Model Test Study On Longitudinal Deformation Failure Mechanism And Reinforcement Measures Of Shield Tunnel

At present,shield tunnelling is widely adopted in urban rail transit and underground utility tunnel and other urban tunnel construction.Under the influence of external construction operations such as excavation of adjacent deep foundation pit,water and soil loss caused by construction of connecting passage,underpass engineering,shield tunnel is prone to excessive longitudinal uneven deformation,which will lead to water leakage,lining structure cracking,dislocation and other diseases of tunnel structure,endangering the normal operation and lining structural safety of the tunnel.Therefore,it is necessary to explore the longitudinal deformation and failure mechanism of shield tunnel and the bearing mechanism after the implementation of longitudinal structural reinforcement measures.In this paper,through carrying out a number of 24-ring shield tunnel load-structure model tests,the longitudinal deformation mechanism and failure mode of shield tunnel,as well as the bearing capacity and failure characteristics of shield tunnel after longitudinal reinforcement are explored.Then,the longitudinal reinforcement effect is introduced into the longitudinal equivalent continuum model through theoretical derivation.The main work and research results are summarized as follows.(1)Taking the general Metro Shield Tunnel in Guangzhou as the prototype,through reasonable experimental means,fully considering the stress characteristics of lining structure,joint structure characteristics,foundation reaction and surrounding rock lateral confinement,based on the self-designed longitudinal deformation test platform of shield tunnel model,the fine simulation of scaled shield tunnel model is realized.(2)Through analyzing the detailed deformation law of the circumferentiao joints shield tunnel model in the loading process,it is proved that the longitudinal deformation mode of the shield tunnel is a mixed mode of "bending + dislocation".Also,the failure process from the local failure of the arch bottom bolt joint to the loss of the longitudinal bending bearing capacity of the circumferential joint,and the influence of the failure of the circumferential joint on the transverse stress and deformation of the shield tunnel are both expounded.The rationality of Timoshenko beam theory applied to the analysis of longitudinal deformation of shield tunnel is verified based on the 5-ring shield segment shear test to determine the shear stiffness of ring joint.(3)According to the model test results of longitudinal channel steel reinforcement model of shield tunnel,the longitudinal reinforcement has a significant control effect on the opening deformation and dislocation of circumferential joints.The failure load of circumferential joints is 1.74 times and 2.04 times of that of non reinforced staggered joint and through joint tunnel models,and the overall longitudinal stiffness of tunnel is 2.02 ～ 2.18 times of that of non reinforced staggered joint tunnel.At the same time,it reveals the longitudinal and transverse continuous failure mechanism of the longitudinal reinforced shield tunnel,which results in the brittle shear failure of the annular joint and the instability of the segment cross section.(4)The longitudinal equivalent continuous model of shield tunnel considering longitudinal channel reinforcement is compared with the test results,which proves the rationality of the derived formula,and further parametric analysis of the influence of channel reinforcement position and axial stiffness on the reinforcement effect is carried out.