Softening and Preshearing Effects in Sand

Abstract

An experimental investigation of the behavior of sand near failure was undertaken to study the shape, location and movement of the plastic yield surface in the hardening regime and in the softening regime near peak failure. Triaxial compression tests on sand specimens at four different relative densities were performed, and it was confirmed that the yield surface defined as a contour of constant plastic work as measured from the origin of stress captures the behavior of soil with good accuracy in both the hardening and in the softening regime. It was observed that preshearing to peak failure produced effects similar to overconsolidation observed in clays in the region of lower confining pressures. In this region, the yield surface was found to move out beyond the failure surface for normally consolidated sand, i.e. the sand became stronger. In the region of confining pressures higher than that employed during initial preshearing to peak failure, the yield surface was located inside the failure surface and the sand was found to harden. The observed patterns of yielding is captured with good accuracy by the yield criterion employed in an existing single hardening constitutive model.