Quarry wall stability assessment using TLS method Ľudovít Kovanič, M.Sc., PhD. 1,a *, Peter Blišťan, assoc. prof., PhD. 2,b

Transcription

1 Advanced Materials Research Vols (2014) pp Submitted: Online available since 2014/Oct/01 at Accepted: (2014) Trans Tech Publications, Switzerland doi: / Quarry wall stability assessment using TLS method Ľudovít Kovanič, M.Sc., PhD. 1,a *, Peter Blišťan, assoc. prof., PhD. 2,b 1 Institute of geodesy, cartography and geographic information systems, Faculty of mining, ecology, processing and geotechnologies, Technical University of Kosice, Park Komenskeho 19, Kosice, Slovakia 2 Institute of geodesy, cartography and geographic information systems, Faculty of mining, ecology, processing and geotechnologies, Technical University of Kosice, Park Komenskeho 19, Kosice, Slovakia a Ludo.Kovanic@tuke.sk, b Peter.Blistan@tuke.sk Keywords: 3D laser scanning, open-pit quarry, spatial data modelling, rock slope stability. Abstract: The aim of this paper is to test the possibility of terrestrial laser scanning use to analyze the stability of quarry walls. In recent years the laser scanners started being tested and used for the documentation of geological structures and various phenomena such as landslides, rock collapses and observation of their morphological changes. The subject of our research was a quarry wall in the open-pit mine Brestov, with a significant bench or block disintegration of the andesite massif and therefore, there is a risk of rock blocks crashing. Selected quarry wall was repeatedly measured in the autumn and spring season by a terrestrial laser scanner and movements of rock blocks were evaluated. The observation results show that on the selected quarry wall there were no major movements or block collapse detected and the wall is stable after the winter shutdown. Introduction The problem that sometimes occurs in surface mining and quarrying is the safe operation of the quarry in terms of the stability of the fracture walls when the extraction process is discontinued for a longer period. Under specific combination of factors, such as incoherence rocks (minerals) and disregard massif properties in the establishment of quarry foundations [1], undesired processes such as wall slips or rock collapse by disjunctive structures may be caused. These phenomena may substantially affect the safety of the mining operation and even block the extraction. Rock massif stability monitoring using terrestrial laser scanning Several geodetic methods are used to analyze changes or deformations of rock objects. According to authors [2] measurement can be performed by classical geodetic technology based on spatial polar method characterized by few millimeter accuracy and terrestrial laser scanning (TLS), where acuracy of single point measurement ranges between 3-5 mm. The accuracy of photogrammetric methods depends mainly on the distance from the imaging position of the observed object, therefore, at short distances (less than 5 m) the submillimeter and at greater distances (20-30 m) subcentimeter accuracy can be achieved [3]. Terrestrial laser scanning systems (TLS) currently provide the most progressive and most effective solution for collecting large amounts of spatial data in order to create digital 3D models of objects, enclosed or inaccessible spaces. TLS measurement principle is based on the principles of total stations (TS) [4]. The TLS measurement result is point cloud - a set of discrete spatial points defined by the coordinates X, Y, Z with intensity and color values optionable. It is necessary to further process the raw data to create the final model of the measured object, usually expressed as a triangulated irregular network (TIN) [5,6]. Stability monitoring of the quarry wall in open-pit mine Brestov The aim of the research in the area Brestov was the testing of methodology for assessment of stability of the quarry wall, which was based on a comparison of two models of wall surfaces All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, (ID: /10/14,10:38:19)

2 604 Frontiers of Energy, Materials and Information Engineering obtained by two surveying periods. This is not a classical evaluation of the observed point shift (group of points), but the whole models comparison of the rock wall in detail documented in the form of point clouds obtained by TLS. Two wall models were mutually compared and their shape similarity was evaluated as the horizontal difference between them. In case there is no movement of the blocks, both surfaces will be identical. In case of a change in the shape of a monitored object, the surfaces at the position of change are nonconforming. The size of these changes can be expressed numerically, graphically or using a mesh view with color scale, which reflects changes of the wall shape and also concurrently localizes changes on created models. Survey site description Village Brestov (Fig. 1) belongs to the Prešov district Slovak Republic. The andesite quarry is located about 1 km west of the village. Andesites are fine-grained, light gray coloured, they contain feldspar and quartz with significant pyroxene and amphibole excrescences. The bench disintegration, good splitting and workability are their main characteristics. Given the petrographic characteristics of the raw material and the geological structure of the quarry, on some quarry levels there are cases of rough bench and block disintengration (Fig. 2). It is caused by the presence of a disruption and fractural geological structures in the andesite massif. This phenomenon causes stability problems of fracture walls, because mainly after winter season there is a risk of large rock blocks release and their spontaneous fall on the lower levels. For these reasons, especially in quarries where mining does not have regular or uninterrupted cycle, regular wall stability monitoring using appropriate geodetic methods is necessary (Fig. 2). Fig.1. Geographical position of survey site quarry Brestov. Fig.2. Surveying works in a quarry Brestov. Bench and block disintegration with collapsed rock block.

