Geosynthetic clay liner
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A geosynthetic clay liner (GCL) is a woven fabric-like material, primarily used for the lining of landfills. It is a kind of geomembrane and geosynthetic, which incorporates a bentonite or other clay, which has a very low hydraulic conductivity. The resulting lower permeability slows the rate of seepage out of the landfill. Due to environmental laws, any seepage from landfills must be collected and properly disposed of, otherwise contamination of the surrounding ground water could cause major environmental and/or ecological problems. The lower the hydraulic conductivity the more effective the GCL will be at retaining seepage inside of the landfill. Bentonite composed predominantly (>70%) of Montmorillonite or other expansive clays, are preferred and most commonly used in GCLs. A general GCL construction would consist of two layers of geosynthetics stitched together enclosing a layer of processed sodium bentonite. Typically, woven and/or non-woven textile geosynthetics are used, however polyethylene or geomembrane layers or geogrid geotextiles materials have also been incorporated into the design or in place of a textile layer to increase strength.GCLs are produced by several large companies in North America, Europe, and Asia. The United States Environmental Protection Agency currently regulates landfill construction and design in the US through several legislations.
The use of GCLs as a separate category of geosynthetics appears to have been in the United States 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 for 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 on many occasions.
Differences Between Geosynthetic Clay Liners and Compacted Clay Liners
|Material||Bentonite clay, adhesives, geotextiles and/or geomembranes||Native soils or blends of soil and bentonite clay|
|Construction||Factory manufactured and then installed in the field||Construction and/or amended in the field|
|Thickness||~ 6 mm||300 to 900 mm|
|Permeability of clay||10−10 to 10−12 m/s||10−9 to 10−10 m/s|
|Speed and ease of construction||Rapid, simple installation||Slow, complicated construction|
|Installed cost||$0.05 to $0.10 per m2||Highly variable (estimated range $0.07 to $0.30 per m2)|
|Experience||CQC and CQA are critical||Highly workforce dependent|
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