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New GCL Test Determines Flux and Hydraulic-Conductivity Values

A new test method from ASTM International checks the stability of geosynthetic clay liners (GCL) for use in manufacturing quality control.

D 6766, Standard Test Method for Evaluation of Hydraulic Properties of Geosynthetic Clay Liners Permeated with Potentially Incompatible Liquids, describes laboratory measurement of both flux and hydraulic conductivity of GCL-specimens utilizing a flexible wall parameter.

The test method measures one-dimensional, laminar flow of chemicals, landfill leachate, or contaminated water through a saturated/hydrated GCL specimen under a set of conditions, such as an index test. It tells if the flux and/or hydraulic conductivity of a GCL specimen exceeds the certified value stated by the manufacturer and/or required by the regulatory agencies when permeated with potentially incompatible liquids. Although the resulting flux and hydraulic conductivity values don’t represent GCL in-service conditions, the test method allows the requester to establish a set of test conditions.

“The standard will allow for a basis to develop a body of data regarding how certain liquids affect GCLs at certain confining pressures,” says Jim Olsta, P.E., technical manager, Lining Technologies Group, CETCO, Arlington Heights, Ill. “If the permeant liquid is incompatible with sodium bentonite, then the geosynthetic clay liner’s hydraulic conductivity may increase. This could result in higher than expected flux through the GCL. Based upon current research, applications with low confining pressure, such as covers and tank farms, are most vulnerable.”

D 6766 applies to GCL products having geotextile backings and may not apply to GCL products with geomembrane backings.

A task group of ASTM Committee D35 on Geosynthetics developed the standard. Olsta chaired the group of engineers, manufacturers, and test-lab representatives who used research published by the University of Wisconsin and Colorado State University to determine the ultimate end-point of the test.

For further information, contact James Olsta, Lining Technologies Group, CETCO, Arlington Heights, Ill. (phone: 847/392-5800, ext. 7912). Committee D35 meets Jan. 15-17 in Albuquerque. For meeting or membership details, contact Maxine Topping, manager, Technical Committee Operations, ASTM International (phone: 610/832-9737). //

Copyright 2002, ASTM