Research On Mechanical Behavior Of Cracking Of Shield Tunnel Lining Against Impact Force Of Train Derailment

The safety of high-speed trains has drawn increasing public attention in China in recent times. Given the background of high-speed railway construction, there is a threat of train derailment and impact onto the walls of tunnel shield linings with curves and ramps sufficient to cause structural damage. For this reason, it is very important to evaluate the safety and stability of shield tunnel lining under different train impact loads. In order to study the cracking mechanical behavior of shield tunnel lining under train impact loads and the dynamic response of bolt, a coupling model has been established which took all the following factors into account-the dynamic boundary conditions, the segment joints, the three-dimensional contacts between segments, the nonlinear cracking of segments and joint bolts. The main works and results are as follows:(1) Based on the description of common cracking models of concrete crack analysis, the characteristics and applicable scope of different cracking models are compared. The cracking model based on extended finite element method is chosen to study the extension of dynamic crack, and the basic theory of extended finite element method is described as well as its element numerical integration method. Then, the application of extended finite element method in ABAQUS is introduced, and the initial judging criterion of cracks is analyzed as well as the extension criterion.(2) A three-dimensional train model is established to obtain characteristic curves of train-to-tunnel impact forces, and the empirical formula generated by multi-peaks gaussian fitting is proposed. The cracking model of single segment lining is established, and the extension path of dynamic crack is captured. Then, the generating area, the extension time and extension length of segment crack are studied. The time history distribution characteristics of crack opening are analyzed, and the relationship among segment joint, impact position and crack extension is revealed. At last, the dynamic response of circumferential bending bolt and vertical straight bolt such as stress, deformation, velocity and acceleration are compared.(3) The evolution of crack and the time-history curves of crack opening are studied by establishing a model of double-lined shield tunnel, then, the cracking mechanical behavior of single segment lining and double lining shield tunnel is compared as well as the dynamic response of joints. The role that the secondary lining plays in protecting segment lining and restricting segment lining cracking is revealed.(4) Based on the cracking model of single segment lining, the evolution of joint bolt crack and the time-history curves of crack opening are studied by applying nonlinear cracking on joint bolts. The cracking mechanical behavior of single segment lining under different conditions -taking the bolt cracking into account or not taking the bolt cracking into account is compared, so that the role that bolt cracking plays in dynamic cracking of segment lining is revealed.