The Use of Remote Sensing Techniques for Monitoring and Characterization of Slope Instability

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.Understanding changes in slope geometry and knowledge of underlying engineering properties of the rock mass are essential for the safe design of man-made slopes and to reduce the significant risks associated with slope failure. Recent advances in the geomatics industry have provided the capability to obtain accurate, fully geo-referenced three-dimensional datasets that can be subsequently interrogated to provide engineering-based solutions for monitoring of deformation processes, rock mass characterization and additional insight into any underlying failure mechanisms. Importantly, data can also be used to spatially locate and map geological features and provide displacement or deformation rate information relating to movement of critical sections or regions of a slope. This paper explores the benefits that can be obtained by incorporating different remote sensing techniques and conventional measurement devices to provide a comprehensive database required for development of an effective slope monitoring and risk management program. The integration of different techniques, such as high accuracy discrete point measurement at critical locations, which can be used to complement larger scale less dense three-dimensional survey will be explored. Case studies using a combination of aerial and terrestrial laser scanning, unmanned aerial vehicle and hand-held scanning devices will demonstrate their ability to provide spatial data for informing decision making processes and ensuring compliance with Regulations

UAV-mounted Ground Penetrating Radar: an example for the stability analysis of a mountain rock debris slope

This paper describes scientific research conducted to highlight the potential of an integrated GPR-UAV system in engineering-geological applications. The analysis focused on the stability of a natural scree slope in the Germanasca Valley, in the western Italian Alps. As a consequence of its steep shape and the related geological hazard, the study used different remote sensed methodologies such as UAV photogrammetry and geophysics survey by a GPR-drone integrated system. Furthermore, conventional in-situ surveys led to the collection of geological and geomorphological data. The use of the UAV-mounted GPR allowed us to investigate the bedrock depth under the detrital slope deposit, using a non-invasive technique able to conduct surveys on inaccessible areas prone to hazardous conditions for operators. The collected evidence and the results of the analysis highlighted the stability of the slope with Factors of Safety, verified in static conditions (i.e., natural static condition and static condition with snow cover), slightly above the stability limit value of 1. On the contrary, the dynamic loading conditions (i.e., seismic action applied) showed a Factor of Safety below the stability limit value. The UAV-mounted GPR represented an essential contribution to the surveys allowing the definition of the interface debris deposit-bedrock, which are useful to design the slope model and to evaluate the scree slope stability in different conditions

Analisi di stabilità di un pendio detritico montano tramite impiego di georadar installato su drone

Il presente lavoro descrive le attività svolte in merito alla verifica della stabilità di un pendio detritico naturale posto in zona montana di difficile accesso nella catena delle Alpi Occidentali. I dati necessari alle analisi sono stati raccolti ed elaborati attraverso tecniche geomatiche quali, in particolare, rilievi fotogrammetrici con drone con lo scopo di acquisire delle foto prospettiche dalle quali produrre una nuvola di punti georeferenziata e successivamente un ortofotomosaico. Il rilievo è stato eseguito con un drone tipo DJI Mavic 2 Pro. Contestualmente ai rilievi fotogrammetrici sono stati eseguiti rilievi topografici di Ground Control Points necessari nella fase di orientamento esterno dei fotogrammi. I fotogrammi sono stati elaborati utilizzando il software Agisoft Metashape. La nuvola 3D densa prodotta è stata successivamente interpolata in modo da generare un modello digitale denso della superficie (DDSM) in formato raster. Sulla base del DDSM sono state ortocorrette le immagini fotografiche ottenendo degli ortofotomosaici. Allo scopo di determinare lo spessore della coltre detritica naturale al di sopra del bedrock, sono stati eseguiti 2 rilievi geofisici utilizzando lo strumento COBRA Plug‐In GPR Model SE-150, installato su drone DJI M600Pro. L’indagine si è svolta sorvolandolo direttamente l’area di interesse a circa 1.5 metri dalla superficie e raggiungendo aree altrimenti non investigabili per motivi di sicurezza. I dati del rilievo georadar sono stati elaborati con l’ausilio dell’applicativo PRISM® 2.6. La nuvola di punti 3D ottenuta dal rilievo fotogrammetrico ha permesso la ricostruzione delle corrette geometrie del corpo detritico naturale. Tramite il software open source CloudCompare Omnia, sono stati selezionati profili rappresentativi dell’area di interesse in seguito importati all’interno del software RocScience Slide2. La ricostruzione della profondità del contatto tra la copertura detritica e il bedrock è stata eseguita estrapolando le informazioni ricavate dalle tracce georadar più prossime al profilo di interesse. Le verifiche sono state effettuate valutando diversi scenari quali: condizioni statiche, dinamiche con presenza di sisma, condizioni statiche con presenza di neve e dinamiche con presenza contemporanea di neve e sisma. L’impiego del georadar installato su un drone si è dimostrato un ottimo metodo di indagine in situazioni in cui l’area di studio risulta essere inaccessibile alle classiche analisi geofisiche per motivi morfologici e di sicurezza. La combinazione quindi di dati ottenuti tramite rilievi topo-cartografici e areofotogrammetrici con rilievo geofisico da drone ha permesso lo studio della stabilità di un versante naturale in area critica

