Abstract:  In order to provide a reference for the design of fire prevention and rescue in highaltitude tunnel, a fullscale model tunnel is established by fire dynamics simulator(FDS), and 5 different ambient pressures are provided. And then the influence of different ambient pressures on the maximum temperature around tunnel crown in case of fire is studied. The study results show that: (1) Under the same heat release rate(HRR), the maximum temperature around tunnel crown increases with the decrease of ambient pressure. (2) The variation of air density and entrainment strength caused by the decrease of ambient pressure is the main factor causing the maximum temperature variation around tunnel crown. A prediction model for the maximum temperature around tunnel crown considering ambient pressure is proposed based on theoretical analysis and numerical simulation results. The prediction model shows that the maximum temperature around tunnel crown is proportional to the 2/3 power of the dimensionless HRR considering the ambient pressure. Finally, the reliability of the prediction model is verified by the existing model test data.

Key words: tunnel fire, maximum temperature around tunnel crown, ambient pressure, smoke entrainment, fire dynamics simulator(FDS)