Comparative study of relating equations in coupled thermal-hydraulic finite element analyses

The generalized Clapeyron equation, the experimental curve of the water content and the porosity constraint condition are relating equations for coupled thermal-hydraulic analyses (THA). Based on a literature review and numerical case studies, the applicability of each of these relating equations is discussed for the THA of high-speed railway subgrades in cold regions. The efficiency of each relating equation is assessed through a series of numerical case studies and comparisons with experimental results. Based on the heat transport and water migration equations, the results indicate that the generalized Clapeyron equation and the experimental curve of the liquid water content can effectively reproduce the temperature variation, water migration and phase transition in a single one-way freezing process with the sufficient replenishment of water in unfrozen regions. Furthermore, the porosity constraint condition is applicable as a relating equation for freezing unsaturated soils with vapours and saturated soils with little water migration.