Digital twin based framework for rockfall hazard assessment: remote analysis of an urban cliff in Palermo (Italy)

Abstract

Rockfall phenomena influence human activities in areas where anthropic expansion reaches the slopes of the reliefs. The rockfall hazard assessment is particularly required when exposed elements exist in the area, causing the conditions for a risk scenario. Since direct data acquisition (i.e., in contact with the rock face) for rockfall hazard characterization is not always feasible due to logistical constraints and exposure to the factors generating the hazard, indirect (i.e., remote) approaches have emerged over the past decades as a reliable solution. The main goal of these approaches is to generate a three-dimensional model of the analyzed rock mass, making it possible to extract parameters for the characterization of discontinuity systems and to perform stability analyses remotely. The proposed case study focuses on a portion of the eastern sector of Mount Pellegrino (Sicily), overlooking an urban area of Palermo that includes, among other elements, the monumental cemetery of Santa Maria dei Rotoli. The mount, a carbonate massif that rises 606 a.s.l. within the city of Palermo, has historically been affected by rockfall phenomena. The cemetery represents a vulnerable element to be preserved, both as an artistic and historical heritage site and as a place where human lives are exposed due to tourism and religious activities. In this context, a Terrestrial Laser Scanning (TLS) survey was conducted, allowing the acquisition of a high-resolution 3D point cloud model of the rock face. Once processed and filtered, the point cloud can be considered the geometric basis of a digital twin of the investigated rock front, serving as the raw dataset from which to extract useful information for the geomechanical characterization. Whitin this context, the application of rock mass classification systems can be considered a first digital twin–enabled step, allowing the identification of more critical sectors where specific analyses were subsequently performed to determine quantitative parameters for hazard analysis.