Field work in the role of teaching and research of rock properties

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1 5 th International Symposium Topical Problems in the Field of Electrical and Power Engineering, Doctoral School of Energy and Geotechnology Kuressaare, Estonia, January 14 19, 28 Field work in the role of teaching and research of rock properties Veiko Karu, Margit Kolats, Vivika Väizene, Ain Anepaio, Ingo Valgma Tallinn University of Technology, Department of Mining Science begins with measuring Abstract Data for mining and geotechnological research and teaching comes mainly from field measurements and laboratory tests and modelling. All these are closely related. Measuring is useless without structuring, analysing or modelling of the data. At the same time samples have to be analysed in the laboratory, producing additional data from fieldwork. In addition to analysing, new results and conclusions have to be produced. For that purpose, modelling of mineral deposits and mining operations is used. One of the most important purposes of the analyses has to become making data understandable to the audience. This is possible with lately invented visualisation software that is part of mine planning and design computer programs. Keywords Fieldwork, mining, geotechnology, experiments, testing, modelling, visualisation. Introduction Institutions are making efforts, to get young people to study there, stay by the speciality they have chosen and continue their studies to get the master or PhD degree. According to the developmental plan of TUT for the years , the studies should be filled more with practical assignments. This could be something that makes the science club work, because practical work fixates new information from the lectures [1]. The science club of mining and geology was started in the spring semester of 26, where the excursions to the phosphorite grounds in Maardu and to the limestone deposit in Harku took place to assess the effects of mining ( Fieldworks and at the same time the activities of science club have following goals: (1) find a supervisor for every student from the beginning, so that he/she could adjust better to the speciality; (2) introduce the students different aspects about the chosen speciality, that higher education recommends; (3) help to make the studies successful and decrease dropping out of school; (4) increase the quality of student s work; (5) to notificate students of scientifical work and include them in the work; (6) tighten the communication between academicians and students. [2]. It is possible to apply the results in all the scientifical actions and they redound in student s bachelor and master thesis, in institute s scientifical reports, in the scientifical work the institute orders etc. To test the student s self-expression ability and to develop it, there are several performances in the science club and on the institute s seminars that students have to attend. The result of it is, that student s are more successful in presenting their final thesis, because they have several opportunities to improve their ability to talk in front of a big audience. As a result of the science club s actions, there is more cooperation with the private section, different institutions, departments and universities. In the process of the work posters, WebPages and reports of all the field work, that the science club has been to, are made. Student s participation in the science club helps them to broaden the mind, they are more successful in their studies and they get an idea of their future work they get to know, what kind of assignments they are going to solve. 1 Today s fieldwork gives data for future mining technology Data for mining and geotechnological research and teaching comes mainly from field measurements and laboratory test and modelling. All these are closely related. Measuring is useless without structuring, analysing or modelling. At the same time samples have to be analysed in the laboratory, producing additional data from fieldwork. In addition to analysing, new results and conclusions have to be produced. For that purpose, modelling of mineral deposits and mining operations is used. The main aim of using modern measurements in real mining conditions is providing sense, data and experience of physical processes where mining equipment is and will be working. One of the most important purposes of the analyses has to become making data understandable to the audience. This is 66

2 possible with lately invented visualisation software that is part of mine planning and design computer programs. 2 Rock classification and compressive strength Rock classification and compressive strength are evaluated by three main methods, pressing the prepared samples (Figure 1), with PLT (point load test), and with rock classification hammer. The results are used for planning of rock breaking, cutting and stability as the main figures for mining operations. Figure 1 Preparing and pressing rock sample with uniaxial press The sample is drilled and sawed from specimen. If surface of sample is too coarse it will be brushed up smoother. When samples are ready they are crushed with compression testing machine. From results can be seen what compressive strength material has. These tests are important when you are dealing with underground mines or have to decide what kind machines you need for mining. Compressive strength is calculated by level and speed applied force, prepared area, weight of the sample and height. As shown in following table the compressive strength 21 MPa for oil shale demonstrates suitability for most mechanical breaking machines (Table 1). Table 1 Compressive strength of oil shale sample DIGIMAX PLUS V1.23R S.N. :7285 Test : 5 Id :1PK Area [ mm2]: Weight[ g]: Fm [ kn ]: Rm [ MPa ]: COMPRESSION CH1 Age[ Days ]: 28 Operator :AIN 4/7/7 13:16:4 Sample :CYLINDER 67

