Experimental and Numerical Simulation Studies on Water and Salt Migration in Loess-Like Sulfate Saline Soils under Evaporation Conditions

Loess-like sulfate saline soils are prevalent in the arid and semiarid regions of northwest China. Their engineering properties are highly unstable due to the dynamic interactions among water, heat, salt, and energy, which are influenced by climate change. Evaporation, in particular, has a significant impact on shallow saline soils, leading to the redistribution of salts. The water–salt migration behavior of loess-like sulfate saline soils under evaporation was investigated through numerical modeling and laboratory soil column experiments to better understand these processes. The findings reveal that an increase in initial salt content significantly reduces the soil’s evaporation rate. Specifically, as the initial salt content rises from 0.5% to 1.5%, 3%, and 5%, the initial evaporation rate decreases by 16.9%, 32.3%, and 44.2%, respectively. Additionally, higher initial salt content corresponds to increased soil water content. There is obvious water–salt migration at soil depths of 0 to 25 cm. The phenomenon of water and salt migration was more pronounced in the shallower layers of the soil. At a depth of 35 cm, the content of water and salt was close to the initial values. Under conditions of extreme evaporation intensity, the initial evaporation rate is markedly higher compared to that under laboratory conditions. Extreme evaporation intensity also significantly influences the soil water content at depths of 0 and 5 cm, with its effects most pronounced during the early stages of evaporation. Over time, the duration of evaporation plays a more critical role in altering the water and salt content of shallow soil layers than in salt migration. However, the impact on salt migration is more significant than its effect on water migration.