Influence of Convection Term on Temperature Field during Soil Freezing

In recent years, the numerical model of frozen soil has mainly focused on the water-heat equation of unsaturated soil, which is of great significance to predicting engineering stability in frozen soil areas. In these numerical models, the change of freezing temperature is usually ignored, and 0 °C is often used as the freezing condition. In addition, most equations only consider the effect of latent heat released during water freezing on the frozen soil and ignore the effect of high-temperature water on the heat transfer of frozen soil when unfrozen water migrates to the frozen zone. Therefore, there will be deviations under long-time simulation. At the same time, due to excessive attention to the moisture field and neglect of the selection of the temperature field, there is no clear conclusion on when to choose the heat transfer equation with the convection term. The equation in this paper considered the change of freezing temperature under different initial saturation conditions and the convection effect during moisture migration. Through COMSOL 5.5 software simulation, they were combined with the experiment to verify. Three different hydrothermal equations were selected to analyze the effects of latent heat and the effects of convection on the temperature field under different initial saturation conditions. The results show that the convection term plays an essential role in the heat transfer equation for unsaturated soil with high initial saturation. Additionally, the frost heave occurs mainly above the ice front interface. This study provides a reference for when to choose the heat transfer equation with convective terms and can provide help for the construction and prediction of frozen soil in the future.