Study Of Collapse Mechanism And Controlling Method Of Steel And Ductile Cast Iron Segmental Lining Of Shield Tunnel

Shield tunnel collapse usually brings huge casualties and economic losses.Relevant case studies show that most of the shield tunnel collapse accidents are caused by the local failure of tunnel lining.However,based on the above problems,this paper studies the collapse mechanism and control methods of steel/ductile cast iron segment lining in shield tunnels under two external pressures,hydrostatic pressure and earth pressure,which may lead to structural damage.It focuses on the analysis of various factors affecting the local large deformation(buckling)of segment lining in shield tunnels.Through introducing the case of shield tunnel collapse accident,the necessity of research significance is discussed.On this basis,the research status of shield tunnel collapse is summarized,and practical data for subsequent analysis are obtained.According to the structural design principle of shield tunnel lining,a three-dimensional refined model of shield tunnel lining ring including ribs,bolts and joint plates,which can reflect the actual situation of steel/ductile iron segments,is established.The model can reflect the material and geometric nonlinearity.Firstly,the local buckling characteristics of single-ring lining under external pressures are studied by using the above-mentioned model,and the stress and local buckling characteristics of high-strength bolts and segment lining are analyzed during the research process.Based on this,the mechanism of tunnel collapse caused by the local failure of tunnel lining is discussed.Secondly,a refined model of shield tunnel with 6-ring lining segments is introduced to study the progressive collapse process caused by local buckling of the structure,and the effects of bolt joint stiffness,backfill grouting and diameter-thickness ratio on the buckling of the lining structure are analyzed.The results show that the shield tunnel lining structure will exhibit unstable local buckling deformation when the load exceeds the ultimate bearing capacity under external pressure.In addition,the stiffness of radial bolted joints has a significant effect on the buckling characteristics of segments.With the increase of bending stiffness of radial joints and thickness of lining segments,the buckling strength of structures under static loads increases accordingly.Finally,according to the calculation and analysis results of single-ring lining and multi-ring lining,an active control method is proposed to control the progressive collapse of shield tunnel caused by local buckling.The main idea of this method is to consider controlling and replacing the collapsed lining,thereby reducing the possible damage caused by the continuous collapse of shield tunnel.