Utilization of Point Clouds Characteristics in Interpretation and Evaluation

Mechanics, Materials Science & Engineering, September 2016

ISSN 2412-5954

Utilization of Point Clouds Characteristics in Interpretation and Evaluation Geophysical Resistivity Surveying of Unstable Running Block Marcel Brejcha1

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1 2 Technical Univerzity of Ostrava, Faculty of Mining and Geology, Institute of Geodesy and Mine Surveying, 17, listopadu 15/2172, 708 33 Ostrava-Poruba, Czech Republic DOI 10.13140/RG.2.1.1577.2401

Keywords: 3D model, point clouds, active rock collapse, point cloud, electrical resistivity tomography.

ABSTRACT. Close to human residences the places often abound where anthropogenic activity and external factors cause dangerous places. The project of successful design of measures to ensure stability of unstable running blocks depends on chosen approaches and primary resource preparation. Utilization of modern technologies in their taking and processing is required nowadays. The paper settled part with efficient utilization of unusual method of processing of geophysical resistivity method.

1. Introduction. In the paper described way of mapping and interpretation of geophysical survey is the new approach example of resource preparation for project processing of active rock collapse and its stabilization in the sandstone massif, which outcrops delimite the Jizera river valley. In last ten locality. Many active measures were done including breaks of rocky blocks and installation of protective solid safety nets. Specification of requiring resources from mapping and geophysical 1).

2. Definition of technical requirements for surveying activity. Active rock collapse problems are based particularly on geomorphological pertinence and the characteristics of locality.

Geomorphology of the region and locality is the result of tectonic development and resulting weathering and its source. Natural processes in the locality are stressed by anthropogenic activity, historically long-term settled area. Along the river Jizera there is the washtub-shaped valley counterbored to calcific sandstones, which make bank cliffs, usually in two levels, in the surrounding of the soluted locality with strong profile on the left side a cut-bank of the river stream.

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Fig. 1. Area Rozatov.

2.1 Geological connections and description of the area. about 7 km long rocky salient, which starts about 2 km northerly and ends in the south of the historical most substantial part rocky stage, is in many places anthropogenically modelled

mining of thick-

modern building on the upper plateau of the stages or in their foothills, usually with the cleaning of fallen cambering materials in pediment. It causes the highlighting and uncovering of the whole profile naturally made, almost vertical, and up to 25m high slope (absolute height of the upper edge of the slope over the horizontal part of pediment). ky salient, which starts about 2 km the Old Town, a hump of rocky stage, is in many places anthropogenically modelled

mining of thick-

or in their foothills, usually with the cleaning of fallen cambering materials in pediment. It causes the highlighting and uncovering of the whole profile naturally made, almost vertical, and up to 25m high slope (absolute height of the upper edge of the slope over the horizontal part of pediment).

The important road is founded on the lower and younger level of the rock-cut terrace and the old and new-build constructions along it very often reach the river flats of Jizera (particularly gardens and meadows).

The dividing of the slope structures and their forms of erosions and cambering has come from the geomorphological classification.

In connection with the past mining of thick-bedded sandstones in this locality the natural conditions are strongly anthropogenically changed. Pediment is leveled and maintained, area of accumulation in the foothill of the quarry face is missing. The origin statement is observable compared with the

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The upper konvex part over the rocky stage is the result of natural processes and anthropogenic activity. The direct margin over the edge of the face is made of weathering cover from petrean loam.

Its basement complex is represented by slab-disintegrated incoherent sandstones with the transformation to less weathered thick-bedded sandstones. The phenomenon, which is typical for the soluted quarry face, is the breaking of triangular blocks with different bulk on the cross of the joints and opened bedding joints. On the quarry face there are observed frequent breaks with cascade character, i.e. after the fall of a small block the stability of upper-laying block becomes weaker and after its fall the block in the upper level releases again, etc.

A few places with potential danger of rocky collapse are identified in the solved quarry face along the joint systems in the direction of NNW SSE. The total capacity of rock, which can be touched by this danger, is more than over 100 m3.

Based on the facts the basic requirements for geodetic surveying realized in the locality have been set by these criterions: Detailed 3D model particularly of vertical parts of the rocky massif face; Surveying of visible bassets of massif; Possibility of specific identification a evaluation the joint system; Link to binding reference systems; Precision of surveying of detailed points with code 3; Possibility of interpretation of the electric resistivity tomography results; Possibility of realization of subsequent project activities in common CAD program systems.

