Geocomposite are basically combinations of two or more different types of geosynthetic. As most of the individual components are thermoplastic they can be thermally laminated, but adhesive bonding and needle punching are also used.  Examples include: geotextile-geonet; geotextile-geogrid; geonet-geomembrane; or what is termed a geosynthetic clay liner (GCL). There is almost no limit to the variety of geocomposites that are possible and the development of these materials results from the anticipated usefulness of their multifunctionalities and the opportunity for more rapid installation than by using the individual components. The three main geocomposite material types are: drainage geocomposites, reinforcement geocomposites and fluid barrier geocomposites.
Control of water is critical to the stability of most geotechnical constructions and drainage geocomposites have become important materials for such a requirement. Common configurations of drainage geocomposites are of a geonet sandwich between two nonwoven geotextile filters (termed a blanket drain), or a sandwiched thick or thin preformed core (panel drain, edge drain or wick drain). Blanket drains are commonly used as liquid collection - removal layers.
Reinforcement geocomposites are structures in which a spun-bonded or melt blown nonwoven web is incorporated into a knitted geogrid by the stich-knit action of holding yarns or bonded by needle punching to one or both sides of a woven or knitted geogrid. The nonwoven adds separation and filtration functions to the geogrid reinforcement to give the multifunctionality of the geocomposite.
Both woven and nonwoven geotextiles can serve as moisture barriers when impregnated with bituminous, rubber-bitumen, or polymeric mixtures. Such impregnation reduces both the cross-plane and in-plane flow capacity of the geotextiles to a minimum.  However, for liquid containment applications what is referred to as a geosynthetic clay liner will be more effective.  
Geosynthetic clay liners (GCLs) are geocomposites that are typically prefabricated with a sodium bentonite clay layer sandwiched between two geotextile layers; two needle-punched nonwovens layers or one needle-punched nonwoven and one woven layer.  The process commonly involves attaching the top and bottom layers by stitching or needle-punching through the bentonite core which also gives the structure its internal shear resistance. When hydrated the bentonite core swells and becomes an effective barrier to liquid or gas.
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