BY MR. TANVEER MALIK, MR. T. K.
MRS. YOGITA AGRAWAL AND DR. ASHUTOSHSHUKLA
Geotextiles, an emerging field in the civil engineering and
other fields, offer great potential in varied areas of
applications globally. Geotextiles play a significant part in
modern pavement design and maintenance techniques. There is a
tremendous growth in their use worldwide for transportation
applications and other civil engineering applications.
Geotextiles are ideal materials for infrastructural works such
as roads, harbors and many others. They have a bright future, as
they have multifunctional characteristics. The paper provides an
overview of various natural as well as synthetic textile fibers
used for application as geotextiles and use of geotextiles in
Geotextiles were one of the first textile products in human
history. Excavations of ancient Egyptian sites show the use of
mats made of grass and linen. Geotextiles were used in roadway
construction in the days of the Pharaohs to stabilize roadways
and their edges. These early geotextiles were made of natural
fibers, fabrics or vegetation mixed with soil to improve road
quality, particularly when roads were made on unstable soil.
Only recently have geotextiles been used and evaluated for
modern road construction. Geotextiles have proven to be among
the most versatile and cost-effective ground modification
materials. Their use has expanded rapidly into nearly all areas
of civil, geotechnical, environmental, coastal, and hydraulic
Geotextiles used in civil engineering applications are expected
to carry out one or more functions over if given design life.
There are five defined functions, these are; drainage,
separation, filtration, protection and reinforcement.
Geotextiles are normally manufactured by either woven or
non-woven techniques. The functional requirements of the
geotextile in a given application will determine the performance
properties required, and any assessment of the products
durability will be based on the degradation of these properties
over a given time.
Geotextiles particularly refers to permeable fabric or synthetic
material, woven or non-woven, which can be used with
geotechnical engineering material. They apply to a broad range
of civil engineering construction, paving, drainage and other
applications. Geotextiles are extensively used with soil, rock,
earth or any other geotechnical engineering-related material.
Geotextile Forming Fibres and Polymers
Different fibers from both natural as well as synthetic category
can be used as geotextiles for various applications.
Natural fibers in the form of paper strips, jute nets, wood
shavings or wool mulch are being used as geotextiles. In certain
soil reinforcement applications, geotextiles have to serve for
more than 100 years. But biodegradable natural geotextiles are
deliberately manufactured to have relatively short period of
life. They are generally used for prevention of soil erosion
until vegetation can become properly established on the ground
surface. The commonly used natural fibers are
These are subtropical bastfibers, which are obtained from their
plants 5 to 6 times a year. The fibers have silky luster and
have white appearance even in the unbleached condition. They
constitute of pure cellulose and possess highest tenacity among
all plant fibers.
This is a versatile vegetable fiber, which is biodegradable and
has the ability to mix with the soil and serve as a nutrient for
vegetation. Their quick biodegradability becomes weakness for
their use as a geotextile. However, their life span can be
extended even up to 20 years through different treatments and
bleedings. Thus, it is possible to manufacture designed
biodegradable jute geotextile, having specific tenacity,
porosity, permeability, and transmissibility according to need
and location specificity. Soil, soil composition, water, water
quality, water flow, landscape etc. physical situation
determines the application and choice of what kind of jute
geotextiles should be used. In contrast to synthetic geotextiles,
though jute geotextiles are less durable but they also have some
advantages in certain area to be used particularly in
agro-mulching and similar area to where quick consolidation are
to take place. For erosion control and rural road
considerations, soil protection from natural and seasonal
degradation caused by rain, water, monsoon, wind and cold
weather are very important parameters. Jute geotextiles, as
separator, reinforcing and drainage activities, along with
topsoil erosion in shoulder and cracking are used quite
satisfactorily. Furthermore, after degradation of jute
geotextiles, ligomass is formed, which increases the soil
organic content, fertility, texture and also enhance vegetative
growth with further consolidation and stability of soil.
The four main synthetic polymers most widely used as the raw
material for geotextiles are polyester, polyamide, polyethylene
and polypropylene. The oldest of these is polyethylene, which
was discovered in 1931 by ICI. Another group of polymers with a
long production history is the polyamide family, the first of
which was discovered in 1935. The next oldest of the four main
polymer families relevant to geotextile manufacture is
polyester, which was announced in 1941. The most recent polymer
family relevant to geotextiles to be developed was
There are two most important typesof polyamides, namely Nylon 6
and Nylon 6,6 but they are used very little in geotextiles. The
first one an aliphatic polyamide obtained by the polymerization
of petroleum derivative ε-caprolactam. The second type is also
an aliphatic polyamide obtained by the polymerization of a salt
of adipic acid and hexamethylenediamine. These are manufactured
in the form of threads, which are cut into granules. They have
more strength but less moduli than polypropylene and polyester.
