Analysis of deformation and failure mechanism of shallow buried bias loess tunnel induced by fracture dominant infiltration under rainfall environment

The change of water environment is the main factor inducing loess tunnel disasters, and the existence of dominant channels plays an important role in the infiltration of water into the surrounding rock. Taking the Pianqiao Tunnel as the engineering background, based on on-site research, the evolution process, infiltration characteristics of dominant channels, and tunnel structural response laws during rainfall were explored through physical model experiments and numerical simulations, further revealing the deformation and failure mechanism of loess tunnels induced by crack dominant infiltration. The results indicate that the development of dominant channels are the result of the coupling effect of the formation of "new" cracks and the extension and expansion of "old" cracks. Under the influence of dominant channels, the infiltration mode gradually changes from steady-state infiltration to fissure controlled dominant infiltration, changing the migration path of surrounding rock water while accelerating water infiltration into deep surrounding rock. As the depth of the crack increases, the range of influence of dominant infiltration becomes larger, and the infiltration front gradually changes from "curved" shape to "funnel-shaped" shape. The local temporary saturation zone formed at the end of the crack intensifies the deformation of the surrounding rock, resulting in a significant asymmetry in the stress distribution of the tunnel, with the tunnel structure under the dominant channels being most affected. When a through crack appears, the settlement of the vault caused by dominant infiltration reaches 56.3 mm, and the structural stress increases by 140 kPa compared to uniform infiltration.