1,721,062 research outputs found
La Deformazione Gravitativa Profonda (DGPV) di Beauregard: Modellazione Numerica di Prove di Taglio
No full textIn particular I studied the deep-seated gravitational deformation recognized on the western slope of the stream named Dora di Valgrisenche, upstream of Valgrisenche (Aosta), and its interaction with the Beauregard arcgravity dam. A complete understanding of these DSGSD phenomena and their interaction with the Beauregard dam implies a correct definition of the geological-structural model and a geotechnical characterization of the affected materials. In order to test the cataclastic materials which come from the shear zone of the studied phenomena, the Multidisciplinary High Quality Laboratory DIPLAB (DIsaster Planning LABoratory) of the Structural and Geotechnical Engineering Department of the Politecnico of Torino, in collaboration with G.D.S. Instrument Ltd., developed a new direct shear test apparatus (High Pressure Back Pressure Shear Apparatus - HPBPSA) which allows to control the value of the pore pressure in the sample, simulating the rise of the groundwater level. To reproduce the functioning of HPBPSA, a numerical model was built, in order to simulate a direct shear test carried out with the High Pressure Back Pressure Shear Apparatus on the shear zone material of the Beauregard DSGSD. The numerical model, which was built with FLAC 5.0 (finite difference analysis), works accepting some simplified assumptions with respect to the experimental reality
The Rock Engineering System (RES) applied to landslide susceptibility zonation of the northeastern flank of Etna: methodological approach and results
No full textGround deformations in the northeastern flank of Etna are well known. Despite only a few landslide events have been documented, these have significantly involved and damaged lifelines and buildings. These events are mainly related to the activity of the volcano-tectonic structures and associated seismicity, as in the case of the 2002 reactivation of the Presa landslide during an increased activity of the Pernicana fault system. In order to highlight the areal distribution of potentially unstable slopes based on a detailed, site-specific study of the factors responsible for landslide, and to ultimately contribute to risk management, a landslide susceptibility analysis of the northeastern flank of Etna in the Pernicana area was carried out, and a susceptibility map at 1:10.000 scale was produced, extending over an area of 168 km2. Different methods are proposed in the literature to obtain the regional distribution of potentially unstable slopes, depending on the problem scale, the slope dynamic evolution in the geological context, and the availability of data. Among semi-quantitative approaches, the present research combines the Rock Engineering System (RES) methodology with parameter zonation mapping in a GIS environment. The RES method represents a structured approach to manage a high number of interacting factors involved in the instability problem. A numerically coded, site-specific interaction matrix (IM) analyzes the cause-effect relationship in these factors, and calculates the degree of interactivity of each parameter, normalized by the overall
interactivity of the system (weight factor). In the specific Etna case, the considered parameters are: slope attitude, lithotechnical properties (lithology, structural complexity, soil and rock mass quality), land use, tectonic structures, seismic activity (horizontal acceleration) and hydrogeological conditions (groundwater and drainage). Thematic maps are prepared at 1:10.000 scale for each of these parameters, and instability-related numerical ratings are assigned to classes. An instability index map is then produced by assigning, to each areal elementary cell (in our case a 10 m pixel),
the sum of the products of each weight factor to the normalized parameter rating coming from each input zonation map. This map is then opportunely classified in landslide susceptibility classes (expressed as a percentage), enabling to discriminate areas prone to instability. Overall, the study area is characterized by a low propensity to slope instability. Few areas have an instability index
of more than 45% of the theoretical maximum imposed by the matrix. These are located in the few steep slopes associated with active faults, and strongly depending on the seismic activity. Some other areas correspond to limited outcrops characterized by significantly reduced lithotechnical properties (low shear strength). The produced susceptibility map combines the application of the RES with the parameter zonation, following methodology which had never been applied up to now in in active volcanic environments. The comparison of the results with the ground deformation evidence coming from monitoring networks suggests the validity of the approach
Numerical Model of the Stromboli Volcano (Italy) Including the Effect of Magma Pressure in the Dyke System.
