Numerical study on the hydro-thermal-chemical–mechanical coupling mechanism in sulfate saline soil under freeze–thaw cycles

Water-heat-salt migration inevitably leads to instability and failure in roads, slopes, channels, and tower foundations in sulfate saline soil regions undergoing freeze–thaw (F-T) cycles, severely compromising the safety and stability of long-term operations in cold region engineering. F-T tests were performed on sulfate saline soil under different F-T cycle modes to investigate the impact of F-T cycle frequency and cooling duration on water-salt transfer and soil deformation. This study revealed the coupled mechanism of water-heat-salt-mechanics in sulfate saline soil under variable F-T conditions and established a hydro-thermal-chemical–mechanical coupled model. The study indicates that the progression of salt spatiotemporal distribution during F-T cycles are initial salt accumulation in the frozen zone near the freezing front, an upward shift of the salt peak, salts redistribution as subflorescence and efflorescence, and surface salt accumulation. These factors are closely related to soil deformation. Longer cooling durations promote salt accumulation near the freezing front, while shorter durations and more F-T cycles encourage salt migration to the surface layer. The model’s reliability is validated by the good agreement between calculated results and experimental data. Understanding these multiphase-multifield coupling mechanism in sulfate saline soils can help address engineering issues associated with salt-frost heave.