Dynamic Shear Strength of a Needle-Punched GCL for Monotonic Loading: Fid-Bau Portal

Dynamic Shear Strength of a Needle-Punched GCL for Monotonic Loading

Fox, Patrick J. / Sura, Joseph M. / Nye, Christopher J.

This paper presents an experimental investigation of the dynamic internal shear strength of a hydrated woven/nonwoven needle-punched 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.