Considering the intense threats of explosion caused by gas leaks or terrorist activities in highway tunnels, a Three-Dimensional (3D) Finite-Element (FE) method was used to study the dynamic response and damage mechanism of tunnel lining structures subjected to internal blast loading. Motivated by the reality that explosion in tunnels damages not only the lining structures but also lives and properties of people, a study based on the gas explosion in Luodai Tunnel is carried out. The coupled fluid-solid interaction was considered in this study, and the explosive-gas-lining system was modeled by using AUTODYN. The result of the numerical study shows that the part of inverted arch close to the hypocenter damages first under the impact load of gas explosion, followed by the sidewall nearby two arch springing exhibiting various degrees of damage. Eventually, the entire tunnel lining was divided into pieces of concrete blocks by the longitudinal and circumferential cracks, and the carrying capacity of the lining structure was degenerated. In addition, the deformation caused by a direct blast impact can also increase steadily because of the continuous fluctuation of the explosion shock wave due to inertia.
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