Study on the Influence of Geo-Stress Field on the Fracture Pattern of Secondary Tunnel Lining

The crack of lining is a serious problem that is easy to encounter during construction and operation period of soft rock tunnels. Statical analysis, similarity model tests and numerical simulations were adopted to reveal the influence of geo-stress field on the evolutional process of lining cracks. The results show that: (1) Circumferential crack is a dominant type, followed by longitudinal crack, oblique crack and reticulate crack. In addition, cracks with length being smaller than 0.3 mm or cracks at haunch have largest proportion corresponding to crack length or crack location. (2) Cracks appear at the vault and arch springing firstly as the result of bending failure and compression-shear failure respectively when the direction of maximum principal stress is horizontal, while cracks occur at spandrel and arch springing firstly when the direction of the maximum principal stress is vertical. (3) The stress redistribution process of lining is more complex and the stress path is longer for lining with larger cross-sectional area. (4) When one void exists behind lining, the fracture pattern of lining affected by both the lateral pressure coefficient and the position of void. This study can provide reference for the structural design of secondary lining under different geo-stress fields, that is, the hoop reinforcement of vault and circumferential reinforcement of arch springing should be strengthened when the direction of the maximum principal stress is horizontal, while the hoop reinforcement of arch springing and circumferential reinforcement of spandrel should be strengthened when the direction of the maximum principal stress is vertical.