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The internal shear strength of geosynthetic clay liners (GCLs) can be evaluated through direct shear testing in accordance with ASTM D6243 under a specific set of boundary conditions for a given normal stress. In order to prevent slippage at the GCL–gripping system interface and ensure an internal shear failure of the GCL, a gripping surface made of spikes 1 to 2mm tall mounted on a rigid substrate is recommended in the standard method and has been commonly used. It is recognized that certain boundary effects exist as a result of the aggressive gripping system. To improve the hydraulic performance and/or protect the bentonite core, a multi-component GCL is designed to have a thin membrane or film laminated or glued to one of the carrier geotextiles. It is necessary to investigate the boundary effect on the multi-component GCL internal shear strength tests, because the film– or membrane–geotextile interface is more prone to interference from the rough gripping surface recommended by the current standard. A series of internal shear strength tests were conducted on the same multi-component GCL product under different gripping conditions. It was found that tests using the aggressive gripping system yield a significantly higher peak shear strength of the multi-component GCL and a lower residual shear strength at large displacements.
multi-component GCL, shear strength, stability, direct shear, gripping surface, boundary effect
Research Associate, Louisiana Transportation Research Center, Louisiana State Univ., Baton Rouge, LA
Lab Manager, SGI Testing Services, LLC, Norcross, GA