They are also readily prone to hydrolysis.
Polyester is synthesized by polymerizing ethylene glycol with
dimethyle terephthalate or with terephthalic acid. The fiber has
high strength modulus, creep resistance and general chemical
inertness due too which it is more suitable for geotextiles. It
is attacked by polar solvent like benzyl alcohol, phenol, and
meta-cresol. At pH range of 7 to 10, its life span is about 50
years. It possesses high resistance to ultraviolet radiations.
However, the installation should be undertaken with care to
avoid unnecessary exposure to light.
Polyethylene can be produced in a highly crystalline form, which
is an extremely important characteristic in fiber forming
polymer. Three main groups of polyethylene are Low density
polyethylene (LDPE, density 9.2-9.3 g/cc), Linear low-density
polyethylene (LLDPE, density 9.20-9.45 g/cc) and
polyethylene (HDPE, density 9.40-9.6 g/cc).
Polypropylene is a crystalline thermoplastic produced by
polymerizing propylene monomers in the presence of
stereo-specific Zeigler-Natta catalytic system. Homo-polymers
and co-polymers are two types of polypropylene. Homo polymers
are used for fiber and yarn applications whereas co-polymers are
used for varied industrial applications. Propylene is mainly
available in granular form.
Both polyethylene and polypropylene fibers are creep prone due
to their low glass transition temperature. These polymers are
purely hydrocarbons and are chemically inert. They swell by
organic solvent and have excellent resistance to diesel and
lubricating oils. Soil burial studies have shown that except for
low molecular weight component present, neither HDPE nor
polyethylene is attacked by microorganisms.
Polyvinyl chloride (PVC):
Polyvinyl chloride is mainly used in geo membranes and as a
thermo plastic coating materials. The basic raw materials
utilized for production of PVC is vinyl chloride. PVC is
available in free- flowing powder form.
Essential Properties of Geotextiles
The three main properties which are required and specified for a
geotextile are as follows:
These are the properties that produces the required working
effect. They are all developed from the combination of all the
physical form of the polymer fiber, their textile construction
and the polymer chemical characteristics. For example, the
mechanical response of a geotextile will depend upon the
orientation and regularity of the fibers as well as the type of
polymer from which it is made. Also the chemical resistance of a
geotextile will depend upon the size of individual component
fiber in the fabric as well as their chemical composition. Fine
fibers with a large specific surface area are subject to more
rapid chemical attack than coarse fibers of same polymer.
Mechanical responses include the ability of a textile to perform
work in a stressed environment and its ability to resist damage
in an arduous environment.
The filteration performance of a geotextile is governed by
several factors. To understand this, it is essential to be aware
that the function of the textile is not truly a filter in the
literal sense. In general, filters remove particles suspended in
a fluid. For example, dust filters in air-conditioning units, or
water filters, which are intended to remove impurities from
suspension. Quite the opposite state of affairs exists with
geotextile filters. The geotextile function is to hold intact a
freshly prepared soil surface, so that water may exude from the
soil surface and through the textile without breaking down that
surface. If water is allowed to flow between the textile and the
soil interface with particles in suspension, it will tend to dug
up the textile which will fail in its function. In practice, it
has been found that, in conjunction with a textile, the soil
will tend to filter itself, provided that the integrity of its
external surface is maintained. The actual process taking place
is the passage of a liquid form a solid medium that is held
intact by a permeable textile. The process is not one of
restraining the passage of solids that are suspended within a
Geotextile are rarely called upon to resist extremely aggressive
chemical environments. Particular examples of where they are,
however, include their use in the basal layers of chemical
effluent containers are waste disposal sites. This can happen if
and when leaks occur, permitting effluent to pass through the
impermeable liner of the textiles have been incorporated
directly in the leach ate disposal system above the impermeable
liner. Ultraviolet light will tend to cause damage to most
polymers, but the inclusion of additives, in the form of
antioxidants chemicals and carbon black powder, can considerably
reduce this effect. The only time when a geotextile is going to
be exposed to sunlight is during the construction period.
Basic Function of Geotextile
Every textile product applied under the soil is a geotextile.
