Temperature distribution and freezing range of a railway tunnel in cold regions under high-speed train piston effect

High-speed train piston effect redistributes the temperature field and increases the frost damage of tunnel in cold regions. To reveal the temperature distribution and freezing range of a tunnel in cold regions under train piston effect, field monitoring and simulation studies are conducted. The results indicate that piston effect causes the air pressure in tunnel to fluctuate violently, and creates a pressure difference between train head and train tail. As a high-speed train enters tunnel, air in front of train head is pushed toward the tunnel exit, while air outside the tunnel is drawn into the tunnel, and flows toward the low-pressure zone behind train tail. Under the influence of piston effect, the tunnel temperature decreases, the freezing length increases from 1462 to 1605 m, and the freezing depth is also amplified. The maximum and minimum freezing depths occur at tunnel entrance and tunnel exit, respectively. The most significant effect is located at the tunnel side wall close to train. Air temperature at the tunnel site, train speed and train formation length have significant influence on the freezing range. Both the freezing length and freezing depth increase with lower air temperature, higher train speed and longer train formation.