Abstract: From the point of view of the mobilized plane, material anisotropy has been proved to be the fundamental reason to cause the non-coaxiality of soils, which is consistent with a conclusion in the material mechanics. When angles between the two conjugate mobilized planes and the bedding plane are not equal, shear components of the plastic strain increment will occur in the principal stress plane. As a result, the direction of principal plastic strain increment will not be coaxial with the direction of principal stress. Based on this conclusion, numerical modeling of non-coaxiality should also be carried out according to an anisotropic constitutive model. The newly proposed anisotropic transformed stress method considering the effect of anisotropy is also capable of reflecting the non-coaxiality, because it changes the relative magnitudes of stress components and obtains an anisotropic transformed stress tensor with different principal directions from the ordinary stress tensor. Using this method, non-coaxial behaviors of soils can be described under the framework of the existing elastoplastic constitutive models. As an example, the anisotropic UH model is adopted to predict the non-coaxial deformation under different loading conditions to verify this method.

Key words: soils, non-coaxiality, anisotropy, transformed stress, constitutive model