Study On Longitudinal Seismic Response Of Large Diameter Shield Tunnel With Hard And Soft Abrupt Formation

With the development of urbanization,urban traffic pressure is increasing,large and medium-sized cities actively carry out urban rail transit and other infrastructure design.And shield tunneling has become the preferred method for urban subway tunnels because of its rapid construction,safe excavation,and little environmental impact.At the same time,the depth and diameter of shield tunnel are getting larger and larger,and the geological conditions passing through are more and more complicated.In recent years,there are many types of research on the seismic response of shield tunnels inhomogeneous formation,and fewer researches on complex strata.There are many types of research on the seismic response of small diameter shield tunnels,and greater than 10.0m large diameter shield tunnels are studied.The transverse bending stiffness of shield tunnels is usually several times of the longitudinal bending stiffness,but there are more studies on the transverse seismic action of shield tunnels,and fewer studies on the longitudinal seismic action.Therefore,the mechanical response law of large diameter shield tunnels subjected to longitudinal seismic action in complex strata needs to be studied urgently.Based on the study of the seismic response of shield tunnels at home and abroad,a wide-area two-dimensional model and a local three-dimensional soil-concrete segment structure and a fine numerical model of bolts between pipe rings are established by using the large-scale general finite element software ABAQUS.In this paper,the acceleration variation law of large diameter shield tunnel subjected to the longitudinal earthquake in complex strata is studied,and the risk assessment is carried out to determine the dangerous area.The longitudinal seismic response of largediameter shield tunnels in complex strata is studied.The acceleration change rule and risk assessment were carried out to determine the dangerous area.On this basis,the pipe-ring structure,joint opening and staggering,bolt internal force in the dangerous area are further analyzed,and the longitudinal seismic response law of large diameter shield tunnels passing through soft and hard abrupt strata is obtained.On the basis of numerical simulation,shaking table test preparation was carried out.Silica gel was used as the material of the model structure.Shaking table test was designed and carried out,which verified the correctness of numerical simulation and model test.The results show that the areas with shallow buried depth,complicated geological conditions and close to shield tunnels are often the dangerous areas under seismic action.At the junction of soft and hard soil,the structural stress of shield tunnel,the internal force of bolts,the opening and staggering of pipe-ring joints will change abruptly,and the sudden change of stress and staggering of joint opening of shield tunnel bolts will reduce the attenuation distance in hard soil layer,while the attenuation distance in soft soil layer is larger.The defamation law of shield tunnel joint is consistent with the internal force response law of bolt.Only when the bolt axial force reaches a certain value,the joint opening and bolt internal force show a linear relationship.The defamation law of tunnel joint has consistency and follow-up with the internal force response law of bolt.Only when the axial force of bolt reaches the critical point of deformation,the relationship between the opening of joint and the internal force of bolt is linear.Because of the angle between the interface of soft and hard soil and the axis of the tunnel,the peak internal force of the bolts at the vault and the vault bottom is offset,that is,to the interface of soft and hard soil.