Dynamic shear strength of GMX/GCL composite liner for monotonic loading

This paper presents an experimental investigation of the dynamic shear strength of a composite liner consisting of a high-density polyethylene (HDPE) textured geomembrane (GMX) over a hydrated nonwoven/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 five normal stress levels ranging from 13 to 2071 kPa and five shear displacement rates ranging from 0.1 to 30,000 mm=min. GCL internal failures occurred at high normal stress and low displacement rate. As normal stress decreased or displacement rate increased, failure mode transitioned to the GMX/GCL interface. Peak strength envelopes are slightly nonlinear (concave-down) and show dependence on displacement rate at higher normal stress. Large-displacement strength envelopes show greater dependence on displacement rate at higher normal stress due to the effect of changing failure mode. The standard displacement rate for static shear tests of GMX/GCL composite liners (1 mm=min) yielded conservative values of peak shear strength but unconservative values of large-displacement shear strength for some normal stress conditions. The GMX/GCL composite liner experienced significant post-peak strength reduction for all test conditions.