Three-dimensional noncoaxial plasticity modeling of shear band formation in geomaterials

Accurate prediction of shear band formation in geomaterials is crucial in the solution of various stability problems in geotechnical engineering. The initiation of shear band is strongly dependent on the constitutive description of the prelocalization homogeneous deformation. Conventional plasticity models assume that coaxiality exists between the directions of principal stresses and the directions of plastic strain increments. Accumulating evidence has however shown that this assumption is not appropriate. In this paper, a noncoaxial constitutive modeling platform is presented in a general three-dimensional stress space. It is shown that the classical vertex-like structure, which has been widely adopted to describe the noncoaxial constitutive response, only represents the two-dimensional condition. Examples are presented to demonstrate the capability of the modeling platform in capturing the initiation and orientation of shear band in a granular soil. The significance of the noncoaxiality effects is illustrated by comparisons of the predictions produced by coaxial and noncoaxial (both two-dimensional and three-dimensional) plasticity models.