Noncoaxial Theory of Plasticity Incorporating Initial Soil Anisotropy

In this paper, a noncoaxial plane strain soil model is developed in the framework of initial soil strength anisotropy that is described by taking the internal friction angle to be a function of principal stress orientations. The conventional Mohr-Coulomb (M-C) yield criterion is generalized to give an anisotropic yield criterion, with the curve in the deviatoric stress space forming an ellipse. Both rotational and eccentric ellipses are discussed. The formulation of noncoaxial constitutive equations is described by a general form in terms of the plastic strain rate. In this form, the plastic strain rate is divided into two parts: the conventional component that is derived from the classical plastic potential theory and the noncoaxial component that is assumed to be tangential to the yield surface. The newly proposed model is validated by the analytical calculations and discrete element modeling (DEM) simulation results in simple shear tests. Conclusions can be drawn that this model is generally capable of capturing the DEM observations of simple shear testing.