Mine monitoring using 3D scanning

Assistant PhD Maria-Roberta GRIDAN Lecturer PhD Floarea Maria BREBU Lecturer PhD Alina Corina BĂLĂ

Overland Communications Ways, Foundations and Cadastral Survey Politehnica University Timisoara

No 2A Traian Lalescu Timisoara, Romania

roberta.gridan@upt.ro floarea.brebu@upt.ro

Abstract: - The advantage of a real prognosis determination is the fact that in time the investments in these types of areas can be made on time and with maximum efficiency. Practice has demonstrated that by using 3D modeling and the analysis of the movements of the areas located in mining areas, the experts in the field have better tools to perform a good prognosis in time and a good monitoring in time of the techniques used for land protection and for the protection of the existing constructions in the affected areas. The purpose of this paper is to highlight the importance of terrestrial laser scanning for displacements and deformations monitoring, that may occur in the horizon +210. The 3D scanning result will contain relevant information about displacements and deformations that may occur at this horizon, if they are homogeneous or if there is a local buckling. Key-Words: - Terrestrial 3D laser scanner, 3D models, deformations, salt mine, scan resolution, displacements

1 Introduction 3D modeling (also known as meshing) is the process of developing a mathematical representation of any three-dimensional surface of object via specialized software. The product is called a 3D model. In the last decade, more and more engineers all over the word started exploring 3D modeling instead of using the traditional two-dimensional drawings [1]. For instance, designing a dynamic framework for planning and development, based on 3D models can help to create the master plan of any populated area. 3D modeling offers multiple advantages, namely correcting heights, interconnecting the object’s components, creating a new product based on the primary elements. Thus, the designing process is facilitated together with an effortless manipulation of the complex data. Terrestrial 3D laser scanners – a new class of survey instruments– have recently become very popular and are increasingly used in providing as-built and modeling data in various applications, including land surveying, mobile mapping, roads/tracks, monitoring, city modeling, facility management, archaeological studies, architecture, cultural heritage conservation, mining, industry, geology, civil engineering, bridge structures, and highway surveys [2].

3D refers to objects that been created in 3 position (X, Y and Z). Nowadays, there are a lot 3D objects that you can see in cultural heritage, civil engineering, digital terrain model, product designs etc. Even though they are commonly seen these days, their creation is not a simple fact. One needs 3D programs or specialized applications or websites that offer ready-made 3D models but not to specific scale. The starting point of the modelling approach is a mathematical principle of decomposition of a mixed process into parts that reflect its complementary aspects, random and non-random.

2 Mine monitoring using 3D scanning The Ocnele Mari City from Ramnicu Valcea County, Romania, lies in a depression at an altitude about 320 m, being surrounded by hills with an altitude between 400 and 600 m. Under these hills is a massive salt about 600 m thick, which is this place main natural resource and which was mined from ancient times, in fact giving this city’ name ("ocna" means "salt mine"). The salt mine from Ocnele Mari is the largest in our country, having an area over 20,000 square meters and the galleries length exceeds 13,000 meters [3]. In the saline (salt mine known as the saline) salt

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mining was done and still doing through lumps extraction (Maglite).

Fig.1 Ocnele Mari salt mine location map

The salt mining from Ocnele Mari is unique and the most important from the south-western Romania (hence the name Ocnele Mari), this fact is mentioned in all historical documents since the eighteenth century. Mining takes place in two horizons - horizons +226 and +210 horizon, the operation method is currently the most modern in the world: the small room and landing square method. The purpose of this paper is to highlight the importance of terrestrial laser scanning for displacements and deformations monitoring, that may occur in the horizon +210.

Fig.2 Image from +210 horizon

The 3D scanning result will contain relevant information about displacements and deformations

that may occur at this horizon, if they are homogeneous or if there is a local buckling.

