Research On Lateral Seismic Performance Of Shield Tunnel In Typical Soil-rock Abrupt Stratum

As an important part of urban lifeline engineering,the subway shield tunnel should not only meet the requirements of bearing capacity but also have good seismic performance in urban underground engineering construction.Based on the engineering background of Jinan Metro Line 2,this thesis studies the lateral seismic performance of the tunnel crossing the soil-rock abrupt stratum.Firstly,the site seismic response calculation and comparative analysis are carried out on the selected soil-rock combination stratum and single soil stratum calculation section.Secondly,the lateral seismic performance of shield tunnel in soil-rock combination stratum is simplified by static force method and response acceleration method respectively.Static force method equivalents seismic action to static load based on load-structure model,and then applies static load to load-structure model to solve the problem.Response acceleration method is based on stratum-structure integral finite element model,and the equivalent horizontal acceleration function along the depth distribution is obtained through site seismic response analysis,which is input to stratum-structure integral finite element model to solve the problem.The calculation shows that the maximum shear force and bending moment of shield tunnel occur at the soil-rock interface,and the soil-rock abrupt stratum is more unfavorable to the seismic resistance of tunnel.Thirdly,the nonlinear dynamic time history method is used to study the lateral seismic performance of shield tunnel in soil-rock abrupt stratum.The influence of ground motion input,segment parameters and stratum conditions on the dynamic response of shield tunnel is analyzed.Finally,the suitability of three seismic calculation methods is compared and analyzed.After the above research,the following research results are obtained:1.Horizontal displacement curve of stratum changes uniformly along the depth of single soil stratum at the most unfavorable moment of structural stress,while abrupt change occurs at the interface of soil-rock in soil-rock combination stratum.2.The dynamic response of the tunnel in the abrupt stratum of soil-rock is significantly different from that in the single stratum.The internal force and stress of the tunnel in the single stratum are roughly symmetrically distributed.In the soil-rock abrupt stratum,the displacement,shear force and bending moment of the tunnel in the soil layer are greater than those in the rock layer.The shear force,bending moment and stress are abruptly changed at the interface of soil-rock,and the abrupt value is the maximum value of structural force.Therefore,the soil-rock abrupt stratum is more unfavorable to the seismic resistance of the structure.3.The position and dip angle of the soil-rock interface change,and the internal force and stress of the tunnel will also change.The shear force,bending moment and stress change at the soil-rock interface,and the mutation value is the maximum force of the structure.When the soil-rock interface is located between the arch waist and 45°below the arch waist,the internal force and stress value of the tunnel reach the maximum.Therefore,when the tunnel is located in the soil-rock mutation stratum,the soil-rock interface should be regarded as the weak link in the seismic design of the tunnel.The soil-rock interface should be regarded as the control section in the reinforcement calculation,and the corresponding damping measures should be set to improve the seismic performance of the tunnel.4.With the increase of segment strength and thickness,the deformation of tunnel decreases but the deformation difference is small,while the shear force and bending moment of tunnel increase.Therefore,it is low cost performance to improve seismic performance of shield tunnel by changing segment parameters.5.The static force method,the response acceleration method and the nonlinear dynamic time history method are used to calculate the shield tunnel crossing the typical soil-rock abrupt stratum.The comparative analysis shows that the calculation results of the response acceleration method are too conservative,and the static method is suitable when the peak acceleration of the seismic wave is 0.10 g.Nonlinear dynamic time history method is suitable for seismic wave peak acceleration > 0.10 g.