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GCL shear strength concerns

Q&A: GMA Techline | July 1, 2024 | By:

Q: We are worried about the midplane shear strength of our GCL in a seismically active zone of our landfill. The GCL is a single component of a double composite liner system. It is backing up the primary geomembrane in the upper composite liner system. Should we be concerned?

A: GCL shear strength is a primary design consideration for facilities involving slopes due to the low strength of hydrated bentonite. One needs to account for both interface and midplane failures in a comprehensive slope stability design. However, I have never seen a midplane needlepunch GCL in my career. For this reason, the GRI GCL-3 specification value is rather low at 2.1 lb./in (360 N/m). There has been much research on this topic. The following references may help you:

Fox, P.J., Nye, C.J., Morrison, T.C., Hunter, J.G., and Olsta, J.T. 2006. “Large Dynamic Direct Shear Machine for Geosynthetic Clay Liners.” Geotechnical Testing Journal, 29(5), 392-400.

Fox, P.J., and Stark, T.D. 2004. “State-of-the-Art Report: GCL Shear Strength and Its Measurement.” Geosynthetics International, 11(3), 141-175.

Koerner, R. M., Soong, T.Y. and Gontar, A. 1998. “Selected Aspects of GCL Shear Strength Testing.”
Proc. GeoBento ’98, BRGM Foundation, Paris, France, pp. 97-110.

McCartney, J.S., Zornberg, J.G. and Swan, R.H. 2004. “Effect of Specimen Conditioning on Geosynthetic Clay Liner Shear Strength.” Proc. GeoAsia 2004, Seoul, Korea, pp. 635-643.

Von Maubeuge, K. P. and H. Ehrenberg. 2000. “Comparison of Peel Bond and Shear Tensile Test Methods for Needlepunched Geosynthetic Clay Liners.” Geotextiles and Geomembranes, 18(2-4), 203-214.

Please note, I would be much more concerned with an interface failure in your complex cross section and the landfill filling sequence. Please understand that I am not minimizing your concern; it is real. However, there may be more pressing items to worry about.

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