| In recent years,the urbanization process has been accelerating,and the urban metro transportation systems has gradually grown in importance as a means of ensuring sustainable urban development,resolving travel and land use issues,and implementing logical planning and development of urban underground space.The stability issues with TBM tunnels in the strata are gradually coming to light as more and more urban subways are built and put into service,particularly in the tunnel structure through the composite strata with soft and hard conditions.In order to investigate the computational model theory,joint flexural mechanical behavior,and longitudinal stability law of the TBM tunnel lining structure under such unique composite ground conditions as soil-rock transition,this thesis draws on the Chongqing Rail Line 5 interdistrict tunnel project.The primary elements consist of:(1)The shell-spring-contact calculation model is built,and the load system of the soil-rock transition section lining structure is improved,by analyzing the existing theory of calculation model of shield tunnel lining structure,taking into account the joint effect and longitudinal spatial force characteristics of the model,and combining the inhomogeneity condition of soil-rock transition section stratum and the research demand of longitudinal stability of lining structure.(2)To investigate the flexural mechanical behavior of the tube sheet joint under various axial bending loads and the force change properties of some special components,a three-dimensional finite element model of a 6.6m OD TBM tunnel joint was developed.Analysis and clarification were done on the impacts of axial force and bending moment on joint angle,joint aperture,bolt tensile stress,and concrete compressive stress at the end of the tube sheet.The values of flexural stiffness of joints are then calculated using the principle of tangent method,and it is confirmed that rising bending moment has a weakening effect on flexural stiffness of joints while increasing axial force has a strengthening effect.(3)A model of the overall lining structure of the TBM tunnel was developed based on the shell-spring-contact model in order to examine how the transition section’s stratigraphic conditions and the structure’s own assembly form affect the longitudinal stability of the tunnel lining structure.The effects of each factor were further clarified by analyzing the internal forces and deformation of the lining structure in terms of the length of the transition section,formation resistance coefficient,lateral pressure coefficient,and formation differences.The proposed favorable assembly suggestion for the soil-rock transition of soft and hard uneven strata is based on the analysis of the impact of the structure’s own assembly form.By comparing the monitoring data with the outcomes of actual engineering numerical simulation,the model’s dependability is finally confirmed.(4)In order to provide experience for safe tunnel construction and repair and maintenance work under normal operating conditions,it is necessary to summarize the stability problems of the TBM tunnel lining structure,divide them into apparent lining structure diseases and longitudinal deformation of lining structure,and elaborate on their causative factors and deterioration effects. |
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