Numerical study on effect of natural wind and piston wind on anti-freezing length of tunnels with high geo-temperature in cold region

Abstract

Taking Zilashan Tunnel as an example, a three-dimensional unsteady heat transfer model of surrounding rock, tunnel lining and wind flow was established. The reliability of the temperature calculation model was verified by a 1:30 model test and field test. The influences of natural wind speed, natural wind temperature, train speed and traffic volume on the anti-freezing length of tunnels in cold regions were studied. In particular, this paper focuses on the influence of piston wind direction on the anti-freezing length of the tunnel during 50 years of operation. The results show that the maximum anti-freezing length is positively correlated with the velocity of the natural wind, and the maximum anti-freezing length increases by 787 m on average when the velocity of the natural wind increases by 1 m/s. The maximum anti-freezing length is 2352 m when only the influence of natural wind is considered. When the average temperature of the natural wind is greater than 5 °C, the anti-freezing length of Zilashan Tunnel is 0 m. The maximum anti-freezing length increases with the increase of train speed. The anti-freezing length is the longest when the natural wind is in the same direction as the piston wind, and the minimum anti-freezing length is more than 1200 m under different train speeds. When the traffic volume is 20 trains/day, the anti-freezing length increases with the increase of train speed regardless of the direction of piston wind. Under most working conditions, the surrounding rock near the tunnel entrance will freeze; when the traffic volume is greater than 20 trains/day, the surrounding rock near the tunnel exit will freeze with the natural wind speed and train speed at 1.5 m/s and 200 km/h respectively.