Ventilation Design of an Extra-Long Single-Bore Double-Track Railway Tunnel with High Traffic Density

Harmful gases produced by diesel locomotives tend to accumulate within tunnels, posing risks such as dizziness, vomiting, coma, and even death to the working staff, particularly in long tunnels with high traffic density. As the number of such structures increases, ventilation in extra-long tunnels represents a critical challenge within the engineering area. In this study, the ventilation of an extra-long single-bore double-track tunnel operating with diesel locomotives is investigated. Through scale model tests and based on the inspection sensor data, the natural diffusion patterns of harmful gases under various operating conditions were elucidated. Based on the local resistance coefficient optimization theory and numerical simulations, the ventilation shafts of the tunnel were optimally designed, and an overall ventilation scheme was developed. The ventilation effect of the tunnel was verified through improved scale model tests. The results show that harmful gases primarily diffuse towards the higher elevation tunnel entrance, with only gases near the lower entrance escaping from it. Under the same operating conditions, NO₂ diffuses more slowly than CO, making it harder to discharge. Applying the local resistance coefficient optimization theory, the inclined and vertical shafts of the tunnel can be effectively optimized. The optimized ventilation shafts, coupled with jet fans, can reduce harmful gas concentrations below safety limits within one minute. The methodologies and findings presented here can offer valuable guidance for the ventilation design of similar infrastructures.