Geotextiles:
Geotextiles are
defined as planar material or product which is manufactured from polymeric
material and is used with soil, earth or rock or other geotechnical engineering
related material as an important part of a human made project or system.
Reasons for acceptance by Civil Engineers:
- Used in increasing tensile strength of soil as soil itself does not posses tensile strength.
- Secondly, it is useful in layered construction of pavements, retaining walls and foundations. Also, they are flexible in nature
Major functions of Geotextiles:
Reinforcement: It
provides strength to soil that is weak in tension and posses no tensile
strength of its own.
Separation: The main
role of separation is to prevent intermixing of two dissimilar materials as intermixing
of stone and fine soil affects the drainage and strength of the stones.
Applications: In
roadways, below embankment fill and soft foundation spill and below rail
ballast.
Drainage: The main
function is to transfer the liquid with in the plane of Geotextiles. Mainly
non-woven Geotextiles, geonets and geocomposites are used.
Application: Around
trench drains and edge drains, behind retaining walls and bridges and for slope
stabilization.
Filtration: Allows
flow of liquids from soil across the plane of geotextile, retain soil particles
and avoid clogging. Geocomposites are used for this purpose.
Erosion: Prevents
washing off of the upper layer of the soil due to wind forces. Geomats,
geocells, bionets are used for the same.
Classification of Geosynthetic:
Woven or non-woven
Geotextiles:
Woven Geotextiles:
Posses high tensile strength and relatively low strain.
Functions: load
distribution, separation and reinforcement.
Non-woven
Geotextiles: High strain and stretch considerably under load.
Function: Major
function includes filtration and drainage.
Geotextiles:
Can be woven,
non-woven or knitted, mechanical and hydraulic properties vary widely.
Application: Used for
separation, drainage, reinforcement.
Geogrids:
Geogrids are open
grid like configuration having large apertures, can be have both unidirectional
or bidirectional properties. Have more strength but low strain.
Application:
Reinforcement applications
Geocomposites:
Combines attributes
of two or more materials to serve specific application
Factory fabricated
unit with two or more geosynthetic components.
Geomembranes:
Geomembranes are
basically impervious polymeric sheets which are manufactured for containment
purpose
Application: linings,
covers for solid storage facilities etc.
Geosynthetic Clay
liners (GCLs)
They are fabricated
rolls of bentonite clay sandwiched between two geosynthetic products
Application: used in
environmental and containment applications.
Geotubes:
Flexible forms of
geotextiles generally used for containment for pollutant sediments present in
water bodies
Applications: Coal
sludge, municipal sludge etc.
Geopipes:
Plastic pipes
subjected to high compressive loads. They are smooth walled or corrugated
Application: Drainage
Geotextile
properties:
Intrinsic physical
properties:
Tensile strength: It
is important for all geotextile functions and installations
Compressibility: It
reduces transmissivity and permittivity as the pore structure changes
Seam strength, tear
strength, burst strength, impact strength and puncture strength
Mechanical
Properties:
- Shear strength depends on the friction between soil and geotextile
- Tests performed are direct shear test and pullout tests
Endurance properties:
- Abrasion: wearing of material by rubbing actions against large soil particles
- Creep: It refer to the elongation of the material
- Clogging, UV degradation and chemical, biological degradation.
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