Study On Seismic Failure Mechanism Of Subway Station And The Seismic Response Of Closely-attached Subway Structures

With the development of subway and maturation of construction technology, thecross-section form of station and tunnel has been changed. The transfer station hasbeen gradually increased, the phenomenon of space cross-station been increasingcommon. The diversification of subway station structure form and universality ofspace cross-station is the development trend of the future subway. The space-cross ofstation-station and station-tunnel and the connecting channel between them of Metrotransfer station or transport hub constitute a complex interaction of underground spacestructure. A greater deformation and additional internal forces will be generated in theconnection point under earthquake. In addition, the transverse shear deformationcaused by seismic waves in the structure will make another structure in a complexstress state of longitudinal tension or bending. In short, the deformation and stressstate of underground three-dimensional structure under earthquake is more complexand more significant interaction.This work was financially supported by a grant from the Major State BasicResearch Development Program of China (973Program),‖the earthquake damageand seismic theory of unban underground infrastructure‖. No.2007CB714203, andsupported by Beijing Municipal Natural Science Foundation.‖Study on seismicresponse and design method of three-dimensional intersected underground subwaystructures‖. No.8111001. According to the geological conditions in Beijing, thesubway station structure, and the typical combination of characteristics of station andtunnel, this article focuses on two aspects of analysis and research related to failuremechanism and mode of typical subway station structure and seismic response ofthree-dimensional intersected underground subway structures. The specific researchcontents and results are as follows:Taking silt soil image photographed by scanning electron microscope as theresearch object, use image treatment technology for microstructure observation andquantitative analysis of soil, solve the parameter of particle composition of soil, suchas porosity, grain diameter and granular shape. These works provide physicalparameters for granular flow model developing. And then simulate the tri-axial test ofthe soil and study the variation rules of property of silt soil with micro-parameters,such as friction coefficient, parallel-bond and stiffness ratio.A continuum-discrete element coupled model is built based on a large-scaleshaking table test of typical subway station in Beijing, to simulate the seismicresponses and the damage process of subway station structure model. In the couplingmodel, the soil is simulated by finite-difference method, and the structure is simulatedby particle flow code. Interfaces are built between the adjacent nodes on the boundaryof FLAC model and used as walls in PFC. Displacement calculated by FLAC inlarge-strain model transfer to PFC through interfaces, and the interaction force between particle and walls transfer to FLAC, so as to approach the couplingcalculation. The result shows that the experimental results can be well fitted. Theinterior column and nodes of column and plates are weak parts of subway stationstructure model during inputting earthquake waves. The whole damage process andenergy conversion process of structure model can be divided into three phases. Thechange of porosity, average number of contacts and contact force and the energyconversion law can response the damage process of structure model.Design and carry out shaking table test of different combinations of subwaystation and tunnel. Establish the treatment method of similar ratio with mainlycontrolling factors of over burden quality. Enter the different types of seismic waves.The main contents are as follows: the vibration characteristic of free field and itsdynamic nature of change and evolution of physical properties during the vibration,seismic force and deformation characteristics of arch station and the variation of earthpressure and deformation of soil-structure interaction, seismic force and interactionlaw of parallel tunnels, interaction law of seismic response of different combinationsof subway station and tunnel.The following laws are obtained by the analysis of shaking table test results andnumerical simulation by FLAC based on the shaking table test. The natural frequencyof soil decreases and damping ratio increases in the process of vibration. The topdisplacement of model box is larger than the bottom, and the distribution law of theacceleration is contrary. The effect of absorbing seismic waves of model boxboundary is good. The filtering nature of soil is obvious. The acceleration response ofshallow soil is weakened with the structure buried. The interaction force between soiland structure is comparatively large, and the distribution law is obviously differentaccording to different depths and structure sizes. The strains of columns and walls arelarger than which of beams and plates. The structure stress concentration is located onnodes. The interaction force is controlled by vertical earth pressure. The distributionof maximum strain value is transfer from columns and walls to beams and plates andtends to uniform. The existence of parallel tunnel structure intensifies the reflectionand exacerbates of shear waves in the soil, which amplify the response of acceleration,earth pressure, and strain of single tunnel. About the combinations of subway stationand tunnels, the bottom tunnels structure can absorb the earthquake waves comingfrom shaking table test, and reduce the seismic response of the upper station structure.The week effect reduces with soil thickness increasing.