To study the effect of increased rainfall on the heat and mass transfer and deformation characteristics of sulfate saline soil, a geometric similarity ratio model (1:6) of the natural site was created inside the self-developed indoor baseplate-atmospheric dual-temperature control model box. For the first time, combined with the characteristics of the surface energy change, the characteristics of water-heat-salt-mechanical coupling changes within sulfate saline soil under normal rainfall and twice the increase in rainfall were studied. The results show that the increased rainfall leads to a more significant decrease in upward shortwave radiation and downward longwave radiation, as well as a more significant increase in the surface net radiation and surface evaporation rate. Additionally, the increase in rainfall leads to an obvious cooling trend in the surface temperature. Compared with normal rainfall, an increase in rainfall leads to a significant increase in soil water content and conductivity, while soil heat flux and temperature significantly decrease. The increased rainfall caused a temperature drop of 1.6 degrees C at 5 cm of saline soil. Moreover, the increased rainfall leads to an increase in the heat release time of sulfate saline soil. Meanwhile, the impact of increased rainfall on the soil water content, conductivity, and temperature gradually weakens with increasing depth. The increased rainfall can exacerbate thawing settlement deformation and alleviate salt frost heave deformation. Compared with normal rainfall, twice the increase in rainfall results in a 0.9 mm increase in thawing settlement deformation and a 2.5 mm decrease in salt frost heave deformation.

The theoretical and experimental studies have been carried out on the water and salt migration and deformation characteristics of sulfate saline soil during freeze-thaw cycles. Based on the theory of unsaturated soil mechanics and the thermoelastic continuum and considering the influence of phase change within the pore on thermodynamic and hydrodynamic parameters, the multi-physical fields coupled model of hydro-thermal-salt-mechanical in unsaturated sulfate saline soil has been established. The variation processes of the temperature field, water field, salt field, and stress field of the soil during freeze-thaw cycles were analyzed, and the validity of the theoretical model was verified by indoor experiments. The results show that there are significant attenuation and hysteresis effects when heat is transferred in the soil during freeze-thaw cycles. The water content of migration in the soil increases with the height of the soil column, while the increment of migration water content decreases with the number of freeze-thaw cycles. The formation and dissolution of salt crystals from top to bottom and the sudden increase in the salt crystallization rate are mainly caused by variations in the solubility of the salt solutions due to temperature changes. The formation and dissolution of ice and salt crystals in the soil induce expansion and contraction, and the freeze-thaw cycle conditions have a significant effect on the expansion and residual deformation of the soil.

Salt weathering is a common deterioration phenomenon that affects outdoor cultural properties, and it is important to precisely predict the heat, moisture, and salt transfer in porous materials to suppress salt weathering. Osmosis and osmotic pressure were considered in the field of soil research, especially in clay research, but not in the field of outdoor cultural properties and building materials, which are the main target of salt weathering. Osmosis in clay is supposed to be caused by its surface charge. However, it has been suggested that sandstones and bricks that constitute cultural properties and buildings also have surface charge as clay. Thus, osmosis and osmotic pressure can occur in building materials, which may lead to materials degradation. In this study, we derive basic equations, based on nonequilibrium thermodynamics, for the simultaneous heat, dry air, water vapor, liquid water, cation, and anion transfer in building materials by considering osmosis. This equation was compared with existing model for heat and moisture transfer equations as well as models that considered the salt transfer. Based on the previous research for osmosis in clay, we summarized conditions under which osmosis occurs in building materials and presented an outlook for modeling the physical properties of materials related to osmosis.

Hydrothermal processes are key components in permafrost dynamics; these processes are integral to global warming. In this study the coupled heat and mass transfer model for (CoupModel) the soil-plant-atmosphere-system is applied in high-altitude permafrost regions and to model hydrothermal transfer processes in freeze-thaw cycles. Measured meteorological forcing and soil and vegetation properties are used in the CoupModel for the period from January 1, 2009 to December 31, 2012 at the Tanggula observation site in the Qinghai-Tibet Plateau. A 24-h time step is used in the model simulation. The results show that the simulated soil temperature and water content, as well as the frozen depth compare well with the measured data. The coefficient of determination (R (2)) is 0.97 for the mean soil temperature and 0.73 for the mean soil water content, respectively. The simulated soil heat flux at a depth of 0-20 cm is also consistent with the monitored data. An analysis is performed on the simulated hydrothermal transfer processes from the deep soil layer to the upper one during the freezing and thawing period. At the beginning of the freezing period, the water in the deep soil layer moves upward to the freezing front and releases heat during the freezing process. When the soil layer is completely frozen, there are no vertical water exchanges between the soil layers, and the heat exchange process is controlled by the vertical soil temperature gradient. During the thawing period, the downward heat process becomes more active due to increased incoming shortwave radiation at the ground surface. The melt water is quickly dissolved in the soil, and the soil water movement only changes in the shallow soil layer. Subsequently, the model was used to provide an evaluation of the potential response of the active layer to different scenarios of initial water content and climate warming at the Tanggula site. The results reveal that the soil water content and the organic layer provide protection against active layer deepening in summer, so climate warming will cause the permafrost active layer to become deeper and permafrost degradation.