Experimental study on smoke characteristics of bifurcated tunnel fire

Abstract

The fire risk of bifurcated tunnels is increasing as rapid development of the urban underground traffic in China. Because of the special bifurcation structure, the temperature distribution of bifurcated tunnel fire is different from the traditional single tube tunnel fire. However, so far, there are few studies on this aspect of bifurcated tunnel fire. Therefore, it is of great significance to study the smoke characteristics of bifurcated tunnel fire. In this paper, a series of experiments were carried out in a 1:10 scale bifurcated tunnel to study the effects of the branch and the longitudinal ventilation velocity on the smoke characteristics in the bifurcated tunnel. The main conclusions are as follows: (1) When the fire source is located at the bifurcated point, the existence of the branch will make the temperature of the fire source area rise significantly. However, it has no influence on the temperature variation of the tunnel when the fire source is located at upstream of the bifurcated point. (2) Whether the fire source is located at upstream of the bifurcated point or at the bifurcated point, as the longitudinal ventilation velocity increases, the ceiling temperature of the central axis of the tunnel decreases, and the position of the maximum temperature point moves towards downstream. (3) The maximum temperature in the tunnel decreases linearly with the longitudinal ventilation velocity whether there is a branch or not. (4) When the fire source is located at upstream of the bifurcated point, the temperature on the central axis of the branch ceiling rises up firstly and then reduces with the increase of the longitudinal ventilation velocity. At the entrance of the branch, the temperature increases firstly and then decreases, and this phenomenon is more obvious with the higher longitudinal ventilation velocity.