Fracture Network and Rock Slope Stability Analysis of Quarry Areas by Digital Outcrop Modelling and open-sources Algorithms: an example from Montorfano (Southern Alps, Italy)

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Digitization of rock outcrops (e.g., LiDAR, SfM, SLAM) and digitalization of rock fracture data (e.g., Coltop, DSE, CloudCompare) have recently been greatly improved; however, disciplines related to rock mechanics, such as engineering geology, geomechanics, hydrogeology, reservoir engineering, and structural geology, still face two critical limitations (Elmo and Stead, 2021; Yang et al., 2022). First, geological and geotechnical data collection and processing methods remain largely unchanged for decades (e.g., Markland, 1976; ISRM, 1981; ASTM D5878-19, 2019). These methods are often qualitative, prone to significant biases, and reliant on outdated classification and characterization systems, such as manual scanline measurements, photo interpretation, and indices like RQD, RMR, and GSI. Second, despite the shift towards digital approaches, there is still a lack of standardized and statistically robust digital workflows for analyzing fractured rock masses (Yang et al., 2022). For this reason, in this study, we propose an open-source workflow for characterizing fracture networks and analyzing rock slope stability. Our approach integrates UAV-based digital photogrammetry with Digital Outcrop Models (DOM), utilizing CloudCompare software alongside DICE and ROKA algorithms. This workflow was applied to a steep granite slope in Southern Alps near Monte Montorfano, Italy. Manual digitalization in CloudCompare produced a robust dataset of discontinuities—including faults, fractures, and dikes—that influence slope stability. DICE enabled calculations of areal (P21) and volumetric (P32) fracture intensity, as well as intersection density/intensity (I20, I30, and I31). Spatial analysis revealed a general increase in fracture damage with distance from the main fault, though this trend displayed abrupt variations better modeled by an oscillatory pattern than by a simple exponential or power law. ROKA identified critical discontinuities prone to planar sliding, flexural toppling, and wedge sliding, offering more reliable results than traditional kinematic analyses (e.g., Markland test). By visualizing discontinuity planes, intersection metrics, and failure mechanisms directly on DICE and ROKA point clouds, the workflow enabled detailed geometric characterization of the fractured rock slope. High-resolution 3D maps produced through this workflow facilitate robust and user-friendly slope zoning, delivering high-quality, timely information essential for planning effective mitigation strategies.

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