Ambient temperature prediction model and cooling requirement analyze in the high-altitude construction tunnel passing through the abnormally high geothermal region

The investigation of the ambient temperature distribution in tunnels with abnormally high temperatures during the construction period, as well as the calculation of the cooling demand around the working face are important for high-temperature tunnels. After analyzing the heat transfer mechanism of one-end ventilation, the finite difference method was applied for establishing the ambient temperature forecast model. In addition, the ambient temperature variation characteristics were explored combination with tunnel geotemperature distribution considering the impacts of wind temperatures and volumes. The following are the main conclusions: (1) The difference between predicted data and actual monitoring data, which was less than 0.077. (2) When the air leakage rate is reduced from 5% to 1%, the maximum ambient temperature is reduced by 2.2 ℃, and the location of the highest ambient temperature moved away from the working face. (3) The ambient temperature distribution (from the tunnel excavation face to the entrance) showed a growing and then decreasing trend when the tunnel construction length was in the range of 2000 m. And as the construction length extended to 2990 m, the ambient temperature distribution showed the trend of increasing → decreasing → increasing → decreasing. (4) As the wind volume was greater than 120 m3/s and the wind temperature was below 10 °C, there was no cooling capacity gap within 100 m of the tunnel excavation face.