Investigation of the effects of two parameters of longitudinal axis rotation angle (bend) and local variation of tunnel cross section on reduction of pressure due to explosion at the tunnel opening

Explosions at the entrance of tunnels and underground spaces can lead to losses. To decrease side effects of such explosions, some approaches like dead_end, bends, geometric barriers and anti-explosion doors are available. Using geometric barriers, especially the waveguides, is the most commonly used and economical way. The purpose of this paper is to investigate the effect of the angle of rotation of the longitudinal axis (bend) and the local variation of the tunnel area on reducing the impact of explosions. Appropriate angle of rotation of the longitudinal axis and suitable location for local variation of the tunnel cross section in line with the tunnel are calculated, by numerical analysis, using Abaqus software.  Finally, proper characteristics are used to propose a method, requiring the least drilling in construction (the most economical method), and generating the highest reduction in the effects of the explosion (the highest vulnerability reduction) in explosions near and away from the span. The results show that the localized change in the tunnel cross-section at the end of the direct path and the change in the angle of rotation of the long axis from 135 ° to 90 ° (90 °) will lead to the greatest reduction in pressure.