An anisotropic bounding surface elastoplastic constitutive model for frozen sulfate saline silty clay under cyclic loading

To study the mechanical properties of frozen saline soil under cyclic loading, the cyclic tri-axial compressive experiments of 36 samples are performed for frozen saline silty clay with 0.0, 0.5, 1.5 and 2.5% of Na2SO4 contents at the temperature of −6 °C, respectively. The experimental results illustrate that the effect of the salt contents and confining pressures on the strength and deformation properties of frozen sulfate saline soils under cyclic loading is significant. To understand the deformation characteristics of frozen sulfate saline silty clay (this kind of saline soil), a bounding surface elastoplastic constitutive model is presented based on the test results and bounding surface plasticity theory. The proposed model includes the effects of salt contents and confining pressures on dynamic characteristics, therefore, it can suitably describe the dynamic stress-strain response of frozen saline soil under cyclic dynamic loading. This proposed model includes: (1) Critical stress ratio calculation formula, considering the effect of salt contents and confining pressures, is proposed. Critical stress ratio and bounding surface shape parameter varying with confining pressures are introduced into plastic potential surface function and bounding surface function to describe pressure melting and crushing characteristics of frozen soils under high confining pressures. (2) The influence of the initial anisotropy and the induced anisotropy by dynamic loads on bounding surface of rotation hardening is considered. A non-associated flow rule together with a mixed hardening rule is used to describe the plastic flow rule and hardening rule of soils during cyclic loading, respectively. (3) A radial mapping rule with mobile mapping origin is employed to simulate elastoplastic properties of soils during cyclic loading. By comparing its simulated results with the test results of cyclic triaxial compression tests, it is found that the proposed model in this paper can well predict deformation characteristics of this kind of saline soil under cyclic loading.