Comparing GCLs

Geosynthetics | October 2011

GMA techline answers from Bob Koerner

RE: GCLs
I need some assistance in comparing two geosynthetic clay liners for a project where the specification gives a total bentonite mass required of 4500g/m² and a target hydraulic conductivity of < 5 × 10-11.

We have an option of a liner that far exceeds the requirement of the hydraulic conductivity, with a slightly lower bentonite mass.

Are there studies available showing the advantage of extra bentonite other than achieving the hydraulic conductivity, such as the bentonite’s performance as an attenuation layer?

(Michael | New Zealand)

Reply: Good question and let me address the bentonite mass from a historical perspective.

The industry did, indeed, start at 4500g/m² but the focus shifted to hydraulic conductivity shortly thereafter. It was found that 4000 and then 3700g/m² was adequate from this perspective.

Thus, current specifications, such as GRI-GCL3 call for a minimum mass of 3700g/m².

I have not had push-back from specifiers for using this value in years. That said, your value of hydraulic conductivity is right on.

Robert M. Koerner, Ph.D., P.E., NAE; E-mail: Robert.Koerner@coe.drexel.edu.

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