Study On Propagation Of Shock Wave At Urban Subway Entrances Under Internal Blast Loading

As a part of the modern urban traffic, the underground construction plays a decisive role. It not only alleviates the traffic pressure of ground, but also bears the function of crossing partly. At the same time, the characteristic of openness also makes the underground engineering of city facilities become a target of terrorist attacks, such as subway and urben tunnels. In the subway of big cities, the crowd has a higher density. Once the terrorist explosion happened, it would cause serious consequences which could be unbearable to contemplate, and it would make potential economic loss and great harm to society. In order to solve these problems, the existing studies focus on the propagation of explosion shock wave in tunnel, subway station and subway trains. The research on the tunnel and subway entrances are relatively scarce. However, the tunnel entrances are set to be the position where are leading to the center of the security checking and the distribution center of people flow. These are the top priority of the anti-terrorism work.In view of these, this paper uses ANSYS/LS-DYNA finite element simulation software to simulate 18 different conditions of the tunnel entrances model. And the same surface turning and different surface turning models are respectively established. This method is validated to be validity and feasibility by comparison between the experience formula and the calculation results. This paper obtains several propagation laws of the shock wave in urban tunnel and subway entrances by comparing among the slope angle, the charge weight and the blasting position.In this paper, the results show that: For the same surface turning models, the smaller the slope angle is, the greater of overpressure stress spreading to the straightway(leading to the ticket hall in subway) is. The weakening effect of ramp on shock wave increases with the increasing of slope angle. The reflection on the bottom and the side wall plays a mainly role on the flow field of straight section in the corner composed by the straight road and ramp. At the same time, the angle of the slope makes the shock wave a fixed shape of shock front at the beginning of the spread. In the late stage, it produces complex Maher reflection phenomenon. The second and third peaks of blast wave constantly appear at the bottom of straightway and ramp near 1/3 part of the end. For the different surface turning models, the angle of the slope of the straightway increases the reflection of shock wave.The smaller slope angle is, the earlier tunnel shock wave peak of overpressure appears. The angle of the slope slows down the shock wave speed. And the time differentiation trend in large angle model is more obvious. At the same time, the corner in space of ”L” also have the same effect on the shock wave. The attenuation coefficient is about 0.6. The overpressure in tunnel entrances is weakened with the increase of the slope angle. And the angle of the slope consumes the shock wave of tunnel entrances. When the charge weight increases, the process of the shock which spreads from slope to straightway would produces inregular reflection.Finally, this study puts forward some references about the explosion-proof design of urban subway entrances which are based on the simulation results. And the suggestions of strengthening on weak structure parts under the effect of blast waves are proposed.