Study On Synergistic Bearing Mechanism Of Shield Tunnel Lining Reinforced By UHPC

To solve the problem of structural damage and deformation overruns that often occur in shield tunnel,this study focuses on the repair technology and synergistic bearing mechanism of segmental lining reinforced by UHPC.First,based on the ground-structure method,an elaborate solid model including reinforcing rebar,bent bolts,and longitudinal joint was established by finite element software.The deformation and failure process of segmental rings,which correlated with ground,under different adjacent excavation depths was analyzed.Result shows that the longitudinal joints are the weak parts of the segmental rings.Subsequently,to study the longitudinal joints reinforced by UHPC,the full-scale test and numerical simulation were successively carried out.The characteristics of the composite structure,which including failure mode,relationship between applied force and deformation,concrete crack,and stress mode of joint were analyzed.It used the full-scale test data to verify the rationality of the parameters in numerical model,and the reinforcement effect of joints under different damage levels were investigated when the load still applies.Finally,the basic design method of UHPC reinforcement technology in shield tunnel was proposed by combining the previous relevant full-scale tests.Main research results are as follows:(1)The deformation and failure mechanism of shield tunnel segmental lining by adjacent excavation was illuminated.The increasing and transferring of bending moment and axial forces in the segmental rings,which causes by the change of surround ground stress under adjacent excavation,results in structural damage or section yield,such as connecting bolts yield and concrete in the pressure zone of the longitudinal joints crush.Therefore,the transverse deformation of the tunnel increases,and the overall stiffness of the tunnel decreases since the failure of the longitudinal joints.The deformation mode of horizontal ellipse occurs in segmental rings.Finally,when there are 5 yielding sections,the tunnel enters the failure stage.The failure process of segmental rings can be divided into the elastic stage,the elastic-plastic stage,the plastic stage,and the failure stage.(2)A method to evaluate the service state and repairability of segmental lining was proposed.It can quickly identify the service state and repairability of segmental lining by comparing the indexes,which is the current disease and transverse deformation values of the tunnel structure,with the characteristic indexes for the tunnel,which is obtained by measurement and numerical simulation in advance.The indicators,which include warning,reinforcement,and control indicators,can be used to evaluate the service state of the shield tunnel,corresponding to the deformation values of the first yielding bolt,the fourth yielding section and the last yielding bolt in the tunnel,respectively.The repair stages,which include easy,repairable,and difficult repair stages,can be used in the real project to evaluate the repairability.The critical points corresponding to the deformation values of the fourth section yields and the first longitudinal joint concrete crushes in the tunnel,respectively.(3)The UHPC reinforcement effect on the ultimate load-bearing capacity of longitudinal joints was given.Comparing the joints of unreinforced and reinforced in the initial state,the failure modes of both sagging and hogging bending moment joints change after reinforcement.The ultimate load-bearing capacity of the joint increases by 503.3% and 72.2%,and the bending stiffness of the joint increases by 177.9% and 3803.2%,respectively.Comparing the joints of reinforced in the initial state and the pre-damaged state,the failure modes of sagging bending moment joints change after reinforcement,while hogging bending moment joints do not change.The ultimate load-bearing capacity of the joint increases by 26.1%and-4.6%,and the bending stiffness of the joint increases by 405.3% and-1.2%,respectively.(4)The failure mechanism of the composite structure of segmental lining reinforced by UHPC was revealed.The composite structure is composed of RC,UHPC,and steel,where the bonding interface of UHPC-steel does not failure,and the failure dominate by peeling and slipping at the RC-UHPC bonding interface.For the anchor screws,some of them fracture in the sagging moment reinforcement joint during the failure process,with the stress state of tension-shear,while them still work in the hogging moment joint.Finally,the composite structure does not completely detaches or fractures and still has ductility.(5)The practical recommended reinforcement opportunity of the shield tunnel segmental rings was proposed.From the view of the load-bearing capacity of the sagging moment longitudinal joint,before the outer edge concrete contact,the later the reinforcement,the greater the increase in the ultimate load-bearing capacity,while the converse after the outer edge concrete contact.From the view of the deformation of the sagging moment longitudinal joint,the later the reinforcement,the smaller the allowable deformation,the greater the stiffness,and the more violent the response when damages.To improve the reinforcement benefit,the proposed reinforcement opportunity for the segmental rings is at the specified range,which is from the first yielding section appears to the first longitudinal joint concrete crush.Meanwhile,the reinforcement benefit increases first and then decreases.