3 Mapping of solved locality. Locality mapping has been done in these phases: 1. Building and stabilizing of survey points no. 4001 to 4007 by the method GNSS surveying in RTK mode. Surveying network has been completed with points no. 5001 to 5005 localized directly in the quarry face (chosen important, unequivocally identified and colorfully different apical formation of identification during later processing of photogrammetric surveying. After reciprocal surveying of lengths and directions all the network has been leveled by the method of least squares.

2. Photogrammetrical data capture UAV (by pilotless aircraft) with parameters needed for 3D modelling with high-resolution (Fig. 2 and Fig. 3). Photogrammetric work were realized in two phases: taking surveying pictures by the vertically oriented camera (DJI_0001 DJI0043 (Fig. 2) and by squarely on vertical face of rock massif oriented camera (DJI_0052 DJI_0059 (Fig. 3)).

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Fig. 2. Point cloud and cameras position.

Fig. 3. Camera location and image overlap.

Proccessing of photogrammetric surveying including final issues for subsequent processing in Bentley Microstation and AutoCAD was provided by AGISOFT PhotoScan Professional software.

The basic requirement for 3D processing was the final precision of surveying represented by the standard error of image correlation realized by control points with relation to binding reference systems S-JTSK and Bpv (Tab. 1).

From the table it is evident, that in case of convenient decomposition of control points in the vertical part of the quarry face, the results with required conditions can be achieved, even in big amount of projections and difficult terrain settings. Further deployment of UAV technology in quarry enviroment can be found in [1], [2] and [3].

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Table 1. Control Points

In SW Agisoft PhotScan the point clouds were exported in las, dxf and jpeg georeferenced ortophoto map, for subsequent processing. Administration of heavy data load has been proceed by [4]. The drawing of wire model was added with geophysical control points surveyed by the polar method with electric resistivity tomography and with the longitudinal profile axis were constructed from them (Fig. 4). For subsequent project documentation, the borderline map of plots of land was constructed Evaluation of joint system in the locality was made by the measuring of direction and inclination from the space model by the authorial methodology, which allows the measuring the direction and inclination from the image reconstruction to the cloud of oriented 3D points also in physically una Bentley Microstation provided the joint system drawing in wire model (Fig. 5) and then the rose diagram of direction and inclination of the joints in the locality (Fig. 6).

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Fig. 4. ERT profiles.

Fig. 5. Joint system drawing.

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Fig. 6. Rose diagram of inclination of the joints direction.

4. Setting of the geophysical method Electrical Resistivity Tomography. During the realization of geomorphological analysis of solved unstable rocky block the geophysical method Electical Resistivity Tomography (ERT) was used. The base of surveying by ERT is founded on the calculation of decomposition of resistivity under the earth. The initial preliminary parameter is the measured electrical potential caused by the passing of direct current between the pair of electrodes. The disposition of electrodes and other configuration is influenced by local lithological structure and geological characteristics of solved formation. ERT primary results capture is followed by processing of survey points by two-dimensional tomographical inversion with their subsequent modification by the statistic methods. The result is the two-dimensional model of resistivity decomposition under the earth in the axis of measured profile (Fig. 7). Detailed ERT method description is listed in [6].

Fig. 7. Two-dimensional interpretation of surveying results by ERT of solved rock block.

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Utilization of ERT for identification of subareal structures supposes preliminary knowledge of the solved locality. The important atribute of succesful utilization of this method is the creation of comparison-reference model from the data captured on the base of surveying of the structural elements in the rock face, from the boreholes and probes. That is why the first ERT surveyed profile was done close to the rock face.

4.1 ERT results used together with data procured by UAV technology. Spatial objects, which are represented by point clouds, can be analysed simply with high precision. It was achieved because new technologies use instruments for processing huge point clouds with high users comfort. At processing of primary data procured by image correlation, the characteristics of point clouds have been used to get detailed data about surface qualities of the solved rock massif. For interpretation and surveying of the formations like joints, cracks and other structures there have been used Carlson Point Cloud 2016 system, which has a lot of functions available for point cloud analyses. That is why it was important to find how to use ERT results effectively.

4.2 Transformation of resistivity values surveyed by ERT to point cloud structure. ERT surveying was realized by specialized company, which during the work acted upon the geodetically established profiles. Then voxelisation of surveyed values was provided and distribution of electrical resistivity in the rock massif to the form of grids with measurement 0.2 m (Fig.8). Subsequently their export to data files in ASCII format was done. This text file contained spatial coordinates of individual exported points from grid structured expressed by S-JTSK system and relevant electrical resistivity (Fig. 9).

