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The deformation and failure of mining slopes in layered rocks predominantly result from shear landslides. However, the instability process of the Pusa rock avalanche in Guizhou, China, revealed a unique damage phenomenon: prominent breaking and toppling of rock blocks occurred in the central section of the mountain, with a lack of commonly observed shear landslide features. This paper aims to investigate the underlying reasons behind this distinctive damage pattern. The study employs various methods including geological survey, UAV aerial survey, physical simulation, and discrete element numerical simulation. The findings indicate that the geological conditions, characterized by a hard upper layer and a soft lower layer along with underground mining activities, play a significant role in triggering the landslide. Furthermore, the presence of a columnar structured rock mass emerges as the primary factor influencing the instability of the Pusa rock avalanche. To elucidate the mining failure mechanism of the rock mass with vertical joints, we propose a "subsidence-buckling" failure model. Following the subsidence and collapse of the roof rock mass in the goaf, the columnar rock mass in the upper and middle portions of the slope undergoes deflection and deformation, forming a three-hinged arch structure. This structural configuration converts the pressure exerted by the overlying rock mass into both vertical pressure and lateral thrust. Under the influence of external loads, the slope experiences buckling failure, ultimately leading to instability upon fragmentation. By shedding light on these findings, this study contributes to a better understanding of the spatiotemporal evolution of mining slope fractures and their impact on slope stability. [ABSTRACT FROM AUTHOR]