Abstract: Moisture-temperature coupling control equations are introduced into the heat and mass balance equation for the consideration of phase change. Smoothed Particle Hydrodynamics method is used to solve the equations, where both moisture transfer driven by temperature and heat transfer by water are considered. While the phase transition process is ignored, the model can directly degrade to a generic coupled model of moisture and heat at normal temperature. Therefore it can be used to study freezing and thawing cycle of frozen soils (e. g., seasonal or daily variation in ground temperature). To validate the model, the solution of a semi-infinite unsaturated porous medium subject to a frozen wall is studied. The comparison result shows that the process of moisture migration impacts on heat transfer, with the degree intensifying as time. In addition, the model is used in an unsaturated subgrade with periodical temperature boundary. The temperature and moisture distribution of subgrade are different when considering different solar radiation in sunny and shady slope. The evolution of water content field and thermal field is given at the end. Since the algorithm can basically reflect the real physical process of phase change, it’s credible to study other problems in the field of frozen soil by SPH method.

Key words: unsaturated porous media, phase change, hydro-thermal coupling, SPH method, subgrade