Design And Mechanical Performance Study Of Quasi-rectangular Shield Tail And Steel Segment

The quasi-rectangular cross section tunnel has great advantages in space utilization and tunneling in complex environment over round cross section tunnel.However,due to that few researches have been done on the design and calculation methods of the quasi-rectangular lining structure,the mechanical performance of the steel lining structure and the flexural rigidity of the joints,this kind of tunnel has not been fully developed.Because of the shortages mentioned above,this paper studies these issues based on the project of Ningbo Metro Line 3 and Line 4,and some achievements has been obtained in both research and project level.Regarding to the problem of low rigidity and large deformation of shield tail in the construction of Ningbo Metro Line 3,the ABAQUS finite element software was employed to analyze the mechanical performance of optimized quasi-rectangular shield tail at design conditions.The stability analysis of shield tail shell and the initial defects impact on it were also explored.Besides,parametric analysis is adopted to study the influence of casing thickness and shell thickness on the mechanical behavior of shieldtail structures.The results show that the appropriate thickness of the shield could satisfy the deformation requirements.In this dissertation,the scope of application,advantages and disadvantages of currently adopted calculation models and load models of lining structures are summarized and analyzed.A calculation and load model suitable for quasi-rectangular lining structures are proposed.On the basis of this,the section and longitudinal rib of quasi-rectangular steel segments was designed.And the mechanical properties of the quasi-rectangular section under the design condition were analyzed by numerical simulation.The design was verified to meet the requirements of strength and stiffness for the tunnel with special section.Using parametric analysis method,the influence of each design parameter on the calculation result is studied.Based on the research of various segment joints,the double row bolt joints suitable for steel segments were designed and analyzed.Based on the steel segment and joint designed in this dissertation,of which the finite element is carried out.The relationship between the bending rigidity of doublerow bolts joint and the bending moment as well as axial force of the joint is studied and the formula describing them is also fitted.Besides,influence of prestressing force on flexural rigidity of high strength bolts is analyzed.These results can be taken advantage of in the design and analysis of quasi-rectangular steel segment.