Research Of Shaking Table Test For Large-scale Shield Tunnel Under Non-uniform Ground Motion Excitation

With the development of urbanization and the utilization of underground space in China,shield tunnel is developing towards super long,large diameter,large section and complex formation conditions.In previous study,people saw that tunnel structures are constrained by soil and are not vulnerable to structural damage in seismic motion.Therefore,the seismic design is not generally considered in the tunnel design,resulting in a serious lag in the study of seismic performance of the tunnel structure.However,after the Hanshin earthquake in1995,researchers began to study the seismic response characteristics and seismic performance of underground structures in depth because many tunnel structures suffered serious damage.Shield tunnel is expensive,highly technical demanding and often located in a complex soil environment.The stiffness of the section of shield tunnel is larger than that of the joint.Even if the segment produces small displacement,it will cause the joint to deform greatly.It is of great scientific significance and engineering value to study the seismic response mechanism and seismic performance of shield tunnel joint and its dynamic analysis method.Non-uniform excitation ground motion is one of the most important factors for the damage of long shield tunnel.Nowadays,this problem has caused a lot of research.But limited by the test equipment,few researchers have carried out the test study of shield tunnel response under non-uniform excitation.Most of the current tests on non-uniform excitation are carried out in two relatively independent shear boxes which ignore the propagation of seismic waves in the ground,so the accuracy of the test results cannot be improved.In this connection,a kind of shear laminar box system and a new type of flexible joint were designed.The shear laminar box system could effectively consider the seismic propagation in the shear box during the vibration process in this paper.Based on the Shantou Suai tunnel,a large-shield tunnel(aseismic tunnel and damping tunnel)shaking table testwere carried out to research the seismic response law of tunnel structure under the uniform excitation and non-uniform excitation and verify the seismic performance of the new type of flexible joint.Firstly,this paper discusses the development of tunnels in China and the research significance of seismic response of tunnel structures,introduces the common types of earthquake damage of tunnel structures,and focuses on the research status of shaking table test,non-uniform excitation and the research methods of shield tunnel seismic performance at home and abroad.Secondly,the scheme,preparation and design process of the shaking table test are discussed.The test techniques of non-uniform excitation shaking table are systematically expounded,including model similarity ratio,the design of model soil,the introduction of new flexible joint,the manufacture of model soil,the construction of structure model,the arrangement of the sensors and the loading case.After the test,a large number of data were obtained.This paper analyzes the law of soil acceleration propagation,structural dynamic characteristics,acceleration and its frequency,model structure strain change,pressure at pipe wall,opening quantity at joint,etc.,so as to obtains the regular understanding of large shield tunnel structure in acceleration propagation,strain change and so on.The main conclusion:(1)The soil has a scaling effect on seismic excitation,and the bottom bedrock can improve the propagation efficiency of seismic movement.The existence of tunnel structure will also have a certain impact on the propagation of earthquake.(2)The seismic motion mainly causes the axial strain of tunnel structure.(3)The value of strain and opening width in non-uniform excitation are larger than those in the uniform excitation.Therefore,the non-uniform excitation cannot be ignored.(4)The pressure of the tunnel segments are obviously affected by the strength of the ground vibration,and the flexible joints can effectively absorb the stress and deformation during the shaking process.(5)The unrecoverable opening width produced in damping tunnel is obviously less than that of the aseismic tunnel,which indicates that the flexible joint has good shock-absorbing performance and can better protects the tunnel structure from being destroyed by during the earthquake motion.