Analysis On Structural Response Of Shield Tunnel Lining Considering Nonlinearity Of Segments And Joints

As a major social project related to people’s livelihood,the subway has become an indispensable part of the modern urban traffic network.Its social importance also asks for higher structural stability and operational safety of shield tunnels.In the actual operation process,diseases such as lining cracking,chipping,water seepage and wet stains are common,where the behavior of the segment body and joints are obviously nonlinear.Therefore,the study of nonlinear response of the shield tunnel,especially the ovalisation and damage mechanism under the combined action of soil and rock has important engineering significance.The response mechanism of shield tunnel lining is complex.From the local to overall lining structure,there are obvious nonlinear mechanical behaviors in each part:the longitudinal joint is the weak link between the lining,and the rotational stiffness related to the axial force has been clearly expressed,while linear simplification is often considered in the overall analysis.The segment body has a similiar crack and failure mechanism with a general beam,and there is a certain coupling effect between the lining softening and the joint rotation behavior.When the soil surrounding the lining is taken into consideration,the combined action greatly affects the service performance and safety reserve of the tunnel structure.In view of this,based on nonlinear numerical analysis methods,the paper considered the material nonlinearity of joints and segments.At the same time,the interaction of soil and structure was effectively considered based on nonlinear soil spring or nonlinear interface element.In addition,based on measured statistics and existing test,the models were verified and clarified the response mechanism of the lining structure to some extent.The main research contents are as follows:(1)Based on the existing full-scale test results,the validity of the numerical model of a single segment was verified.The nonlinear behavior of concrete,steel and their interaction were accurately simulated by the smeared crack model and embedded bar element respectively.Three smeared crack models including rotating crack model,fixed crack model and multi-directional fixed crack model were considered in parameter analysis of applicability.Besides,two key parameters in structural nonlinear analysis,meshing size and fracture energy,were considered in sensitive analysis,where suggested values were given,laying a foundation for the further analysis of the overall nonlinear behavior of the lining.(2)An 2D FEM model based on layer structure method was put forward,which focused on the nonlinear response of TBM tunnel lining.Nonlinear mechanical behaviors of soil,concrete,reinforcement and contacts were considered in this model.The numerical results matched well with the tunnel monitoring settlement and crack distribution,which verified the effectiveness of the FEM model.The parameter analysis was carried out for the surface loading parameters,the buried depth of the tunnel and the rotation angle of the ring.Based on the calculation results,the quantitative relationship between the overall cracking index and the ovalisation of the lining was given.(3)Based on the field data of metro line 1 in a city of soft soil area,the disease state and crack pattern of the whole line and a typical section in this area were statistically analyzed.Statistical results show that the distribution of the cracks was demonstrably related to the ovalisation of the ring.Based on the established 2D numerical model with layer structure method,the sensitivity analysis of the soil parameters was carried out.The crack characteristic of the segment and its influencing factors were illustrated from calculation results.(4)A shell-spring lining 3D model of single ring based on Janssen joint was established in the paper,in order to evaluating the effect of softening behavior of segments on the overall response of the lining.Meanwhile,a shield lining model with linear-material segment was used as a control group.The influence of softening behavior of segments was clarified by parameter analysis of different ground conditions and load modes.(5)Learning from the composition system and loading method of the continuum model,a numerical model considering the interaction of soil and tunnel was established on the basis of the previous chapter.The nonlinear rotation stiffness of the segment joints and the three-dimensional assembly effect were considered in the model,and the numerical results matched well with the test results.A parametric analysis was carried out to study the effect of the lateral pressure coefficient and the soil stiffness,clarifying the interaction mechanism of soil and ovalisation of lining.