A novel transport model to predict the moisture-heat-gas-salt behavior in unsaturated saline soil under evaporation

Soil desertification and salinization are common in arid and semi-arid regions, and can result in roads being buried by quicksand or corroded by salts. Therefore, it is important to investigate the salt transportation under evaporation in these regions. To analyze the transport law of moisture, heat, gas, and salt in unsaturated saline soil, a series of evaporation tests were conducted. Based on these tests, the novel mass and energy conservation equations suitable for medium transfer in unsaturated saline soil were then developed. In the model, the non-equilibrium phase process between the liquid water and vapor was considered. Meanwhile, the convective heat transfer caused by small temperature difference between the liquid pore water and soil grains was also considered. Validation of the model was illustrated by comparisons between the simulation and experimental results. It is found that the evaporation of pore water is accompanied by the precipitation of solute. The vapor condensation at low temperature zone can dilute the solute concentration. In addition, the permeability of surface has significant effect on the moisture-heat-gas-salt migration. The novel model can effectively describe the moisture-heat-gas-salt interaction process and reveal the temperature difference between soil grains and pore fluid under the evaporation of pore water.