Numerical study of the thermo-mechanical behaviour of energy tunnels under terrain asymmetric loads in cold regions

The integration of heat exchanger pipes into the lining of energy tunnels enables active heating to prevent frost damage, particularly in the entrance sections of tunnels in cold regions. These entrance sections are typically shallow and may feature varying slope angles. However, the non-uniform ground thermal response and tunnel thermally induced stress distributions induced by the asymmetric geometry are not adequately addressed in existing research focused on symmetric or level-ground conditions. This study specifically targets these critical gaps by investigating the coupled thermal and mechanical response in such challenging settings. Through numerical simulations, this paper examines the thermo-mechanical behaviour of tunnels equipped with heat exchange pipes during frost conditions, focusing on a high-latitude asymmetric terrain tunnel. The paper further explores the impact of tunnel burial depth and slope angle on the mechanical response during thermal operation. The simulation results demonstrate that the heat exchange pipes can prevent the development of sub-zero temperatures to the surrounding rock and mitigate frost damage to the tunnel structure. However, without insulation, the system exacerbates the development of tensile stresses. Regarding burial depth, the mechanical response of the tunnel is significantly affected within a specific range but stabilizes as depth increases. Comparatively, slope angle has a smaller overall impact on mechanical response. Nevertheless, as the slope angle increases, the influence of thermal operations on asymmetry becomes more pronounced. The findings of this study provide valuable insights into the design and optimization of energy tunnels in cold regions, contributing to their long-term safety and sustainable operation.