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.