Adapted Critical Ambient Temperature at the Entrance of Tunnel to the Maximum Ventilation Cooling Capacity

It is normal practice to combine ventilation and mechanical cooling to solve the issue of heat damage in the high geothermal and deeply buried long tunnel of Darui Railway in Gaoligongshan. For a certain area under construction, when the ventilation cooling capacity reaches the limit and the air temperature in the tunnel cannot meet the specifications, mechanical refrigeration equipment must be turned on. Therefore, an axisymmetric two-dimensional heat conduction model of the surrounding rock combining radial and axial heat flow is derived, and an air heat exchange model is given. Analytical solutions of air temperature in tunnels are further deduced; also, the calculation results match well with the data measured in practice. The critical atmospheric temperature at the entrance is solved iteratively when the maximum air temperature near the excavation face is 28 ℃ under different return air speeds and underground hot water heat dissipation power in the tunnel, considering the slagging process of a specific area under construction as an example. It was found that the critical temperature is negatively correlated with the heat-dissipated power of underground hot water and positively correlated with the return air velocity. Compared to the local meteorological conditions, one can obtain the change block of the ambient temperature at the entrance with ventilation cooling alone when the temperature near the working face meets the specification requirements and further develop the plan of refrigeration equipment operation.