Structural performance of a railway tunnel under different fire scenarios

Tunnel fires are low-probability high-consequence events that could lead to loss of lives, property damage, and long service disruptions. The rapid rise of gas temperature in excess of 1000 °C within the confined tunnel space can affect the structural integrity of the tunnel. Although tunnel fires may not necessarily cause collapse, significant structural damage and disruption to rail services can lead to major economic losses. The objective of this paper is to investigate the expected structural damage in a cut-and-cover tunnel if exposed to a fire event. The analyses are completed by numerical simulations. In the first part of this work, the effects of fire scenario and variability in thermal properties of material, on the potential volume of damaged tunnel lining that would require repair are investigated. In case of tunnels, historical events show that limited accessibility to suppress the fire can cause the fire to burn for days. The fire scenarios considered in this work are defined based on (a) the worst-case envelop hydrocarbon fires such as the Rijswaterstaat (RWS) fire curve and the RABT ZTV fire curve, and (b) the potential heat release rates in railway tunnels. In the second part of this study, the effect of fire scenario on structural performance of a cut-and-cover tunnel is studied. The geometry and cross section of the Howard street tunnel in Baltimore that experienced a major fire in 2001 is used as the case study. The results show that the fire scenario and duration, while contains significant uncertainty, is one of the most influential factors on evaluating response of the tunnel structures.