Deformation mechanisms of salt-frost heave and dissolution-thaw collapse in sulfate saline soil

To clarify the deformation mechanisms of sulfate saline soil in seasonally frozen regions, this study develops a coupled water–vapor-heat-salt-mechanics (WVHSM) model that explicitly incorporates vapor diffusion, phase-transition crystallization, and mechanical responses. The model is evaluated against F-T cycling experiments under water-salt replenishment conditions and supported by microstructural observations. The results show that it can reasonably reproduce the measured temperature evolution, water-salt redistribution, and deformation responses during F-T processes. Under F-T action, freezing-induced suction drives the coordinated migration of water and salt toward the freezing front, exhibiting a pronounced “salt migration with water” behavior and forming an enriched “pot-cover effect” in the surface layer. Regarding the crystallization process, in addition to supersaturation-induced precipitation, the model also considers the contribution of solute rejection associated with ice crystal growth. The simulation results suggest that incorporating this effect helps better describe the cumulative growth and volumetric expansion of salt crystals under the present testing conditions. Microstructural results further indicate that repeated F-T cycles promote the evolution of fine pores into larger pores and connected cracks; structural damage weakens the skeletal constraint of the soil while significantly enhancing permeability, thereby aggravating salt accumulation. Based on these findings, a multi-physical cyclic feedback mechanism of “replenishment-crystallization-damage-dissolution” under groundwater supply conditions is proposed as an important process underlying salt-frost heave and dissolution-thaw collapse in sulfate saline soil. These findings provide a theoretical basis for understanding the F-T-crystallization coupling mechanism of sulfate saline soil and offer a model reference for infrastructure design, long-term service performance evaluation, and hazard prevention in saline regions.