A theoretical model for ground surface temperature under seasonal snow cover condition and numerical application in THM coupling of permafrost subgrade

Snow possesses poor heat conduction properties due to its high reflectivity and low thermal conductivity, which significantly influences the energy exchange between the ground and the atmosphere. The randomness of the change in snow depth also exacerbates the complexity of the frost damage problem in highway engineering in cold regions. The conventional snow model is predicated on empirical formulas and a plethora of undetermined parameters, which renders it challenging to achieve the efficient integration of the dynamic change of snow depth and the multi-physical field coupling process of frozen soil. In this study, we proposed a simple and efficient method to equivalent the dynamic boundary conditions to periodic time-varying boundary conditions for simulating the variation of ground surface temperature under seasonal snow cover conditions. The accuracy of the method was verified using measured data. The present study developed a functional relationship between land surface temperature and ground surface temperature in seasonal snow cover areas by comparing the differences in the variation of ground surface temperature under the conditions of four kinds of snow melting time and seven kinds of maximum snow depths in the annual cycle. Finally, based on the engineering geological information of the surveyed Genhe-Mangui highway, we established a thermal-hydro-mechanical (THM) coupling model of permafrost snow-covered subgrade, and fully considered the randomness of the maximum snow depth. This work can provide a practical theoretical model for predicting the ground surface temperature of snow-covered ground, and offer a novel understanding of the frost damage caused by snow-covered subgrade.