Geotechnical Engineering

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DHARM

SOIL STABILISATION 717

17.6.1 Geosynthetics
‘‘Geotextile’’ means a textile used in geotechnical practice and is of relatively recent origin. A
brief treatment of the evolution, functions, and applications of geosynthetics in Civil Engi-
neering practice is given herein:
Forms of geotextiles have been used since time immemorial. The Chinese have used
wood, bamboo and straw to strengthen soils; even the Great Wall included reinforced soil
structures in some of its portions. The Dutch, in their age-old battle with the sea, have exten-
sively used willow fascines to reinforce dikes and protect them from wave action. The Romans
used reed and wood for soil reinforcement; even animal hides were used in the Middle Ages.
Cotton fabrics were tried for strengthening road pavements in the USA between 1926 and
1935 A.D.
During the Second World War, the British Army used rolls of fascines or canvas to
strengthen the ground during their invasion of France. The advent of synthetic fibres in the
twentieth century spurred geotextile techniques—the first synthetic fibre, made from Poly
Vinyl Chloride (PVC) in 1913, the advent of nylon in 1930, polyester fibre in 1949, and
polypropylene fibre in 1954 have all contributed to this. Another major advance was the devel-
opment in the mid-1960’s of manufacturing process for non-woven fabrics made from continu-
ous synthetic filament (Spun-bonded non-woven fabrics) in France, the U.K., and the U.S.A.
The term ‘‘Geosynthetics’’ has been proposed by J.E. Fleut, Jr. in 1983 to encompass all
these synthetic materials, including geomembranes. Systematic applications followed the ad-
vent of a synthetic fibre capable of resisting rot. Today geosynthetics are being widely used in
a number of applications in geotechnical practice the world over.
Geosynthetics are classified into the following:
(a) Geotextiles: These are permeable textiles—woven or non-woven synthetic poly-
mers. Woven fabrics consist of two threads (warp and weft) combined systematically by mak-
ing them cross each other perpendicularly. Threads could be multi-filaments or thick
monofilaments, or tape threads got by splitting a plastic film. Multi-filament threads are made
of polyester and polyamide; polypropylene and polyethylene are used to make tape threads.
Non-woven fabrics consist of randomly placed short fibres (60 to 150 mm) or continuous
filaments. First, the randomly placed fibres form a web with no strength. In the second stage,
strength is obtained by mechanical bonding through needle punching, by chemical bonding, or
by thermal bonding.
(b) Geogrids: These are relatively stiff net-like materials with large open spaces be-
tween the ribs that make up the structure. They can be used to reinforce aggregate layers in
bituminous pavements and for construction of geo-cells for improvement of bearing capacity.


(c) Geomembrances: A continuous membrance—type liner composed of asphaltic, poly-
meric materials with sufficiently low permeability so as to control fluid migration.


(d) Geocomposites: These are various combinations of geotextiles, geogrids, geomem-
brances and/or other materials to serve all the primary functions with better performance.


Functions of Geosynthetics


Geosynthetics are increasingly being used in many fields of geotechnical engineering. Differ-
ent functions or specialized actions of geosynthetics are to be distinguished.

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