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

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 volumetric hardening law, 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. The detailed model formulation is presented including an innovative approach for finding image stress points on the bounding surface which offers an original conception of changing the projection center even at the absence of plastic loading. Moreover, a modification procedure is discussed to improve the performance of the proposed model for simulating the highly overconsolidated clays. The proposed modifications besides the novel mapping rule form a novel framework that improves the simulation capabilities of the models with elliptical yield/bounding surfaces, particularly in the case of highly overconsolidated clays, and is applicable to all constitutive models with elliptical yield/bounding surfaces. Furthermore, 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 capability in capturing important aspects of natural clays response during straining, in particular the combined effects of small strain nonlinearity with fabric orientation