Transverse Seismic Response Analysis Of The Shield Tunnel Under Horizontal And Vertical Bidirectional Earthquake Loading

In recent decades,shield tunnels,which serve as important components of urban transit systems,have been increasingly constructed in earthquake-active regions.Considering their importance to society and economy,it is very necessary to conduct research on the seismic performance of shield tunnels and its mechanism.In recent years of strong earthquakes at domestic and abroad,many underground structures in the near-field area have been severely damaged,and the vertical acceleration of near-field ground vibrations was often relatively large,but there are still many scientific problems need to be solved urgently in terms of the seismic response characteristics and seismic performance of shield tunnels under the action of horizontal and vertical bidirectional earthquakes.To address these problems,the centrifuge shaking-table test and the finite element numerical simulation method had been used in this thesis to deeply study the response mechanism of the shield tunnel under the action of horizontal and vertical bidirectional earthquakes.The main research contents and results are as follows:1、According to the similarity theory of the flexural stiffness and tensile stiffness of the cross section,combined with the existing processing equipment and technical level,a large scale reduced shield tunnel model which was capable of simulating the tunnel assembled by segment and connected by bolts had been designed and produced,which could realize the reduced-scale model test study that considered the influence of joints on the seismic response of shield tunnels.According to the working principle of resistance strain gauges,combined with the characteristics of the large scale reduced shield tunnel model segment joints,a miniature displacement measuring instrument was designed,and the measurement method of the relative opening displacement of the segment joints was proposed to solve the problem of measuring the relative displacement of the joints of the reduced-scale model of the shield tunnel in the centrifuge shaking-table test.2、Based on the whole tunnel model,the seismic dynamic tests of the tunnel system under horizontal earthquake loading as well as under horizontal and vertical earthquake loadings were carried out,the influence characteristics and the reasons on the seismic responses of the shield tunnels by the vertical seismic loading were analyzed.The centrifuge shaking-table test of the assembled segment tunnel model under the horizontal and vertical earthquake loadings was also carried out.The relative displacement of the segment joint and the internal force distribution of the segment under unidirectional and bidirectional earthquake loadings were obtained.The influence and importance of segment joints on the seismic response of the shield tunnel were analyzed and identified.3、Considering the correlation between the initial shear modulus and the reference shear strain with the confining pressure,the nonlinear viscoelastic constitutive model was revised,and based on the explicit module of ABAQUS finite element software,the explicit subroutine module of this nonlinear viscoelastic constitutive model was developed.Using the prototype scale,the finite element model of the centrifuge shaking-table test was established,and the segment joints were reasonably simulated.By comparing the results of centrifuge shaking-table tests and the results of numerical simulations,the effectiveness and rationality of the established shield tunnel finite element model were validated.At the same time,through the simulation of the loading test of the actual engineering shield tunnel joint,the effectiveness of the simulation method of the bolt joints between the segments of the actual prototype shield tunnel was further validated.4、Using the validated finite element numerical simulation method,the seismic dynamic finite element numerical analysis model of the shield tunnel system was established,the seismic responses of the shield tunnels under horizontal and vertical bidirectional earthquake loading were studied.The internal force distribution of the lining segments was obtained,together with the relative displacement of the joint and the law of variety of the bolt force.The factors such as the buried depth of the tunnels,the distance between twin-tunnels,the location of the sealing segment,the relative stiffness between the soil and the tunnel structure,the correlation coefficient of the initial shear modulus and the reference shear strain of the soil and the confining pressure,the type of input seismic motion and the maximum acceleration amplitude were analyzed.Through detailed comparison analysis,the seismic response mechanism of the shield tunnel under the action of bidirection earthquake was revealed,and some suggestions for seismic resistance of the shield tunnel structure under the action of the bidirection earthquake loading were given.The research results in this thesis clarify the dual effects of the vertical seismic acceleration,including changing the progation of the shear wave and enhancing the vertical compression of the soil layer.The results also explain the important influence mechanism of the shield tunnel lining structure on the lateral seismic response of the shield tunnel.It provides a valuable reference for the seismic design of shield tunnel in engineering practice to consider the action of near-field earthquake.