How well do we understand the undrained strain softening response in soft sensitive clays?

Abstract

Many geomaterials exhibit a reduction in strength after attaining their peak strength states. This behavior, also known as strain softening, has commonly been attributed to reductions in the cohesion and/or friction angle of the materials. This holds true especially when these strength parameters are evaluated at a very large strain levels. However, for the strain levels achieved by standard undrained triaxial tests on soft sensitive clays show that the friction angle and cohesion of these materials remain almost unchanged, even when they display a significant reduction in post-peak shear strength under undrained condition. In such conditions, the increase in shear-induced pore pressure is observed to be responsible for the observed undrained softening in soft sensitive clays. This paper elaborates on this aspect based on the behavior of soft sensitive Norwegian clays.