Research on the mechanism and theoretical model of water vapor freezing in unsaturated soil subgrade

In seasonally frozen soil regions, changes in relative humidity (RH) within the pores of unsaturated soil subgrade induce the migration and freezing of water vapor (water in the form of a gas resulting from heating water or ice). This phenomenon significantly affects the deformation and strength of the soil. Investigating the freezing characteristics of water vapor in unsaturated soil subgrade and establishing mathematical models are essential for uncovering the mechanisms behind structural disasters in these formations. This study addresses the unique four-phase nature of unsaturated frozen soils. A new formula for the surface tension of water vapor ice interface has been proposed, which solves the key blank of the interface assumption. This enables accurate simulation of water vapor freezing dynamics in unsaturated frozen soil. Modifying the Kelvin equation based on the model of variable pore diameter results in a more accurate representation of the relationship between changing porosity, pore volume, and equilibrium RH during freezing. Regression analysis is conducted using data from the International Association for the Properties of Water and Water vapor. The calculation formula for the saturated vapor pressure of frozen soil below zero degrees is revised. Dynamic water vapor freezing experiments and numerical simulations are performed on sandy soils with varying pore parameters (porosity and pore volume) to verify the necessity of the model of variable pore diameter in water vapor freezing theory. The results demonstrated that the amount of frozen water vapor increases with an increase in pore size and RH. This research primarily lays the foundation for the frost heave theory of water vapor in unsaturated frozen soils and provides a theoretical basis for further multifield coupling studies.