A spatial motion-based approach for hazard assessment of unstable rock mass collapses: a case study from hydropower station areas in Southwestern China

Southwestern China serves as a crucial base for the construction of hydropower stations. Unstable rock mass collapses pose a significant threat to both station facilities and personnel. Traditional geological surveys rarely involve detailed zoning of rockfall risk areas. This study proposes a slope hazard zoning method based on the three-dimensional spatial motion characteristics of collapsing unstable rock masses. Using the site area of a pumped-storage power station in southwestern China as a case study, the research first employed UAVs and field surveys to identify the spatial locations and geometric attributes of all unstable rock masses in the area. Secondly, a high-precision 3D geological model overlaid with orthophotos was constructed utilizing traditional geological survey data and photogrammetric techniques. Then, RocPro3D numerical simulation software was used to model the 3D motion of each unstable rock mass, analyzing the spatial geometric relationship between the rockfalls and hydraulic engineering structures. Finally, based on limit equilibrium analysis of rock mass stability, a grid-based weighted overlay method for the spatial quantitative zoning of hazard within the engineering site was developed. This method comprehensively considers three key motion characteristic parameters: kinetic energy, bounce height, and trajectory density of the falling rocks. The approach provides a scientific basis for the protective design, engineering layout, and construction site selection related to unstable rock masses on slopes in hydropower projects.