This study is a part of an investigation project to examine emergencies in a large cross sectional tunnel, to be constructed on the New Toumei Expressway in Japan. Backlayering characteristics, the most important behavior in tunnel fires, are investigated through largeeddy simulation for various longitudinal air flows and fire sizes. The accuracy of this simulator has been previously confirmed by comparing with experimental results. In this study, specifically, stationary vehicles in a tunnel are considered in the simulation for the first time. Their presence induces turbulence in the longitudinal air flow and greatly affects the backlayering characteristics. However, earlier studies have not yet considered these effects. The results show that the presence of stationary vehicles reduces the backlayering length. Furthermore, the ratio of large-sized vehicles to total traffic is found to have little effect on fire behavior.

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