Viscoplasticity of Transversely Isotropic Clays

Abstract

A viscoplastic constitutive relation of the endochronic type (i.e., the inelastic strain increments are characterized by an intrinsic time) is formulated to describe the behavior of transversely isotropic clays produced by one-dimensional consolidation. The formulation contains eight material parameters in addition to those needed for isotropic clays. The hardening and softening functions and the densification-dilatancy function are assumed to be given by the same expressions previously found for isotropic clays, but the invariants involved in these expressions are replaced by the proper transversely isotropic invariants. The pore pressure is determined from the volume change and the compressibility of the water, and the constitutive relation is written in terms of the effective stresses. The elastic moduli are assumed to be functions of hydrostatic stress and inelastic dilatancy, and they are correlated with the consolidation stress. Experimental curves of axial strain for various anisotropically consolidated clays have been fit by a time-independent version of the theory, and a satisfatory agreement has been achieved.