Fig.3 Scan System TX5

The quality aspect of surveying using laser scanners needs careful consideration throughout the measurement and processing process. Quality starts with a full understanding of project specification. This understanding allows the correct choice of scanner, correct scan resolution, appropriate registration method and so on [3]. 3 Data analyzing The 3D Laser Scans at Ocnele Mari salt mine were performed using five Trimble spherical prisms.

Fig.4 Trimble spherical prisms type on site

After scanning a point cloud file in the local coordinate system was achieved. This file contains the 3D point position, the operator name, the station name, the targets setting points and the coordinate system position. Data, obtained from TX5 Trimble laser scanner measurements, post processing was done with

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Trimble RealWorks software. If the registration obtained results correspond from geometrically point of view and we consider them acceptable, meaning that the resulted deviations are within the required accuracy, it results an unwrought point cloud in a unique single coordinate system.

Fig.5. Unwrought point cloud resulted from scanning

The next operation in the post processing process is to filter the resulting data, which requires the point elimination, which are not from subject scanned area and also removing items containing noise influence, poor reflection on the scanned area, obstacles or peoples which appear in scan, etc. The disposal from the point density can be with the five nodes implemented in the standard command "Point cloud density", without reduction, minimal and medium reduction, high and very high reduction. After filtering and setting these operations will move to data modeling in order to obtain the geo- 3D model of scanned mining horizon.

Fig.6 The 3D model of the scanned mining horizon

Based on the 3D model of the +210 mining horizon and on a reference plane can calculate the movement of the scanned area from the salt mine and the differences between measured surfaces at different times.

Fig.7 Setting the reference plane for deformations

computing

In order to carry out studies on land, to properly apply solutions and measures that prevent soil erosion, land reclamation works cooperate with a number of other disciplines such as: soil science, geology, topography, cadastre and GIS as a tool of analysis [5]. Complex 3D models of faults, horsts, grabens, folds, salt domes and many other complex geologic structures are easily created 3D volumetric models [6].

Fig.8 Created 3D volumetric model [6]

4 Conclusion In context of evolving technology, more and more potential domains for 3D laser scanning

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applicability appeared, starting from its obvious advantages: measurements without direct contact, high precision, quickness data acquisition, results delivery in a shorter time, etc. Laser scanning technology represents a first reference for 3D modeling and data analysis, being able to be used for studies on many important directions and in various fields, such as: geophysics, mining, hydrology, environmental protection, constructions, archeology, meteorology, etc. These are some of the reasons for which a possible prognosis in time of the movement of special constructions can make the investments in these areas continuous and made with maximum efficiency. References: [1] Herban S.I., Vîlceanu C.B., 3D modeling using

terrestrial Leica C 10 Scanstation, Scientific Bulletin of the Politehnica University Transactions on Hydrotehnics, No.2, 2011 pp.95-98

[2] C. Muşat, S. Herban, Determinate dynamic deformation of construction using the integrated system Leica 1200, Journal of Geodesy and Cadastre, Alba Iulia, RevCad no.10, pp. 145-153

[3] Clara Beatrice VÎLCEANU, Ioan Sorin HERBAN, Carmen GRECEA, Creating 3D Models Of Heritage Objects Using Photogrammetric Image Processing, AIP Conference Proceedings 1558, 1599 (2013); pp. 1599-1602.

[4] Ioan Sorin Herban, Clara – Beatrice Vîlceanu, TERRESTRIAL LASER SCANNING USED FOR 3D MODELING, Proceedings of the 12th International Multidisciplinary Scientific GeoConference SGEM 2012, ISSN 1314-2704, pp. 795-803;

[5] L. Dimen, T. Borşan, C.D. Brătan - Using GIS Technology for Soil Erosion Analysis. A case study: The hydrographical Basin of “Buturoiului Valley”, Jidvei, Alba County, Journal of Environmental Protection and Ecology ISSN 1311-5065, Vol. 14, 2013;

[6] http://www.ctech.com/wp-content/uploads/2010/12/CoalBasin.png

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