Study On Mechanical And Numerical Model For Road Tunnel Defects Diagnosis

Tunnel defects are considered as great hazards to road tunnel because they endanger the safety of transportational vehicles and shorten the time-span of maintaining cycle and the life of the road tunnel. Studies on road tunnel health evaluation will provide evidence for tunnel maintaining, repairing and reinforcement. The author classify negative effect of tunnel defect into two categories, the degradation of normal transportation capability and the reduction of beating capacity of the structure, the latter of which is the basis of normal transportation capability and is the emphasis of the thesis.According to studies on road tunnel defect, tunnel inspection technology, defects classification method, defects parameter qualification method and defects cause analysis are studied and the author outlines the sketch of tunnel defects studies. Based on the methodology of tunnel health diagnosis and the demand of computational model for tunnel defects, the author presents a new tunnel defects classification method and parameter classification system. Based on the defects classification method and its parameter system, the mechanical models including tunnel lining crack, deficiency of lining thickness, deterioration of concrete, additional load are developed within load-structure model and numerical code is programmed. Then the safety status of Shangwang Tunnel is analyzed with the program, and the sensitivity of defects parameter are analysed with the model.As the defects of road-tunnel is closely related with tunnel construction method as well as the interaction between the tunnel lining and the surrounding rock, the FEM method including the surrounding rock and tunnel lining are setup and the contact element are applied to simulate the interaction between the lining and the rock. Holes between the rock and lining and deficiency of lining thickness are simulated with the model and the effects of defects on the safety status of the structure are analyzed systematically. At last, the sensitivity of defects parameter are analysed.As one of the most frequently-seen defects, Cracks in tunnel lining can greatly reduce the bearing capacity of the lining and eventually cause total collapse of the structure, but the traditional concrete-steel theory cannot evaluate the safety status of structures with cracks. Considering the complexity of stress state in tunnel lining and the propagation of cracks in tunnel lining, the author present three micro propagation modes for modeâ…¡crack. By analyzing the three propagation modes with the traditional strength theory, the author conclude that modeâ…¡crack and compound crack in fact obey the max-circular stress law of fracture. On such conclusion the author modifies a method computing the stress intensity factor of corresponding crack. By this method the author bring deep insight into the new propagation mechanism and a new method is presented to evaluate the safety factor of structure with cracks by considering both the concrete-steel theory and fracture mechanics. At last the method is applied to evaluate the effect of crack length, crack surface friction coefficient, crack position and crack angle in tunnel lining..