9.5 GEOSYNTHETIC REINFORCEMENT
Geosynthetics are porous, flexible, man-made fabrics which act to reinforce and increase the stability of structures such as earth fills, and thereby allow steeper cut slopes and less grading in hillside terrain. Geosynthetics of various tensile strengths are used for a variety of stability problems, with a common use being reinforcement of unpaved roads constructed on weak soils. Geosynthetics and Geosynthetics -related materials are generally classified on the basis of their manufacturing process. Geosynthetics can be knitting, woven, non-woven or composite. Related Geosynthetics products in use are webs, mats, nets, grids, plastic sheets or composite structure. Geosynthetics have been used for filtration, drainage, separation, reinforcement, fluid barrier and protection.
Geosynthetics are classified into the following:
(a) Geotextiles: These are permeable textiles—woven or non-woven synthetic polymers. Woven fabrics consist of two threads (warp and weft) combined systematically by making them cross each other perpendicularly. Threads could be multi-filaments or thick mono filaments, or tape threads. 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.
(b) Geogrids: These are relatively stiff net-like materials with large open spaces between the ribs that make up the structure. They can be used to reinforce aggregate layers in pavements and for construction of geo-cells for improvement of bearing capacity. Geogrids are formed by a regular network of tensile elements with apertures of sufficient size to interlock with surrounding fill material.
(c) Geomembrances: A continuous membrane—type liner composed of asphaltic, polymeric materials with sufficiently low permeability so as to control fluid migration. Geomembranes are low permeability geosynthetics used as fluid barriers.
(d) Geocomposites: These are various combinations of geotextiles, geogrids, geomembrances and/or other materials to serve all the primary functions with better performance.
Most geosynthetics are made from synthetic polymers such as polypropylene, polyester, polyethylene, polyamide, PVC, etc. These materials are highly resistant to biological and chemical degradation. Natural fibers such as cotton, jute, bamboo, etc., can be used as geotextiles and geogrids, especially for temporary applications. In contrast to the smooth surfaces that steel reinforcements usually have, most geosynthetics have fabric-like surfaces (geotextiles) or grid structures (geogrids) that produce much better bonding between soil and the reinforcement.
Figure 25: installing of Geogrids and growing vegetations
Figure 26: Application of Geosynthetic