No full textThe Stromboli island, in the Aeolian archipelago (Italy), is one of the most active volcanoes in Europe. In the last 13,000 years, its growth has been complicated by four sector collapses affecting the NW flank, the latest of which resulting in the formation of Sciara del Fuoco (SdF) horseshoe-shaped depression. Slope instability phenomena are represented not only by giant deep-seated gravitational slope deformations, but also by more frequent large landslides, such as occurred in December 2002-January 2003, and shallow landslides, involving loose or weakly cemented deposits, that constitute a natural hazard and affect residential and tourists safety. It is noteworthy that in volcanic environment the instability factors are manifold and much more complex than in other non-volcanic contexts. This paper deals with the Stromboli NW flank instability, and focuses on the effects of magma pressure in the feeding system. Two main objectives have been pursued: (1) to test a methodological approach, in order to evaluate a complex instability process; (2) to contribute to the understanding of volcano deformation and collapse mechanisms and associated hazard. A numerical model was developed by the Finite Difference Method and the FLAC 4.0 code, considering a cross-section of the entire volcano, orthogonal to the SdF and including both subaerial and submerged slopes. The stability of the volcano was analysed under gravity alone, and by introducing the magma pressure effect, both related to magmastatic and overpressure components. The results indicate that gravity alone is not sufficient to affect the stability of the volcano slopes, nor is the magmastatic pressure component. If an excess magma pressure component is introduced, instability is produced in accordance with field evidences and recent slope dynamics
The Cimaganda rockslide (2012) : recent geomorphological evolution of the paleo-event
Full text linkThe San Giacomo Valley (Sondrio, Italy), as many alpine areas, is quite frequently affected by rock slope landslides at different scales, due to its geological and morphological features. Their interaction with anthropic activities represents one of the main natural risk along the Valley. The analysis and understanding of slope instability processes are thus so crucial to forecast landslide events, and to plan risk mitigation and civil protection actions. This work deals with the study of the Cimaganda rockslide, occurred in September 2012 after some days of persistent rainfall. It involved a rock volume of about 20.000 m3, blocking the main road (SS36) and isolating the municipality of Madesimo and Campodolcino in the upper Valley. The rockslide developed in an active geomorphological context, along the right flank of the historical Cimaganda landslide, dated at least to the 17th century with a volume involved valued in 7.5 million of m3. Following a procedural scheme including field surveys, remote sensing and geomechanical laboratory tests, this work develops an accurate characterization of the slope, that lead to a solid geological and geomechanical conceptual model extended to the slope directed involved in the 2012 event and to the surrounding area of the historical large landslide. Geological, geomorphological and geomechanical surveys allowed to recognize typical features of deep-seated gravitational deformations and largescale stress release: trenches and counter-slopes at the crown of the ancient landslide, sub-vertical tensile fracturing along the slope and shear planes mainly along the right flank. Using Finite Element Method (FEM) the conceptual model was built specifying the joint network orientation and the elasto-plastic properties of rock and joints. Hydraulics properties and anisotropy conductivities of rock mass, necessary to simulate hydrogeological flow, were calculated based on joint features of each discontinuity set. First, the numerical modelling, developed to simulate the slope scenarios before the landslide event, was able to reproduce a deformation pattern coherent with filed observations. Then, the introduction of a rainfall infiltration process, as triggering factor, with a semi-coupled hydro-mechanical analysis, allowed to simulate the evolution of the 2012 rockslide. This work represents a solid base to improve the analysis of the Cimaganda paleo-landslide and explore instability-forecasting scenarios in order to enhance rockslide risk management
Applicazione di modelli reologici tempo dipendenti nell'evoluzione di deformazioni gravitative profonde
No full textA preliminary analysis of the effects of creep on the development of a deep-seated gravitational slope deformation (DSGSD), carried out by numerical modeling, is described. The slope rock mass evolution has been simulated applying different creep rheological models.
