Numerical study of the thermal characteristics of a shallow tunnel section with a two-phase closed thermosyphon group in a permafrost region under climate warming

Permafrost is very sensitive to temperature changes. Climate warming would cause the increase of ground temperature and accelerate the degradation of permafrost. One of the important future issues is how to control ground temperature to meet the demand of the engineering stability in permafrost regions under climate warming. In this study, a two-phase closed thermosyphon (TPCT) group is applied to adjust and control the ground temperature for a shallow tunnel section in a permafrost region. A composite heat transfer model, including the air turbulent heat transfer inside the tunnel, the air-TPCT-soil coupled heat transfer for the TPCT group, and the heat conduction with phase change in the soil layers and the tunnel structure layers, is developed for the tunnel with a TPCT group. The numerical results indicate that under the climate warming, the TPCT group can cool down the soil layers in the shallow tunnel section and ensure the thermal stability of the tunnel. Therefore, we conclude that it is an effective method to adjust the ground temperature of permafrost, without active control instrumentation or aid of other external energy. The research results could also provide help for applications of TPCTs in other cold regions engineering.