Abstract: Herringbone tunnels are often found in mountain tunnels and new-built urban traffic tunnels. The smoke flow is complicated in case of fire and controlling the smoke effectively with longitudinal ventilation is relatively difficult. By setting up a 1：20 herringbone tunnel model test rig, the critical ventilation speed under different slope composition and different fire power in asymmetric herringbone tunnel was studied. The results show that when the longitudinal ventilation flows from the small slope side to the large slop side, the critical ventilation speed is greater than that in the normal tunnel with the same tunnel cross-section and same fire power. The critical ventilation speed increases with the increase of the slope difference on both sides of the variable slope point. When longitudinal ventilation flow from large slope side, the critical ventilation speed is less than that in the normal tunnel, and the critical ventilation speed decreases with the increase of the slope difference. For the engineering application, the slope correction of the critical ventilation speed model of the normal tunnel is carried out based on the experimental results, and the correction coefficient of the critical ventilation speed is obtained.

Key words: herringbone tunnel, longitudinal ventilation, critical ventilation speed, small-scale experiment