Influence of cracks at the invert on the mechanical behavior of the tunnel structures

Abstract Studies show that lining cracks are one of the most common anomalies that occur in the operational tunnels. Therefore, investigating the performance of the cracked linings is of significant importance during the tunnel maintenance. In the present study, model tests and numerical simulations are performed to investigate the influence of the longitudinal cracks at the invert on the mechanical behavior of the tunnel linings. Obtained results show that (1) the pre-existing cracks at the invert aggravate the crushing failure at the back of the fracture zone, leading to the brittle instability of the tunnel; (2) the deformation process of the cracked tunnels initially develops linearly up to a drastic increase. Moreover, the magnitude and the growth of the deformation at the damaged area of cracked linings before the abrupt failure are larger than those of the intact linings; (3) the cracks result in a distinct decrease in the bending moment at the damaged area, whereas the thrust force is less sensitive to the number of cracks; (4) the pre-existing cracks in the invert weaken the lining's ability to resist the pressure of surrounding rock and increase the share of the arch foot in the contact pressure; (5) the pre-existing cracks at the invert reduce the bearing area of linings, thereby weakening the flexural stiffness and favoring the crushing failure at the invert, which is the main reason for the decrease in the bearing capacity of the cracked tunnels.