Geosynthetic clay liners

:"Also see Geosynthetics."

Geosynthetic clay liners (or GCLs) are factory manufactured hydraulic barriers consisting of a thin layer of bentonite (or other very low permeability material) supported by geotextiles and/or geomembranes, being mechanically held together by needling, stitching, or chemical adhesives. Sodium bentonite is the usual type, but calcium bentonite can be modified to give a similar product.

The use of GCLs as a separate category of geosynthetics appears to have been in the U.S. in 1988 in solid waste containment as a backup to a geomembrane. The product was Claymax® which is bentonite mixed with an adhesive so as to bond the clay between two geotextiles; one below (the carrier textile) and the other above (the cover textile) the bentonite in the center. About the same time a different product in Germany, Bentofix®, was manufactured by placing bentonite powder between two geotextiles and then needle punching the three-component system together.

Other names used for GCLs since their initiation are “clay blankets”, “bentonite blankets”, “bentonite mats”, “prefabricated bentonite clay blankets” and “clay geosynthetic barriers”, the latter currently favored by the International Organization for Standardization (ISO). The engineering function of a GCL is containment as a hydraulic barrier to water, leachate or other liquids and sometimes gases. As such, they are used as replacements to either compacted clay liners or geomembranes, or they are used in a composite manner to augment the more traditional liner materials. The ultimate in liner security is probably a three component composite geomembrane/geosynthetic clay liner/compacted clay liner which has seen use as a landfill liner in many occasions.