.
 PERMEABILITY CHARACTERISTICS
 The ability of a geosynthetic to transmit a fluid is called
PERMEABILITY.
 The flow of fluid may take place either across the plane (Figure 25) or
along the plane (Figure 26) of the geotextile.
 The permeability across the plane of geotextile
is called PERMITTIVITY and
the permeability along the plane of
geotextile is called TRANSMISSIVITY.
4 PERMEABILITY [ASTM D 4491]
 This is derived from the pemittivity test using the nominal thickness of the geotextile.
 The permittivity is divided by the thickness to determine permeability. It is done to
supposedly allow one to compare the geotextile’s permeability to the soil’s permeability.
 The problem is that geotextiles vary in thickness. Introducing thickness into the
equation nullifies a designer's ability to compare geotextiles, because the permeability
value is related to geotextile thickness, rather than geotextile cross-plane flow.
 Not only do geotextile thicknesses vary, but needlepunched nonwoven thicknesses
decrease under load.
 Adding a geotextile's thickness to the equation does not make the geotextile a "soil" or
give one a design test value to compare to soil just because both now have cm/sec as their
units.
 Water Flow Rate [ASTM D 4491] The amount of water that travels through the
geotextile expressed in gallons per minute per square foot.
5 PERMITTIVITY [ASTM D 4491]
 Permittivity is the mechanism by which water moves through the fabric.
 The permittivity test measures the quantity of water which can pass through a
geotextile perpendicular to the surface of the geotextile.
 The permittivity may be measured either in a constant head or falling head test,
although constant head testing is more common due to the high flow rates through
geotextiles which make it is difficult to obtain readings of head change versus time in
the falling head test.
 In the constant head test, a head of 50 mm water is maintained on the geotextile
throughout the test. The quantity of flow is measured versus time.
 In the falling head test, a column of water is allowed to flow through the geotextile and
reading of head changes versus time is taken.
 The flow rate of water through the geotextile needs to be slow enough to obtain
accurate readings.
6 TRANSMISSIVITY(Θ)
 For flow of water within the plane of the geotextile, the variation of
geotextile thickness is again a major issue.
 Thus a new term transmissivity (in-plane permeability) was introduced.
 The transmissivity of any geosynthetic may be defined as the product of
coefficient of permeability for in-plane water flow and its thickness.
 This property is the preferred measure of the in-plane water flow capacity
of a geosynthetic and widely used in drainage applications.
𝜃=𝑘𝑝×𝑡………… (7)
where θ = transmissivity (sec-1) kp = permeability in the plane of the
geotextile (m/sec) t = thickness of the geotextile (m)
 The transmissivity is determined in the same way as permeability in case
of soils. Therefore, either constant head or falling head concepts are used.
 ENDURANCE PROPERTIES:
Endurance properties are related to construction survivability and the
creep behaviour of geosynthetics. The latter is important to study to avoid
long term movement of the soil-geosynthetics system.Some of the
endurance properties of geotextiles includes:
i. Installation damage
ii. Creep response & Confined Creep response
iii. Stress relaxation
iv. Abrasion
v. Long-Term clogging
vi. Gradient ratio clogging
vii. Hydraulic conductivity ratio
1. CREEP:
Creep is the time-dependent increase in accumulative strain or elongation in a
geosynthetic resulting from an applied constant load.
 Test for determining the creep behaviour of a geosynthetic.
 200 mm wide specimen.
 load applied using weights, or mechanical, hydraulic or pneumatic systems.
 test duration : 100 h.
 for a full analysis of creep properties, durations of 10,000 h will be necessary.
 Drainage applications.
 Containment applications.
 At higher loads, creep leads ultimately to stress rupture, also known as creep rupture
or static fatigue.
 The higher the applied load, the shorter the time to rupture.
 creep data should not be extrapolated beyond one order of magnitude
2 ABRASION
 Abrasion of a geosynthetic is defined as the wearing away of any part of it
by rubbing against a stationary platform by an abradant with specified
surface characteristics.
 The ability of a geosynthetic to resist wear due to friction or rubbing is
called abrasion resistance.
