Study On The Collapse Mechanism Of The Shallow Buried Subway Station Under The Intense Earthquake

Previous scholars believed that the underground structure had good seismic performance due to the confining effect of surrounding soil.However,the collapse of the Daikai station in 1995 in the Hanshin earthquake made a warning for scholars both at home and abroad.With the development of urbanization,the underground rail transit system has become a necessary transportation facility for medium and large cities to solve the current situation of ground traffic congestion.In order to serve the urban super population agglomeration,the subway station structures have developed in the complicate structures of multi-layer,multi-spans,multi line transfer,and Commercial Street combination,and have super high commercial value.At present,domestic and foreign scholars have a lot of research results on the earthquake damage mechanism of Daikai subway station,however it is difficult to reach a consensus,and there is still a lack of systematic research on the seismic damage response of common configuration subway stations under oblique incidence earthquake.This paper studies the seismic failure response of the metro station and different structures by theoretical analysis and numerical simulation.The main research contents include the following four aspects.（1）Based on the time delay method and elastic mechanics,the artificial stress boundary of two-dimensional or three-dimensional normal incidence or oblique incidence of ground motion was derived.The code for generating the explicit and implicit viscoelastic artificial boundary and nodal force of ground motion based on ABAQUS finite element platform were compiled,and the effectiveness and accuracy of the code were verified.（2）In order to apply the unified hardening model to ABAQUS finite element site simulation,the algorithm of the constitutive model was derived based on the closest point projection method and stress transformation method,and then the single integration point code and the interface of ABAQUS are implemented by FORTRAN language.And the effectiveness and accuracy of the algorithm were verified through the prediction of soil triaxial test and circular bearing plate test by UMAT subroutine and the single integration point code.（3）The nonlinear dynamic constitutive model of soil mass,such as viscoelastic elastic plastic model,unified hardening model and classical Mohr Coulomb model,which is commonly used by scholars at home and abroad,was used to simulate the site soil.The seismic response of Daikai metro station under different ground motion combinations and different soil models for site was analyzed,and the failure response mechanism of Daikai metro station was discussed.（4）Based on the viscoelastic boundary and equivalent boundary force method,the seismic damage of subway station structures with different structures,different oblique incidence angles,different combined styles of ground motions,different soil shear wave velocities（elastic and elastic-plastic models）,different buried depths and different finite element dimensions were simulated.This paper mainly discussed the difference of displacement and failure response of subway stations with different structures under vertical and oblique incidence,the spatial effect of multi-storey and multi span subway stations under oblique incidence,the failure response of SV wave and P wave combination,shear wave velocity of soil in different sites and buried depth of structure without considering stratum loss.In addition,the applicability of the equivalent boundary force method based on the elastic theory to the site soil of the elasto-plastic model was discussed,and the influence of the three-dimensional central column simplification to the plane stress problem on the elasto-plastic dynamic analysis of the structure was also discussed.This paper has 94 figures,22 tables and 203 references.