Finite strain, anisotropic modified Cam clay model with plastic spin. I: Theory

There are several approaches that can take into account the micromechanical and anisotropic behavior of soils. One is Dafalias's plastic spin approach. It is a convenient approach that utilizes an internal variable called "the plastic spin tensor." The plastic spin is a function of the embedded stress (back stress) that causes the induced anisotropy and, consequently, the isotropic soil models cannot account for it. This paper presents a formulation of the plastic spin and related constitutive equations based on Dafalias's "anisotropic modified Cam clay model" with an updated Lagrangian reference frame. The required parameters are the typical consolidation and stress-strain parameters. The only additional parameters used in this work are the back-stress parameters c and x. These features are relatively simple and easy to use compared to other models.