Constitutive Model for Drained Compression of Unsaturated Clay to High Stresses

Abstract

A constitutive model is presented in this paper to describe the isotropic compression response of unsaturated, compacted clay under drained conditions over a wide range of mean effective stresses. The model captures the key transition points of the compression curves at different stress levels, ranging from the preconsolidation stress, to pressurized saturation, to the initiation of void closure. The results from drained, isotropic compression tests on compacted clay specimens having different initial degrees of saturation up to a mean total stress of 160 MPa were used for model calibration. The suction hardening effect on the preconsolidation stress and the nonlinear compression curve of unsaturated clay up to the point of pressurized saturation were captured using an extended form of an existing effective stress-based constitutive model. For higher mean stresses, an empirical relationship to consider the transition to void closure was incorporated to fit the observed compression curves of the compacted clay specimens. The transition to void closure was found to be affected by the initial compaction conditions despite the fact that all of the specimens were pressure saturated in this mean stress range.