BS-CLAY1: Anisotropic bounding surface constitutive model for natural clays

Abstract

In this paper, a multi-surface anisotropic constitutive model is proposed for clayey soils, based on bounding surface theory and a classical anisotropic critical state-based model. In the proposed model, in addition to the volumetric hardening law, a rotational hardening rule is also incorporated into the bounding surface formulation with a non-associated flow rule. The model uses the bounding surface plasticity theory to produce a more realistic representation of the nonlinear behavior of clays with high overconsolidation ratios. Detailed model formulation is presented including an innovative approach to find image stress points on the bounding surface which offers an original conception of changing the projection center, even at the absence of plastic loading. A modified procedure is also discussed to improve the performance of the proposed model for simulating the response of highly overconsolidated clays. The proposed modifications, together with the novel mapping rule, form a new framework that can be used to improve the simulation capabilities of different constitutive models that have elliptical yield/bounding surfaces. The efficiency of the framework is demonstrated by comparing the simulation results against element test data from a number of different clays at lightly to highly overconsolidated conditions. The new model shows promising capabilities in capturing the important aspects of natural clays response during straining, in particular for the combined effects of small strain nonlinearity with fabric orientation.