Damage mechanism of tunnel portal subjected to severe gas explosion

To investigate the damage mechanism of tunnel portal subjected to gas explosion in the Luodaiguzhen tunnel, equivalent and quantitative studies were carried out on the accumulation of gases in the tunnel, and a fully coupled numerical model with dimensions that were consistent with the actual dimensions was established by LS-DYNA and verified. The RHT model was used to simulate the concrete, and some parameters were modified. The propagation traits and strength of the blast shock wave and the damage mechanism of the tunnel portal were studied. The studies show that the strength of the shock wave is significantly enhanced due to its numerous irregular reflection. This results in a complicated wave field. The wave aggregates in local regions, and the pressure in the tunnel is 1.2-2.4 MPa. The wave near the lining travels faster during propagation, and its shape changes from the spherical to horn. The strength of the wave in the vault of the tunnel portal is increased by 56% to reach 2.8 MPa, and diffraction occurs in the vicinity of tunnel portal. After the wave is propagated from the tunnel, its strength gradually decreases, and the wave, which originally moves along the sidewall and floor, continues to travel along the longitudinal direction. The shock wave along the arch moves upward and forms a "mushroom cloud". The corner of the sidewall is destroyed completely during the explosion, and the lining suffers serious damage within 7 m of detonation, and the arch is almost intact in the range of 7-15 m. The tunnel portal is also severely damage. Without the constraint of surrounding rock, the displacement of the vault in the Y and X directions of the portal is 0.26 and 0.14 m, respectively, and the tensile stresses that acted at the front and back surfaces of the portal are 7.9-31.5 MPa and 4.9-15.6 MPa, respectively, and multiple peak stresses occur on the back surface of the portal. The damage of the portal is mainly caused by the tensile stress. By comparison, the numerical simulation results of the damage characteristics of the tunnel portal basically agreed with the actual situations. Therefore, the results can provide useful references for the treatment of lining hazards.