Direct shear testing of GCLs at elevated temperature and in a non-standard solution

The objective of this study was to develop, verify, and assess a direct shear apparatus to measure the internal shear strength of geosynthetic clay liners (GCLs) when exposed to elevated temperature and non-standard hydration solutions. Shear boxes were developed to facilitate testing 300 mm square and 150 mm square specimens. Preliminary experiments documented the effectiveness of a GCL gripping system and a two-stage hydration procedure. Direct shear experiments were performed to evaluate the new apparatus with respect to the following variables: (i) specimen size; (ii) GCL peel strength; (iii) GCL heat treatment; (iv) test temperature; and (v) hydration solution. Direct shear results were verified via comparison to literature, which also supported the use of 150 mm square GCL specimens to measure internal shear behavior and shear strength. Shear tests on heat-treated and non-heat-treated GCLs at 20 degrees C and 80 degrees C yielded a 40% reduction in internal peak strength with increase in temperature. Hydration in a high-alkaline synthetic mining solution indicated a loss in peak strength with increasing hydration times from 15 to 60 days. A systematic reduction in peak and large-displacement shear strength with increasing normal stress was observed for 60 days' hydration in the alkaline solution relative to hydration for 4 days in de-ionized water.