Aiming at the shortcomings of traditional constitutive theory failure to describe the non-coaxial deformation of soil for simple shear test

a constitutive model amended with non-coaxial plasticity theory is employed to improve it. Based on the critical state and state-dependent theories

with the method of macro-meso-incorporation

a novel anisotropy state variable is introduced in the model to describe the anisotropy of sand. In view of the geometric relationship of meso-fabric and stress state

the state of sand changes in the principal stress axes rotation condition

and the dilatancy and hardening law of model is the function of sand state

so the model can describe the effect of inherently anisotropy on deformation of sand in this condition. The non-coaxial plasticity theory employed to amend the constitutive model

a three-dimensional non-coaxial model for anisotropic sand is presented. The loading conditions of simple shear test causes the rotation of principal stress axis relative to the soil deposition direction; the amended constitutive model can describe the effect of inherently anisotropy and stress-induced anisotropy on deformation characters under the principal stress rotation conditions; so the amended model can describe the whole characters of simple shear test with clear physical meaning. The verification with simple shear test results of rod mass and Toyoura sand shows that the amended model can well simulate deformation properties.