Study On Transverse Mechanical Behavior Of Shield Tunnel Based On Model Tests And Its Application In Surface Surcharge

In recent years,subway has developed rapidly in many cities because of its convenience and fast speed.Among different kinds of tunnel,the shield tunnel assembled by the segments through segment joints is the most commonly used.However,with the development of urbanization,many existing shield tunnels will be affected by external engineering activities inevitably.And in the shield tunnel,there are more and more accidents caused by surface surcharge.Therefore,this paper uses the model test to investigate the influence of different factors on the transverse mechanical behavior of the shield tunnel.Based on the tests and combined with finite element method,the influence of surface loading on the deformation of existing shield tunnel is studied,which can provide a theoretical basis and reference for the protection of existing shield tunnel in surface surcharge project.The research contents and conclusions are summarized as follows:(1)Taking the typical shield tunnel with an outer diameter of 6m in Guangzhou Metro as the prototype,a scaled shield tunnel model was designed and constructed.Then,through the lateral loading test of the shield tunnel model,this paper studied the interaction between the rings of shield tunnel and the influence of segment joint and segment assemble method on the transverse mechanical behavior of shield tunnel.(2)Based on the model test,this paper investigated the transverse effective rigidity ratio of the shield tunnel from the beginning of loading to structural failure.The results show that the transverse effective rigidity ratio of tunnel is not a constant.When the structure is in the elastic stage,the transverse effective rigidity ratios of the throughjoint and the staggered-joint assembled shield tunnel fluctuate around a fixed value.Their ranges vary from 0.50 to0.65 and from 0.66 to 0.73 respectively.When the structure exceeds the elastic stage,the transverse effective rigidity ratio decreases rapidly.However,the decline rate slows down when the transverse effective rigidity ratio decrease to a certain value.(3)Based on the modified routine method and combined with the variation curve of the transverse effective rigidity ratios obtained from the experiments with the increase of the tunnel ellipticity,a method for calculating the ellipticity of the shield tunnel under the influence of external operations was proposed,which can also consider the change of the transverse effective rigidity ratios.The feasibility and accuracy of the method were verified with practical engineering measured data.(4)Based on model test,combined with finite element analysis,the influence of surface loading on the deformation of existing shield tunnel was analyzed.The results show that under the effect of surface loading the deformation of the shield tunnel is maximum when the shield tunnel locates near the edge of the surface loading area..The results also show that the influence zone of tunnel deformation caused by surface surcharge can be divided into significant influence zone,general influence zone and weak influence zone,and can be influenced by different assemble methods.