Comparative Study On Longitudinal Seismic Response Analysis Methods Of Shield Tunnel

Shield tunnel is the main structural form of underground rail transit in China,and the research on its seismic safety has very important social and economic significance.At present,the research on seismic performance of tunnel is still concentrated in the direction of tunnel cross section,while the research on longitudinal seismic performance is relatively few;In recent years,more and more attention has been paid to the longitudinal earthquake resistance of tunnels,and some new seismic calculation methods have emerged,but the comparative study among these methods is still lacking;In addition,for the earthquake resistance of underground engineering,different input methods may have a great influence on the calculation results.Therefore,this paper explores a more appropriate method of ground motion input,and studies several common methods of longitudinal seismic calculation of shield tunnel by using self programmed synthetic artificial seismic wave.The main work and achievements are as follows(1)Summary and Realization of ground motion input and dynamic artificial boundaryThis paper summarizes the principle of viscoelastic boundary and seismic stress input,and uses the python secondary development interface of ABAQUS to realize it in ABAQUS.Compared with the results of theoretical solution and other input methods,the results show that the stress input method is in good agreement with the theoretical solution,and it is suitable for underground engineering seismic.(2)Three methods were used to analyze and compare the seismic response of shield tunnelLongitudinal response displacement method,generalized longitudinal response displacement method and dynamic time history analysis method are used to calculate the longitudinal seismic resistance of shield tunnel.From the point of view of the maximum internal force,the calculation value of longitudinal response displacement method is more safe;According to the envelope diagram of the longitudinal internal force of the tunnel,the seismic internal force of the straight tunnel is evenly distributed along the longitudinal direction.(3)The longitudinal seismic parameter analysis of shield tunnel was carried outBy changing the parameters of earthquake magnitude,buried depth and section size,the influence of these parameters on the internal force of tunnel longitudinal seismic response obtained by each method was observed.The results show that the internal force increases significantly with the increase of earthquake magnitude,and the calculation results of longitudinal response displacement method tend to be unsafe;The increase of buried depth will make the internal force smaller,but the influence is limited,and the calculation results of each method are almost the same;When the cross-section is large,the two longitudinal response displacement methods are unsafe,and the influence of cross-section size on axial force is relatively weak.(4)The seismic response of a tunnel passing through soft and hard uneven soil was studiedThe shield tunnel is placed in the longitudinal soft hard uneven stratum,and the internal force response law under earthquake action was studied.The results show that the area with large internal force will appear near the interface,and it is mainly located in the soft soil side,while the hard soil side is relatively weak.The length of the area where the lateral bending moment of soft soil increases significantly is about2 times of the tunnel section diameter,and the axial force can reach 4-8 times;The larger the modulus difference between soft and hard soil is,the more unfavorable it is to the longitudinal earthquake resistance of tunnel.