Influence of mechanical wind heated by ground temperature on ambient temperature in tunnels: Numerical modeling, case study and analysis

A numerical heat transfer model of a tunnel in a cold region is proposed, and the accuracy of the model is verified by a laboratory model tunnel and field test. The effects of natural airflow velocity, natural airflow temperature, mechanical airflow velocity and jet fan operation time on ambient temperature in tunnels with high ground temperature are investigated. The result shows that mechanical ventilation can effectively reduce the range of ambient temperature below 0 °C in tunnels (RATB) with high ground temperature in a cold area. The lower the natural airflow temperature, the better the temperature control effect of mechanical ventilation. The RATB of Zilashan tunnel will exceed 5000 m without considering the influence of mechanical ventilation with natural airflow velocity at 3.0 m/s. The RATB decreases linearly with mechanical ventilation under different natural airflow velocities, natural airflow temperatures and jet fan operation time. Increasing the mechanical airflow velocity cannot effectively reduce the RATB considering the influence of mechanical ventilation with natural airflow velocity higher than 2.0 m/s. When considering mechanical ventilation to prevent freezing injury to the tunnel, the jet fan operation time shall not be less than 3.0 h. The longer the operation time of the jet fan, the faster the attenuation rate of RATB. When the jet fan operation time is 5.0 h, the attenuation rate of RATB is 8.6 times greater than when the jet fan operation time is 1.0 h with natural airflow velocity at 1.50 m/s. The existence of an insulation layer will greatly increase the antifreeze length of rock and antifreeze length can be controlled within 650 m under proper ventilation conditions in the Zilashan tunnel.