Distributed optical fiber sensors and terrestrial laser scanner surveys for the monitoring of an underground marble quarry

The sensing applications nowadays are always more used for structural and engineering-geological applications. In this work, an experimental monitoring system of an underground marble quarry, located in the Apuan Alps (Tuscany, Italy) is presented. The system is composed by Distributed Optical Fiber Sensors (DOFS) based on Brillouin Frequency Shift (BFS). By using a control unit, multitemporal data of strain and temperature were measured thanks to the installation of 250 linear meters of DOFS placed around two pillars. Terrestrial Laser Scanning (TLS) surveys, aided by GNSS (Global Navigation Satellite System) and TS (Total Station) measurements, were executed with the aim of: i) identifying physically inaccessible rock joints (i.e. height of the pillars), ii) georeferencing the DOFS and, iii) locating any strain phenomenon. The integration of a DOFS monitoring system with geomatic technologies has given the possibility to initialize a real-time monitoring system aimed at protecting the safety of the workers from possible rocky wall collapses. The results obtained in this work are the texturized 3D model of the analyzed pillars, the DEM and the orthophoto of the quarry, and the profiles of BFS, strain and temperature variation. This research was funded by Tuscany Region (Italy) though the POR FESR 2014-2020 plan

Hazard Assessment of Rocky Slopes: An Integrated Photogrammetry–GIS Approach Including Fracture Density and Probability of Failure Data

Natural rock slopes require accurate engineering–geological characterization to determine their stability conditions. Given that a natural rock mass is often characterized by a non-uniform fracture distribution, the correct, detailed, and accurate characterization of the discontinuity pattern of the rock mass is essential. This is crucial, for example, for identifying the possibility and the probability of kinematic releases. In addition, complete stability analyses of possible rockfall events should be performed and used to create hazard maps capable of identifying the most dangerous parts of a rock mass. This paper shows a working approach that combines traditional geological surveys and remote sensing techniques for engineering–geological investigations in a natural rock slope in Northern Italy. Discontinuities were identified and mapped in a deterministic way by using semi-automatic procedures that were based on detailed 3D Unmanned Aerial Vehicle photogrammetric-based point cloud data and provided georeferenced representations of thousands of fractures. In this way, detailed documentation of the geo-mechanical and geo-structural characteristics of discontinuities were obtained and subsequently used to create fracture density maps. Then, traditional kinematic analyses and probabilistic stability analyses were performed using limit equilibrium methods. The results were then managed in a GIS environment to create a final hazard map that classifies different portions of the rock slope based on three factors: kinematic predisposition to rockfall (planar sliding, wedge sliding, toppling), fracture density, and probability of failure. The integration of the three hazard factors allowed the identification of the most hazardous areas through a deterministic and accurate procedure, with a high level of reliability. The adopted approach can therefore be very useful to determine the areas in which to prioritize remediation measures with the aim of reducing the level of risk

