1,720,973 research outputs found
Analysis of the interaction between buried pipelines for the transport of fluids and landslides
No full textThe aim of this work is the study of the factors that influence the interaction between buried pipelines for the transport of fluids, e.g. gas and water, and Permanent Ground Deformation (PGD), in particular landslides. Pipelines have a fundamental role both in normal operating conditions and in emergency situations. Eventual leakage of the fluids caused by structural damage could cause environmental disasters, financial costs and abuses of resources. In the present work, the methodology proposed by Suresh et al. (2007) was adopted for the calculation of the structural deformation due to the landslide. Furthermore, sensitivity analysis permitted to highlight the influence of different factors, e.g. The pipelines diameter, on the value of the deformation due to their interaction with landslide. The study was applied in different areas of the northern Apennines, selected as representative of the landslide phenomena occurring in Emilia-Romagna region
How rock block shape can influence the kinematics and direction of slope displacement: Results from the San Leo rock plateau, Italy
No full textThe kinematic behavior of slope failures in fractured rock masses is strongly influenced by the presence of discontinuities. Block size and shape are controlled by fracture orientation, intensity and length. A preliminary analysis of these parameters was conducted in the north-eastern cliff of the San Leo plateau (Italy). Classical stereographic projection analysis, coupled with GIS, and a limit equilibrium approach were applied to analyze the blocks shape and the block kinematic constraint and thereby define the expected movement directions of selected rock wedges. Our analyses provided further insights into the instability mechanisms involving the sub-vertical cliff faces. The data are also useful in the interpretation of the data collected by the slope monitoring system. By deriving the expected direction of movements, its effectiveness can be improved. The size distribution and the shape of the blocks in the landslide deposit were mapped and classified, providing the constraint for more advanced geomechanical analyses
Modelling groundwater and slope processes in a calcarenitic slab: The case of San Leo (northern Apennines)
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An investigation into the development of toppling at the edge of fractured rock plateaux using a numerical modelling approach
No full textThis is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.The mechanisms controlling the onset of minor slope instability at the edges of rocky plateaux exhibiting lateral spreading phenomena are yet to be fully understood. Hypotheses have recently been introduced to explain the influence of groundwater within these plateaux on geomorphological processes leading to slope instability. We present a back analysis of a recent landslide which occurred on 27th February 2014 in the town of San Leo, Italy. The role of the softening of basal clay shales and erosion due to seepage is investigated using finite element geomechanical models. Both processes were observed in the field and are related to groundwater discharging along the contact between the rocky slab and the clay-rich substratum. Fracture propagation paths involving pre-existing discontinuities and intact rock bridges failure were simulated using a simplified discrete fracture network (DFN) model coupled with a Voronoi polygonal mesh approach. Model results allow the failure to be classified as a secondary toppling phenomenon. Moreover, a critical amount of undermining was indicated by the models agreeing with field observations made prior to the failure. Based on the modelling results, an interpretation of the overall mechanism inducing failures at the edges of fractured rock slabs is given. In particular, the inter-relationships between groundwater flow and geomorphic processes acting within the rock masses are presented
Hydrogeological features of a highly fractured rock-slab
No full textIn many geological contexts, the hydrogeological features of highly fractured rock slabs can drive slope instability processes. This is the case of San Leo (northern Apennines of Italy), where groundwater processes were recognized as predisposing factor for the last large-scale rock fall that took place the 27th of February 2014. In the present work, the hydrogeological features of the San Leo slab were analyzed by means of spring-discharge analysis, piezometric monitoring data and slug tests. The maximum spring yield, the depletion coefficient and the hydraulic conductivity values were estimated. Time-series analyses were used to better understand the groundwater behavior within the rock slab and to estimate its response to rainfall regime. Moreover, the calculation of the groundwater flow direction and modulus in the unsaturated zone was performed. Results highlight the presence of two systems, which are probably related to the characteristics of different joint sets (aperture, spacing); the hydraulic conductivity values were shown to vary with depth. A first general interpretation of the aquifer behavior is given, which is related to the main structural elements of the slab
INTEGRATION OF GEOMATICS TECHNIQUES FOR DIGITIZING HIGHLY RELEVANT GEOLOGICAL AND CULTURAL HERITAGE SITES: THE CASE OF SAN LEO (ITALY)
Full text linkThe research activities described in this contribution were carried out at San Leo (Italy). The town is located on the top of a quadrangular rock slab affected by a complex system of fractures and has a wealth of cultural heritage, as evidenced by the UNESCO’s nomination.
The management of this fragile set requires a comprehensive system of geometrical information to analyse and preserve all the geological and cultural features. In this perspective, the latest Geomatics techniques were used to perform some detailed surveys and to manage the great amount of acquired geometrical knowledge of both natural (the cliff) and historical heritage. All the data were also georeferenced in a unique reference system.
In particular, high accurate terrestrial laser scanner surveys were performed for the whole cliff, in order to obtain a dense point cloud useful for a large number of geological studies, among others the analyses of the last rockslide by comparing pre- and post-event data.
Moreover, the geometrical representation of the historical centre was performed using different approaches, in order to generate an accurate DTM and DSM of the site. For these purposes, a large scale numerical map was used, integrating the data with GNSS and laser surveys of the area.
