Shear Stiffness And Deformation Mechanism Of Rectangular Pipe Jacking F-Type Socket Joint

Rectangular pipe jacking tunnel has the advantages of large section utilization,shallow soil cover and low construction cost,which has a wide application prospect in urban highdensity areas.With more and more projects of urban subway underpass rectangular pipe jacking tunnel,the safety problem of rectangular pipe jacking tunnel structure is more and more prominent.The failure cases of tunnel show that the failure of tunnel is usually caused by the failure of pipe jacking joint.Pipe jacking joint is the lowest part of pipe jacking strength and stability.Because the joint part should meet the water stop and shear characteristics,it is particularly important to study and analyze the properties of pipe jacking joint.However,there are many structural parameters of F-type socket joint in rectangular pipe jacking tunnel,and the mechanism of stress and deformation is very complex.The key theoretical problems such as internal force deformation relationship model and stiffness model,deformation mechanism and failure mode,deformation control standard and so on are still unclear,which need to be further studied.In this paper,a large section rectangular pipe jacking tunnel is taken as the prototype,and the F-type socket joint is taken as the object.The full-scale method is used to study its shear performance:(1)By analyzing the assembly process of rectangular pipe jacking f-joint and the elastic recovery process of olecranon rubber,the finite element analysis model is established and calculated.Using Mooney Rivlin strain energy function to analyze the sealing effect of socket and rubber ring,the stress distribution and contact pressure distribution law of olecranon rubber ring in the whole load stage are obtained,and the sealing condition of rectangular pipe jacking joint in this state is judged to be good.Through the analysis of contact pressure between steel ring and olecranon rubber ring in the process of elastic recovery,the failure of waterproof seal is obtained The criterion of joint waterproof seal failure and the standard of deformation control are established for the rectangular pipe jacking tunnel.(2)In order to analyze the shear stiffness of the rectangular pipe jacking segment joint,the shear capacity characteristics of the complete segment joint were numerically simulated by the finite element method.By establishing a three-dimensional refined joint model,the failure characteristics and failure mechanism of the segment joint under shear force are studied,and the shear relative shear deformation curve of the joint is obtained.The curve parameters are fitted by Origin,and the shear stiffness of the joint at different stages is obtained.(3)In order to explore the influencing factors of shear stiffness of F-type socket joint,different single factor variables were analyzed.By changing the thickness and length of steel collar,the radius of chamfering,the wall thickness of segment,the coefficient of foundation bed,and adding connecting bolts in the joint structure,the influence on the shear stiffness of the joint is studied.The finite element parameter analysis shows that the increase of the thickness,length,chamfer radius,foundation reaction and pipe section thickness of the steel collar can improve the shear stiffness of this type of pipe joint,and the addition of connecting bolts has a significant impact on the shear stiffness and shear bearing capacity of the structure joint.