Mitigation strategies of underground tunnels against blast loading

An evaluation of mitigation strategies of underground tunnels against explosions is important to the society. Therefore, a small scale tunnel was modeled against blast loading using finite element software ABAQUS. The inelastic behavior of concrete and steel bar has been incorporated through concrete damage plasticity model and Johnson-cook models respectively, available in ABAQUS. The Drucker-Prager model as well as acoustic infinite medium have been used to model the damage behavior of soil and tunnel respectively. The simulated results thus obtained from the present study were compared with the experimental results available in the literature and found in good agreement. Further, the simulations were carried to predict the damage intensity in tunnel in terms of acceleration, impulse velocity, displacement, and Mises stresses. There are many parameters which were taken into consideration to assess the mitigation strategies for the underground tunnels. The critical parameters include the influence of tunnel shapes, lining materials, lining thickness, burial depth of the tunnels, inclusion of a barrier in between the blast source-the tunnel and layered configuration of tunnel lining, and were considered to evaluate the mitigation strategy. It was concluded that the square shape of tunnel was most vulnerable as compared to circular and U-shaped tunnels. It was also concluded that plain concrete monolithic lining as well as layered configuration consisting of Dytherm foam layer between Steel Fiber reinforced Concrete layers, was found to be more vulnerable among the chosen lining materials. Also, the thickness of lining and burial depth of the tunnel found to be a significant role against blast loading.