Study On Seismic Effect Of Large Diameter Urban Railway Tunnel Underpassing Main Channel Of The Middle Route Of South-to-north Water Diversion Project

This paper focused on the background of large diameter shield tunnel of the Zhengzhou Airport Intercity Railway underpassing main channel of the middle route of South-to-North Water Diversion Project.Based on plane strain model and 3D model,the applicability,regularity of seismic design methods and mutual dynamic response of the main channel structure and constructed beneath the railway tunnel were studied and analyzed by using finite element analysis software ANSYS with various seismic design methods such as dynamic time history analysis method,response displacement method,response acceleration method,and integrated response displacement method.(1)Based on plane strain model,the change regularities of structural internal forces of tunnel under 11 operating parameters such as different soil conditions and buried depths were analyzed and compared by four kinds of methods,including dynamic time history analysis method,response displacement method,response acceleration method,and integrated response displacement method.The results showed that there were similar internal force changes calculated by the response displacement method and the dynamic time history analysis method,respectively,and the calculation results are closer and even both higher than that by the dynamic time history analysis method.Therefore,the response displacement method can be recommended as the optimal seismic design method for this project and similar projects.(2)Based on plane strain model,the effecting law and mechanism of different influencing factors of response displacement method under earthquake condition for internal forces of tunnel lining structure were studied(15 operating parameters such as different soil conditions,different buried depths,ground surface with existing building structures and foundation pits et al.),highlighting the applicability of response displacement method in the seismic design of this tunnel.As the following results: the variation range of internal force extreme values are within 1.0% under different soil conditions;the internal force of thestructure decreases with the increase of burial depth.Notably,the extreme values of bending moment with different soil conditions and different burial depths are located near the arch shoulder and arch waist,while the extreme values of shear force appear near the top,bottom and middle of both sides of the tunnel.(3)The 3D complex spatial simulation analysis and calculation model of tunnel lining-tunnel surrounding rock-overlying rock-the channel lining of South-to-North Water Diversion Project was established.The displacement,acceleration,and stress etc.parameters for underpassing the South-to-North Water Diversion Project under earthquake were researched through the key measuring points of typical sections by using dynamic time history analysis method and applying horizontal El centro wave along the tunnel horizontal and longitudinal.As the following results: the intensity of horizontal earthquake is larger than that of longitudinal earthquake,the underpassing tunnel could reduce the vertical displacement of the upper main channel structure to some degree,and the peak vertical displacement of the center of the channel bottom reaches 5.2 mm,less than the control standard of 15 mm,illustrating the safety of total main channel structure.The structure of the main channel of the South-to-North Water Diversion Project will affect the circumferential stress of the underpass tunnel,resulting in the greater circumferential stress of the two cross sections than that of other sections,with the peak stress reaching 2.48 MPa.(4)Analyzed and compared the calculation results of the 3D model with the plane strain model,and as the following conclusions: the circumferential stress deformation law of the two model is similar at the peak moment,and the extreme values of circumferential stress both appear near the arch shoulder,the location where the internal structure is connected,additionally,the peak vertical dynamic deflection of the center of the channel bottom under the plane strain model is reduced by 16.7% compared with the 3D model.The circumferential stress of tunnel calculated by response displacement method under plane strain model that is closer to the result obtained through time history analysis of 3D model,and which difference is low to 0.4%.Considering the complexity of the spring coefficient of foundation,it is suggested to multiply the safety factor by 1.10 times when the seismic design of the tunnel underpass section is carried out by response displacement method.