Quantification of chloride saline soil freezing-thawing temperature threshold based on thermodynamic theory

The salinity and soil structure are crucial to the freezing and thawing characteristics of soils in saline soil area. Here, we developed a high-precision freeze-thaw temperature model for chloride-salted soils. The temperature threshold for the soil freeze-thaw cycle, which is both physically meaningful and easily measurable and quantifiable, was determined based on experimental observations. Moreover, we examined the relationship between soil freeze-thaw characteristics and the levels of salt content and soil type. Specifically, in the testing of more than 60 soil samples made from different salt contents of sand, silt, and silty clay, the freezing-thawing temperature model shows RMSE = 0.5 K and MPAE = 0.16%. The maximum/minimum value of the soil temperature curve slope can be used to determine the starting and ending temperatures of freeze-thaw cycles, which represents the release rate of phase change latent heat from the side. Sand exhibits greater sensitivity to salt content in terms of freeze-thaw properties. When the salt content > 0.4%, the minimum supercooling point, maximum superheating point and equilibrium freeze-thaw point of sand are lower than those of silty clay. However, the freezing end point and melting starting point consistently conform to the sequence "sand > silt > silty clay", which is due to their reliance on the bound water content and its bound strength. We provide a comprehensive analysis of the freezing-thawing properties of saline soils. These findings provide valuable guidance for establishing temperature boundary conditions in numerical simulations for cold zone engineering purposes.