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Questo progetto di ricerca, ha affrontato una vasta gamma di aspetti relativi ai fenomeni di crollo roccioso. L'indagine ha compreso l'analisi di casi di studio reali con l'obiettivo di comprendere la distribuzione dei frammenti in relazione al volume e alla topografia. Inoltre, sono state condotte simulazioni numeriche allo scopo di valutare l'impatto della frammentazione sull'analisi della pericolosità. Allo stesso tempo, sono stati condotti esperimenti in situ e di laboratorio al fine di approfondire la comprensione delle dinamiche di frammentazione. Questo approccio multidisciplinare ha fornito intuizioni sul comportamento dei crolli rocciosi, la frammentazione e le relative implicazioni per la valutazione della pericolosità e la gestione del rischio in regioni montuose. In particolare, la tesi si è concentrata su quattro obiettivi principali: L'analisi di casi di studio di crolli rocciosi, con un focus specifico sull'esame delle distribuzioni delle dimensioni dei blocchi nel deposito finale dei frammenti dei crolli. Questo approccio ha consentito di proporre indicatori che forniscono informazioni dettagliate sulle dinamiche di frammentazione durante gli eventi di crollo. Nello specifico, nel Capitolo 1 sono stati descritti tre indicatori chiave correlati alla frammentazione nei crolli rocciosi: la distanza percorsa rispetto alle dimensioni dei frammenti, la relazione di scala di potenza tra il deposito e le dimensioni dei frammenti, l'angolo di copertura e la dispersione laterale. Questi indicatori forniscono importanti informazioni sulla presenza di frammentazione dinamica durante gli eventi di crollo, permettendo di distinguere tra le caratteristiche del deposito primario e quelle dei blocchi/frammenti, mentre evidenziano la mobilità e il consumo di energia associati alla frammentazione. La quantificazione e la valutazione della frammentazione nelle dinamiche e nella pericolosità dei crolli rocciosi attraverso una modellazione dettagliata e l'analisi di, This research project, titled "Rockfall Volume Distribution, Fragmentation, and Frequency in the Context of Climate Change," aimed to explore various aspects of rockfall phenomena. The investigation included the analysis of real case studies to understand fragment distribution in relation to volume and topography, numerical simulations to assess the impact of fragmentation on hazard analysis, and in-situ and laboratory experiments to enhance the understanding of fragmentation dynamics. This multidisciplinary approach sought to provide some insights into how rockfalls behave, how fragmentation occurs, and the implications for hazard assessment and risk management in mountainous regions. Specifically, the thesis attempted to focus on four main objectives: 1. The analysis of real case studies of rockfalls, with a specific focus on examining the distributions of block sizes in the final deposit of rockfall fragments. This approach aimed to propose some indicators that could provide information about the dynamics of fragmentation during rockfall events. 2. The quantification and evaluation of fragmentation in rockfall dynamics and hazard assessment through detailed modeling and analysis of real case studies. This approach aimed to examine how fragmentation processes influence rockfall hazard and the importance of explicitly modeling fragmentation for accurate hazard assessment. 3. The analysis of the fragmentation process through experiments conducted at different scales (full-scale and laboratory-scale) to investigate behaviors observed in real case studies, focusing on dispersion, deposition, and mobility of rockfalls, as well as the effects of discontinuities. Despite the complexities and challenges in this area of study, the analysis of fragmentation in rockfalls remains of significant importance for various reasons. This work aimed to contribute to the enrichment of the understanding of this topic, impacting context of risk assessment and management in mountainous r

Rock avalanches display a distinct and complicated behavior that is not yet completely understood. Analyzing the deposit characteristics is crucial for studying the comminution mechanism during its emplacement. Combining field investigation, image processing, and numerical modeling, we explore the deposit characteristics and comminution process of the Wangjiapo rock avalanche triggered by the Mw6.2 Ludian earthquake. First, we use UAV photogrammetry to obtain a three-dimensional point cloud model and a digital orthophoto, from which we semi-automatically extract the geometry and position of 80,602 blocks by adopting a new block photo-analytical procedure, in addition to a further 4388 coarse blocks that were mapped from manual procedure. We analyze the longitudinal and transversal variation of the block distribution within the deposit. Large boulder content was more abundant in the middle part, while the fine blocks were distributed more evenly. Blocks were prevalently equant-sphere (ES) shaped with no dependence on volume and location, but the roundness increased significantly with runout. Additionally, we find fractal dimensions ranging from 1.42 to 1.83, lower with respect to other rock avalanches, probably due to the high weakness of materials. Furthermore, we propose two comminution models based on the significant differences observed between the eastern deposit II and western deposit III, which were caused by variably-cemented breccias. Finally, numerical modeling indicates that the large amount of fine material damped the grain-grain velocity during runout, leading to a limited spread of the rock avalanche and so explaining the short displacement of the front observed.

