Abstract: Based on qualitative understanding of the so-called pot-cover effect on moisture transport in the road subgrade soil, a mathematical model is proposed to analyze multi-phase transportation, heat conduction, and water-vapor transition. A one-dimensional finite element model for subgrade soil column is developed to investigate moisture transport and phase change under temperature gradient, as well as the mechanism and influencing factors of pot-cover effect. The numerical results indicate that the temperature profile and soil texture may have significant influence on pot-cover effect. Pot-cover effect is more likely observed in silt subgrade than in sand or clay subgrade. The temperature profile of lower temperature at the top subgrade more easily leads to the pot-cover effect. These results provide reference for further understanding the pot-cover effect in subgrade soil.

Key words: unsaturated soil, pot-cover effect, multi-phase flow, phase transition model