Structural Dynamic Response Of Utility Tunnel Caused By Internal Explosion

Since the 911 incident,terrorist attacks in the world have become increasingly rampant.As an important lifeline project of the city,utility tunnel plays an important role in the operation of the city.It is the target of terrorist attack and the probability of being threatened by explosion,which is increasing day by day.The study of structure dynamic response of utility tunnel caused by internal explosion has important theoretical significance and practical engineering value for the anti-explosion and protection design of utility tunnel.In this paper,the structure dynamic response of utility tunnel caused by internal explosion is studied by combining the method of utility tunnel scale model test and numerical simulation calculation.The primary work completed and conclusions are as follows:(1)According to the similarity theory,a 1:8 scale pipe gallery model was designed and made based on the prototype of the three-cabin reinforced concrete utility tunnel with 32 m pipe length;Two test conditions were developed,which were mainly used to analyze and study the shock wave propagation law,pressure field distribution,structural dynamic response and failure mode under explosion in gas cabin,to provide experimental verification for numerical calculation.The test results showed that the air pressure in the area near the explosion center was much greater than that in the area far from the explosion center,and the dynamic response was more intense and the structural damage was more serious,among which the inner plate and corner of the gas cabin were the most seriously damaged.(2)Finite element numerical simulation method was used to verify the validity of numerical calculation by comparing the test results.Then,the propagation law of shock wave in the tunnel and the distribution characteristics of overpressure were studied,and the influence of different explosion quantities and charge positions on it was explored.In the area near the center of explosion,the results showed that the shock wave reflected at the wall and converged in the corner,and the stable plane wave propagated forward with the increase of the distance between the center of explosion.The peak value of overpressure in the area near the explosion center and the corner was larger.With the distance between the explosion center increasing,the peak value of overpressure at each point decreased rapidly.As the distance between the explosion center continue increasing,the attenuation rate of the peak value of overpressure decreased,causing continuous damage to the structure.(3)In order to comprehensively design requirements of anti-explosion protection of the utility tunnel,a three-dimensional finite element model of the interaction of "structure-soilair-explosive" was established and the validity of the model was verified.The structure dynamic response and local damage of the utility tunnel caused by internal explosion with different explosion quantities and explosion positions were studied.The calculation results showed that when the explosion was located at the centroid of the section,the structure dynamic response of the utility tunnel was stronger than that when the explosion was located at the bottom plate and the corner.Except for the part that contacted the explosion,the dynamic response of the inner plate of the gas cabin was the largest,and the inner plate of the gas cabin was more significantly affected by the explosion amount.Due to the damage of some positions,energy absorption and pressure relief led to the smaller dynamic response generated by the larger explosion amount in some positions.The structural damage mainly occurred in the inner plate and the upper and lower corners of the inner plate.With the increase of loading,the structure damage became more serious,and the inner plate failed first.When the explosion position was different,the damage of the structure was more serious except the contact area of the explosion,and the damage of the structure was more serious when the explosion was located in the centroid of the cross section.The anti-explosion performance of the inner panels of the gas cabin should be enhanced during the protection design,and the post-disaster repair mainly focuses on the structures near the explosion center.(4)After the explosion-proof wall was set at one end of the tunnel,the structure would be subjected to two strong shock waves,and the overpressure peak value of the structure would be increased compared with that without the explosion-proof wall.With the increasing of the distance from the explosion center,the peak value of the overpressure of the shock wave would decay more slowly.The dynamic response of the structure was almost the same as that without explosion wall,but the time of blast load increased.The damage of the structure was more serious than that without explosion wall,and the damage of the structure was more significant with the increasing of explosion.Therefore,some reinforcement measures should be taken for the near range structure of the explosion-proof wall during the protection design.