A water-heat-vapor coupling model of unsaturated frozen soil is established based on energy and mass conservation equations by considering ice-water and water-vapor phase changes

and influences of heat transfer by water vapor and temperature potential on water vapor migration are also considered. The smoothed particle hydrodynamics (SPH) can be used to calculate their evolution process conveniently. In the solution

ice content and vapor content are solved at first

and then followed by solving of unfrozen water content and temperature field. With two steps as such

coupling of temperature field between water and vapor field is implemented. Distributions of unsteady temperature field

volumetric moisture content and water vapor flux in semi-infinite medium with thermal boundary conditions of the first kind are simulated. The results are compared with the analytical solutions without coupling. The water and vapor transfer shows a greater impact on the thermal field. Under the seasonal periodic temperature boundary

the distributions of thermal field and volume moisture content of embankment section are predicted in high compatibility with the actual data

which can well reveal the characteristics of water-thermal-vapor transfer and its phase transformation in unsaturated frozen soil.