Indirect Rock Mass Characterization Using High-Resolution 3D Point Clouds Applied in Hazardous Rock Slopes

Rockfalls are among the most critical phenomena in geomechanics due to the significant risk they pose to human lives and infrastructure. Rockfall risk is defined by the interplay between hazard and the potential impact on exposed elements. Specifically, hazard assessment relies on the propensity for detachment (estimated frequency), event magnitude (volume), and intensity (kinetic energy).
Detachment propensity is governed by predisposing structural conditions and analyzed by the probability of failure modes, such as planar sliding, wedge sliding, or toppling, in relation to the main discontinuity sets. Conversely, magnitude and intensity depend on the probable volume of the unstable block and its potential propagation path.
Traditional geo-structural surveys, based on direct acquisition using standard instruments (e.g., geological compass and measuring tape), characterize, among other parameters, discontinuities in terms of orientation (dip angle/dip direction), spacing, and persistence. While the orientation of discontinuities, combined with mechanical properties, allows for the evaluation of the propensity to detachment, the definition of spacing and persistence is crucial for estimating block volume. However, this deterministic approach is often difficult to generalize to an entire slope, making accurate volume definition a persistent challenge.
To address this limitation and avoid the risks associated with direct data acquisition in hazardous areas, indirect remote sensing approaches have gained prominence. This study addresses the rockfall hazard characterization of a critical slope in the Palermo Mountain System (Sicily, southern Italy), where frequent rockfalls have disrupted vehicular traffic. Utilizing a Terrestrial Laser Scanner (TLS), the authors applied an indirect characterization method. Multitemporal acquisitions enabled a high-resolution 3D Point Cloud-based analysis, allowing for a more accurate and safe definition of hazard parameters in this complex environment.