Abstract
Underground structures are proven to be one of the vital part of modern transportation system. With the growing importance of tunnels for mobility, they are being subjected to threats of severe terrorist activities. Urban tunnels are mainly located in the upper few kilometers and are highly susceptible to deformations even at very low strain rates. Therefore, in the present study, an attempt is made to understand the behavior and pattern of tunnel damage subjected to the different dynamic loading conditions, through the simulation of natural as well as artificial stress states such as loads due to overburden, impact, and blast. The new methodology is proposed to overcome the difficulties of field test during a surface blast. In the present study, the combination of experimental and numerical approaches is used to analysis and design tunnels under impact and blast loads. The investigation is carried out in four steps; firstly, the impact testing is performed in the laboratory on small-scale physical models of tunnel prepared using proper scaling laws. Secondly, the numerical investigation of the physical model is performed under laboratory conditions, and then the experimental and numerical results are compared for the validation purpose. Thirdly, the numerical analysis of impact loading on prototype is carried out. The tunnel deformation results of small scale model and prototype under impact loading are compared for the validation of the prototype model. Finally, the effect of blast loading on the tunnel deformation of the prototype is investigated. It is found from the numerical simulations that the deformation at the tunnel crown in prototype under impact loading is 10 times more than that of a small scale physical model. It is also observed that the deformation of tunnel crown in prototype under impact load is equal to that of blast load due to 500 kg TNT. Therefore, it can be concluded that the methodology proposed in the present work can be utilized by the practicing engineers and academicians for the safe and economical design of tunnels subjected to impact and blast loading.
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