Dynamic shear strength of a needle-punched GCL for monotonic loading

This paper presents an experimental investigation of the dynamic internal shear strength of a hydrated woven/nonwoven needlepunched geosynthetic clay liner (GCL) for monotonic (i.e., single direction) loading conditions. Displacement-controlled shear tests were conducted using a large direct shear machine for four normal stress levels ranging from 141 to 1,382 kPa and seven shear displacement rates R ranging from 0.1 to 30,000 mm=min. For each normal stress, peak shear strength first increased and then decreased with increasing displacement rate. Maximum values of peak strength occurred for R = 100-10,000 mm=min and were 16-23% higher than corresponding static values measured at R = 0.1 mm=min. For each normal stress, residual shear strength first decreased and then increased with increasing displacement rate, with minimum values occurring at R = 1 mm=min. On a relative basis, residual strengths show greater dependence on displacement rate than peak strengths. The standard displacement rate for static shear tests of hydrated GCLs (0.1 mm=min) generally yielded conservative values of peak shear strength but unconservative values of residual shear strength, especially for higher normal stress levels. The GCL experienced large post-peak strength reduction for all test conditions.