1,720,973 research outputs found
Fracture characterization of flysch formation by terrestrial digital photogrammetry: an example in the Antola Formation (upper Staffora Valley, Italy)
No full textReliability and uncertainties of the analysis of an unstable rock slope performed on RPAS digital outcrop models: The case of the gallivaggio landslide (Western Alps, Italy)
Full text linkA stability investigation based on Digital Outcrop Models (DOMs) acquired in emergency conditions by photogrammetric surveys based on Remote Piloted Aerial System (RPAS) was conducted on an unstable rock slope near Gallivaggio (Western Alps, Italy). The predicted mechanism of failure and volume of the unstable portion of the slope were successively verified on the DOMs acquired after the rockfall that effectively collapsed the May 29th, 2018. The comparison of the pre-and post-landslide 3D models shows that the estimated mode of failure was substantially correct. At the same time, the predicted volume of rock involved in the landslide was overestimated by around 10%. To verify if this error was due to the limited accuracy of the models georeferenced in emergency considering only the Global Navigation Satellite System/Inertial Measurement Unit (GNSS/IMU)-information of RPAS, several Ground Control Points (GCPs) were acquired after the failure. The analyses indicate that the instrumental error in the volume calculation due to the direct-georeferencing method is only of the 1.7%. In contrast, the significant part is due to the geological uncertainty in the reconstruction of the real irregular geometry of the invisible part of the failure surface. The results, however, confirm the satisfying relative accuracy of the direct-georeferenced DOMs, compatible with most geological and geoengineering purposes
Syndepositional fractures and architecture of the lastoni di formin carbonate platform: Insights from virtual outcrop models and field studies
No full textThe recent rapid improvement of Unmanned Aerial Vehicles, together with advances in photogrammetry and Structure from Motion techniques, have enhanced the role of Digital Outcrop Models in many field of geology, due to the possibility to obtain quantitative information from large and inaccessible areas. In this study we integrated Digital Outcrop Modeling techniques and field survey to investigate the architecture of the Middle Triassic platform of Lastoni di Formin. (Italian Dolomites). The research highlighted the presence of two superimposed carbonate bodies. The lower unit (Cassian I) is dominated by low-angle clinoforms dipping north-northeastward and prograding over the basinal San Cassiano Fm. The upper unit (Cassian II) is characterized by a thick sequence of peritidal cycles connected northward to another generation of clinoforms. The inner platform beds of the upper unit display a lateral thickening that is particularly evident near the shelf break, and that has been interpreted as due to the increased subsidence and the consequent down-to-basin tilting of the outermost part of the platform. Moreover, the structural analysis performed on the Digital Outcrop Models and supported by field observations, highlighted the presence of an early generation of faults and joints that indicate an early gravitational deformation of the buildup, possibly caused by the platform progradation and compaction-induced subsidence of the San Cassiano basinal deposits. These WNW-ESE synsedimentary structures are formed by normal faults and extensional joints that are oriented nearly perpendicular to the direction of progradation of the carbonate platform
An Open-Source Algorithm for 3D ROck Slope Kinematic Analysis (ROKA)
No full textThe Markland test is one of the most diffused and adopted methods of kinematic analysis for the identification of critical intersections of rock discontinuities that could generate rock failures. Traditionally, the kinematic analysis is based on the use of a stereographic approach that is able to identify the critical combination between the orientations of discontinuities and the rock wall. The recent improvements in the use of Digital Outcrop Models (DOMs) created the conditions for the development of a new automatized approach. We present ROck Slope Kinematic Analysis (ROKA) which is an open-source algorithm aimed at performing the Kinematic Analysis using the discontinuity measures collected onto a 3D DOM. The presented algorithm is able to make a local identification of the possible critical combination between the identified discontinuities and the orientation of the slope. Using this approach, the algorithm is able to identify on the slope the presence of critical combinations according to the traditional kinematic analysis of planar failure, flexural toppling, wedge failure, and direct toppling modes of failures and then visualize them on DOMs. In this way, the traditional approach is more effective and can be adopted for a more detailed analysis of large and complex areas
Analysis by UAV digital photogrammetry of folds and related fractures in the monte antola flysch formation (Ponte organasco, Italy)
No full textThe deformation structures (folds and fractures) affecting Monte Antola flysch formation in the area of Ponte Organasco (Northern Apennines-Italy) were analyzed by Unmanned Aerial Vehicle Digital Photogrammetry (UAVDP). This technique allowed the realization of Digital Outcrop Models (DOMs) interpreted in a stereoscopic environment by collecting a large number of digital structural measures (strata, fractures and successively fold axes and axial planes). In particular, by UAVDP was possible to analyze the relationships between folds and fractures all along the study structures. The structural analysis revealed the presence of a series of NE-vergent folds characterized by a typical Apenninic trend and affected by four main sets of fractures. Fractures are always sub-orthogonal to the bedding, maintains constant angular relationships with the bedding and seems linked to the folding deformation. The study shows that the UAVDP technique can overcome the main limitations of field structural analysis such as the scarce presence and the inaccessibility (total or partial) of rock outcrops and allows for acquiring images of rock outcrops at a detailed scale from user-inaccessible positions and different points of view and analyze inaccessible parts of outcrops
Detection and geometric characterization of rock mass discontinuities using a 3D high-resolution digital outcrop model generated from RPAS imagery – Ormea rock slope, Italy