Geotextiles form one of the two largest groups of geosynthetics.
The mode of operation of a geotextile in any application is
defined by six discrete functions: separation, filtration,
drainage, reinforcement, sealing and protection. Depending on
the application the geotextile performs one or more of these
functions simultaneously. Depending on the required function,
they are used in open-mesh versions, such as a woven or, rarely,
warp-knitted structure, or with a closed fabric surface, such as
Separation is function to prevent mutual mixing between 2 layers
of soil having different particle sizes or different properties.
It is used in all classes of roads and similar civil foundation,
as the base of construction on contaminated layer is the single
most cause of premature failure. The use of separator prevents
pumping effect created by dynamic load and also helps the
passage of water while retaining soil particles. In theses types
of geotextiles, thickness and permeability are most important
characteristic properties. The effect of separation is
illustrated in figure given below.
It is defined as the establishment of a stable interface between
the drain and the surrounding soil. In all soils water flow will
induce the movement of fine particles. Initially a portion of
this fraction will be halted at the filter interface; some will
be halted within the filter itself while the rest will pass into
the drain. The geotextile provides an ideal interface for the
creation of a reverse filter in the soil adjacent to the
geotextile. Infiltration, fabrics can be either woven or
non-woven, to permit the passage of water while retaining soil
particles. Porosity and permeability are the major properties of
geotextiles, which involves in filtration action.
The function of drainage is to gather water, which is not
required functionally by the structure, such as rainwater or
surplus water in the soil, and discharge it. This refers to the
ability of thick nonwoven geotextile whose three-dimensional
structure provides an avenue for flow of water through the plane
of the geotextile. Above Figure also illustrates the
transmissivity function of geotextile. Here the geotextile
promotes a lateral flow thereby dissipating the kinetic energy
of the capillary rise of ground water.
This is the synergistic improvement in the total system strength
created by the introduction of a geotextile into a soil and
developed primarily through the following three mechanisms i.e.
lateral restraint through interfacial friction between
geotextile and soil/aggregate, forcing the potential bearing
surface failure plane to develop at alternate higher shear
strength surface and membrane type of support of the wheel
loads. In this method, the structural stability of the soil is
greatly improved by the tensile strength of the geosynthetic
material. Due to their high soil fabric friction coefficient and
high tensile strength, heavy grades of geotextiles are used to
reinforce earth structures allowing the use of local fill
material. Reinforcement provided by geotextiles allow
embankments and roads to be built over very weak soils and
allows for steeper embankments to be built.
A non-woven geotextile performs this function when impregnated
with asphalt or other polymeric mixes rendering it relatively
impermeable to both cross-plane and in-plane flow. The classic
application of a geotextile as a liquid barrier is paved road
rehabilitation, as shown in Figure given below. Here the
non-woven geotextile is placed on the existing pavement surface
following the application of an asphalt tack coat. The
geotextile absorbs asphalt to become a waterproofing membrane
minimizing vertical flow of water into the pavement structure.
Erosion of earth embankments by wave action, currents and
repeated drawdown is a constant problem requiring the use of
non-erodible protection in the form of rock beaching or mattress
structures. Beneath these is placed a layer of geotextile to
prevent leakage of fine material. The geotextile is easily
placed, even under water. Soil waste and hazardous landfill
structures are designated with impervious geo-membrane layer
along with geotextile thus ensuring that no ground water
contamination takes place. It also acts as drainage gallery. It
is used in the thermal power stations for disposing off the fly
ashes in the ash-ponds constructed with impervious geo-membrane
layer along with geotextile that protects the membrane from
punching and soil polluting.
Application Areas of Geotextiles
Modern geotextiles are usually made from synthetic polymers-
polypropylenes, polyesters, polyethylene, and polyamides - which
do not decay under biological and chemical processes. This makes
them useful in road construction and maintenance.
Geotextiles in Road Industry
In the road industry there are four primary uses for geotextiles
Separation, Drainage, Filtration and Reinforcement.
In separation, inserting a properly designed geotextile will
keep layers of different sized particles separated from one
another. In drainage, water is allowed to pass either downward
through the geotextile into the subsoil, or laterally within the
geotextile which functions as a drain. In filtration, the fabric
allows water to move through the soil while restricting the
movement of soil particles. In reinforcement, the geotextile can
actually strengthen the earth or it can increase apparent soil
support. For example, when placed on sand it distributes the
load evenly to reduce rutting.
