From rock mass to rockfall activity: A comprehensive rockfall assessment using 3D kinematic analysis and change detection

Rockfalls are highly hazardous rock mass instabilities that pose significant risks to people, property and infrastructure located within the vicinity of affected natural and engineered rock faces. Quantifying the expected size and frequency of rock slope detachments – related to the interaction of environmental factors with pre-existing discontinuities – is a key part of managing rockfall hazard. This paper proposes a new magnitude-frequency analysis approach incorporating detailed geostructural information and the different behaviours of common geological strata across multiple sites with unique slope and environmental factors. In-situ block size distributions derived from 3D kinematic analyses of discrete fracture networks (DFN) are compared with magnitude-frequency relationships resulting from VoxFall-based change detection analyses. Over 2000 detachments observed from two years of approximately monthly photogrammetric surveys conducted along four coastal cliffs in Newcastle (Australia) are compared with more than 1300 potentially unstable blocks identified via 3D kinematic analyses. Spatial and magnitude-frequency analyses showed that rockfall activity varied significantly across several strata and sites, explained by variations in geostructural, morphological and environmental features. Direct comparisons of predicted and observed block size distributions showed good agreement, demonstrating that the proposed approach can explain variations in rockfall activity across different geological strata. • 3D kinematic analyses reveal rockfall magnitude-frequency relationships. • Within the same geological unit, slope geometry influences rockfall activity. • Precursory rockfalls are observed months before large rockfall events.