A bounding surface model for frozen sulfate saline silty clay considering rotation of principal stress axes

Abstract

Research results show that rotation of principal stress axes (RPSA) has a large influence on the mechanical properties of soil. To study the mechanical and deformation properties of frozen saline soil under RPSA, in this paper, a constitutive model considering RPSA is proposed for frozen saline soil by considering the plastic deformation caused by the increase of principal stress amplitude and the plastic deformation caused by RPSA separately. The proposed model has the following properties: (1) For the part of principal stress amplitude increase, the critical stress ratio Mc(s)g(θ) changing with hydrostatic pressure is adopted to describe pressure melting and crushing phenomenon characteristic of frozen saline soil under high confining pressure. A function of plastic shear strain and plastic volumetric strain is taken as hardening parameter to control the size of the bounding surface under plastic volumetric compression mechanism. (2) Based on the experimental results, a new shape function is presented for frozen soil, and the proposed shape function is introduced into bounding surface function and plastic potential function to control the shapes change of bounding surface and plastic potential surface. (3) For the part of RPSA, a more accurate method for determining loading direction and a formula for solving non-coaxial angle are given. A plastic modulus formula considering the effects of hydrostatic pressure, generalized shear stress, and anisotropy is proposed. A dilatancy equation which can reflect the effect of intermediate principal stress coefficient is presented. By comparing the simulated results of the proposed model with the experimental results, it is found that the proposed model not only can reflect the effect of the increase of principal stress amplitude on the mechanical and deformation behaviors of frozen saline soil, but also can describe the effect of RPSA on the mechanical and deformation behaviors of frozen soil.