Abstract: In order to explore the influence of transverse fire location and fire area on the critical velocity, the FDS software was used to study the critical velocity of central fire and near wall fire in the U-shaped section dual lane road tunnel, and the results were compared with those in the rectangular section tunnel. The results show that when HRRPUA is constant, the critical velocity increases with the fire area. The critical velocity of the near wall fire is smaller than that of the central fire, which is different from that in rectangular section tunnel. As the fire area gets bigger, the ratio of critical velocity of near wall fire and central fire approaches to 1, and the mirror effect cannot explain the difference of the critical velocity of near wall fire and central fire in the U-shaped section tunnel.

Key words: road tunnel, critical velocity, transverse fire location, fire area, U-shaped section