Experimental investigation on maximum ceiling temperature and longitudinal attenuation in a closed tunnel with an inclined shaft

For tunnel fires with open and closed tunnel ends, the smoke flow pattern and air supply conditions vary considerably, resulting in different maximum excess ceiling temperature (ΔT_max) and its longitudinal distribution (ΔT_x). However, few studies have focused on the tunnel closed at both ends with an inclined shaft (typical tunnel structure during construction). Hence, tunnel model 1 (tunnel closed at both ends with an inclined shaft) and tunnel model 2 (tunnel open at both ends) are built for comparison and analysis. The results show that tunnel model 1 has higher ceiling temperatures and slower attenuation than tunnel model 2. Therefore, the ΔT_x in tunnel model 1 needs to be re-analyzed in detail. Different inclined shaft slopes, fire heat release rates, longitudinal and vertical fire positions are considered. In tunnel model 1, for h (lifting height of burner surface) = 0, the ΔT_max value tends to be constant for the same heat release rate, irrespective of the longitudinal fire position. For h = 5 cm, the ΔT_max value takes on a rising trend with the fire moving downstream. Moreover, the inclined shaft slope within this study has little influence on ΔT_x. As the fire moves downstream, the downstream ΔT_x/ΔT_max value decreases more rapidly. From h = 0 to h = 5 cm, the value of ΔT_x/ΔT_max drops slightly faster, but the gap is small and can be ignored. Finally, the experimental correlations are proposed to estimate the longitudinal ceiling temperature distribution in a closed tunnel with an inclined shaft.