Experimental investigation on the influence of portal-blocking speed on fire behaviors in tunnel structure

Abstract

This work provides a series of fire tests in a 1/7 model tunnel to explore the influence of portal-blocking speed on tunnel fire behaviors. Burning rate, ceiling temperature, temperature distribution inside tunnel and thermal characteristic near tunnel portal are obtained and analyzed. Results shown that the comprehensive effect of portal-blocking speed on fire behavior is related to fuel area of fire source. For the fire scenario with small fuel area (Sfuel≤0.18 m2), the effect of blocking speed is not significant. While for the fire scenario with large fuel area (Sfuel≥0.54 m2), burning rate decreases rapidly, due to the blocking of tunnel portals. A critical blocking ratio existed due to the competitive between two action mechanisms of the reduction of air supplement and heat loss. The larger the fuel area is, the smaller the critical blocking ratio is. There is a delay effect on the burning suppression of fire source. For the fire scenario with large fuel area (Sfuel≥0.54 m2), the ceiling temperature distribution was more “uniform”, compared to that of the fire scenario with small fuel area (Sfuel≤0.18 m2). The faster blocking speed can make the ceiling temperature decay to a relatively low level earlier. The larger the fuel area is, the better the suppression effect of blocking strategy is. Earlier and faster blocking operation can effectively suppress the high temperature region, which is beneficial to the protection of tunnel lining.