Finally, many surveys were performed with different approaches on some of the most relevant monuments of the town. In fact, these surveys were performed by terrestrial laser scanner, light structured scanner and photogrammetry, the last mainly applied with the Structure from Motion approach
La geomatica per la modellazione 3D di placche rocciose di grandi dimensioni e applicazioni geologiche: il caso della rupe di San Leo (RN)
No full textIl lavoro si riferisce all’uso delle moderne tecniche geomatiche, in particolare il laser a scansione terrestre, per il rilevamento e la modellazione tridimensionale di una grande placca rocciosa ai fini di una accurata descrizione geometrica, nel supporto ad analisi di carattere geologico e per scopi di monitoraggio. L’esperienza illustrata si riferisce alla rupe su cui sorge l’abitato di San Leo (RN); la cittadina è situata sulla sommità di una placca lapidea di forma quadrangolare, con dimensioni di circa 500x600 m e delimitata da pareti verticali di altezza fino a circa 100 m. L’area è caratterizzata da fenomeni di instabilità dei versanti in evoluzione, il cui evento più recente è la frana che ha interessato la parete nordorientale nel 2014.
Nel corso del 2013 è stato eseguito il rilievo dei versanti Sud e Ovest della rupe utilizzando il sistema Riegl VZ400 supportato dalla tecnica GNSS per l’allineamento e la georeferenziazione; il modello tridimensionale ottenuto è stato integrato per i rimanenti due versanti con nuvole di punti di minore densità acquisite da terzi in epoca precedente e per la parte sommitale con i dati altimetrici desunti da base cartografica, integrati e validati con un rilievo GNSS cinematico.
La disponibilità di un modello tridimensionale dettagliato e georeferenziato della rupe ha consentito di effettuare analisi finalizzate all’individuazione delle discontinuità sull’intero ammasso roccioso, anche nelle zone difficilmente raggiungibili con i metodi tradizionali di rilievo geomeccanico.
L’esperienza maturata, ancora in corso, ha evidenziato come, ad integrazione del rilievo tradizionale, la sinergia delle diverse metodologie adottate possa permettere un’investigazione accurata ed in remoto, in totale sicurezza, delle caratteristiche geologiche e geomorfologiche in contesti operativi che presentano problematiche oggettive di sicurezza ed accessibilità. Nella trattazione vengono descritte le fasi di rilievo ed elaborazione dati, evidenziando le problematiche operative e le soluzioni tecniche adottate, fino alla estrazione dei dati geometrici dal modello 3D della rupe.The work refers to the use of modern geomatic techniques, in particular the terrestrial laser scanning, for surveying and three-dimensional modelling of a large rock plate for the purpose of its accurate geometric description, in support to geological analyses and monitoring. The experience carried out is referred to San Leo’s cliff (RN); the town lays on the top of a quadrangular rock slab, with dimensions of about 500x600 m bounded by vertical walls of height up to about 100 m. The area is characterized by active and dormant slope instability processes, as the landslide which affected the northeastern wall in 2014.
The survey of the side walls was performed with a terrestrial laser scanner supported by GNSS measurements for geo-referencing; the 3D model of the summit was completed with elevation data derived from cartographic database, integrated and validated with a kinematic GNSS survey. The availability of a complete three-dimensional model of the cliff, detailed and georeferenced, allowed the rock mass to be analysed, even in dangerous areas, difficult to be surveyed with traditional geomechanical methods.
The experience has shown that, complementary to traditional surveys, the synergy of the different adopted approaches may allow an accurate investigation with no-contact – and then in complete safety - of geological and geomorphological characteristics also in contexts with serious accessibility issues. In the paper, the phases of survey and processing of the data will be described, highlighting the operational issues and the technical solutions for the extraction of geometric data from the 3D model of the cliff
Terrestrial Remote Sensing techniques to complement conventional geomechanical surveys for the assessment of landslide hazard: The San Leo case study (Italy)
Full text linkThe San Leo village, located near to Rimini (northern Italy), was built in the medieval period on the top of a calcarenite and sandstone plateau, affected by lateral spreading associated with secondary rock falls and topples. In fact, a number of landslides endangered the historical town since centuries. In order to describe the structural features driving these slope instability phenomena, a complete Terrestrial Laser Scanner (TLS) survey all around the San Leo cliff was performed. Moreover, Close-Range Photogrammetric (CRP) surveys and conventional geomechanical surveys on scanlines have been carried out. The 3D geometry of the cliffs was extracted and critical areas have been investigated in detail using dense Digital Surface Models (DSMs) obtained from CRP or TLS. The results were used to define the structural features of the plateau, to recognize more fractured areas, and to perform kinematic analyses, in order to assess the joint sets predisposing to slope instability at the cliff scale. The creation of a 3D model was also fundamental for the implementation of the geological model to be used in numerical modelling for hydrogeological characterization and slope stability analyses
Lateral spreading and associated slope processes in fractured rock slabs
No full textLandslides of the lateral spreading type, involving brittle geological units overlying ductile terrains, are a common occurrence in the sandstone and limestone plateaux of the northern Apennines of Italy. These instability phenomena can become particularly risky, when historical towns and cultural heritage sites built on the top of them are endangered. Neverthless, the mechanisms controlling the developing of related instabilities, i.e. toppling and rock falls, at the edges of rock plateaux are not fully understood yet. In addition, the groundwater flow path developing at the contact between the more permeable units, i.e. the jointed rock slab, and the relatively impermeable clay-rich units have not been already studied in details, even if they may play a role in this kind of instability processes, acting as eventual predisposing and/or triggering factors. Field survey, Terrestrial Laser Scanner and Close Range Photogrammetry techniques, laboratory tests on the involved materials, hydrogeological monitoring and modelling, displacements evaluation and stability analysis through continuum and discontinuum numerical codes have been performed on the San Leo case study, with the aim to bring further insights for the understanding and the assessment of the slope processes taking place in this geological context.
The current research permitted to relate the aquifer behaviour of the rocky slab to slope instability processes. The aquifer hosted in the fractured slab leads to the development of perennial and ephemeral springs at the contact between the two units. The related piping erosion phenomena, together with slope processes in the clay-shales led to the progressive undermining of the slab. The cliff becomes progressively unstable due to undermining and undergoes large-scale landslides due to fall or topple
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