Modellazione stocastica della fratturazione (Metodo Discrete Fracture Network) a supporto della stima previsionale di resa all’interno di bacini estrattivi di pietre ornamentali

The present paper shows a working approach aimed at improving quarry yield prediction accuracy in ornamental stone basins. In such contest, the yield prediction is subjected toa degree of uncertainty due to several factors, as the fracture network, the geomechanical properties of the rock and other qualitative characteristics of the ornamental stones. To decrease such uncertainty, we proposed an approach based on the Discrete Fracture Network (DFN) technique. The DFN is a stochastic approach for reproducing the discontinuity pattern starting from deterministic measurements of different parameters acquired during field surveys, as for example fracture intensity and density. A specific algorithm creates a fracture network compatible from a statistic point of view with the data collected on the quarry rock faces, overcoming the limitations of a purely deterministic approach. This study used the DFN methodology in a marble quarry (Apuan Alps, Italy), where it has been possible to increase the reliability of the quarry yield prediction in terms of dimension of extractable intact blocks, which is the starting point of a series of other qualitative considerations

Il Lidar terrestre per la caratterizzazione degli ammassi rocciosi

Operare in sicurezza e in tempi brevi è un aspetto importante quando si vuole eseguire uno studio geologico, soprattutto in cave in sotterraneo. L’attività estrattiva implica l'impossibilità di accedere ad alcune aree, perché non sicure, oppure non permette di soffermarsi su un affioramento per effettuare le osservazioni geologiche del caso. Per questo motivo negli ultimi anni si è sviluppato un nuovo approccio di rilevamento attraverso il quale si possono ottenere modelli tridimensionali ad altissima risoluzione delle superfici investigate. In quest'ottica il lidar terrestre rappresenta attualmente uno dei più accurati e veloci strumenti investigativi per l’acquisizione a distanza d’informazioni geometriche riguardanti le superfici osservate. Grazie a tali peculiarità è possibile proporre questa tecnologia per la caratterizzazione degli ammassi rocciosi e, in particolare, per la mappatura di dettaglio delle discontinuità che lo caratterizzano. Tuttavia, il solo dato puntuale ricavabile dallo scanner, senza foto di dettaglio, spesso non consente un’osservazione completa delle discontinuità tantomeno una corretta interpretazione. Da questa limitazione nasce l’idea di riconoscere e misurare le fratture non sulla nuvola di punti o sul Modello Digitale della Superficie, come viene spesso fatto nelle cave a cielo aperto o in versanti naturali, ma sfruttando il dato fotografico tramite il plug-in, libero per MicrosoftTM Internet Explorer, denominato LeicaTM Truview. Quest’ultimo permette di visualizzare la nuvola di punti attraverso una serie di immagini panoramiche (3D) ad alta risoluzione, di modificare la vista rispetto al punto di osservazione e di rappresentare le fratture in forma di insiemi di punti allineati e georeferenziati. L’analisi spaziale dei dati puntuali permette successivamente di ricostruire la giacitura di ogni singola frattura identificata a monitor e misurare la sua persistenza e spaziatura. L'accuratezza con la quale il dataset geomatico viene ricostruito si verifica confrontando, nelle aree accessibili, gli stereonet ottenuti da un’analisi di densità con quelli elaborati a partire da misure effettuate in modo tradizionale (con bussola da geologo). L’integrazione tra i rilievi geomatici e geomeccanici permette infine di creare un nuovo dataset costituito da immagini 3D ad alta risoluzione sulle quali vengono implementate le informazioni strutturali e geomeccaniche rilevate in campagna. Infatti, nonostante i vantaggi ricavabili dalla procedura illustrata, non è possibile prescindere dal rilievo tradizionale di campagna per la misura di altre proprietà fondamentali delle singole discontinuità quali la scabrezza, l’alterazione, la resistenza a compressione, l’apertura, l’umidità, il riempimento e la terminazione. In definitiva, i passi in avanti effettuati in campo geologico verso il digitale sono enormi anche se l'integrazione con i classici metodi di rilevamento è ancora oggi un fattore imprescindibile

