Abstract: We conducted monitoring of peripheral rock deformation and performed discrete-continuous coupling numerical analysis on 11 typical inclined thin-layered carbonaceous slate tunnels of the Yunnan Shangri-la-Lijiang Expressway. This study investigated the large deformation characteristics and unloading failure mechanisms of peripheral rock in these tunnels, and proposed corresponding countermeasures. The results indicate that: (1) The peripheral rock deformation of inclined thin carbonaceous slate tunnels is significantly influenced by excavation unloading and construction disturbances. The deformation is characterized by large quantitative values, rapid rates, and long durations. Additionally, crown settlement is greater than horizontal convergence, indicating significant unloading deformation of the peripheral rock, which exhibits asymmetric spatial distribution characteristics. (2) Peripheral deformation failure further develops with the construction of each step. After excavating the upper step, bending failure occurs in the peripheral rock on the left shoulder of the tunnel, forming an initial unloading area with pronounced asymmetric characteristics. As construction progresses through the middle and lower steps, the bending failure of the left shoulder’s peripheral rock continues to develop, while shear-slip failures gradually occur in the crown and right shoulder, ultimately leading to an expansion of the overall unloading failure area. (3) Pre-reinforcement of the strata is the primary effective method for controlling the deformation of inclined thin-layered carbonaceous slate. This approach can be combined with strategies to reduce construction disturbances and optimize the timing and parameters of support for the comprehensive treatment of peripheral deformation.

Key words: tunnel, inclined thin-layered carbonaceous slate, discrete-continuum coupled analysis, unloading large deformation, countermeasures