Abstract: When a high-speed train passes through a tunnel with a 25‰ single-sided slope, the internal and external pressure wave generated by the high speed of the train couples with atmospheric pressure changes, resulting in distinctive internal and external pressure variations. Therefore, it is necessary to study the aerodynamic loads and in-train pressure comfort of high-speed trains passing through steep tunnels under various atmospheric pressures. In this study, real-train test methods are employed to obtain internal and external pressure data of a high-speed train passing through the Xi′an Bei station-Hanzhong station of the Xi′an-Chengdu high-speed railway. The results demonstrate the following: (1) When a single train descends through a 25‰ extra-long tunnel, the external pressure variation trend is consistent with the changes in atmospheric pressure due to decreasing tunnel altitude. (2) As the tunnel length increases from1 541.2 m to 8 399.2 m for both uphill and downhill single-sided slopes, the maximum internal and external pressure peaks of the train occur closer to the tunnel exit. Additionally, the maximum internal and external pressure peaks of the train increase linearly with the tunnel length. (3) As tunnel length increases, the airtightness of the train′s head and tail continuously decreases, resulting in an increase in the Δp/1 s, Δp/3 s, Δp/10 s, and Δp/60 s, which correspondingly leads to a deteriorating in-train pressure comfort environment. When the train passes through long, steep tunnel groups, both the train′s airtightness performance and in-train comfort environment worsen. (4) Compared to the logic control of the pressure protection valve, keeping the pressure protection valve closed throughout the journey results in smaller internal pressure variations and maximum pressure changes at different time intervals, thereby improving the in-train comfort environment.

Key words: long tunnels with steep slopes, tunnel groups, internal and external pressure, pressure comfort environment, real-train test