Study of a strength prediction model of unsaturated compacted expansive soil under freeze–thaw cycles

The physical and mechanical properties of expansive soil are degraded under the influence of freeze–thaw cycles due to the phase change of water in the soil, resulting in serious engineering disasters. Unsaturated expansive soil’s stress–strain relationship, elastic modulus, shear strength, and other mechanical parameters are studied. The results show that (1) when the water content does not exceed the optimal water content, strain softening occurs. When the moisture content exceeds the optimum water content, the expansive soil’s stress–strain curve shifts from strain softening to strain hardening. (2) Freeze–thaw cycles have a greater impact on the strength of expansive soil with high moisture content, with the greatest strength damage occurring after the first freeze–thaw cycles. Additionally, a prediction model for the failure strength of unsaturated compacted expansive soil under the coupling action of freeze–thaw cycles and initial moisture content change was developed, providing a theoretical foundation for the engineering construction of unsaturated expansive soil in seasonal freezing regions.