Analysis of the water-vapor-heat coupling migration of unsaturated soil slope in seasonal frozen regions

An unsaturated seasonal frozen soil slope of the Dandong-Altay highway is used as the research object. This paper is based on vapor-liquid migration and heat conduction multi-field coupling theory. The ice-water phase transition and vapor-liquid transition of water are also considered. The empirical relationship between unfrozen moisture content and ice volume fraction is introduced. A numerical model of the whole freeze-thaw process is established. The results show that: during the freezing period, the freezing depth increases faster before the temperature drops to the annual minimum temperature. Before entering the thawing period, the freezing depth is close to the maximum. After entering the thawing period, ice melting continuously absorbs heat from the frozen layer. Under the two-way action of external warming and geothermal heat, the deep freezing depth does not decrease for a long time. But it increases slowly and then decreases gradually. When the unsaturated soil slope is unfrozen, the engineering hazards of the slope caused by the migration of vapor are relatively small. After it enters the freezing state, the influence of vapor migration will increase significantly. The total volume moisture content of the frozen area is about 0.08 m3/m3 higher than without considering vapor migration.