Comparative study on ventilation and smoke extraction systems of different super-long river-crossing subway tunnels under fire scenarios

With the rapid growth of the population density, the above-ground transportation mode cannot withstand the drastic increase in travel pressure. Therefore, the construction of river-crossing tunnels has gradually become an effective way to alleviate traffic dilemmas. To further investigate the ventilation and smoke extraction systems in tunnels, four different kinds of practical river-crossing tunnels: Double-Line Tunnel, Unilateral-Line Tunnel (ULT), Single-Tube Tunnel, and the Double-Circular Tunnel (DCT) are selected for a detailed comparison. It is found that the ceiling smoke temperature and the carbon dioxide concentration produced in a fire of the ULT are the lowest. Meanwhile, the results show that the smoke temperature, visibility at a height of 2 m above the ground and smoke layer sedimentation height of the ULT are obviously lower than that in the DCT. Based on the excellent performance of the ULT, the internal exhaust vent groups (EVGs) layout is rearranged. It comes to conclusion that the fire risks caused by the number of smoke exhaust groups are completely different, and the risk ranking of the three smoke extraction schemes is: 1-EVG>3-EVGs>2-EVGs. Moreover, the consequence corresponding to the −0.43° slope segment is the most harmful, and the damage of the +1.60° slope segment is minimal. All the parameters obtained by a series of simulations provide effective reference and support for fire protection design of actual tunnel construction. In particular, it plays a guiding role in the practical engineering implementation.