Numerical study on ventilation cooling in a high geothermal tunnel of the Sichuan-Tibet Railway considering the tunnel drilling process

Ventilation cooling is a crucial measure to solve the high temperature hazards in high geothermal tunnels of the Sichuan-Tibet Railway during construction. In this paper, two numerical models of a cross tunnel in the Layue Tunnel were developed using the finite volume method to investigate the impact of tunnel drilling process and ventilation parameters on tunnel ventilation under various surrounding rock temperatures. The heat generated by the tunnel drilling process significantly increases the temperature of the tunnel. Furthermore, the presence of construction equipment also affects the velocity distribution. These factors need to be considered in the calculation. The simulation results indicate that the tunnel temperature decreases as the inlet air velocity increases, following a quadratic pattern. Increasing air velocity can also improve the efficiency of tunnel ventilation. Additionally, with increasing inlet air temperature and surrounding rock temperature, the tunnel temperature increases linearly. According to the simulation results, the functional relationship between tunnel temperature, ventilation parameters and surrounding rock temperature has been established. The fitting functions can be used as references for the ventilation design of the Layue Tunnel construction. To reduce the temperature in the work area to 28 ℃ within 40 min, as the inlet air velocity not exceeding 20 m/s and the surrounding rock temperatures are 50 ℃, 60 ℃ and 70 ℃, the inlet air temperature should be lower than 24.9 ℃, 23.7 ℃ and 22.4 ℃, respectively.