Characterization of spatial heterogeneity in an open-pit mine slope based on boreholes and UAV photogrammetry, with stability assessment and application to monitoring layout: a case study

Open-pit mine slopes are prone to concealed weak zones owing to weathering, discontinuity cutting, and variations in rock-mass quality; these zones may fail abruptly under mining disturbance. To identify potential risk areas before visible deformation and optimize monitoring layout, this study focuses on the east slope of the Yanshan Iron Mine. Data from 82 borehole cores were integrated with slope-surface discontinuities automatically extracted from UAV-derived point clouds. Rock Quality Designation (RQD) and discontinuity parameters were incorporated into the Geological Strength Index (GSI) framework through empirical relationships, and a three-dimensional heterogeneous mechanical parameter field was established using the Hoek-Brown criterion. Based on this model, targeted field monitoring was arranged with reference to numerical simulation and limit equilibrium analyses. The results show that the heterogeneous model captures the overall increase in rock-mass mechanical parameters from the slope surface toward the interior. Shallow weathered zones and local fractured zones are the main weak areas. Compared with the homogeneous model, the heterogeneous model more reasonably represents shallow local sliding failure. Field stress responses indicate a potential slip surface at 12–16 m depth. The proposed method supports risk identification, monitoring optimization, and early hazard prevention.