Study on Stability of Soil Slope in Seasonally Frozen Region Based on Water Transfer and Strength Deterioration under Freeze–Thaw Cycles

Based on the water–heat coupling model, this paper analyzes water migration laws and the change characteristics of the freeze–thaw interface under freeze–thaw cycles to determine the linkage migration range of the slope water state and the most unfavorable potential sliding surface. Then through freeze–thaw cycle tests and triaxial compression tests, the strength deterioration law of slope soil in the freeze–thaw area under freeze–thaw cycles is determined. Finally, a stability calculation method of seasonally frozen soil slopes under long-term service is established, using the limit equilibrium strip method. The results show that: the maximum freezing depth increases slowly with the number of freeze–thaw cycles and then stabilizes. The most unfavorable potential sliding surface will also inevitably migrate in association with the maximum freezing depth. The total volume moisture content of the slope tends to increase slightly with the number of freeze–thaw cycles when there is groundwater recharge in the seasonally frozen soil slope. In seasonally frozen soil slopes under long-term service, the thawing area during spring thaw is commonly saturated or oversaturated. With the increase in the number of freeze–thaw cycles, the soil cohesion and internal friction angle of the slope in the freeze–thaw area decrease rapidly at first and then gradually become stable. Therefore, the slope stability coefficient also presents the same progressive law. The first three freeze–thaw cycles have a greater influence on the stability of the slope. Managing slope instability caused by freeze–thaw cycles during the service period is crucial in designing seasonally frozen soil slopes.