Study on the Critical Velocity and Back-Layering Length in Serpentine Curved Road Tunnels

To figure out the effect of fire location on critical velocity and back-layering length in serpentine curved road tunnel, as well as the determine the most dangerous fire location, based on Paomashan No. 1 tunnel project, numerical calculation method was used to simulate the critical velocity and back-layering length in serpentine curved road tunnel under different cross-section location of fire source and different longitudinal location of fire source. The results show that: As for the steady stage of both primary curve and reverse curve in serpentine curved tunnel, the critical velocity for a fire near the convex wall is higher than other cross-section fire locations. As for the transition stage of reverse curve in serpentine curved tunnel, the critical velocity for a fire near the concave wall is higher than other cross-section fire locations. The most dangerous fire location is located near the convex wall of the steady stage in serpentine curved tunnel. When the fire scale is 30 MW, the maximum critical velocity of the serpentine curved tunnel with radius of 1000 m is 4.3 m/s, which is 8% higher than that of the straight tunnel. With the decrease of ventilation wind speed, the back-layering length for different fire locations in serpentine curved tunnel increases linearly. The growth rate of back-layering length for a fire near the convex wall and the concave wall is basically the same, while the growth rate of back-layering length for a middle fire is significantly greater than that for a side-wall fire.