The studied DSGSD is located in the Central Italian Alps (Val S. Giacomo). It is characterized by three main scarps, different sets of tensile trenches, and counterscarps, mapped during a detailed geomorphological survey. The mechanical behaviour of the rock masses, in terms of elastoplastic parameters, has been defined on the base of laboratory and in situ tests.
In order to simulate this instability process a stress-strain-time numerical modeling has been applied by a finite difference numerical code (FLAC).
First, the slope conceptual model was represented by a constant dipping slope, uniform lithology (ortogneiss) and the presence of the water table at different elevations. The effects of different constitutive model laws have been considered: the visco-elastic Maxwell model; the visco-elastic Burger model and the elasto-visco-plastic Burger model. The modeling has been performed simulating the melting of the ancient glacier, starting from its maximum load.
Because of the difficulty to determine rock mass creep parameters, for each of the rheological models a sensitivity analysis has been performed, varying the physical-mechanical properties.
In accordance with the geological data, milonitic zones, characterized by low mechanical properties, have been introduced in the middle part of the slope, and two weathered superficial layers have been added, identifying new instability processes.The elasto-visco-plastic Burger constitutive model develop a stress/stain system more consistent with the present morphology
Geomechanical surveys and geostatistical analyses in Valchiavenna (Italian Central Alps)
Full text linkThe present study concerns the forecast of geomechanical features in rock masses and how mechanical properties can be regarded as regionalized variables. It considers an area of about 200 km2, extended in the Italian Central Alps along the Valchiavenna Valley (SO) - San Giacomo and Bregaglia valleys - where different civil and mining works are present. The regional geological setting is related to the Pennidic Nappe arrangement, characterized by the emplacement of sub-horizontal gneissic bodies resulting from the Mesoalpine isoclinalic folding of crystalline basements (“Tambò” and “Suretta” Units) emplaced throw East and separated by metasedimentary cover units.
More than one hundred detailed structural and geomechanical field surveys, mainly located in San Giacomo Valley, were carried out in order to characterize the rock masses, in accordance with the I.S.R.M. suggested methods. The procedure allowed to identify the number of joint sets and their average orientations, supplying a quantitative description of the discontinuities in terms of spacing, persistence, roughness, aperture, filling, wall strength and weathering. From the collected data the rock mass quality indexes have been evaluated in each surveyed site.
Geostatistical methods have been applied to study the spatial distribution of the main rock masses characteristics, such as joint set orientation, fracture intensity and joint spacing, being the direct survey data local. Where no data are available the rock mass features have been estimated, the results obtained by kriging and conditional simulation techniques are presented
Mount Farinaccio rockfall : comparision between kinematic simulations and experimental field tests
Full text linkI fenomeni di caduta massi sono frequenti nelle aree alpine e, per mitigare i rischi che creano alla popolazione ed agli insediamenti umani, è indispensabile una corretta previsione delle possibili traiettorie e dei parametri cinematici del moto che i blocchi in incipienza di movimento assumerebbero qualora si staccassero dalla parete. Il presente contributo riguarda lo studio dettagliato del moto di caduta massi e della sua propagazione, ottenuto grazie alla realizzazione di prove sperimentali effettuate in Val Grosina (SO). I risultati della sperimentazione sono stati paragonati con quelli provenienti da simulazioni cinematiche precedentemente effettuate nell’area d’indagine, utilizzando differenti metodi, sia bidimensionali sia tridimensionali. In una prima serie di simulazioni i dati di input caratterizzanti il moto dei blocchi sono stati ipotizzati sulla base dei valori bibliografici, ottenuti in contesti geologici e geomorfologici simili a quello di indagine, mentre in una seconda serie tali valori sono stati stimati basandosi sulla posizione di arresto di alcuni blocchi crollati nell’area di studio nel 2010. Il confronto dei risultati ottenuti utilizzando i diversi approcci con quelli sperimentali, mostra che, per ottenere previsioni affidabili delle traiettorie dei blocchi e quindi mappe di pericolosità attendibili, è necessario effettuare un’accurata calibrazione dei parametri che caratterizzano il moto di caduta
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