Geosynthetic clay liners (GCLs) have seen increasing usage of GCLs in the mining industry. Potentially, GCLs could cut costs in the liner design of heap leach pads and tailings piles. However, little is known about the behavior of GCLs under the extremely high normal loads encountered in some of these applications. To study the internal shear behavior of a needlepunched GCL under high normal loads two sets of shear tests were performed. The first set of tests was conducted in a standard 300 mm by 300 mm (12 in. by 12 in.) direct shear box at normal loads of 350, 700, and 1050 kPa (50, 100 and 150 psi). The second set of tests was conducted in a smaller 150 mm by 150 mm (6 in. by 6 in.) direct shear box at normal loads of 1050, 1750, and 2800 kPa (150, 250 and 400 psi). The smaller shear box was used at the higher normal loads due to limitations in the application of the higher normal stresses to the larger shear box. A common normal load of 1050 kPa (150 psi) allowed for comparing results of the two shear boxes. Test results indicated good correlation between the small and large shear boxes. At 1050 kPa (150-psi) normal load, the peak internal strength of the GCL for the large and small shear boxes was 332 kPa (48.2 psi) and 334 kPa (48.4 psi), respectively. At the highest normal load, 2880 kPa (400 psi), the GCL had a peak strength of 668 kPa (96.9 psi). In addition to the direct shear box test results, the peel strength test result for the same GCL sample is indicated. Peel strength tests have been correlated to direct shear strength and used as an index test in MQC and CQA test programs.
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