A method is presented for analysing the stability of rock structures based on the propagation of geological discontinuities. Discontinuities are modelled as flat cracks and their propagation is analysed using fracture mechanics methods. As rock structures are brittle, these phenomena can be studied using linear elastic fracture mechanics (LEFM). Problems in the application of LEFM methods are analysed, with regard to the states of compressive stress present in rock. A numerical procedure is described which simulates the propagation of natural discontinuities in rock; the crack propagation trajectories determined from this analysis are compared with experimental results obtained on mortar specimens. The applicability of the method to the study of rock mass stability is shown with reference to the behaviour of rock slopes. L'article présente une méthode permettant d'analyser la stabilité de structures rocheuses. Cette méthode est fondéve sur Pétude de la propagation de discontinuités géologiques. Ces discontinuitésont modévlisées par des fissures planes dont la propagation est analyséve à l'aide de méthodes de la mecanique des fractures. Comme Ion de l'étude du comportement fragile des structures rocheuses, ces phénoménes peuvent être étudiés à l'aide de mécanismes linéaires de fracturation élastique (LEFM). Différents problémes rencontrés lors de l'application des méthodes LEFM sont analyses, notamment en relation avec la contrainte de compression régnant dam la roche. Une procédure numérique permettant de simuler la propagation des discontinuités naturelles de la roche est ensuite décrit. Les trajectoires de propagation des fissures déterminées Iors de cette analyse sont comparées aux résultats expérimentaux obtenus sur des échantillons de mortier. L'applicabilité de cette méthode à l'étude de la stabilité des masses rocheuses est démontrée par des références au comportement des pentes rocheuses.

Abstract. Rockfalls are common instabilities in alpine areas and can cause significant damage. Since high mountains have been affected by an increasing number of these phenomena in the last years, a possible correlation with permafrost degradation induced by climate change has been hypothesized.To investigate this topic, a monitoring system, made of 5 triaxial geophones and 1 thermometer, was installed in 2007 at the Carrel hut (3829 m a.s.l., Matterhorn, Northwestern Alps), in the frame of the Interreg IIIA Alcotra project n. 196 "Permadataroc".The preliminary data processing relates to the classification of recorded signals, the identification of the significant microseismic events and the analysis of their distribution in time and space. The first results indicated a possible correlation between clusters of events and temperature trend, and a concentration of events in specific sectors of the rock mass.Research is still in progress. The recording of data for a longer period is planned to fully understand seasonal trends and spatial distribution of microseismic activity, and possible relations with permafrost degradation. Nevertheless, the preliminary observations prove that the monitoring system can detect noises generated by rock slope deformation. Once fully developed, this technique could become a helpful tool for early warning and preliminary stability assessments.

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Rockfalls evolve rapidly and unpredictably in mountain environments and can cause considerable losses to human societies, structures, economical activities, and also natural and historical heritage. Rockfall risk analyses are complex and multi-scale processes involving several disciplines and techniques. This complexity is due to the main features of rockfall phenomena, which are extremely variable over space and time. Today, a considerable number of methods exists for protecting land, as well as assessing and managing the risk level. These methodologies are often very different from each other, depending on the data required, the purposes of the analysis, and the reference scale adopted, i.e., the analysis level of detail. Nevertheless, several questions still remain open with reference to each phase of the hazard and risk process. This paper is devoted to a general overview of existing risk estimation methodologies and a critical analysis of some open questions with the aim of highlighting possible further research topics. A typical risk assessment framework is exemplified by analyzing a real case study. Each step of the process is treated at both the detailed and the large scale in order to highlight the main characteristics of each level of detail.

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This paper reports preliminary results of a feasibility project developed in cooperation with National Agency for Cultural Heritage Preservation of Georgia, and aimed at envisaging the stability conditions of the Vardzia monastery slope (rupestrian city cave in the south-western Georgia). The aim is the implementation of a low-impact monitoring system together with long-term mitigation/conservation policies. A field analysis was conducted to reconstruct geometry of the rocky cliff, characteristics of discontinuities, main failure modes, and volume of potential unstable blocks and geomechanical parameters. Instability processes are the combination of causative factors such as the following: lithology, frequency and orientation of discontinuities, slope orientation, physical and mechanical characteristics of slope-forming materials, and morphological and hydrological boundary conditions. The combined adoption of different survey techniques (e.g., 3D laser scanner, ground-based radar interferometry) could be the best solution in the interdisciplinary field of cultural heritage preservation policies. The collected data will be the basis for future activities to be completed in collaboration with local authorities for a complete hazard and risk characterization for the monastery site and the development of an early warning system to allow safe exploitation for touristic activities and for historical site preservation.

Background: Tailings dams are made up of mining residue deposits, and they represent a high risk, in terms of mechanical instability. In the event of collapse, the tailings in such dams may be released and flow over long distances, with the potential risk of extensive damage to property and life. The traditional geotechnical assessment of tailings facilities has mainly concentrated on the stability of tailings dams, while relatively few studies have investigated the flow of tailings released after dam failure. In this context, it is possible to state that, if the complex rheological behaviour of the tailings material is captured correctly during the flow, numerical modelling can be used to contribute to a better comprehension of the flow characteristics and for the assessment of the possible extension of the impact area. Results: Considering the wide range of possible rheological behaviour that tailings flows can assume (from laminar to turbulent), this paper presents the new version of a computer model, which was designed to simulate the motion of rapid flow movements across 3D terrain. This new version integrates the existing rheological kernel (Frictional, Voellmy) with two new rheological laws (Bingham and Turbulent), and adds the possibility of changing the rheological properties of the flowing mass during the propagation process. The code has been applied to the disastrous flow that was caused by the failure of a pair of tailings impoundments in the Stava Creek Valley (Italy) in 1985. Since different interpretations on this flow behaviour already exist in literature, and since a large number of changes in the rheological values along the run-out path have been proposed to recreate its dynamics, new simulations, carried out with different rheological combinations, are presented and discussed here in order to obtain a better understanding of the flow dynamics and to identify the rheology that reproduces the phenomenon that occurred with the fewest possible changes in the rheological values along the runout path. The latter aspect is particularly important when numerical analyses are used for prediction purposes. Conclusions: The great rheological flexibility of the new code has allowed the Voellmy rheology and a combination of its parameters to be identified as the most suitable to describe the Stava flow, even where the run-out path presented critical characteristics.

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