Abstract: In order to study the influence of mainline slope on fire smoke spread in mainline tunnel of bifurcated tunnel, the numerical simulation method was used to analyze the temperature distribution in tunnel under different mainline slope and fire source power of the mainline before the bifurcation. A maximum temperature rise prediction model of tunnel ceiling and a longitudinal temperature rise attenuation prediction model of downstream mainline tunnel were proposed considering mainline slope and fire source power. The results show that under the given heat release rate, the maximum temperature rise in the tunnel decreases with the increase of the mainline slope. The larger the slope of the main tunnel, the more obvious the inclination of the plume flow downstream of the main tunnel, and the maximum temperature under the ceiling shifted downstream. The thickness of the smoke layer in the downstream of the main tunnel decreases with the increase of the tunnel slope, and the longitudinal temperature rise in the downstream of the main tunnel also decreases.

Key words: bifurcation tunnel, maximum temperature, longitudinal temperature attenuation, tunnel fire