Crack characteristics and propagation patterns in water diversion tunnels based on intelligent detection data

To investigate the characteristics and propagation patterns of cracks in water diversion tunnels during operation, this study utilized tunnel engineering projects in southwestern China. Based on the intelligent inspection data for lining surface defects, combined with mechanical models and numerical simulation methods, the distribution characteristics and propagation processes of lining cracks under internal water pressure were analyzed. The results indicate that cracks are the primary defect type, with lengths concentrated in the range of 0–5 m, and are predominantly distributed at the top of the tunnel entrance section. Owing to the influence of the surrounding rock stress, the tunnel top becomes a high-risk area for crack initiation, and the local stress significantly increases after the lining cracks. Meanwhile, the circumferential stress exhibited a decreasing trend along the tunnel length, resulting in the formation of more cracks at the inlet. Numerical simulations show that the deformation of cracks at the top of the tunnel entrance is most severe, and the crack propagation follows a pattern of “depth extension–penetration through the lining–turn toward the inner wall”. The simulation results agree well with the mechanistic analysis of the inspection results.