Geosynthetic Clay Liner’s (GCLs) are an established sealing product in the geoenvironmental industry. They are used in landfill applications as caps and base liners, secondary containment for fuel storage facilities, as well as within various other containment structures such as dams, canals, rivers, and lakes. Rolled out like a carpet to provide a durable impermeable liner, Geosynthetic Clay Liners consist of a layer of high swelling sodium bentonite sandwiched between two geotextiles. Manufactured around the world in different techniques, the Canadian manufactured GCL, is mechanically bonded by needlepunching from one nonwoven geotextile through the bentonite to the other nonwoven or woven geotextile. The low hydraulic conductivity of the GCLs are used mainly as a replacement to thick, difficult to build compacted clay liners to provide a barrier to liquids and gases, offering both a technical and economical advantage. GCLs, with an average thickness of 7mm, offer a volume advantage over Compacted Clay Liners. They are more capable of withstanding freeze-thaw and wet-dry cycles; offer substantial construction cost savings in reduced on-site QC/QA and a quicker installation. Furthermore, GCLs offer equivalent or lower rates of release of fluids and chemicals than Compacted Clay Liners (CCLs). Bentonite is a clay mineral with expansive characteristics and low permeability, where montmorillonite is the chief mineral. Montmorillonite, swells when contacted with water approximately 900% by volume or 700% by weight. When hydrated under confinement, the bentonite swells to form a low permeability clay liner, the equivalent hydraulic protection of several feet of compacted clay. A relatively new engineering material for some, geosynthetic clay liners have been used extensively over the past two decades, and are finding increasing use in every sector of the environmental industry. This paper will review the technical properties of these materials, their documentation at the research level, their integrity as a sealing barrier and recent field applications in the pipeline industry. Further, because these materials are factory produced, their properties are predictable, assisting the engineer to design with a high confidence level. Technical properties and economical benefits are sure to further increase GCL installations around the world to protect our environment and more importantly our groundwater.

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