Fig. 8. Surveyed data in ASCII format.

Fig. 9. Interpretation of electrical resistivity progress in the rock massif in longitudinal profiles.

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Data structure describing point clouds offers, besides the information about spatial position of individual points, information about other parameters, for example values R, G, B, describing real colour of particular points, or intensity of laser ray reflexion [7]. The parameter of reflexion intensity was used in additional processing of surveyed values by ERT method. Electrical resistivity values in every point were set to the point cloud as substitution for values of laser reflexion intensity.

Sequentially, after retrieval to programme system Carlson Point Cloud 2016, structure borderlines were made in the form of vectors. These profiles represented by the spatially localised points were processed as the point clouds. This way of display was used to create three profiles, surveyed by ERT method with represented intensity of laser ray reflexion in colour hypsometry. Their interpretation in Autodesk ReCap system is in Fig. 10 and Fig. 11.

Fig. 10. Display of measured electrical resistivity as a substitution for ray reflexion intensity in Autodesk ReCap 360.

Such prepared data were added to the point cloud taken by image correlation method from the UAV technology resources (Fig. 11). This way created spatial model has allowed quality base for detailed analyses of the condition of the solved unstable rock massif.

Fig. 11. Data combination of rock block surface and measured results ERT in Autodesk ReCap 360.

Summary. The application of described process of mapping by the photogrammetric method added by surveying of control points of geotechnical research has, compared with earlier research workings MMSE Journal. Open Access www.mmse.xyz

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in solved areas, unequivocally better basis for a project documentation. Compared with the wire model, or digital model of terrain, made from data by polar method surveying of detailed points, the point cloud taken by photogrammetry offers more complex information about the progress of geological failures and joint system.

CAD software systems for processing of point clouds guarantee the direct measurability of other important geological information including bedding, direction and inclination. Combined with the possibility of interpretation of geotechnical research results by electrical resistivity tomography into the homogenous point cloud together with the digital terrain model, this technique offers the most complex resources for the structure evaluation of the rock mass, risks of rock collapse and definition and proposals of available arrangements.

Unequivocal benefit for an investor is the time effectivity of this mapping method. Compared with earlier used polar mapping method and subsequent difficult processing of results, this method can save up to 40 % on time, especially in the phase of detailed terrain mapping. The integration of geotechnical research results allows the complex and effective evaluation of the locality and precise spatial orientation of problem places. The benefit of this method is illustrated by the fact, that its utilization is planned in the preparation of arrangements against active rock collapse in other three localities in the Central Bohemian Region.

References [1] Gasinec, J.; Gasincova, S.; Trembeczka, E. Robust Orthogonal Fitting of Plane.

Mineralna, 2014, 15.1: 7 13.

[2] high-capacity tank using terrestrial laser scanning. Acta Montanistica Slovaca, 2014, 19.1: 41 46.

Geological application of uav photogrammetry and terrestrial laser scanning in marble quarrying (Apuan alps, Italy). In Engineering Geology for Society and Territory - Volume 5: Urban Geology, Sustainable Planning and Landscape Exploitation (pp. 979-983). Department of Environment, Earth and Physical Sciences and Centre of Geotechnologies CGT, University of Siena, Via Vetri Vecchi 34, San Giovanni Valdarno, Italy. http://doi.org/10.1007/978-3-319-09048-1_188 [4] Geographical

Data.

Advanced

Science

Letters.

2015,

21(12),

3680-3683.

DOI:

http://openurl.ingenta.com/content/xref?genre=article E for the Czech.Geoinformatics FCE CTU, 8, 9-16.

[6] Daily, W., Ramirez, A., Binley, A., & LeBrecque, D. (2004/05/01). Electrical resistance tomography. The Leading Edge, 23(5), 438-442. http://doi.org/10.1190/1.1729225 [7] Pacina, J., Brejcha, M. (2014). Digital terrain models. nad Labem, Faculty of environment, 2014. ISBN 978-80-7414-815-6.

Cite the paper Utilization of Point Clouds Characteristics in Interpretation and Evaluation Geophysical Resistivity Surveying of Unstable Running Block. Mechanics, Materials Science & Engineering Vol.6, doi: 10.13140/RG.2.1.1577.2401

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