A constitutive model of frozen saline sandy soil based on energy dissipation theory

Abstract

A series of triaxial compression tests are carried out for frozen saline sandy soil with Na2SO4 contents 0.0, 0.5, 1.5, and 2.5% under confining pressures from 0 MPa to 16 MPa at −6 °C, respectively. The test results indicate that, the Critical State Line (CSL) of frozen saline sandy soil is curve and is not through the origin in (p,q) plane, and the soil particles have the properties of initial anisotropic rotational angle and loaded anisotropy in process of loading. In order to describe the deformation properties of frozen saline sandy soil, a new double yield surface constitutive model is proposed based on the triaxial compression tests in this paper. The proposed model contains the influence of salt contents on mechanical characteristics, so it is suitable for describing the stress–strain relation of frozen saline soil. The proposed model has the following properties: (1) By defining a modified effective stress p∗, a critical state strength envelope function is established according to the Modified Cam Clay model. The envelope approximates a straight line under low confining pressures, but it is curve downward under high confining pressures due to pressure melting. (2) The effect of the initial anisotropic rotational angle and loaded anisotropy, during process of loading under plastic volumetric compression mechanism, on yield surface of rotational hardening is taken into account. (3) A paraboloid yield surface function, including the rotational hardening law induced by loading, is proposed under plastic shear mechanism. The universality of the proposed model is verified by the test results of frozen saline sandy soil under different stress paths. Finally, in order to further study the applicability of the proposed model in this paper, the stress–strain relation of the cemented clay is simulated by it. And the influences of the pressure melting phenomenon and the rotational hardening rule on the calculated results of the proposed model are investigated. The research results indicate that the proposed model can simulate not only the mechanics properties of materials whose CSL is straight but also those of materials whose CSL is curved, other than predict the deformation regularity of frozen saline sandy soil well.