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GeotextilesR.SenthilKumar,

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R.Senthil Kumar,KCT,Coimbatore

GEOTEXTILES -Classification- Fibres used -Essential Properties -Stress strain Analysis -Manufacturing Methods- Soil Properties


DefinitionA 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 LElastic modulus H M L L

Strain at failure M M H H

Creep L M H HUnit weight H M L LCost L H L LResistance to

U.V. light H M H H

Alkalis L H H H

Fungus, vermin M M M H

Fuel M M L LDetergents H H H H

H: High; M: Medium; L: Low


Most Common Geotextile Materials Polypropylene and Polyester

Good chemical resistanceLow costHigh 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

MonofilamentMultifilament Slit film

NonwovenNeedle-punchedHeat bondedResin 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 ShapesDensity

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