3 itself on the internal end and, through this, the surface of the rock. The rod reacts and retransmits the rebound to the mass: 2.1 Point Load Test Digital Point Load 45-D55/D is used as the most popular classification test for rock strength (Figure 2). The test consists to compress up to failure a core or irregular block of rock sample by the application of a point load by a couple of steel conical points of standard size.[3] The harder and the more compact the rock, the greater the rebound. During the rebound stroke, the mass moves a pointer that indicates the maximum point of return and at the same time indicates a reference value on the scale (Figure 3). This number is correlated to the compression strength in respect of the impact angle. The samples are tested either in natural or in saturated conditions and three test methods are generally carried on: - Compression along a diameter Axial compression Compression on irregular pieces. Figure 3 Measuring with rock classification hammer Since the rock hammer can be used not only on vertical surfaces but also on slanted surfaces, it is quite obvious that the rebound of the hammer will be affected by gravity; consequently, a test carried out with the plunger head facing upwards, resistance being equal, will produce a higher rebound value than the same test carried out on the floor for example. To compensate these differences, correction factors are used corresponding to the diverse impact positions or angles. (Table 2) Figure 2 Point load tests in the cutting face 2.2 Measuring with Rock classification hammer The rock hammer is a non destructive, portable test device which expends a definite amount of stored energy from a spring, and indicates the degree of rebound of a hammer mass within the instrument, following impact. As the rock hammer rod is pressed against the surface that is to be tested, a spring is loaded. When the rod has disappeared inside the rock hammer completely, a mass is automatically released that strikes the rod Table 3). To estimate the compressive strength of rock under consideration, the rebound number of the test hammer have to be noted and referred to the correlation curves which are obtained through experimentation. The result depends on angle, number of impacts and rock characterisation ( Table 2 Correction factors for diverse impact angles Rebound r z= Downwards -9 z = Upwards z = z = Horizontal z =

4 Table 3 Calculating compressive strength DATA Sample location Feature Coordinate m Coordinate, m Height, m Date Time Rock SPECIAL DATA Impact direction Horizontal position Impact number Average strength Calculations Recalculated strength Coefficents Väo limestone quarry Mark Value x y z Before lunch Building limestone Density, kn/m3 Coefficent Result Compressive strength, MPa 3 Seaving for quality evaluation of aggregate materials For seaving outside of naturally wet material (Figure 4), inside dried material and virtually (Figure 7) any material are used. All methods are compared for choosing most reliably for needed applications. Firstly portion of the crushed material is collected. The material is taken from several places to make sure to get even sample. The size of the sample Formula Parallel α n R Rkorr a b c d z ln s s 31 Rkorr = R + a*r2 + b*r + c z =.195 d +.19 ln s = z Rkorr s = exp (ln s) depends on the particle analysis purposes. Outdoor sample is then brought to the laboratory, where it is divided and put to the oven for drying. According to standard EVS-EN 933-1:2 sample must be in oven at least 24 hours with temperature 11±5 oc. After the sample is dry it will be weighted and then seaved. After seaving every fraction is weighted separately. Results are used for drawing a graph (Figure 5). Figure 4 Collecting samples for saving, crushing, and pressing tests from the working face of surface miner. 69

5 Screen underflow, % 1, 9, 8, 7, 6, 5, 4,, 2, 1, Screen underflow %, Screen size, mm Figure 5 F bed particle analyses -31,5 mm 3.1 Virtual seaving with optical software Virtual seaving is perfomed with optical recognition software [4] for granulometry analysis. This software is used in the situation not favourable for traditional screening. First it is necessary to take picture perpendicularly to the sample. There are 4 main steps to go for getting the results of granulometry analysis (Figure 7). First image has to be captured from digital video or photo camera. Figure 6 Graphic of screen analysis Then it is necessary to set the image scale according to gauge so that software could calculate pixels into centimetres. Thirdly the software automatically generates net using edge detection algorithms. Finally virtual sieve and review results are produced (Figure 6). Accuracy depends on the photo quality, shadows and fragmentation area quality, but it is very quick opportunity instead of using timeconsuming screen analysis. Figure 7 Contour lines and separating different fragments with different colour Seaving results are the quality indicators for aggregate, building, fuel and chemical products. Conclusions The world most used and popular testing equipment allows to produce and evaluate mining conditions. The most easy and useful way is to perform the measurement in the form of science club that has been successfully started in Mining department of Tallinn University of technology. Acknowledgements Field works and this paper is related to the Estonian Science Foundation study- Grant No References: 1. Karu, V; Pärnasalu, R; Õnnis, A. Science Club of Mining and Geology as it Affects Higher Education. Doctoral school of energy and geotechnology. Tallinn University of Technology Karu, V. Science club of Mining and Geology. EU legislation as it affects mining. INFRA TAIEX workshop Digital Point Load Instruction Manual ( [.9.27] 4. Granulometry Analysis Software [ ] 5. Reinsalu, E. (21) Altkaevandatud maa kasutamise tingimused ja piirangud. Keskkonnatehnika, nr 5, lk Jaaniso, V. Õppeaine Pinnasemehaanika ja ehitusgeoloogia otehnika%2alused/pinmeha.doc [.1.27] 7