Effects of freeze-thaw cycles on the deformation and microstructure of silt

In cold regions, freeze-thaw cycles affect the deformation and structure of silt. Identifying the characteristics of silt settlement during freezing and thawing is essential for understanding its deformation behavior and improving frost protection. In this study, silt samples were subjected to seven freeze-thaw cycles. Local deformation development was monitored using particle image velocimetry to reveal the underlying microscopic mechanisms. Subsequently, the changes in the microscopic porosity of pulverized soil before and after undergoing freeze-thaw cycles were evaluated using scanning electron microscopy along with mercury-in-pressure porosimetry. Finally, the effects of temperature and moisture on soil deformation and the relationship between the deformation and microstructure were discussed. The results showed that temperature-driven water transport, redistribution, and microstructural changes due to ice-water phase transition were the main causes of soil deformation. During initial freezing, compressive deformation occurred at the top, followed by expansion. During thawing, the soil generally showed a compressive deformation. However, at the beginning of thawing, expansion deformation occurred at the top. After four freeze-thaw cycles, the soil stabilized and showed overall expansive deformation. After seven freeze-thaw cycles, the pore space structure of the soil changed from a small pore space to a medium pore space and then to a large pore space; the pore contour lines became simpler; and the soil structure changed, ultimately leading to expansion and deformation. Our findings shed new light on the deformation mechanism of silt and can help ensure the safety of infrastructure construction in cold regions.