31396749 geotextiles

Geotextiles
R.SenthilKumar,
sen29iit@yahoo.co.in
sen29iit@gmail.com

R.Senthil Kumar,KCT,Coimbatore
GEOTEXTILES
-Classification
- Fibres used
-Essential Properties
-Stress strain Analysis
-Manufacturing
Methods
- Soil Properties

Definition
A geosynthetic is a material
used in contact with or within
soil to improve construction and
long term performance of the
project.

Types of Geosynthetics
 A Geotextiles is a permeable textile structures made of polymeric
materials and are used mainly in civil engineering applications in
conjunction with soil, rock or water.
 Geogrids are plastic materials formed into a very open grid like
configuration with very large apertures.
 Geomembranes are impervious sheets of rubber or plastics, used
as a moisture or vapor barrier.
 Geonets are structures formed by continuous extrusion of
polymeric ribs placed at acute angles to one another, which on
opening will give net like configuration and used to convey fluids.
 Geocomposites are usually composed of two geosynthetics.

Why Geotextiles?
1. Non-Uniform Consistency:
Soils are made up of different types of particles such as gravel, sands, silt, clay
and possibly organic materials. Many times, the consistency of the soil (types of
particles) can vary throughout the length of the project. This can have a
significant effect on such factors as drainage, settlement, frost heaves, etc., all of
which can create problems.
2. Unstable Soils
In areas where soils consist of clays, silts and organics, especially in areas that
drain poorly, the subgrade may be unstable. As a result, the unstable soil is not
able to provide adequately support for a road or embankment.
3. Moisture problems
Depending upon the consistency of the soil, the presence of moisture can create
such problems as loss of strength, swelling/shrinking, and frost heave.

Common Geosynthetic Materials
 Polypropylene (PP)
 Polyester (PET)
 Polyethylene (PE)
 Polyvinyl Chloride (PVC)
 Polyamide (nylon) (PA)

Properties of Fibres used in Geotextiles
Polyester Polyamide Polypropylene Polyethylene
Strength H M L L
Elastic modulus H M L L
Strain at failure M M H H
Creep L M H H
Unit weight H M L L
Cost L H L L
Resistance to
U.V. light
H M H H
Alkalis L H H H
Fungus, vermin M M M H
Fuel M M L L
Detergents H H H H
H: High; M: Medium; L: Low

Most Common Geotextile Materials
 Polypropylene and Polyester
Good chemical resistance
Low cost
High strength
 Polyvinylidene chloride fibre is used in
Japan and in one or two products in the
United States, but not in Europe.

Types of Geotextiles
 Woven
Monofilament
Multifilament
Slit film
 Nonwoven
Needle-punched
Heat bonded
Resin bonded

MONOFILAMENT WOVEN
GEOTEXTILE (POLYPROPYLENE)

Woven Monofilament

Woven Multifilament

WOVEN SLIT FILM GEOTEXTILE
(POLYPROPYLENE)

Woven Slit Film

NONWOVEN NEEDLEPUNCHED
GEOTETXTILE (POLYPROPYLENE)

Nonwoven Needlepunched

NONWOVEN HEAT
BONDED GEOTEXTILE

Nonwoven Heat Bonded

Geogrid

Geocells

Geonet

Manufacturing Methods
 Woven
Lighter weights are used as soil separators,
filters and erosion control textiles.
Heavier one are used in soil reinforcements in
steep embankments, vertical soil walls.
Plain weave is the most common though
others like basket and twill are also used.
These are woven on wide width looms.

 Knitted
 Knitted fabrics, as used in the field of geotextiles,
are restricted to warp-knitted textiles.
 Warp-knitting machines can produce fine filter
fabrics, medium meshes and large diameter soil
reinforcing grids.
 Heat bonded nonwoven
 Filaments or short fibres are subjected to heat and
melted at their crossover points.
 Bonding additives are added in case of the fibres
with high melting temperature so that at lower
temperatures, these additives will melt and bond
the filaments.

 Needlepunched non woven
 Made out of blended webs of continuous filaments
and staple fibres.
 The fabrics derive mechanical coherence from the
entangling of fibres caused by the barbs on the
reciprocating needle.
 In the case of needle punched textiles, considerable
thicknesses (up to more than 10 mm) and weights
greater than 2000gm2
can be achieved.
 Chemically bonded nonwoven
 It is the least used method. Glue, latex or resin is
added to bind the filaments or short fibres together.
 Impregnated web is cured and/or calendered.

Geotextile Properties
 Physical
 Material - polymer
 Thickness
 Mass per unit area
 Mechanical
 Wide width tensile strength
 Grab strength/elongation
 Trapezoidal tear strength
 Puncture strength
 Hydraulic Properties
 Permittivity / flow rate
 Apparent opening size (AOS)

Mechanical Properties
ASTM Tests should simulate stresses that result in actual field conditions
Tear
Seam
Puncture
(Axi-sym)

Soil Science
Definition of Soil:
 Soil is defined as the entire unconsolidated material that
overlies and is distinguishable from bedrock.
 Composed of loosely bound mineral grains of various
sizes and shapes.
 Contains voids of varying sizes. These voids contain:
 Air
 Water
 Organics

Engineering Properties of Soil
 Varies greatly depending on its physical
properties, however, the behavior of a
soils not exclusively dependant on
physical properties.
 Also dependant on arrangement of
particles (Compaction)

Soil Properties
 Particle Size
Physical properties are influenced by particle size
 Soil > 2 mm
 Sand, 2 - 0.05 mm
 Silt, 0.05 - 0.002 mm
 Clay, <0.002 mm

Gradation of Soil
 Distribution of particles within a soil.
 Soils are either:
Well graded – good distribution of particle sizes
Poorly graded – bad distribution of particles
sizes
 Uniformly graded – only one soil size
 Gap graded – missing soil sizes

Grain Shape
 Influences a soils strength and stability
 Two general shapes:
 Bulky – three dimensional
 Angular – recently been broken
 Sub angular – sharper points and edges are worn
 Sub rounded – further weathered than sub angular
 Rounded – no projections and smooth in texture
 Platy – two dimensional

Soil Particle Shapes
Density
 Determined by the ratio of voids (air and water) to soil particles.
 A denser soil has greater strength and stability than a looser soil.
Moisture
 Most important factor affecting engineering characteristics.
 Moistures affect varies greatly depending on soil type:
 Course grained soils usually remains unchanged.
 Fine grained soils are susceptible to shrinking and swelling.
Plasticity and Cohesion
 Plasticity is the ability of a soil to deform without cracking.
 Fine grained soils, like clay, have a wide range of plasticity.
 Coarse grained soils, like clean sands and gravels, are non plastic

Shear Resistance of Soil
 Related to a soils ability to withstand loads.
 California Bearing Ratio (CBR) is a measure of shearing
resistance
 CBR is a soil’s ability to support a load relative to that of
soil with known strength (limestone).
 Determined by the Soils Test Kit (B2150)

Bearing Capacity
 The ability of a soil to support a load applied by an
engineering structure.
 A soil with insufficient bearing capacity might fail, by shear,
allowing the structure to sink and shift.
 Dense and well graded soil with angular particles generally
has good bearing capacities.

Soil Compaction
Purpose of Compaction :
 Most critical component in horizontal construction.
 Durability and stability of structures is related to proper
compaction.
 Structural failure can often be traced to improper
compaction.

TERMS TO KNOW:
 Infiltration - The movement of water into
the soil
 Percolation - The movement of water
through the soil

31396749 geotextiles

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