Study On The Impact Of Underpassing Metro Station Constructed By The PBA Method On Crossing Bridge

With the development of urban transport, the construction of subway has become the symbol of progress and development of the city, but the construction of subway has greater impact on the surrounding environment, especially on cities with numerous overpasses. Crossing problem has become inevitable. There are many examples of subway tunnels crossing bridges. But the metro station especially shallow station constructed beneath the bridge is also one of the few and the special grade risks. So the research on construction of underpassing metro station beneath the bridge has been very necessary. Based on the project of a metro station constructed beneath a bridge named Huayuanqiao, in this paper, a series of theoretical studies, numerical calculations and field practice approach has been used to study the engineering including follows:(1) Based on the project cost, structural safety, precipitation depth and other aspect analysis, seven method of construction for PBA are summed.(2) Based on the theory of unloading near pile, combined with the Duncan-Chang model considering the modulus change in the process of soil unloading, the Mohr-Coulomb model introduced the tangent modulus and tangent pisson ratio used in Duncan-Chang model is proposed to consider the influence of soil because of unloading, and is developed based on the soft of FLAC3D. Then this method is used in practical engineering calculations and contrasted to the monitored values.(3) Taken the model mentioned above as the basis constitutive relation, combined with the projiect of the metro station construction beneath the Huayuanqiao bridge, deformation of the ground, piles and piers have been studied by the method of numerical simulation for the asymmetric PBA beneath bridges asymmetricly.(4) Combined with five method of five tunnel PBA, the optimal process of construction has been proposed by comparative analysis; The number of tunnel for PBA could be six, five, four and three, the deformation of the bridge has been proposed in erery program, and then combined with the construction of horizontal guide hole and lengthened bridge piles, four cases and the law of deformation are analyzed.(5) Based on the eight kinds of reinforcement measures calculation and analysis including grouting, retaining pile, Composite Bolt Pile, pile patching and grouting for tunnel face, the best measure has been proposed, and then the best reasonable length of pile to protect bridge is optimized.