Study On Dynamic Disaster Mechanism And Fragility Analysis Of Interaction System Of Saturated Soft Soil And Subway Station Structure Subjected To Earthquake Load

The liquefaction of saturated sand(or silt)and the large deformation of soft soil are two typical foundation catastrophic instability phenomena.While,soft soil is widely distributed along the coast of China,along the Yangtze River and along the lake,most of these areas are developed areas and the cities gathered in this area have more subway station structures.Currently,for the particularity and complexity of soft soil mechanical characteristics,the present relevant specification is lagging compared with the liquefied sandy soil site,and only some qualitative or general stipulations are given.There has been difficult to adapt to the rapid development of China's subway construction and meet the new requirements for seismic design of underground subway structures.Therefore,there is a lack of more in-depth and systematic research,and more extensive and intensive studies are still needed on seismic disaster mechanism in saturated soft soil foundation.The project is proposed on the background feature of previous research relation to seismic mechanical behavior of interaction system including soft soil ground and subway station,and the main research work is as follows:1.A typical single-layer double-span type for underground structure was selected,and a set of shaking station tests of subway station structure surround by saturated soft soil with a scale ratio of 1:30 was carried out.In this test,the seismic response characteristics of model system were obtained,such as acceleration,dynamic pore pressure ratio,surface displacement and soil pressure.The seismic responses and failure characteristics of metro station structure embedded in saturated soft soil are revealed by the analysis and studies on the test data.2.The coupled nonlinear numerical models of interaction system were developed using the u-p formulation of Biot's theory to describe the saturated two-phase media,and the model test results were compared and analyzed by using the fully coupled effective stress numerical analysis method.The coupled numerical analyses were verified by shaking table tests.All the numerical results were extracted and visualized by the compiled MATLAB and GID interface program.3.Based on the fully coupled effective stress nonlinear numerical solution method verified by test,a refined finite element model of interaction system was estabilithed to investigate its nonlinear seismic responses and seismic disaster mechanism.In this study,the multi-yield elastoplastic constitutive model was adopted for the soil,and the fiber section elastoplastic constitutive model was adopted for the structure.4.Based on orthogonal experimental design with six factors and three levels,parametric sensitivity analyses with the method of multi-index comprehensive blance are also conducted by the range and varince analysis of the dynamic evaluation indexes such as displacement,acceleration,dynamic pore pressure ratio and structural internal force of the model system due to the parameter variation of soft soil properties.Further,the dynamic evaluation indexes of model system were used to analyze the influencing factors such as the buried depth of structure and the thickness and depth of the saturated soft soil interlayer for investigation the seismic disaster mechanism,failure mode.5.The seismic response of structure was calculated by inputting the artificial seismic wave that was obtained by the power spectrum-triangular series method.The maximum inter-story drift angle was taken as the structural performance parameter of the subway station structure.The structural demand cloud was obtained under the random ground motion sequence.Based on the probabilistic seismic demand model analysis method,the seismic fragility curve of subway station structure was drawn,and the seismic fragility curve was analyzed based on the fragility of performance parameters.The multi-level fragility curves based on probability expression form were converted into a expression form of non-probability single parameter based on fragility index,further,the fragility of subway station structure embedded in different shear wave velocity site and in different saturated soft soil interlayer depths and thickness site were also evaluated.This study will be of great theoretical and practical significance for the understanding of earthquake disaster mechanism,the development of geotechnical earthquake engineering,and seismic design of subway station structure embedded in saturated soft soil foundation.