Research on Blockage Ratio Effects on Large-Profile Tunnel Fire Behaviors

Abstract

In recent years, railway construction in China is in a rapid development stage. As a result, more and more long-profile large-distance tunnels are designed and constructed. To accommodate for rapid deployment of vehicular tunnels, it is necessary to enlarge its profile, namely, to reduce the tunnel blockage ratio since train cross-section remains unchanged. This study has analyzed the impact of blockage ratio on tunnel smoke controlling critical ventilation velocity (CVV) as well as the smoke flow behaviors around the train on fire and in its immediate surroundings, using CFD numerical simulation. The results show that in certain fires, CVV decreases as the blockage ratio increases, and the opposite is also true while CVV increases gradually accelerates, while, temperatures near the top of tunnel roof decrease gradually as the blockage ratio decreases. The smaller the blockage ratio, the smaller the critical high temperature area. As a train passes by, the peak ventilation velocity increases as the blockage ratio increases. Results of this study could provide a theoretical basis for safety design as well as operation of long-large interval tunnels to prevent possible disasters.