Discontinuity mapping using Ground-Based LiDAR: Case study from an open pit mine (original) (raw)
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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.
Detection of Rock Discontinuity Traces Using Terrestrial LiDAR Data and Space-Frequency Transforms
Geotechnical and Geological Engineering, 2017
Part of the rockmass assessment and its application in numerical modelling, within the geotechnical engineering field, is acquiring information such as discontinuity number, density, intensity, size etc., which can be obtained by mapping fracture traces on exposed rockmass surfaces and processing of the recorded field data. Moving past from traditional mapping techniques in the field, fracture traces can be extracted from terrestrial light detection and ranging (LiDAR) point-clouds or LiDAR-derived surface models. However, similarly to field mapping, the extraction of fracture-traces is often done manually. This is an arduous and timely task in most cases. The automatic-detection of such traces is an emerging topic in geotechnical engineering; however, existing methods focus solely on the spatial domain. Spacefrequency representations are ideal for detecting singularities due to their localization in space and frequency. Furthermore, they allow multiscale analysis, which is important for isolating LiDAR-data noise and weak traces in lower scales. In this study, three space-frequency transforms are evaluated, namely, (1) wavelet, (2) contourlet, and (3) shearlet. In addition, the well-known methods of Sobel, Prewitt, and Canny for edge detection are used for comparison purposes. The performance of the different edge-detection methods is tested using data collected from the Brockville Tunnel in Ontario, Canada. Numerical and visual assessment show that contourlets and shearlets achieve the highest agreement with manually-extracted traces that are used for validation. The two methods, along with minimal user interaction, can be used in order to increase the efficiency of rockmass mapping and geometric modelling in stability assessment of tunnels, mines, slopes, and related applications.
Applied Sciences, 2020
Stabilization projects of rock masses cannot be performed without a proper geomechanical characterization. The classical approaches, due to logistic issues, typically are not able to cover extensively the areas under study. Geo-structural analysis on point cloud from terrestrial laser scanning and photogrammetry from unmanned aerial vehicles are valid tools for analysis of discontinuity systems. Such methodologies provide reliable data even in complex environmental settings (active cliffs) or at inaccessible sites (excavation fronts in tunnels), offering advantages in terms of both safety of the operators and economic and time issues. We present the implementation of these techniques at a tuff cliff over the Santa Caterina beach (Campania) and at the main entrance of Castellana Caves (Apulia). In the first case study, we also perform an integration of the two techniques. Both sites are of significant tourist and economic value, and present instability conditions common to wide areas...
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.
Mapping and characterization of rock discontinuities in a tunnel using 3D terrestrial laser scanning
Bulletin of Engineering Geology and the Environment, 2015
This paper attempts to evaluate various methods of geometrical discontinuity characterization using point clouds that are generated with three-dimensional terrestrial laser scanning (3DTLS) in a tunnel. The use of 3DTLS to support discontinuity mapping in tunnels enables the acquisition of a large amount of data without limitations in terms of the tunnel position (wall or roof). Thus, the discontinuity orientation, trace length and frequency were statistically analyzed in different regions of the tunnel to determine the most representative data. Different methods of estimating the mean trace length were compared while considering the variations in the rock face orientation in the tunnel, and the unbiased standard deviation of the trace length was evaluated. The frequencies of discontinuity sets were obtained using scanlines, and aspects of window sampling for density (areal frequency) estimates in tunnels are discussed. The mean trace lengths obtained using rectangular sampling windows (considering the relative frequency of the traces) are more suitable for estimates of different rock face orientations, particularly when the orientation of the discontinuity set varies significantly. In this case, measurements of samples from the tunnel roof presented higher values for both frequency and mean trace length estimates, which demonstrates the importance of data acquisition and evaluation in this region.