3 INSTALLATION DAMAGE
 It should be obvious that installation stresses can cause geotextile damage.
 In some cases the installation process might be more severe than the actual
design stresses for which geotextile is intended.
4 STRESS RELAXATION (CONSTANT STRAIN) TEST:
 Stress relaxation is the common name given to the reduction in stress of
the material while it is maintained under a constant deformation.
 As with creep stress relaxation is the important property.
5. LONG TERM(CLOGGING) TEST:
 One of the greatest endurance concerns is that of the long-term flow capability of the
geotextile with respect to a hydraulic load coming from the upstream soil.
 Tests are needed to assess the potential of excessive geotextile clogging
6. GRADIENT RATIO CLOGGING:
 A test that may be performed in a considerably shorter time then the long-term flow
test and that is aimed at determining the hydraulic compatibility of a soil geotextile
system is the US Army corps of Engineers Gradient ratio test.
 However instead of measuring flow rates the hydraulic head at various location in the
soil geotextile column is measured.
 Head differences are then converted to hydraulic gradient and finally the gradient ratio
value (GR) is calculated.
7. HYDRAULIC CONDUCTIVITY RATIO:
 The use of flexible wall permeameter test to assess not only excessive clogging condition
but also excessive soil loss and equilibrium condition to find out the hydraulic
conductivity ratio.
 DEGRADATION CONSIDERATIONS
DURABILITY: The durability of a geosynthetic may be regarded as its ability to maintain
requisite properties against environmental or other influences over the selected design life.
The durability of a geosynthetic is dependent to a great extent upon the composition of the
polymers from which it is made.
The following are some of the degradation consideration wrt Geosynthetic materials
i. Temperature degradation
ii. Oxidative degradation
iii. Hydrolysis degradation
iv. Chemical degradation
v. Biological degradation
vi. Radioactive degradation
vii. Sunlight (UV) degradation
viii. Synergistic effects
1. TEMPERATURE DEGRADATION:
 Extremely high temperature causes all polymer degradation mechanisms to occur at an
accelerated rate.
 In fact, at the heat of time temperature superposition lifetime prediction techniques is to test
laboratory specimen at the temperature from 50C to 100C and extrapolate the accelerated
degradation down to field anticipated temperatures.
2. OXIDATIVE DEGRADATION:
 While all types of polymers react With oxygen causing degradation the polyolefins (polypropylene
and polyethylene) are generally considered to be the most susceptible to this phenomenon.
 Failure is defined as a change in appearance, weight, dimension or other properties that alter the
material to a degree that is no longer a serviceable for any purpose.
3. HYDROLYSIS DEGRADATION:
 Hydrolysis can cause degradation via either internal or external fibre or yarn reaction.
 Geosynthetics manufactured using polyester resins are particularly affected when the immersion
liquid has very high pH>10 are very low pH<3 .
4. CHEMICAL DEGRADATION:
 It includes provision for reporting changes in weight, dimension appearance and strength.
 Provisions are also made for various exposure times and exposure to chemical reagents at elevated
temperature causing material degradation.
5. Biological degradation:
 In order for microorganisms such as bacteria fungi to degrade polymers, the organism must attach
themselves to the fibre or yarn surfaces and use the polymer as a feedstock.
 This is highly unlikely since all the resins used for geosynthetics are very high in molecular weight with
relatively few chain endings for the biodegradation process to be initiated.
6. Radioactive degradation:
 It is generally discussed when dealing with radioactive waste disposal.
 It is assumed, though clearly not proven that both low level and high level radioactive exposure of
destructive magnitudes can proximity the geotextiles and cause radiation degradation
7. Sunlight (UV) degradation:
 UV Resistance is a measure of the potential for the deterioration of tensile strength in the fabric due to
exposure to ultraviolet light and water.
 It is typically expressed @ 500 hours exposure. For some products, such as ground cover, you will see it
specified as high as 2,500 hours exposure.
8. General aging:
 While specific test standards are not available to measure the aging of geotextile due to the complexity of
many mechanisms involved.
 Geotextile strength and properties get reduced as time lapse and due to the aging of geotextile was reacting