Numerical simulation of fire smoke in extra-long river-crossing subway tunnels

With the gradually increasing number of river-crossing tunnels in recent years, the risk of tunnel fires continues to rise. Therefore, the fire-smoke control effects of different tunnel structures and ventilation and smoke exhaust systems should be studied. The Fire Dynamics Simulator was used to simulate fires in segments with different slopes in Nanjing Metro Line 10 by considering single-hole single-track and single-hole double-track structures. Moreover, variations in temperature, CO concentration, visibility, and the settling height of the smoke layer were analyzed in detail. The results show that, in terms of temperature, CO concentration, and visibility in the −28‰, +8.9‰, +28‰ tunnels, the single-hole double-track tunnel structure has certain advantages. However, in the −7.5‰ tunnel, the single-hole single-track tunnel slightly presents lower risks than the single-hole two-track structure, whereas the settling height of the smoke layer is higher. In general, the fire risk closely associated with the gradients, and results show that the hazard for the section with positive gradient (+8.9‰, +28‰) after a fire were lower than those for the section with negative gradient (−28‰, −7.5‰). Simultaneously, the fire risk is related to the location of the fire due to different serious consequences under different fire scenarios. Comparatively, the damage caused by fire in section −7.5‰ tunnel is the greatest. In terms of the tunnel's own structure and internal facilities, the single-hole double-track tunnel contains an evacuation platform, fireproof doors, and other emergency facilities, so it is a safer choice from the viewpoint of personnel evacuation. In short, combining related parameters after the fire revealed that the single-hole double-track structure is more suitable in the actual design and application processes.