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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