An engineering classification system for the detached granite blocks distributed on slopes

Gentle slopes with large amounts of granite blocks are widespread in granitic areas with warm and humid climate. These blocks pose a potential risk to the existing and planned infrastructure. The instability type and geometry of these blocks will influence their motility and destructive power to some extent. This study aims at creating a classification system that can indicate both the shape and the instability type of these blocks and then developing a block removal scheme. The classification system was constructed based on the mechanical stability analysis of blocks on an inclined surface. This analysis identified key factors affecting stability, including block shape, block weathering roundness, the existing state of a block on a slope, and the friction between the block and the slope. The achieved work allowed the establishment of a direct correlation between block geometry and their instability types. The availability of this classification system was validated by field data and experimental data in the literature. The proposal to remove blocks identified as the toppling types, such as cylindrical-toppling types, cuboid-toppling types, cube-toppling types, was put forward to avoid the uneconomical problem of a complete clearance. Meanwhile, this classification provides a foundation for further research on the instability probability of each type of block and the development of a more refined blocks' removal scheme. The classification approach adopted in this paper can provide a reference for the classification of other lithological blocks under similar engineering geological conditions.