Adaptive anisotropic constitutive modeling of natural clays

In this paper, an adaptive anisotropic constitutive model, namely AA1‐CLAY, is developed for clays based on the critical state framework. The model has a non‐associated flow rule, and it can also reduce to basic critical state constitutive models. A versatile yield surface (YS) is implemented in the model which can generate a broad range of shapes to improve the possibility of capturing experimental yield points of different clay types with high accuracy. In addition to the isotropic hardening rule, an innovative rotational hardening (RH) rule is also incorporated into the model to control the YS rotation rate. The proposed RH rule uses a transitional function to govern the effect of plastic strains at different constant stress ratios more realistically. Furthermore, the equilibrium state of anisotropy, which the YS tends to reach during plastic straining, is defined uniquely based on the experimental findings. The detailed model formulation is presented, and important features of the model are elaborately discussed. The capabilities of the model are also demonstrated by comparing the simulation results of several element tests on a number of different clays against the available experimental data.