Full text linkThe use of a remotely piloted aircraft system (RPAS) and digital photogrammetry is valuable for the detection of discontinuities in areas where field mapping and terrestrial photogrammetry or laser scanner surveys cannot be employed because the slope is unsafe, inaccessible, or characterized by a complex geometry with areas not visible from the ground. Using the Structure-from-Motion method, the acquired images can be used to create a 3D texturized digital outcrop model (TDOM) and a detailed point cloud representing the rock outcrop. Discontinuity orientations in a complex rock outcrop in Italy were mapped in the field using a geological compass and by manual and automated techniques using a TDOM and point cloud generated from RPAS imagery. There was a good agreement between the field measurements and manual mapping in the TDOM. Semi-automated discontinuity mapping using the point cloud was performed using the DSE, qFacet FM, and qFacet KD-tree methods applied to the same 3D model. Significant discrepancies were found between the semi-automatic and manual methods. In particular, the automatic methods did not adequately detect discontinuities that are perpendicular to the slope face (bedding planes in the case study). These differences in detection of discontinuities can adversely influence the kinematic analysis of potential rock slope failure mechanisms. We use the case study to demonstrate a workflow that can accurately map discontinuities with results comparable to field measurements. The combined use of TDOM and RPAS dramatically increases the discontinuity data because RPAS can supply a good coverage of inaccessible or hidden portions of the slope and TDOM is a powerful representation of the reality that can be used to map discontinuity orientations including those that are oriented perpendicular to the slope
DICE: An open-source MATLAB application for quantification and parametrization of digital outcrop model-based fracture datasets
No full textAn open-source MATLAB application (app) named Discontinuity Intensity Calculator and Estimator (DICE) was developed in order to quantitatively characterize the fractures, or in more general, discontinuities within a rocky outcrop in three-dimensional (3D) digital data, such as digital outcrop model (DOM). The workflow proposed for the parametrization of the discontinuities consists of the following steps: (1) Analysis and mapping of the fractures detected within the 3D DOMs; (2) Calculation of the orientation, position and dimensions of discontinuities that are represented by best-fit circular planes; (3) Determining the discontinuity parameters (dimension, distribution, spacing and intensity) by the DICE algorithm using different 3D oriented sampling techniques (3D oriented scanline, 3D oriented circular scan window and spherical scan volume). Different sampling methods were bench tested with a synthetic, as well as a natural case study, and compared in order to understand the advantages and limitations of each technique. The 3D oriented circular scan window appears to be the most effective method for fracture intensity estimation with high accuracy (error 0.4%) and stability with variations in scan radius. (c) 2023 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/)
Relations between Fault and Fracture Network Affecting the Lastoni di Formin Carbonate Platform (Italian Dolomites) and Its Deformation History
No full textIn this study, we analyze the fault and fracture network of the Middle Triassic carbonate platform of the Lastoni di Formin (Italian Dolomites, Italy). The reconstruction of the deformation history is of primary importance for a full comprehension of the present structural setting of this carbonate platform. The huge dimensions of the carbonate body and superb exposure of its vertical cliffs and gently dipping top plateau make the Lastoni di Formin platform an ideal outcrop to integrate traditional fieldwork with Digital Outcrop Modelling analysis. The results of the structural studies partially confirm that the present-day fracture pattern is the result of differential compaction-induced deformation that generated WNW-ESE-trending extensional fractures and normal faults, perpendicular to the direction of progradation of the platform. Successively, extensional tectonics, likely related to the Jurassic rifting phase, led to the formation of NNW-SSE striking fractures and westward-dipping normal faults. A Neogene compressional tectonic event, characterized by N-S to NW-SE crustal shortening, deformed the platform, essentially with strike-slip structures
Finite element analysis of early deformations of carbonate platforms driven by differential compaction of basinal unit
No full textA two-dimensional numerical analysis based on the finite element method and linear elasticity is used to demonstrate how the differential compaction of the basinal unit can cause the early deformation of a prograding and/or aggrading carbonate platform. Our model investigates the modification of the carbonate platform stratal architecture and stress field driven by the process of differential compaction. We compared the results of our model with observations from two Triassic carbonate platforms in the Italian Dolomites: Lastoni di Formin and Nuvolau Mts. (Passo Giau, Italy). We show that the model can explain the modification of stratal architecture, as well as fault and fracture patterns observed on these platforms. In particular, we show that (1) the slope and slope-to-basin transition regions are expected to experience most of the brittle deformation and, differently from what was suggested by previous numerical studies, the formation of platform-ward dipping faults and major fractures with dip angles that tend to decrease moving dip-ward. In addition, (2) the inner platform region can exhibit a slightly tensile regime, which may lead to the formation of syndepositional and/or syndiagenetic fractures. Moreover, (3) in the case of predominantly prograding platforms, the results of the model show a general tilting and thickening of the inner platform strata towards the shelf-slope break.We investigate the relation between the differential compaction of the basinal unit and the early deformation of a growing carbonate platform using a 2D finite element model (a). We compare the results with two Triassic carbonate platforms in the Italian Dolomites: Lastoni di Formin and Nuvolau Mts (b).imag
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