Environmental Engineering Reference
In-Depth Information
A wide range of different geotextiles is available. These differ in the type of polymer
used for manufacture, the type of fibre construction and how this fibre is manufactured
into a fabric.
Giroud and Bonaparte (1993) describe the different types of geotextiles as follows:
Woven geotextiles
are composed of two sets of parallel yarns systematically interlaced
to form a planar structure. Generally, the two sets of yarns are perpendicular. The manner
in which the two sets of yarns are interlaced determines the weave pattern. By using vari-
ous combinations of three basic weave patterns, i.e. plain, twill, and satin, it is possible to
produce an almost unlimited variety of fabric constructions. Woven geotextiles can be
classified according to the type of yarn, as discussed below:
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Multifilament woven geotextiles are made with yarns that comprise many filaments
(typically 100 or more);
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Monofilament woven geotextiles are made with yarns that are single filament;
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Slit film woven geotextiles are obtained by weaving small tapes produced by slitting a
plastic film with blades;
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Fibrillated woven geotextiles are obtained by weaving yarns that are bundles of tape-
like fibers still partially attached to each other. Such bundles are film strips that have
been nicked and broken up into fibrous strands.
Knitted geotextiles
include two types: the classical knits and the insertion knits.
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Classical knits are formed by interlocking a series of loops of one or more yarns to
form a planar structure. The way the loops are interlocked identifies the type of knit,
such as jersey. The knitted geotextiles of the classical knit type are highly deformable
materials;
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Insertion knits are produced by inserting yarns into a knit that is being made. Using this
manufacturing process, it is possible to make geotextiles that combine properties of
wovens, fabrics, and classical knits.
Nonwoven geotextiles
are formed from continuous filaments or from short fibers (also
called staple fibers), arranged in all directions (but not necessarily at random) and bonded
together into a planar structure. Synthetic filaments are produced by extrusion and are,
therefore, continuous, whereas synthetic fibers are obtained by cutting filaments into lengths
of 100-150 mm (4-6 inches). Natural fibers are generally short. For nonwoven geotextiles,
the continuous filaments or short fibers are first arranged into a loose web, then bonded
together using one, or a combination, of the following processes: chemical bonding, thermal
bonding and mechanical bonding by needle-punching.
Chemically bonded nonwoven geotextiles are obtained by bonding the filaments or
fibers together using a cementing medium such as glue, rubber, latex, cellulose derivative
or, more frequently, synthetic resin.
Heatbonded nonwoven geotextiles are obtained by bonding the filaments or
fibers together using heat. When heat is provided by heated rollers that press the fabric,
the resulting heatbonded nonwoven geotextile is relatively stiff and thin, typically
0.5-1 mm.
Needle-punched non-woven geotextiles are obtained by entangling the filaments
or fibers together using thousands of small barbed needles, which are set into a board
and punched through the fabric and withdrawn many times as the fabric passes
under the board. Needle-punched non-woven geotextiles are relatively thick, typically
1-5 mm.
The three bonding processes described above can be combined. For example, needle-
punched non-woven geotextiles are typically compliant, but, if they are exposed to
