Strength criterion for frozen silty clay considering the effect of initial water content

The initial water content and confining pressure significantly affect the deformation and strength behaviors of frozen soils. To investigate the influence of the initial state of water on the mechanical properties of frozen silty clay (FSC), triaxial compression tests are conducted on artificial FSC with five initial water contents (12.5%, 14.0%, 16.0%, 18.0%, and 20.0%) at the temperature of −6 °C. The results show that when the initial water content is 12.5%, the frozen soil samples present strain softening and strain hardening successively with increasing confining pressure. As the initial water content increases, the degree of strain hardening under the same confining pressure gradually weakens. The frozen soil samples mainly present strain softening when the initial water content is more than or equal to 18%. According to the test results, when the initial water contents ranging from 12.5% to 20%, the relationship between the strength and mean stress has three forms: increases nonlinearly, increases first and then decreases, and maintains an approximately constant value. Linear and nonlinear strength envelope equations based on different types of strength envelopes are proposed. Additionally, the relationship between the initial water content and internal friction angle is analyzed. In the p-q plane, based on the nonlinear strength characteristics of FSC with initial water contents of 12.5%, 14.0%, and 16.0%, a modified mean stress expression p* is derived to represent the nonlinear strength criterion equation according to the modified Cam-Clay model. Furthermore, a shape function in the deviatoric plane is proposed by modifying the Lade–Duncan model, and a strength criterion is established by integrating the strength functions in the p-q and deviatoric planes. The proposed strength criterion can effectively represent the nonlinear strength behaviors of FSC, including the effects of the initial water content, ice melting, and crushing.