Geotextiles now are most widely used for stabilizing roads
through separation and drainage. When the native soil beneath a
road is very silty, or constantly wet and mucky then its natural
strength may be too low to support common traffic loads, and it
has a tendency to shift under those loads. Geotextiles keep the
layers of subgrade and base materials separate and manage water
movement through or off the roadbed.
Higher strength woven and nonwoven geotextiles provide
stabilization in addition to the primary function of separation.
Through stabilization, a geotextile can increase the effective
bearing capacity of low strength subgrade soils. A stabilization
geotextile reduces subgrade pumping, over-excavating and
required aggregate thickness. Stabilization geotextiles
substantially reduce construction costs for paved and unpaved
roads. For example, unpaved road aggregate thickness can be
reduced by as much as 30% to 50% when a stabilization geotextile
Geotextiles in pavement Repair:
A major contributor to roadway deterioration is water beneath a
pavement, which softens subgrade soil which destroys pavement
structural capacity. A pavement with a base, which becomes
saturated, as little as 10% of the time will only have 50% of
the life of a pavement where water is kept out of the base. Most
of this water enters through cracks and pores in the pavement
surface. Paving fabrics and repair membranes are engineered to
reduce water infiltration and reflective cracking, thereby
saving on costly repaving cycles. They have been proven to
extend the life of highways, city streets, parking lots, and
airport runways and taxiways. These kinds of geotextiles are
used in new asphalt pavements, beneath overlays of rigid and
flexible pavements, and beneath chip-seal pavements.
Geotextiles in retaining Walls:
Retaining walls help to maximize their land use. However,
building a concrete gravity or crib wall is often impractical
because of their high construction cost. Geotextiles are used
for a wide assortment of reinforcement applications, including
embankments over soft soils, levees and retaining walls.
Geotextiles are well-suited to construction of walls with
timber, precast panel and segmental block facing. In fact a
geotextile retaining wall can be built for less than half the
cost of a conventional wall. Woven geotextiles offer other
significant advantages over conventional methods, such as
simplified installation and construction, and the ability to use
on-site backfill material. Polypropylene geotextiles cost
approximately half the amount of polyester and polyethylene
geogrids, and they require considerably less labor to install.
Geotextiles subsurface Drainage:
Geotextiles have replaced graded soil filters for drainage of
virtually all structures, including groundwater intercept
systems, pavements, building foundations, dams and walls.
Compared to conventional soil filters, geotextiles offer
advantages by providing a consistent and continuous filter,
reduced excavation, reduced environmental impact, simplified,
higher quality construction and a substantial reduction in
Geotextiles erosion Control:
Geotextiles have replaced graded granular filters used beneath
riprap or other armor materials in revetments. Applications
include drainage channels, shorelines, and bridge and pier scour
protection systems. Without a geotextile filter, wave action and
water movement erode subgrade soils from beneath the riprap or
armor. Degradation of the subgrade negates the benefit of the
riprap or armor, resulting in extensive repair and replacement.
The selection of geotextiles for permanent erosion control is
similar to subsurface drainage. However, permanent erosion
control applications usually require higher geotextile strength
properties. The geotextile must survive placement of possibly
very large, angular riprap, plus be able to endure severe wave
Geotextiles waste Containment:
Waste containment and environmental cleanup projects demand
geotextiles with uncompromising physical properties and
consistent product quality. In environmental applications,
geotextiles must retain these critical properties while exposed
to harsh chemical environments. Waste containment fabrics'
serves in a variety of environmental applications, including
filtration of fluid and gas collection systems, protection of
geomembrane liners, waste daily covers and reinforcement.
Geotextiles are specified for municipal waste and hazardous
waste landfills, heap leach pads, sewage treatment lagoons, as
well as waste containment ponds and other surface impoundments.
Geotextiles railroad Stabilization:
Maintaining track bed geometry is critical for efficient
railroad operation. Subgrade pumping into the overlying ballast
can create an uneven track bed, resulting in delayed arrivals
and even derailments. Geotextiles perform multiple functions in railroad applications.
Nonwoven fabrics are used to stabilize both new and
rehabilitated tracks. They prevent contamination of new ballast
with underlying fine-grained soils and provide a mechanism for
lateral water drainage. Using nonwoven geotextiles beneath track
beds ensures that the ballast can sustain the loads for which it
was designed. These geotextiles are used in all track
applications, including switches, turnouts and grade crossings.
High-strength woven geotextiles can also be used to reinforce
weak subgrade soils and reduce required embankment fill
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