Photograph LIDAR Registration Methodology for Rock Discontinuity Measurement
IEEE Geoscience and Remote Sensing Letters, 2018
Rock detachment events along roadways pose public safety concerns but can be predicted and safely handled using geological measurements of discontinuities. With modern sensing technology, these measurements can be taken on 3-D point clouds and 2-D optical images that provide a high level of structural accuracy and visual detail. Doing so allows engineers to obtain the needed data with relative ease while eliminating the biases and hazards inherent in taking manual measurements. This letter presents an approach for fusing the 2-D and 3-D data in natural and unstructured scenes. This includes a novel method for visualizing imagery obtained with very different sensors to maximize their visual similarity making registration a more tangible task. To show the effectiveness of our registration methodology, we evaluate measurements taken manually and digitally on rock facet and cut discontinuity orientations in Rolla, MO. Our method is able to align the 2-D and 3-D data with an accuracy of under 2 cm. The median difference between measurements manually obtained by a geological engineer and those obtained with our proposed software is 3.65.
Integrated rockmass characterization and stability modelling for tunnels using LiDAR
2010
Despite operational constraints, rock tunnel construction projects require a solid understanding of rockmass conditions in order to effectively design excavation and support methods. Where tunnel instability is governed by structural discontinuities, LiDAR or 3D laser scanning technology shows great potential to complement current assessment techniques. LiDAR scans of the rock face offer digital documentation of rockmass conditions from which an interpreter can extract a large quantity of structural data. The authors propose a workflow for applying LiDAR scan data to 3D discontinuum modelling for practical design outputs. RÉSUMÉ La construction de tunnel en roche demande des précises informations géotechniques pour prévoire les conditions futures. À présent, la méthode de rassembler des informations geo-structurelles est beaucoup limitée par accès aux sections de roche non-soutenuees. LiDAR, une technologie seulement récemment appliquée à la géotechnique, montre beaucoup de potentie...
A new methodology was developed to estimate a rock discontinuity roughness using LiDAR data collected from the 4850-ft level of the Sanford Underground Research Facility (SURF) at the former Homestake Gold Mine, Lead, SD. Maptek’s I-Site Studio and Vulcan 3D mine modeling software packages were used for the analysis. The data was obtained using a Z&F IMAGER 5006h LiDAR scanner that had a maximum resolution of 0.01mm. Data preparation was performed in I-site Studio and the points were triangulated to create a surface. The analytical data consisted of ten rectangular point clouds of dimensions of about 1.1 m by 0.56 m. The triangulated surface was imported into Vulcan where data analyses were performed. Results indicated that this method yields a useful way of estimating the roughness of a 3D rock surface by considering orientation (slope) of triangular facets making up the surface. Using the slope angles the surface roughness parameter Z2s was readily determined and correlated with the JRC, resulting in an empirical model that indicated the robustness of the method.
Discontinuity survey and brittle fracture characterisation in open pit slopes using photogrammetry
Proceedings of the First Asia Pacific Slope Stability in Mining Conference, 2016
Remote sensing techniques, such as ground-based photogrammetry and LiDAR, have become routine supplements to traditional rock mass characterisation approaches, greatly enhancing discontinuity survey capability. Concurrently, discrete fracture network simulations, constructed using field discontinuity mapping and borehole logging data, are increasingly being applied to advanced numerical modelling studies of rock slope stability, leading to improved understanding of progressive slope failure involving brittle fracture initiation, propagation, and coalescence. Despite continuing technological advances, predictive modelling of rock slope stability is still limited by our inability to observe the hidden interior structure of a rock mass, and by computational limitations restricting the explicit simulation of small scale material heterogeneity and localisation phenomena inherent to brittle fracture. This paper presents discontinuity mapping observations from a photogrammetry investigation of an Australian open pit mine, with emphasis on the influence of survey scale and resolution on discontinuity characterisation. We also discuss the application of fractography principles to interpretation of brittle rock mass damage, focussing on characterisation of irregular brittle fractures induced by blasting, and on incipient discontinuities which retain cohesion and tensile strength from intact rock bridges. Based on the results, we make recommendations for improving photogrammetry-based discontinuity mapping procedures in order to improve collection of both quantitative data on discontinuity persistence and intensity, and also qualitative characterisation of rock mass damage in open pit slopes.