Analysis Of Tunnel Lining Cracks

The 21^st Century is an era for developing underground space.As a fast and convenient channel,tunnel is the key project in the transit network plan,the security and durability of the tunnel have always been the focus of the academic community.For concrete structures,cracks are inevitable,materials,environment,design,construction and other factors are possible to cause disease in concrete structures.Cracks of lining tunnel always play the main part in threatening the safety of tunnel,studying various mechanisms of cracks is the prerequisite of crack analysis;it is of great significance to research the emergence and development of cracks for evaluating the safety of structural cracks and taking quick measures to repair them.At present,most tunnel tests focus on the ultimate load capacity,the research on the lining cracking mechanism and the stability of cracking lining are not systematic.In view of the above problems,the following research works are carried out in this paper:?1?Collect and reorganize the relevant literature at home and abroad,discuss the mechanism of concrete cracks,and summarize the causes of tunnel cracks;?2?Explain the fracture mechanics theory of concrete,such as the Griffith fracture theory,plastic zone theories at crack tip,tension-softening law in concrete and so on,and sort out numerical methods for modeling cracks;?3?Detail the concept and numerical calculation of the Fictitious Crack Model?FCM?,and obtain the crack equation,present a path-modeling method using the so-called dummy elements and dual nodes,without altering the total numbers of nodes and meshes or specifying the path of crack propagation.Based on this,introduce crack path modeling with dual nodes and the solution scheme for incremental stress analysis;?4?The fundamental difference between single-crack and multiple-crack problems is whether or not the next-step cracking behavior is predictable.For multiple-crack analysis,put forward the Extended Fictitious Crack Model?EFCM?,derive the crack equation,and solve the displacements and stress fields at the crack tip,which provides a theoretical basis for subsequent fracture analysis;?5?Write a complete crack analysis program using Fortran language,carry out numerical simulation of the pure I fracture in the tunnel,draw the Load-Displacement curve,which agrees well with the test results,verify the correctness of the program,then get the crack pattern,load-crack mouth opening displacement?CMOD?relationship curve.