Anisotropic Plasticity Model for Undrained Cyclic Behavior of Clays. I: Theory

Abstract

A constitutive model for the stress‐strain‐pore‐pressure behavior of fluid‐saturated cohesive soils under dynamic loading is developed using the concept of bounding surface plasticity. The model adopts the joint invariants of the second‐order stress tensor and clay fabric tensor as a formalism to account for material anisotropy. The model includes three internal variables: density‐hardening variable representing change in void ratio; rotational hardening variable depicting fabric ellipsoid changes; and, finally, distortional hardening variable controlling the shape of bounding surface. The corresponding evolution laws are formulated using micromechanics arguments and phenomenological observations. In a companion paper, the resulting constitutive equation is shown to capture the essential features of undrained cyclic behavior of clays, including: (1) Degradation of undrained strength and stiffness; (2) development of transient and residual pore pressure and deformation; (3) effect of initial consolidation stress condition and stress history; and (4) effect of loading paths involving rotation of principal stress direction.