Experimental Investigation on Fracture Behaviors of Straight-Wall Tunnels with Defects of Insufficient Lining Thickness

Fractures in straight-wall linings is a common disease that seriously affects the integrity and service life of tunnels. The presence of insufficient lining thickness can be regarded as one of the most important factors causing fractures. In this study, the fracture behaviors of straight-wall tunnels with insufficient lining thickness under progressive compressive loading were investigated. First, the fracture characteristics and failure mode were explored. Subsequently, the deformation behaviors were investigated by digital image correlation (DIC) technology. Finally, the fracture pattern was systematically discussed. The results show that the deformation intensifies in the areas with insufficient lining thickness, which is prone to induce cracks. As the ratio or range of insufficient thickness increases, the severity of fractures intensifies and the failure mode tends to be more complex. In addition, whether the lining comes into contact with the surrounding rock in the area with insufficient thickness has a significant impact on the failure mode. Furthermore, the more serious the defect is, the more obvious the spalling phenomenon will be. Moreover, the failure mode of straight-wall tunnels can basically be attributed to the combined effect of the fractures of defect zones, arch feet and tunnel floor.