3 Advanced Materials Research Vols Surveying works, data processing and results interpretation Measurement in the quarry Brestov was performed in two stages, in autumn 2013 and spring Quarry wall was surveyed using a terrestrial laser scanner Leica ScanStation C10 (Fig. 2). Scanner specifications can be found at the manufacturer's website [7]. Before the start of measurement the surveying baseline was built containing two points and 5002, which were used in both measurement stages as the scanner station and orientation point A 6 inch HDS target placed on a tripod was used. Baseline surveying points were stabilized temporarily using a measuring nail and their coordinates were determined by the GNSS method in the coordinate system S-JTSK and height in the Baltic height system after alignment. These coordinate systems are used in Slovak republic as designated geodetic foundations. Scanning parameters were set to the maximum distance 20m between the scanner and the wall as point grid distance 2x2 cm. This resolution was chosen with respect to the rock block size which is around 1x1x2m (Fig. 2). Fig. 3. Data processing in Trimble RealWorks software. Fig. 4. 3D models of quarry wall obtained in both stages of measurement, their mutual overlap and graphical interpretation of the wall shifts or changes. TLS data processing was performed using specialized software Trimble RealWorks. Fig. 3 shows the original non-reduced point cloud with assigned true colors in RGB mode for each measured point. Subsequently using Delaunay triangulation [8,9] TIN models were generated. Their level of detail is directly dependent on the number of measured points that form the vertices of the triangles. Fig. 4 shows the TIN models of quarry wall in both stages of surveying. Both TIN models were mutually overlapped, and then the difference was calculated the change or shift between two surfaces. The calculated difference between these two surfaces is expressed in the form of colored mesh with color scale showing the values of absolute block displacements on the quarry wall - Fig. 4. From the analysis of results of the absolute displacements we conclude that the documented quarry wall is stable after the winter break of extraction and significant morphological changes of the rock massif, which could be clearly identified as a collapse of rock blocks were not detected. Fig. 4 shows high consistency of the monitored wall surface model. Differences with the values of 1-2 cm can be attributed to the measurement precision and in particular to the grid distance between measured points with respect to the selected scanning resolution.

4 606 Frontiers of Energy, Materials and Information Engineering Conclusion For the special tasks of surveying and geotechnics for the surveying and assessment of morphological changes on the surface of a rock wall it is successfully possible to solve this task by the terrestrial laser scanning method. In recent years, terrestrial laser scanning is used for detailed evaluation of shape changes of rock massifs with expected centimeter values [10]. TLS method was used in the quarry Brestov for a repeated measurement of the quarry wall on which there was an expected movement of loose rock blocks as an effect of weathering (repeated freezing water in cracks and subsequent move stone blocks). From the results of processing and analysis of stage measurements, we concluded that at the monitored quarry wall there are no significant movements of stone blocks identified and monitored quarry wall is with respect to the safety and subsequent works in the quarry stable and secure. Acknowledgement The authors are grateful to the Slovak Research and Development Agency for the support of the projects VEGA 1/1206/12 and APVV References [1] PEELE, R.: Mining Engineers Handbook. J. Wiley and Sons, Inc., New York, [2] WAGNER P., ONDREJKA, P., IGLÁROVÁ, Ľ. a FRAŠTIA, M.: Aktuálne trendy v monitorovaní svahových pohybov. Mineralia Slovaca, č. 2, Roč. 42 (2010), 2010, s [3] PUKANSKÁ, K., SABOVÁ, J., RUSNÁKOVÁ, K. a GAJDOŠÍK, J.: Využitie terestrického laserového skenovania pri zisťovaní morfologických zmien terénov. Uhlí-Rudy-Geologický průzkum. Vol. 15, no. 3 (2008), s [4] FRAŠTIA, M.: Produkcia horninových masívov s rozlíšením a presnosťou vyššími ako 1 cm. In: FRAŠTIA, M.: Laserové verzus optické skenovanie skalných masívov. Mineralia Slovaca, č. 2, roč. 44 (2012), 2012, s [5] HOFIERKA, J.: Spatial interpolation and terrain analysis. In: Bender, O., Evelpidou, N., Krek, A. & A. Vassilopoulos (eds.): Geoinformation Technologies for Geocultural Landscapes: European Perspectives. Leiden, The Netherlands: CRC Press/Balkema (Taylor & Francis Group), 2008, pp [6] HOFIERKA, J., GALLAY, M., KAŇUK, J.: Spatial Interpolation of Airborne Laser Scanning Data with Variable Data Density. Proceedings of the 26th International Cartographic Conference, August 25-30, [7] Leica ScanStation C 10. [online]. [cit ]. Dostupné na internete: C10_Brochure_en.pdf [8] LI, J.: A Review of Spatial Interpolation Methods for Environmental Scientists. Geoscience Australia, Australia, 2008, 137p. [9] BLIŠŤAN, P.: Interpolačné metódy pre modelovanie a vizualizáciu priestorových javov v prostredí GIS. In: Fyzikálne faktory prostredia. Roč. 2, mimoriadne č. (2012), s [10] BLIŠŤAN, P. a KOVANIČ, Ľ. ml.: Geodetic methods for efficient spatial data collection. In: Egrse. Vol. 19, no. 1 (2012), p

5 Frontiers of Energy, Materials and Information Engineering / Quarry Wall Stability Assessment Using TLS Method /