Hydro-thermal behaviors of the ground under different surfaces in the Qinghai-Tibet Plateau

Abstract

The hydro-thermal properties of the ground affect the thermal regimes and surface energy balances. A field experiment in the Qinghai-Tibet Plateau was carried out to analyze the hydro-thermal boundaries, and the variations of the ground temperatures, volumetric unfrozen water contents and matric suctions for different surfaces (i.e., asphalt surface, concrete surface and natural gravel surface). The results show that the asphalt surface significantly changes the permafrost table and ground temperature. The mean annual temperature under the asphalt surface is 2.40 °C higher than that under the concrete surface, and 2.77 °C higher than that under the natural gravel surface. Therefore, the permafrost table under the asphalt surface is deeper than that under the natural gravel and concrete surfaces. In addition, the freezing and thawing processes of the ground under different surfaces are significantly different. Moreover, the volumetric unfrozen water content changes quickly near the ice-water phase transition zone, while the matric suction seldom changes until the volumetric unfrozen water reaches a certain value during the cold seasons, and the volumetric unfrozen water content dramatically changes due to the rainfall during the warm seasons. Furthermore, the volumetric unfrozen water content first decreases, and then increases with depth in the cross sections of the embankments during the cold seasons. The minimum volumetric unfrozen water content lies at the depth of 0.40 m for the natural gravel surface, and 0.90 m for the asphalt and concrete surfaces.