Ground Displacements Estimation through GNSS and Geometric Leveling: A Geological Interpretation of the 2016–2017 Seismic Sequence in Central Italy

Between August 2016 and January 2017, a very energetic seismic sequence induced substantial horizontal and vertical ground displacements in the Central Italian Apennines. After this event, the Italian Military Geographical Institute (IGM), owner and manager of the Italian geodetic networks, executed several topographic surveys in the earthquake area in order to update the coordinates of vertices belonging to the IGM95 geodetic network. The measurements began in the areas where the most significant deformation occurred: the localities of Amatrice and Accumoli, in the Rieti Province, and the area covering Norcia and Castelluccio, in the Province of Perugia, all the way to Visso (Province of Macerata). The activities described in this paper focused on the updated measurement of the IGM95 network points through GNSS and the restatement of extensive parts of the high precision geometric lines that were levelled until reaching stable zones. This unprecedented amount of data was used for a new geological interpretation of the seismic sequence, which confirms some of the previous hypotheses of the scientific community. In the analyzed territory, the latest estimate of the geodetic position points has allowed for an accurate determination of the east and the north and of the altitude components of the displacement induced by the earthquake through a comparison with the previous coordinates. The results confirm that the seismicity was induced by normal faults system activity. Still, they also indicate the possible influence of a significant regional thrust that conditioned the propagation of the seismicity in the area. The obtained maps of the displacement are coherent with other geodetic works and with a rupture propagation driven by the documented geotectonic structure

Correction: Salvini et al. Ground Displacements Estimation through GNSS and Geometric Leveling: A Geological Interpretation of the 2016–2017 Seismic Sequence in Central Italy. <i>Geosciences</i> 2022, <i>12</i>, 167

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Excavation stability analysis in an underground marble quarry in the Apuan Alps (Italy): Application of terrestrial LIDAR, conventional methods and numerical modeling

The excavation of tunnels in a rock mass changes the existing stress state and initiates deformation processes that, in some cases, can cause instability. Stability investigations, using methodologies capable of verifying both the safety conditions and of representing new scenarios in underground works can be greatly enhanced through the use of high-resolution 3D images acquired in combination with ground-based LiDAR. Data from ground-based LiDAR allows the extraction of geological and structural characteristics of the rock mass such as geometries, attitudes, persistence and spacing of joints, even in inaccessible areas. High definition terrestrial laser scanning was adopted in an underground marble quarry, called "Romana", located in the Apuan Alps (Italy), as a support for the geological, geostructural and engineering geological study. Discontinuities were identified and mapped in a deterministic way by using the Leica TruView plug-in which manages laser scanning data and allows representation of the fractures in a georeferenced way either by arcs or by a sequence of aligned points. Given the large quantity of information collected, data were filtered and added to a geodatabase that, after GIS processing and additional in situ engineering geological surveys, was used to create thematic maps illustrating the fracture trends. In this way detailed documentation of the geomechanical and geostructural characteristics of the discontinuities was obtained and subsequently used to model the face stability in different zones of the tunnels. Preliminary analyses were performed by means of numerical modeling in order to calculate approximate stress values around the excavation, and to understand how they change when perturbed. The simulations were carried out using both finite element, (Phase2; without discontinuities), and distinct element methods (UDEC; including discontinuities derived deterministically from remote sensing data). The calculated stress values were then used to perform a 3D stability analysis of excavation rock wedges using block theory software, Unwedge. Model results showed that the presence of discontinuities considerably affects both the stress orientation and stress magnitude around the excavation zone, and must be taken into account to ensure accurate stability analyses. In this context the use of the most recent technologies of remote sensing, together with traditional engineering geological surveys, can provide an important and fundamental contribution. Results of the study to date have been analyzed and discussed with the managers of the underground quarry in order to optimize the planning of future excavations