Advancements in smoke control strategies for metro tunnel cross-passage: A theoretical and numerical study on critical velocity and driving force

Cross-passage is a commonly encountered structure within metro tunnels, providing a swift route for evacuating personnel from the accident tunnel to the safe tunnel opposite. Ventilation in the cross-passage of metro tunnels is established through the collaborative operation of ventilation systems on both sides of the tunnel. Concurrently, smoke movement within the metro tunnel is impacted by factors such as train blockage and the accumulation of heat within the train carriages. The former correlations need further refinement to predict the critical velocity and driving force required to prevent smoke from spreading into a metro tunnel cross-passage. One-dimensional theoretical analysis and full-scale cold smoke experiments were performed to investigate the relationship between the air supply parameters of tunnel fans on both sides and the ventilation velocity in the cross-passage. A calculation model of fan type selection in the opposite side safe tunnel for smoke control in the tunnel cross-passage is proposed. The influence of train location, fire heat release rate, and main tunnel ventilation velocity on critical velocity in the cross-passage was quantified by numerical simulations. The results show that the critical velocity in the cross-passage under unobstructed conditions surpasses that under blocked conditions. Meanwhile, the critical velocity exhibits relative stability under both unobstructed and blocked conditions. On the basis of the dimensionless analysis, a piecewise function was proposed to predict the critical velocity in tunnel cross-passage. The outcomes of this study provide valuable guidance for the implementation of fire prevention and smoke control measures in tunnels with similar structures.