Effect of freeze-thaw cycles on the mechanical properties and constitutive model of saline soil

The freeze-thaw cycle is one of the most common natural physical processes in cold regions and will significantly affect the deformation characteristics of saline soil. To study the mechanical properties and constitutive relationship of saline soil under freeze-thaw cycles, in this paper, a series of freeze-thaw cycle tests and consolidated-drained (CD) triaxial tests were conducted on remodeled saline soil in the Qian'an area of western Jilin, China. Based on the elliptic-parabolic double yield surface constitutive model, a modified model considering the effects of freeze-thaw cycles is established. The results show that the specimen exhibits a strain-hardening stress-strain relationship, and the volumetric strain during shearing exhibits a shear shrinkage characteristic overall. As the number of freeze-thaw cycles increases, the volumetric strain gradually increases, and the shear strength gradually decreases. As the confining pressure increases, the volumetric strain gradually increases. Then, the elliptic function and parabolic function are selected to describe the volume yield surface and the shear yield surface on the p-q plane respectively. By introducing the correlation flow rule, the functional relationship between the deviating stress increment and the axial strain increment and volumetric strain increment is derived. Based on the results of the triaxial test, the variation in the model parameters with the number of freeze-thaw cycles was determined. The results show that as the number of freeze thaw cycles increases, c, phi, h, K, n, M-1, M-2, and a show a decreasing rule, while t shows a gradually increasing rule, and all factors can use logistic function to fit the regression relationship between the model parameters and the number of freeze-thaw cycles. The expression of the model parameters with the number of freeze-thaw cycles as a factor is substituted into the stress strain increment constitutive equation, and a modified double yield surface model considering the effects of freeze-thaw cycles is established. The calculated values of the model are basically consistent with the measured values. This shows that the double yield surface constitutive model can be applied to saline soil.