Mesoscopic Freeze-Thaw Damage Model of Residual Soil Using a Discrete-Element Method under a Laminated-Wall Flexible-Boundary Condition

Freeze-thaw processes can cause slope instability in areas with short-term frozen (STF) soil, resulting in potential safety risks and huge financial losses to a certain extent, as these processes affect the physical and mechanical properties of the soil. However, their adverse effect on the mesoscopic-level mechanical properties of residual soil has not been adequately investigated. To gain an effective understanding in this regard, a laminated-wall approach was adopted to create a flexible boundary for a triaxial-shear test. Simulated stress-strain curves closely matched experimental results, with a maximum relative error of 7.81% at the peak. Moreover, the experimental data collected from real soil subjected to freeze-thaw cycles were used to calibrate the relation between the macroscopic and mesoscopic parameters. The deterioration of the macromechanical and micromechanical parameters of residual soil primarily occurred in the first four freeze-thaw cycles. For eight freeze-thaw cycles, the damage degree of each microparameter remained the same, reaching approximately 0.37. A freeze-thaw damage model of the mesoscopic parameters of residual soil was then constructed through parameter fitting. Using this model, the impact of frost-thaw on slope deformation behaviors was analyzed. A simulation revealed that displacement primarily occurred at the slope toe and the area of influence expanded with an increasing number of freeze-thaw cycles. As freeze-thaw cycles increased, the stress distribution in the X-direction along the top and surface of a slope became more concentrated, impacting mesoscopic parameters. Conversely, the stress in the Z-direction on the slope dispersed across three slopes after four to eight freeze-thaw cycles, with considerable influence during the initial four cycles. The flexible boundary created using the laminated-wall approach and the freeze-thaw damage model of the mesoscopic parameters facilitated an effective understanding of the freeze-thaw effect on residual soil obtained from an STF area.