Discontinuity Characterization of Rock Masses through Terrestrial Laser Scanner and Unmanned Aerial Vehicle Techniques Aimed at Slope Stability Assessment (original) (raw)
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International Journal of Rock Mechanics and Mining Sciences, 2017
, roberto.tomas@ua 1. Introduction Data collection for kinematic and structural analyses in hills or rock slopes still maintains, nowadays, an important manual component. The set of lithological, structural and characteristic observations of the rock mass, directed to engineering design, is referred to as geomechanics observation point or geomechanical station. The properties and orientation of discontinuities and rock matrix of a geomechanics observation point are obtained in situ, by normalized templates([1]; [2]). Subsequent laboratory/office work determines the resistant properties of the discontinuities, evaluates the geomechanical quality of the rock mass (e.g. using the RMR, Q, or GSI indices) and carries out a census of discontinuities, grouping into main sets. Field data are combined with laboratory results, in situ and geophysical tests, with the objective of elaborating a "geomechanical model" of the rock mass. Field characterization plays an important role in preliminary studies and, in many cases, is the only information available in the first stages of investigation and project development. Traditionally, rock mass field data collection has been carried out by physically accessing the slope. However, remote acquisition techniques have provided a new perspective. The main two remote data collection techniques are Interferometric Synthetic Aperture Radar-InSAR-and Light Detection and Ranging-LiDAR [3], [4].InSAR enables high precision measurements of terrain surface movements, and is usually applied to monitor and detect landslides. LiDAR provides a 3D point cloud of the This is a previous version of the article published in
Geomechanical rock mass characterization with Terrestrial Laser Scanning and UAV
2015
Thanks to the improvement of surveying equipments, i.e. Terrestrial Laser Scanners (TLS) and Unmanned Aerial Vehicles (UAV), dense point clouds and very precise 3D models of inaccessible rock cliffs can be obtained. Both commercial and self-developed data processing software packages allow the extraction of some parameters regarding discontinuity sets (i.e. orientation, intensity, Vb, etc.). Nevertheless, maps with the distribution of such parameters are still not common. A procedure for obtaining raster maps with the distribution of significant parameters for the geomechanical characterization of rock cliffs, open pit mine slopes and tunnel faces is presented in this paper. Some selected case studies in the Italian Alps will be presented. reducing shadow areas and providing very detailed 3D models of inaccessible rock cliffs with an accuracy of few centimeters. By applying proper software packages, it’s now possible to extract not only the attitude of rock mass discontinuity surfac...
Remote Sensing
In this work, we describe a comprehensive approach aimed at assessing the slope stability conditions of a tuff cliff located below the village of Sugano (Central Italy) starting from remote geomechanical analysis on high-resolution 3D point clouds collected by terrestrial laser scanner (TLS) surveys. Firstly, the identification of the main joint systems has been made through both manual and automatic analyses on the 3D slope model resulting from the surveys. Afterwards, the identified joint sets were considered to evaluate the slope stability conditions by attributing safety factor (SF) values to the typical rock blocks whose kinematic was proved as compatible with tests for toppling under two independent triggering conditions: hydrostatic water pressure within the joints and seismic action. The results from the remote investigation of the cliff slope provide geometrical information of the blocks more susceptible to instability and pointed out that limit equilibrium condition can be...
Method for Automated Discontinuity Analysis of Rock Slopes with Three-Dimensional Laser Scanning
Transportation Research Record, 2005
Three-dimensional (3D) laser scanning data can be used to characterize discontinuous rock masses in an unbiased, rapid, and accurate manner. With 3D laser scanning, it is now possible to measure rock faces whose access is restricted or rock slopes along highways or railway lines where working conditions are hazardous. The proposed method is less expensive than traditional manual survey and analysis methods. Laser scanning is a relatively new surveying technique that yields a so-called point cloud set of data; every single point represents a point in 3D space of the scanned rock surface. Because the density of the point cloud can be high (on the order of 5 mm to 1 em), it allows for an accurate reconstruction of the original rock surface in the form of a 3D interpolated and meshed surface using different interpolation techniques. Through geometric analysis of this 3D mesh and plotting of the facet orientations in a polar plot, it is possible to observe clusters that represent different rock mass discontinuity sets. With fuzzy k-means clustering algorithms, individual discontinuity sets can be outlined automatically, and the mean orientations of these identified sets can be computed. Assuming a Fisher's distribution, the facet outliers can be removed subsequently. Finally, discontinuity set spacings can be calculated as well.
