The role of intact rock fracture in rockfall initiation

High, near-vertical rock faces were investigated to determine the role of intact rock fracturing in rockfall initiation. Terrestrial LiDAR and photogrammetry were used to characterize historical and recent rockfall failure surfaces at two sites – one natural cliff face, and one engineered mine wall. Intact rock fracturing associated with each rockfall was estimated by comparing failure surface geometry to mapped discontinuity orientation and persistence; and by the application of two point cloud roughness analysis techniques. Estimates of intact rock bridge proportion provided the constraints for input parameters of slope-scale distinct element models. These models used a time-dependent strength degradation code, applied to a Voronoi network, to reproduce observed failure mechanisms. These analyses also provided the basis for proposed LiDAR monitoring at each site, and a system for classifying and prioritizing areas of high rockfall initiation hazard. Results of this research allow for better understanding of the interaction between intact rock bridges and discontinuities in high vertical slopes.