Study On Dynamic Response Of Metro Station System In Saturated Sand Field Under Earthquake

The development and utilization of subway have greatly facilitated the travel of urban people,and can well alleviate the pressure on the ground infrastructure construction the development of the subway.At present,many cities in China have plans to build subway.However,China has a vast territory and complex stratigraphic distribution,andthere are a wide distribution of sand layers such as the Bohai Sea area of the Beijing-Tianjin-Tanggu region and the Yangtze River Delta region.Moreover,these areas are mostly in the earthquake zone of China,and a large number of subway projects have been built or repaired.However,the seismic code for underground structures is not perfect enough,and there are no special considerations for underground structures with special conditions.Therefore,it is necessary to earry out effective analysis of the vibration response of metro stations in liquefiable sites.In this paper,with the finite element software OpenSEES,a free-saturated sand free-soil model and a saturated sand-metro station structure dynamic system model are established,and the actual problem is simplified into a plane strain model.The ground motion response characteristics are studied.The content is as follows:(1)Based on the established model,using Biot dynamic consolidation theory,considering the solid-liquid complete coupling,the dynamic nonlinear numerical analysis of the free-saturated sand field was carried out.Firstly,four kinds of ground motions are selected according to the model site conditions,and the dynamic numerical response of the model under local vibration is analyzed.Further,one of the ground motions is selected,whose peak intensity is changed.Thus,the amplitude modulation of five ground motion peak intensities is calculated.Finally,four soil site models were compared to analyze the dynamic response differences between them.Aiming at the above research contents,the distribution law of ground motion response characteristics under various working conditions is discussed in terms of peak dynamic pressure ratio,acceleration and residual displacement after earthquake.(2)The parameter sensitivity analysis of the metro station structure in the saturated liquefiable site is firstly carried out by extracting the dynamic pore pressure ratio peak value,peak acceleration,displacement response and structural dynamic intermal force coefficient of variation under different buried depth conditions.The impact analysis was carried out.Then,the gray correlation analysis model was established by selecting the four irrelevant variables of shear modulus,permeability coefficient,internal friction angle and ground motion intensity under the condition of determining the buried depth,and the characteristic point dynamic pressure ratio was determined.The gray correlation degree sequence of the acceleration peak and the structural feature section of the station are obtained.Finally,by means of the BP neural network toolbox,the numerical simulation results of the orthogonal design experiment are used as training samples,and the liquefaction prediction is carried out 7m below the middle part of the underground structure.(3)Divide the damage level of the station structure by the maximum displacement angle,the incremental dynamic analysis of the station structure is carried out,and the IDA curve obtained by the calculation is carried out.The seismic probability demand analysis is carried out on the structure,and the regression equation of the structure is given.Based on the seismic probability demand analysis results of the station structUre,the seismic vulnerability curve of the station structure is solved,and the damage surpassing probability of the station structure under the peak intensity of ground motion is analyzed.