Elastoplastic Model for Overconsolidated Clays with Focus on Volume Change under General Loading Conditions

Abstract

Overconsolidated clays are often encountered in geotechnical engineering; therefore, developing a sophisticated model that can accurately describe the mechanical behavior of overconsolidated clays has high practical value. Based on the transformed stress and the subloading surface concept, this paper presents a generalized critical-state model, with special focus on the volume change under three-dimensional loading conditions. Because existing experimental results show that not only the shear strength but also the volume change of clays depend on the loading conditions, a new stress–dilatancy equation (relationship between stress ratio and plastic strain increment ratio) defined in the transformed stress space is established. Then, by introducing the subloading surface concept, a new critical-state model is proposed. The new model not only describes the strain-softening behavior of overconsolidated clays, but also takes into consideration the influence of intermediate principal stress on strength and deformation of clays. The performance of the model is validated by triaxial compression and extension tests and true triaxial tests on normally consolidated and overconsolidated clays.