Experimental study on the temperature longitudinal distribution induced by a branched tunnel fire

Temperature rise induced by tunnel fire is a key factor injuring persons and destroying the tunnel lining structure as well as the facilities. In order to better comprehend the temperature distribution induced by fire in branched tunnel, a series of reduced scale experiments with different longitudinal ventilation velocity and bifurcation angles were conducted to investigate the temperature longitudinal decay in mainline tunnel and ramp in this paper. The heat release rate varied from 1.72 kW to 6.04 kW corresponding to 3.07 MW-10.8 MW in full scale. Three bifurcation angles of 5 degrees, 10 degrees, and 15 degrees were considered to investigate the effect of bifurcation angle on temperature longitudinal distribution in branched tunnel. Results show that the bifurcation angle influences temperature distribution between fire source two sides due to the asymmetric air entrainment. The increasing of heat release rate results in the higher temperature under natural ventilation. The ventilation velocity had a greater enhancing effect on the temperature rise in mainline tunnel due to smoke accumulation effect at downstream of fire source. The exponential correlation is proposed to predict the longitudinal temperature beneath the tunnel ceiling not only in mainline tunnel but also in ramp by taking the bifurcation angle into consideration.