Dynamic Response And Explosion-resistant Protection Of Subway Tunnel Under Terrorist Bombing Load

The safety protection of subway structure gradually becomes a problem demanding urgent solution, with a large number of constructions of subway structures in the country. Based on the terrorist activities in international community and the status quo of subway protection, establishment of explosion impulse response model, propagation laws of the blast wave in subway tunnel, dynamic response of subway tunnel under blast loading and study on foam aluminum used for subway structure protection were introduced. Then the impact of actual explosion process on subway tunnel was simulated by numerical simulation, which is helpful to better understanding of the dynamic response laws of subway tunnel under blast loading and serves the subway construction.In order to accurate analyse blast loading effect, explosion impulse response model was established by dynamic analysis software LS-DYNA. And, fluid-structure coupling computation was utilized in the model which can couple a variety of materials, realize the interaction between fluid and solid, and solve the interaction problem between air and tunnel lining.During the simulated propagation of shock wave in subway tunnel, numerical calculation models under the action of 10-kilogram and 20-kilogram TNT were adopted respectively, and reflection, superposition effect and overpressure attenuation variation of the shock wave were mainly analyzed. Results can be obtained that overpressure of the shock wave at points near the explosion source decay rapidly after going through a maximal peak. However, with the increase of the distance from the explosive center, the overpressure also decays after the maximal peak with a slight decay magnitude. On account of many times reflection in the subway structure when the blast wave propagates forward, positive pressure area of the shock wave is stretched and divided into many parts causing the explosion energy distribution to become uniform. Corresponding analysis of shock wave arrival time of points in different sections and injuries to humans caused by blast overpressure were carried out.In the aspect of dynamic response of subway tunnel, variation laws of displacement, velocity, acceleration and stress as well as dynamic response laws of the surrounding soil of three different sections under the action of 10kg TNT and 20kg TNT were analyzed. The obtained conclusions are:the velocity and acceleration of sections near the explosion decay quickly after going through a maximal peak while with the increase of the distance from the explosive center, the velocity and acceleration of various sections decay much slower. It can be proved that the change of velocity and acceleration is relevant with overpressure. The lining bottom closest to the explosive firstly becomes plastic zone under the action of 20kg TNT. The lining is in tension sate at the initial moment of explosion and the impact on the surrounding soil is gradually weak with the increase of the distance from the explosion. And the influence scope will increase when the quantity of the explosive is increased.The method to add foam aluminum to the inner wall of lining in explosion-resistant protection was used and a simplified calculation of the effect before and after adding foam aluminum was conducted. Calculation results show that the foam aluminum has a good effect on cushioning the impact of blasting load on the lining.