Study on Soil-Water Characteristics and Micro-Mechanism of Sulfate Saline Soil under Freeze-Thaw Action

In order to study the soil-water characteristics and micro-mechanism of sulfate saline soil under freeze-thaw-salt coupling, the soil-water characteristic curves of saline soil with different salt content were tested and fitted with Gardner model, van-Genuchten model, and Fredlund-Xing model, and the microstructure and pore distribution characteristics of sulfate saline soil under freeze-thaw-salt coupling were analyzed. The results indicate that the volumetric water content of sulfate-salted soil decreases as matrix suction increases, with the resulting curves exhibiting a single-peak inverse ‘S’ shape. Notably, for a given volumetric water content, higher salt concentrations correspond to increased matrix suction. Freeze-thaw cycles promote the microstructural disintegration of the soil, leading to an increase in large pore volume and overall porosity. Following these cycles, both the matrix suction and volumetric water content of the soil samples decreased, causing the soil-water characteristic curve to shift leftward with an increasing number of freeze-thaw cycles.To evaluate the test results of saline soil, the G model, V-G model, and F-X model were employed. The F-X model exhibited a low fitting correlation coefficient, while the V-G model demonstrated poor fitting in both high and low suction phases. In contrast, the G model provided an overall good fitting performance. The microstructural changes in soil samples resulting from freeze-thaw actions are critical factors contributing to the reduction of the soil's water-holding capacity. The progressive development of pores and fissures in the samples, influenced by freezing, thawing, and salinity, facilitates the migration of water equilibrium.