Collapse Procedure Simulation And Failure Mechanism Analysis On Subway Stations Under Seismic Loads

Seismic investigations of underground structures show that,earthquakes could cause serious damage or complete collapse of subway stations.Therefore,it is of great significance to study the collapse mechanism of underground structures during earthquake.In this study,the theoretical and numerical simulation methods were used to study the failure mechanism and damage mode of subway structures.The main achievements of this study are as follows.1.Unified strength and 3D elastoplastic constitutive models of geomaterials(1)Firstly,the differences among the shear failure planes of strength theories were discussed.Then a characterized stress,which could reflect the intermediate principal stress effect of geomaterials,was proposed.Secondly,the failure of geomaterials was attributed to shear failure,and then the octahedron plane under the action of characterized stress was applied to uniformly explain the shear failure mechanism of geomaterials.Afterwards,a simple nonlinear unified strength theory was developed on the basis of the characterized stress and the octahedron plane.Finally,the nonlinear unified strength theory was verified by using experimental data from literature.(2)A new approach to directly establish 3D constitutive models,which was based on the characterized stress,was developed to conquer the strength problems in the Camclay model.Then a new elastoplastic constitutive model for normally consolidated clay was established.By introducing the subloading surface and the unified hardening parameter,the established model was developed to describe the 3D strength properties,softening and plastic strain accumulation property under cyclic loading of overconsolidated clay.Finally,a new integration algorithm for constitutive models with the subloading surface was proposed to settle the low efficiency of the return mapping algorithm.Then the developed constitutive model was programming for the following FEM simulation.2.Seismic responses simulation and collapse failure mechanism of underground structures(1)The viscoelastic boundary condition and seismic input were realized within the theoretical framework of near-field wave motion theory.Then a platform for explicit calculation was built,and the accuracy and efficiency of this platform were verified.Afterwards,the collapse procedure of underground structures,taking the Daikai station as an example,was simulated.The numerical results were contrastive analyzed with the seismic investigations.(2)This study concentrated on the seismic responses of the underground structure influenced by the mechanical properties of surrounding soils,the types of seismic loads,the intensity of earthquakes,the functionalities of structural components,the mechanical properties of core components,as well as the deformation incompatibility between the columns and walls.Then the failure mode and collapse mechanism of the Daikai station are discovered systematically.Finally,a concept of core supporting column was proposed for the seismic design of underground structures.(3)The initial stress states of the structures and surrounding soils influenced by the ground loss were studied,and then the effect of the ground loss ratio for simulating the seismic responses of deep buried structures also were discussed.Afterwards,threedimensional numerical models of nonlinear earthquake response simulation of underground structures were built,and the influence of buried depth on the seismic responses of underground structures was systematically explored.Further,a buried depth of strongest seismic response for the underground structures was presented from analysing the structural distortions of underground structures at different buried depths.Finally,some suggestions for the seismic design of the underground structures were given.(4)Based on the concept of core supporting column,the lateral deformation property of columns was selected as the assessment indicator for the seismic performance of underground structures.Then the grading standard for seismic performance was divided,and the seismic performance of underground structures was assessed.Moreover,sliding isolation bearings were introduced to underground structures for aseismic analysis.Then the feasibility of sliding bearings for updating seismic response of underground structures were discussed.