Coupled Failure Mechanism Of Subway Station-Bridge And Seismic Response Numerical Simulation

For the rapid population increase of mega-cities and the development of urban traffic,underground rail transit and urban overpass will cross-build inevitably.There is interaction between underground structure and adjacent ground bridge and coupling dynamic interaction between underground and ground structure during earthquake,especially in high intensity area.The failure mechanism and coupling interaction between underground and ground structure have become one of the important research topics in the field of urban geotechnical seismic engineering and earthquake prevention and disaster reduction.Based on the near-field fluctuation theory and numerical simulation method,the coupling failure mechanism and failure mode of subway station and ground bridge are studied in this paper.The specific research work and achievements are as follows:1.Artificial boundary for near-field wave problemThe soil-structure dynamic interaction model is a complex nonlinear near-field fluctuation problem in open system.It is necessary to set appropriate boundary conditions at the boundary of the intercepted finite region of interest to simulate the effect of the infinite region on the intercepted finite region.At present,the commonly used local artificial boundary conditions usually produce large calculation errors when large angle or grazing incidence,which can not meet the requirements of calculation accuracy.Based on the wave-field decomposition method and the tied degree of freedom boundary proposed by the Zienkiewicz,a "partial decoupling" element is proposed to realize the wave-field decomposition method in the general finite element program,and the mechanism and accuracy analysis of the tied degree of freedom boundary are given from the angle of reflection coefficient and mechanical balance respectively.Finally,the calculation accuracy of the boundary processing method is verified by numerical example.2.3D Elasto-plastic Constitutive Model for soft soil and its further developmentThe dynamic interaction between soil and underground structure in soft site is a strong nonlinear dynamic response problem,and the reasonable description of soil nonlinearity is the key to the reliability of numerical simulation results.Based on the bounding surface theory,a three-dimensional elastoplastic constitutive model of soil is constructed,and it has been developed into a general finite element software Abaqus/Explicit.The model constructed in this paper is to use the stress ratio to describe the stress state of the material in the normalized bias plane,and to use the empirical formula of soil modulus to describe the friction characteristics of the soil;and according to the equivalent stress obtained by the second bias stress invariant,the plastic modulus is derived by combining the one-dimensional Pyke model with the boundary surface theory.By comparing the numerical simulation results with the experimental results and EERA program simulation results,the rationality and accuracy of the constitutive model are verified.Finally,taking a circular underground structure model as an example,the importance of reasonable simulation of large deformation of soil to seismic response of underground structure is further explained by comparing the simulation results of linear elastic model and elastic-plastic model.3.Study on seismic simulation and catastrophe mechanism of rectangular underground structureBased on the seismic damage data of the Daikai Station in the Hanshin earthquake in 1995,the finite element model of nonlinear seismic response analysis of the Daikai station and adjacent tunnels was established.The seismic collapse process of Daikai Station was reproduced by using the fine nonlinear dynamic numerical analysis model.The results show that the middle column is a weak member of rectangular underground structure.For different seismic wave input conditions,the sequence of the middle column failure is two-way input,single vertical component and single horizontal component.Compared with the earthquake damage of large starting station section(collapse)and adjacent tunnel section(non-collapse),the structural form of underground structure(linear stiffness ratio of roof and side wall)has great influence on its seismic response.The structure with rigid roof is prone to global shear deformation under earthquake load.4.Study on earthquake coupling disaster mechanism of subway-station-bridge modelThe finite element calculation model of two-story and three-span subway station underpass viaduct in a soft site is established.The numerical simulation results show a possible coupled failure mode of subway station-bridge,and the seismic interaction and coupled failure mechanism between station and bridge are discussed by comparing the simulation results of elastic model and elastoplastic model.The failure process of station-bridge coupling is as follows:first,the roof and floor of subway station fail,then the side wall loses support and deforms to the inside of the station.Finally,the failure of adjacent foundation is caused by station failure,and the bridge foundation deforms to the station and "falling beam" damage occurs.The bridge has little influence on the seismic response of the subway station,and the damage of the subway station mainly depends on its own seismic performance.After the failure of the subway station,the bridge foundation of the adjacent station will drive the soil in the adjacent area to move towards the station and increase the failure range of the foundation.