Study on the Influence of Cracks on the Mechanical Performance of Tunnel Lining Structure Based on Fracture Mechanics Theory

The problem of tunnel lining cracking is becoming more and more common. The existence of cracks changes the stress state of lining structure and has an adverse impact on the safety of lining structure. In this paper, the mechanical properties of tunnel cracked lining structure are studied. Based on the theories of structural mechanics and fracture mechanics, the performance indexes of cracks in the arch waist of tunnel secondary lining are studied with the reference of stress intensity factor. The numerical simulation calculation is carried out. Finally, the XFEM extended finite element method is used, the crack damage of secondary lining under different crack depths is demonstrated and analyzed, and the theoretical value is compared with the numerical value. The results show that, for the cracked model (the crack depth is 12 cm), the stress and displacement at the arch waist increase greatly compared with the uncracked model and are the most significant with the increase of crack depth. In the initial stage of crack development, the growth of stress and displacement of the structure is not obvious, and the small change of crack depth in the later stage can also cause great growth of stress and displacement. Compared with the uncracked model, when the crack depth is 3 cm, the maximum vertical stress increases by 4.3 times and the maximum settlement increases by 1.3 times. When the crack depth is 18 cm, it increases by 21.2 times and 2.94 times, respectively. The research results can provide a theoretical basis for the prevention and treatment of cracks in the arch waist of tunnel secondary lining during tunnel operation.