Environmental Science & Engineering - January 2002
Geosynthetic clay liners offer many advantages for containment applications
By Bruno Herlin, P.Eng., Terrafix Geosynthetics Inc.
|Geosynthetic clay liner being installed for a secondary containment. Photo - Don Stewart (formerly of Terrafix)|
Geosynthetic clay liners (GCLs) are an established sealing product in the geoenvironmental industry. They are used in landfill caps and base liner applications under roads, railways, secondary containment for above ground tank farms, as well as within various other containment structures such as dams, canals, ponds, rivers and lakes. They are also used for waterproofing of buildings and other similar structures.
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 by different techniques, the Canadian manufactured GCL, Bentofix, is mechanically bonded by needlepunching from one nonwoven geotextile through the bentonite to the other nonwoven or woven geotextile. Because of their low hydraulic conductivity, GCLs are used mainly as a replacement for thick, difficult to build, compacted clay liners to provide a barrier to liquids and gases.
Bentonite, named after an American geologist who discovered this type of clay in about 1890 in Fort Benton, Wyoming, is a clay mineral with expansive characteristics and low permeability, where montmorillonite is the chief mineral. Montmorillonite, named after a deposit located in southern France, 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 layer with the equivalent hydraulic protection of several feet of compacted clay.
|Cover soil installation over a geosynthetic clay liner for a paper mill's effluent lagoon (Red Rock, ON). Photo - Kent von Maubeuge, Naue Fasertechnik|
While exact installation procedures and recommendations may vary from manufacturer to manufacturer, in general, installation consists of rolling out GCL panels on a prepared subgrade, with adjacent panels overlapped a minimum 300 mm. To maintain the integrity of the sealing system, a bead of granular bentonite is applied to the overlap of the adjacent panels. Subsequent to overlap treatment, a minimum 300 mm cover soil (or geomembrane in some cases) is placed. The covering material is always placed in the same shift (same day) as the GCL is deployed to minimize the chance of unconfined hydration, and possible damage to the GCL.
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 waste management industry, including lagoon-lining systems. The technical properties of these materials are well documented and their integrity as a sealing barrier has been demonstrated in field applications. Furthermore, because these materials are factory produced, their properties are predictable, enabling the engineer to design with a high confidence level.
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