Workplace safety in quarries can be evaluated and improved through an accurate mapping of localized hazard. Rock slopes stability is dominantly influenced by the structural setting which, in combination with exploitation methods, affects the risk. This paper describes the application of a rotary wing Remotely Piloted Aircraft System (RPAS) and a terrestrial laser scanner for monitoring the stability of a marble quarry located in the central part of the Apuan Alps Metamorphic Complex, in the municipality of Seravezza (Lucca, Italy). The site, named Piastrone, is u-shaped quarry with the main walls approximately NNE-SSW oriented and an area of about 1.5 ha; elevation ranges from about 1,150 to 1,300 m a.s.l.. The quarry consists of very appreciated ornamental marbles, well known all over the world for their aesthetical and physical-mechanical characteristics. The marbles belong to Mt. Altissimo syncline described at first by Lotti & Zaccagna (1881), Giglia (1967), and more recently by Meccheri et al. (2007) and Lorenzoni et al. (2011). In the open pit it is possible to appreciate good examples of the Altissimo White Statuario marble: a white coarse grained marble, with thin and regular layers not thicker than 2 m, characterized by low concentrations of pyrite and very thin and discontinuous yellow or greyish-green veins of phyllosilicates. The walls of the quarry are somewhere densely fractured, with discontinuity traces of variable lengths, from metric to decametric, that penetrate inward the slopes with thickness difficult to estimate, often exceeding few meters in depth. The intersection between different fracture systems and the slope surface generates rocky blocks and wedges of variable size that may be subject to phenomena of gravitational instability due to the variation of meteorological, hydraulic and dynamic conditions. In such an environmental context, data obtained from traditional engineering-geological surveys, collected at the foot of the slopes and along the wall by climbing technicians, may be used for rock mass characterization. This data, which holds important statistical value, does not provide deterministic information of the complete slope necessary to localize the hazard and plan the remediation works. There are limitations and technical difficulties in the implementation of such rope access survey methods, including the close proximity to the quarry walls which compromises visibility and the ability to recognize large-scale geological features, as well as the unavailability of suitable cartographic maps. In this study, these difficulties were overcome by integrating available data with geometrical and structural info derived from the analysis of geo-referenced 3D point cloud acquired using photogrammetric techniques. Also a terrestrial laser scanning was carried out from two different point of view, even if the elevation of the slopes creates shadows in the data, limiting the feasibility of geo-structural survey. To overcome such a limitation, we utilized a rotary wing Aibotix Aibot X6 RPAS geared with a Nikon Coolpix A camera. The drone flights were executed in manual modality and the images were acquired, according to the characteristics of the area, under different acquisition angles, both from the top and in front of the quarry escarpments. Furthermore, photos were captured very close to the slopes, allowing to produce a dense 3D point cloud by image processing. A topographic survey was carried out in order to guarantee the needed spatial accuracy to the process of images exterior orientation. The coordinates of GCPs and check points were calculated through the post-processing of data collected by using two GPS receivers, operating in static modality with an acquisition time of up to 3 hours, and a Total Station. The photogrammetric processing of image blocks allowed us the creation of dense 3D point cloud, DTM, orthophotos, and 3D textured model with high level of cartographic detail. Post-processing included contemporary observations of 3 permanent GPS stations, and the conversion of GCPs elevation from ellipsoid to orthometric heights using ConveRgo software. The topographic survey included targets used for registering two point clouds acquired by a Leica Scanstation2 laser scanner. By this way, the co-registration of the point clouds from laser scanning and RPAS image processing makes possible the comparison and integration of data. An unique 3D repository was created including updated images of the walls and their morphological and structural setting. By the analysis and interpretation of the 3D point clouds and high detailed and updated photographs, all the rock discontinuities were deterministically characterized in terms of attitude, persistence, and spacing and their distribution mapped on the orthophotos. Furthermore, the main discontinuity sets were identified through a density analysis of attitudes in stereographic projection. The size and shape of potentially unstable blocks identified along the slopes were also measured. Data from the photointerpretation was validated by and integrated with results of scan lines from traditional engineering-geological surveys which were conducted in accessible outcrops. Joint systems were fully characterized and used to classify the rock mass using the Rock Mass Rating method (RMR - Bieniawski, 1989) and the Geological Strength Index (GSI - Hoek, 1994). Finally, the kinematic and dynamic analysis of possible rock failures was performed for all the slopes. The characterization of localized hazard has indicated the deterministic safety factors of rock blocks and wedges, used by the company responsible for the exploitation activities to plan the protection works for safety guarantee and the continuation of marble extraction.
Salvini, R., Mastrorocco, G., Esposito, G., Seddaiu, M. (2016). Characterization of localized hazard in a marble rock slope using a Remotely Piloted Aircraft System (RPAS) and terrestrial laser scanning. In Proceedings of the 3rd International Symposium on Rock Slope Stability, 15-17 November 2016 Lyon (France) (pp.83-84).