Geostructure of Coroglio tuff cliff, Naples (Italy) derived from terrestrial laser scanner data
Journal of Maps, 2015
We present a long-range terrestrial laser scanner application for the geostructural mapping of Coroglio cliff, a tuff rock face exposed along the coastal zone of Campi Flegrei, Napoli. The procedure includes several phases (geomorphological analysis, structural field survey, laser scanner data acquisition and data processing, 3-D model development and analysis, geostructural classification of discontinuity orientation data and 2-D vertical cartographic production). Field data were processed with specific software dedicated to geostructural and geometric analysis. Spatial data were managed with a geographical information system and have been used for the construction of 2-D and 3-D geometric models of the rock cliff surface and geostructural interpretation. The main product of this study is a vertical geostructural map of the Coroglio cliff at 1:500 scale that illustrates the spatial distribution and orientation of the major families of structural discontinuities detected along the exposed surface of the cliff. The cartographic product includes base information useful to identify the main rock failure mechanisms along the cliff and represents a first step for the zonation of areas susceptible to block failures and the planning of monitoring activities.
Bulletin of Engineering Geology and The Environment
A study of rock slope stability was performed using geological surveys and Digital Terrestrial Photogrammetry (DTP) integrated by Laser Scanning (LS) and topographic measurements. The use of DTP is useful especially in inaccessible sites such as natural cliffs. By obtaining oriented stereo images, accurate digital surface models and orthophotos, useful data can be produced showing geometrical characteristics of joints, blocks and slopes such as planes, attitude, spacing, persistence and rock mass volumes. In order to accomplish the analysis, DTP was combined with LS in order to build the Digital Dense Surface Model (DDSM) of the slope. The conventional method of limit equilibrium was applied to study the slope stability using a deterministic approach and to suggest activities of geo-monitoring and engineering solutions for risk mitigation with respect to the environment. Une étude de stabilité de pentes rocheuses a été effectuée à partir de reconnaissances géologiques et d’études de Photogrammétrie Numérique Terrestre (DTP) contrôlées par des investigations par Scanner Laser (LS) et mesures topographiques. L’utilisation de la DTP est particulièrement intéressante pour les sites difficilement accessibles, comme des falaises naturelles. A partir d’images stéréoscopiques orientées, de modèles numériques de surface et d’orthophotos, des données importantes ont été obtenues concernant les caractéristiques géométriques de joints et de blocs, telles que des orientations de plans, des espacements et des extensions de discontinuités et des volumes de masses rocheuses. Afin de réaliser ces analyses, la photogrammétrie numérique a été combinée avec la technique du scanner laser pour construire le Modèle Numérique Dense de Surface (DDSM) de la pente. La méthode conventionnelle de l’équilibre limite a été appliquée pour étudier la stabilité de la pente avec une approche déterministe et pour proposer des techniques de surveillance et des solutions d’ingénierie, respectueuses de l’environnement, permettant de limiter les risques.
Terrestrial Laser Scanning survey of the Sugano cliff (Orvieto, Italy) for slope stability analyses
Rendiconti online della Società Geologica Italiana, 2015
The Terrestrial Laser Scanner (TLS) survey of the Sugano (TR, Italy) cliff has been performed with the aim of assessing by a remote position the main rock mass jointing features (such as dip/dip direction, spacing, opening, persistency etc). Geostructural analysis has been performed on the high resolution 3D point clouds collected in the frame of a two days survey by combining six survey positions. The results from the remote investigation of the cliff allowed to identify the limit equilibrium conditions for all the studied cases and provide geometrical information (volume, surface etc.) of the blocks more susceptible to instability.
An approach to automate discontinuity measurements of rock faces using laser scanning techniques
A recent development in the use of lidar remote sensing techniques is ground-based laser scanning. Laser scanning of rock faces yields the spatial relation between all scanned rock surface points, at a very high resolution, basically a dense "point cloud" in three-dimensional space. The subject of this research is to obtain discontinuity information from the point cloud data set, using an approach that can be automated. The first step in this methodology is to interpolate the point cloud data using 3D Delaunay triangulation in order to create a 3D surface. As a 3D triangulated surface, the scanned rock face is represented by a large number of triangles. The orientation of each triangle can subsequently be computed using basic geometrical rules. Analysis of the kernel density stereo plots of the orientation of all triangles, reveal that specific discontinuity sets can be recognised. Obviously, if this approach can be further developed and fully automated, this would give the site engineer or geologist, in real-time, evidence on the internal structure of any discontinuous rock mass. Particularly in areas where access to rock outcrops is poor, application of this technique will be very promising.
Sustainability
In mountainous areas around the world, dealing with rockfalls means facing some technical survey difficulties due to the low accessibility of areas and the height of slopes. If a cultural heritage is also threatened by such mass movement, the need of specific survey solutions, even in a combined asset, is required. This paper deals with the integration of ground and UAV rock mass surveys aimed at defining the rockfall attitude of an unstable rock cliff sector hosting an example of cultural heritage in tourist area of southern Italy, whose fruition has already been threatened by the occurrence of rockfalls. As an example of the defensive architecture of XII and XIII centuries, the Saracen Castle in Taormina is reached by hundreds of visitors each year, but its access path and the surrounding area are threatened by the unstable condition of the cliff, hosting unstable rock volumes on kinematically critical planes. In order to achieve a reliable geostructural setting of the cliff, aimi...