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GeotextilesR.SenthilKumar,
[email protected]@gmail.com
R.Senthil Kumar,KCT,Coimbatore
GEOTEXTILES -Classification- Fibres used -Essential Properties -Stress strain Analysis -Manufacturing Methods- Soil Properties
R.Senthil Kumar,KCT,Coimbatore
DefinitionA geosynthetic is a material
used in contact with or within soil to improve construction and long term performance of the project.
R.Senthil Kumar,KCT,Coimbatore
R.Senthil Kumar,KCT,Coimbatore
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.
R.Senthil Kumar,KCT,Coimbatore
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.
R.Senthil Kumar,KCT,Coimbatore
Common Geosynthetic Materials
Polypropylene (PP) Polyester (PET) Polyethylene (PE) Polyvinyl Chloride (PVC) Polyamide (nylon) (PA)
R.Senthil Kumar,KCT,Coimbatore
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
R.Senthil Kumar,KCT,Coimbatore
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.
R.Senthil Kumar,KCT,Coimbatore
Types of Geotextiles Woven
MonofilamentMultifilament Slit film
NonwovenNeedle-punchedHeat bondedResin bonded
R.Senthil Kumar,KCT,Coimbatore
MONOFILAMENT WOVEN GEOTEXTILE (POLYPROPYLENE)
R.Senthil Kumar,KCT,Coimbatore
Woven Monofilament
R.Senthil Kumar,KCT,Coimbatore
Woven Multifilament
R.Senthil Kumar,KCT,Coimbatore
WOVEN SLIT FILM GEOTEXTILE (POLYPROPYLENE)
R.Senthil Kumar,KCT,Coimbatore
Woven Slit Film
R.Senthil Kumar,KCT,Coimbatore
NONWOVEN NEEDLEPUNCHED GEOTETXTILE (POLYPROPYLENE)
R.Senthil Kumar,KCT,Coimbatore
Nonwoven Needlepunched
R.Senthil Kumar,KCT,Coimbatore
NONWOVEN HEAT BONDED GEOTEXTILE
R.Senthil Kumar,KCT,Coimbatore
Nonwoven Heat Bonded
R.Senthil Kumar,KCT,Coimbatore
R.Senthil Kumar,KCT,Coimbatore
Geogrid
R.Senthil Kumar,KCT,Coimbatore
Geocells
R.Senthil Kumar,KCT,Coimbatore
Geonet
R.Senthil Kumar,KCT,Coimbatore
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.
R.Senthil Kumar,KCT,Coimbatore
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.
R.Senthil Kumar,KCT,Coimbatore
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.
R.Senthil Kumar,KCT,Coimbatore
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)
R.Senthil Kumar,KCT,Coimbatore
Mechanical Properties
ASTM Tests should simulate stresses that result in actual field conditions
Tear
Seam
Puncture(Axi-sym)
R.Senthil Kumar,KCT,Coimbatore
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
R.Senthil Kumar,KCT,Coimbatore
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)
R.Senthil Kumar,KCT,Coimbatore
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
R.Senthil Kumar,KCT,Coimbatore
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
R.Senthil Kumar,KCT,Coimbatore
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
R.Senthil Kumar,KCT,Coimbatore
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
R.Senthil Kumar,KCT,Coimbatore
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)
R.Senthil Kumar,KCT,Coimbatore
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.
R.Senthil Kumar,KCT,Coimbatore
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.
R.Senthil Kumar,KCT,Coimbatore
TERMS TO KNOW: Infiltration - The movement of water
into the soil
Percolation - The movement of water through the soil