Seismic Response Analysis Of Underground Structures In Soft Soil And The Evaluation Of Environmental Impaction

With the development of national economy and shortages of urban land,the construction of subway receives its golden age.China is a seismic active country,however,So far,there is still lack of a mature seismic analysis method and design code for underground subway structures in China.The previous seismic damages of underground structures prove that restoration of it is difficult as soon as it is damaged by eahrtquake.For subway sturcutre is embedded in soil,it is obvious that the effect of soil-structure dynamic interaction can change the design parameters of ground motion in the soft site,then influence the seismic response of built and ready-built structure.Therefore,anti-seismic of subway structures is important both in theoretical research and engineering.Based on the fast Lagrangian finite difference method,a shallow-buried subway station structure in a representative soft site is selected in this paper.The two-dimensional FEM model with viscous artificial boundary condition is established considering the effect of soil-structure dynamic interaction.Seismic response of shallow-buried subway station structure and influence of built shallow-buried subway structure on design parameters of ground motion in the soft site are investigated numerically.The major sutdies are as follows:Firstly,The seismic response of shallow-buffed subway station structure in soft soil was studied using two-dimensional large deformation FEM model,and effects of soil-structure interaction was considered by viscous boundary.The horizontal relative displacement and acceleration responses of subway station structure has been analyzed and the effects on seismic displacement of different burial depth of subway station structure are investigated. The seismic response of the soil and the corresponding maximum forces of the subway station structure induced by earthquake were compared.Some aseismic measures are proposed for the design of the subway station structure.Secondly,the influence of shallow-buried subway station structure in soft soil on seismic response of free site is numerically investigated.In the case of building the subway structure and free site,the horizontal relative displacement and acceleration responses of subway station structure has been analyzed briefly.Additionally,the paper studys the acceleration, velocity,displacement and the response spectrum of horizontal acceleration at the the ground surface points and the influence of subway station on the peak ground acceleration with different burial depth.Finally based on studying the relation of relative horizontal displacement of subway station and the peak ground displacement relative to the bedrock at the free site,the peak ground displacement relative to the bedrock is a very effective design parameter of ground motion for evaluating the seismic response of underground structures.Thirdly,a FEM model is suggested for analyzing the factors mainly including depth,artificial boundary,soil stiffness and the elements stiffness affecting the relative displacement of shallow-buried subway station structure in soft soil.The rules of variation of the relative horizontal displacement bewteen top and bottom of subway Station structure are generalized. The results can provide a useful guide for the Seismic design of the subway station structure.