Equations and numerical simulation for coupled water and heat transfer in frozen soil

Frost heaving and thaw collapsing are the main defects of subgrade in permafrost areas and are highly related to the coupled heat-moisture migration. Based on the water flow theory of unsaturated soil and the heat transfer theory of soil, the differential equations for coupled water and heat transfer are established. The coupled water and heat transfer problem of frozen soil is solved using the secondary development of COMSOL Multi-physics. To verify the method for simulating the heat-moisture coupled process, the freezing and thawing processes of soil columns are simulated, and the results are compared with the measured data from laboratory tests. Finally, a case study is carried out for the subgrade in Maduo county, Qinghai Province, and the characteristics of the coupled heat-moisture migration in permafrost subgrade are analyzed.