Shaking Table Test Study On Seismic Response Of Shallowly Buried Subway Station In Soil-rock Composite Strat

With the rapid development of the city and the increase of the population,the traditional columned or small span columnless subway stations are no longer able to meet the growing demand for passenger flow.In order to make full use of the advantages of wide-span pillarless subway stations,which have wide vision space and high passenger transport efficiency,Jinan Subway plans to build several such stations.However,Jinan area has typical characteristics of soil-rock strata,and there are great differences in soil-rock stiffness.It is of great engineering significance and theoretical value to study the seismic performance of large-span pillar-free subway stations in soil-rock composite strata.In this paper,a large scale shaking table test system is used to carry out the shaking table test of large-span pillarless subway station structure relying on a subway station project of Jinan rail transit.Firstly,based on the layered shear box,the key technology of shaking table test is designed,the test model of long-span pillar-free subway station is made,and the loading conditions of seismic waves are designed.Based on the analysis of the acceleration of the model system,the strain of each component of the station structure and the structure-foundation dynamic earth pressure,the seismic response and rule of the underground long-span pillar-free subway station are summarized.Finally,MIDAS-GTS finite element software is used to analyze the seismic response characteristics of the stations with and without columns in terms of acceleration response,displacement response and stress response,and further reveal the seismic response rules of the stations without columns.The main research content and work of this paper are as follows:1.Based on the actual size of the station prototype,referring to the table size and working performance of the shaking table system,and based on the second similarity Bockingham-π theorem,elastic modulus E,geometric size L and acceleration a are selected as basic physical quantities,and the similarity ratio coefficients of other physical quantities are determined by the similarity ratio relationship.Through laboratory tests,similar materials of model soil layer and surrounding rock were prepared,station structure model was made,sensor layout was optimized,and Kobe wave,El-Centro wave and Jinan artificial wave were selected as seismic input waves,and different loading conditions were prepared.2.The shaking table test results show that the Kobe wave with low frequency distribution has the greatest influence on the station structure(foundation),and the influence of soil-rock combination formation on the peak acceleration is more obvious when the earthquake grade is larger;The strain increases obviously at the roof of the station,the joint between the side wall and the roof,and the joint between the side wall and the soil-rock interface,which is the weak point of the large-span pillar-free subway station structure in the soil-rock composite stratum.The amplitude of dynamic earth pressure along the depth of the station side wall shows that the soil-rock interface is the peak point and the turning point,and the station structure located at the soil-rock interface should be the focus of seismic design.3.Based on MIDAS-GTS finite element software,the vibration table test of a large-span column-free subway station in soil-rock combination strata was analyzed numerically to verify the rationality of the calculation results and summarize the seismic response rules.On this basis,the seismic response analysis of soil-rock free site and subway station structures with and without columns is carried out.The results show that the seismic response of subway stations with columns is smaller than that of stations without columns under different earthquake types.Compared with stations with columns,the stress distribution at the bottom of the roof span and the axillary Angle of the station without columns is larger,and special attention should be paid to enhancing the seismic performance of these parts in the seismic design.