Investigation of critical tunnel length based on the maximum positive pressure on the trailing carriage of a high-speed train

The passage of a high-speed train through a tunnel exposes it to substantial tunnel pressure waves that are heavily affected by the length of the tunnel. Although there are different criteria for determining the critical tunnel length, none of them consider the characteristics of the maximum positive pressure experienced by the trailing carriage, which has been encountered in field tests in China. To address this problem, by dividing the process of train–tunnel interaction into three stages based on their spatial relationship and analyzing the effects of the train wave signature (TWS), four pressure states on the train were summarized. In particular, for the measuring points located on the trailing carriage, a maximum positive pressure can be observed when the pressure state aligns with the state characterized by the TWS reflecting at the tunnel entrance and partially passing through the measuring location. Therefore, the corresponding critical tunnel length was derived based on this time relationship. Its effectiveness was validated using field test data. The current study will provide valuable insights into the aerodynamic behavior of high-speed trains running in tunnels, contribute to the optimization of tunnel design, and ensure the safety and amenity of railway transportation.