Characterization of localized hazard in a marble rock slope using a Remotely Piloted Aircraft System (RPAS) and terrestrial laser scanning
Salvini, Riccardo;Mastrorocco, Giovanni;
2016-01-01
Abstract
Workplace safety in quarries can be evaluated and improved through an accurate mapping of localized hazard. Rock slopes stability is dominantly influenced by the structural setting which, in combination with exploitation methods, affects the risk. This paper describes the application of a rotary wing Remotely Piloted Aircraft System (RPAS) and a terrestrial laser scanner for monitoring the stability of a marble quarry located in the central part of the Apuan Alps Metamorphic Complex, in the municipality of Seravezza (Lucca, Italy). The site, named Piastrone, is u-shaped quarry with the main walls approximately NNE-SSW oriented and an area of about 1.5 ha; elevation ranges from about 1,150 to 1,300 m a.s.l.. The quarry consists of very appreciated ornamental marbles, well known all over the world for their aesthetical and physical-mechanical characteristics. The marbles belong to Mt. Altissimo syncline described at first by Lotti & Zaccagna (1881), Giglia (1967), and more recently by Meccheri et al. (2007) and Lorenzoni et al. (2011). In the open pit it is possible to appreciate good examples of the Altissimo White Statuario marble: a white coarse grained marble, with thin and regular layers not thicker than 2 m, characterized by low concentrations of pyrite and very thin and discontinuous yellow or greyish-green veins of phyllosilicates. The walls of the quarry are somewhere densely fractured, with discontinuity traces of variable lengths, from metric to decametric, that penetrate inward the slopes with thickness difficult to estimate, often exceeding few meters in depth. The intersection between different fracture systems and the slope surface generates rocky blocks and wedges of variable size that may be subject to phenomena of gravitational instability due to the variation of meteorological, hydraulic and dynamic conditions. In such an environmental context, data obtained from traditional engineering-geological surveys, collected at the foot of the slopes and along the wall by climbing technicians, may be used for rock mass characterization. This data, which holds important statistical value, does not provide deterministic information of the complete slope necessary to localize the hazard and plan the remediation works. There are limitations and technical difficulties in the implementation of such rope access survey methods, including the close proximity to the quarry walls which compromises visibility and the ability to recognize large-scale geological features, as well as the unavailability of suitable cartographic maps. In this study, these difficulties were overcome by integrating available data with geometrical and structural info derived from the analysis of geo-referenced 3D point cloud acquired using photogrammetric techniques. Also a terrestrial laser scanning was carried out from two different point of view, even if the elevation of the slopes creates shadows in the data, limiting the feasibility of geo-structural survey. To overcome such a limitation, we utilized a rotary wing Aibotix Aibot X6 RPAS geared with a Nikon Coolpix A camera. The drone flights were executed in manual modality and the images were acquired, according to the characteristics of the area, under different acquisition angles, both from the top and in front of the quarry escarpments. Furthermore, photos were captured very close to the slopes, allowing to produce a dense 3D point cloud by image processing. A topographic survey was carried out in order to guarantee the needed spatial accuracy to the process of images exterior orientation. The coordinates of GCPs and check points were calculated through the post-processing of data collected by using two GPS receivers, operating in static modality with an acquisition time of up to 3 hours, and a Total Station. The photogrammetric processing of image blocks allowed us the creation of dense 3D point cloud, DTM, orthophotos, and 3D textured model with high level of cartographic detail. Post-processing included contemporary observations of 3 permanent GPS stations, and the conversion of GCPs elevation from ellipsoid to orthometric heights using ConveRgo software. The topographic survey included targets used for registering two point clouds acquired by a Leica Scanstation2 laser scanner. By this way, the co-registration of the point clouds from laser scanning and RPAS image processing makes possible the comparison and integration of data. An unique 3D repository was created including updated images of the walls and their morphological and structural setting. By the analysis and interpretation of the 3D point clouds and high detailed and updated photographs, all the rock discontinuities were deterministically characterized in terms of attitude, persistence, and spacing and their distribution mapped on the orthophotos. Furthermore, the main discontinuity sets were identified through a density analysis of attitudes in stereographic projection. The size and shape of potentially unstable blocks identified along the slopes were also measured. Data from the photointerpretation was validated by and integrated with results of scan lines from traditional engineering-geological surveys which were conducted in accessible outcrops. Joint systems were fully characterized and used to classify the rock mass using the Rock Mass Rating method (RMR - Bieniawski, 1989) and the Geological Strength Index (GSI - Hoek, 1994). Finally, the kinematic and dynamic analysis of possible rock failures was performed for all the slopes. The characterization of localized hazard has indicated the deterministic safety factors of rock blocks and wedges, used by the company responsible for the exploitation activities to plan the protection works for safety guarantee and the continuation of marble extraction.File | Dimensione | Formato | |
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https://hdl.handle.net/11365/1010365