The process and dynamics of rock fragmentation during the collapse of rockfalls and rock avalanches is a poorly developed topic. The most severe fragmentation often leads to the formation of a rock dust that rises to form a cloud suspended in the air. The understanding of fragmentation processes is hampered by the environmental disturbances that alter the dust cloud deposit shortly after deposition. Here, we study the fragmentation of the October 2017 Pousset rockfall, detached from a NNE facing steep bedrock wall in the permafrost zone, that involved 8,300m3 of metamorphic rock and fell about 800 m. The collapse generated large boulders which rolled downslope and a thick and large dust cloud. The source and deposit were investigated, and dust cloud material was sampled at different locations to reconstruct an exponential thickness distribution and perform grain size characterization. The fragmentation energy was estimated by integrating the spectrum of the grains assuming that the fragmentation energy is proportional to the generated area. The fragmentation energy was found to be about 0.4% of the initial potential energy. Most probable fragmentation points and block deposition areas were evaluated and positioned by means of the HyStone 3D rockfall simulator. Furthermore, we calculated the flow rate of the suspended powder generated by the fragmentation process and compared the results with observations available for the evolution of the phenomenon and the collected samples. The Pousset event, in its relatively simple dynamics, may be a good testing ground to address the current theories of rockfall and rock avalanche fragmentation and dust cloud behavior.

The presence of trees along the slope and block fragmentation at impact strongly affect rockfall dynamics and hazard as a consequence. However, these phenomena are rarely simulated explicitly in rockfall studies. We performed rockfall simulations by using the 3D rockfall simulator Hy-Stone, modeling both the presence of trees and fragmentation through specific algorithms implemented in the code. By comparing these simulations with a more classical approach that attempts to account implicitly for such phenomena in the model parameters and by using a new probabilistic rockfall hazard analysis (PRHA) method, we were able to quantify the impact of these phenomena on the design of countermeasures and on hazard. We demonstrated that hazard changes significantly when accounting explicitly for these phenomena and that a classical implicit approach usually overestimates both the hazard level and the 95th percentile of kinetic energy, leading to an oversizing of mitigation measures.

The risk management of rainfall-induced landslides requires reliable rainfall thresholds to issue early warning alerts. The practical application of these thresholds often leads to misclassifications, either false negative or false positive, which induce costs for the society. Since missed-alarm (false negative) and false-alarm (false positive) cost may be significantly different, it is necessary to find an optimal threshold that accounts for and minimises such costs, tuning the false-alarm and missed-alarm rates. In this paper, we propose a new methodology to develop cost-sensitive rainfall thresholds, and we also analyse several factors that produce uncertainty, such as the accuracy of rainfall intensity values at landslide location, the time of occurrence, the minimum rainfall amount to define the non-triggering event, and the variability of cost scenarios. Starting from a detailed mapping of landslides that occurred during five large-scale rainfall events in the Italian Central Alps, we first developed rainfall threshold curves with a ROC-based approach by using both rain gauge and bias-adjusted weather radar data. Then, based on a reference cost scenario in which we quantified several cost items for both missed alarms and false alarms, we developed cost-sensitive rainfall threshold curves by using cost-curve approach (Drummond and Holte 2000). Finally, we studied the sensitivity of cost items. The study confirms how important is the information regarding rainfall intensity at the landslide site for the development of rainfall thresholds. Although the use of bias-corrected radar strongly improves these values, a large uncertainty related to the exact time of landslide occurrence still remains, negatively affecting the analysis. Accounting for the different missed-alarm and false-alarm misclassification costs is important because different combinations of these costs make an increase or decrease of the rainfall thresholds convenient. In our reference cost scenari

The aim of this paper is to achieve a quantitative assessment of rockfall protection forest efficiency at regional scale, considering site specific forest, morphological and lithological parameters. At first, a semi-automatic GIS-based method, integrated with a multi-scenario 3D-rockfall model realized by using the simulation code HY-STONE, was used to map protection forests of Regione Lombardia (central Italian Alps). For each different forest type, a rockfall protective efficiency was assessed by using empirical (energy line angle) and modelling (HY-STONE) approaches. The empirical approach shows an increase of the energy line angle value from about 36° for the bare slopes to over 40° in forested slopes, with a value ranging from 37° to 44° for different forests types. The modelling approach is based on a new efficiency index EEI ranging from 0 (minimum efficiency, equal to no forest condition) to 1 (maximum efficiency): the efficiency of different forest types ranges from 0.08 to 0.98 by using average values of the controlling parameters. To modulate the efficiency in each single forest at regional scale, a set of parametric simulations was performed to evaluate the effects of controlling parameters. The parametric simulations show that block volume, slope gradient, DBH (diameter at breast height) and forest density are the most important parameters at controlling the efficiency. These parameters were used within a multiple linear regression function to associate a protection efficiency to each specific protection forest in the regional map. This allows to discriminate quantitatively the individual forests according to their actual efficiency. Most of the protection forest area (46%) shows an efficiency greater than 0.50 and only the 24% of the total covered area shows a value lower than 0.25.