Use of 3D Laser Scanner Technology to Monitor Coal Pillar Deformation

Transcription

1 University of Wollongong Research Online Coal Operators' Conference Faculty of Engineering and Inforation Sciences 2016 Use of 3D Laser Scanner Technology to Monitor Coal Pillar Deforation Radovan Kukutsch Institute of Geonics, Czech Republic Vlastiil Kajzar Institute of Geonics, Czech Republic Petr Waclawik Institute of Geonics, Czech Republic Jan Necik University of Wollongong Publication Details Radovan Kukutsch,Vlastiil Kajzar, Petr Waclawik and Jan Necik, Use of 3D Laser Scanner Technology to Monitor Coal Pillar Deforation, in Naj Aziz and Bob Kininonth (eds.), Proceedings of the 16th Coal Operators' Conference, Mining Engineering, University of Wollongong, February 2016, Research Online is the open access institutional repository for the University of Wollongong. For further inforation contact the UOW Library:

2 USE OF 3D LASER SCANNER TECHNOLOGY TO MONITOR COAL PILLAR DEFORMATION Radovan Kukutsch, 1 Vlastiil Kajzar, Petr Waclawik and Jan Necik ABSTRACT: Although the roo and pillar ining ethod is world-known and widely used, in ters of the Czech coal ines located in the Upper Silesian Coal Basin it is still in the testing phase. Unfavourable ining, geotechnical conditions at large depths and the ban by Czech ining authorities prevented this ethod fro being used on rock bolt reinforceent without other roof support. Typically, large aounts of unexploited coal reserves are left in the shaft protective pillars. This coal can be ined if strata subsidence is iniised. Due to its low subsidence characteristics the roo and pillar ining ethod without pillar extraction has been trialled at the CSM Coal Mine at the end of During the pillar developent phase coplex geotechnical onitoring was undertaken including the frequent scanning of pillar oveent using 3D laser scanning technology. The laser scanner enabled coplex capture of the entire space around the onitored pillars during the period of pillar foration and afterwards. The tie-lapse scanning ethod easured changes in the ine roadway surface profiles including pillar displaceents, roof oveents, floor heave and other dynaic phenoena. The tie-lapse scanning indicated variable pillar rib oveent ranging fro a few c to a axiu of 50 c with an average of approxiately 25 to 30 c. The scans indicated that the botto of the sea displaced ore than the top of the rib side due to large floor heave. The weak floor consisting of siltstone and coal beds experienced large floor heave however, due to floor brushing no reliable floor displaceents are available. In contrast to the large oveents in the rib and the floor, the strong roof strata did not show any significant oveents. The purpose of this work is to highlight the iportance of terrestrial laser scanning as an essential engineering design tool to evaluate the displaceents and deforations of ine excavations at large depths. The 3D scanning results gave relevant inforation about displaceents and deforations that occurred at the tested site and thereby helped to iprove safety underground. INTRODUCTION Laser scanning has started to be a widely applied technology in a variety of industries. These scanning systes excel in their ability to provide contactless deterination of spatial coordinates of any object such as buildings, interior space, terrain and other structures. To survey the entire area of interest it is usually necessary to take scans fro several locations that are autoatically stitched together. The ethod can be used with exceptional speed, accuracy, coprehensiveness and safety. The scanned objects are visualised in the for of a point cloud, which can be subsequently used for a wide variety of analytical tasks, and also to generate 3-diensional odels of these objects. This technology can be widely used in ines for specific tasks such as onitoring of strata conditions when developing ine excavations, assessing the long ter stability of underground workings, easuring convergence profiles, investigating surface oveent and enabling voluetric calculations. Based on the intensity of the reflected laser signal, it is also possible to quantify the aterial type, fro the resulting point cloud. The ethod can also be used in design work connected with CAD / GIS tools. The priary objective of laser scanning underground is a coplete capture of the scanned area geoetry at the tie of scanning. Fro these results, it is possible to deterine the shape and size of scanned ine workings, the position of ine supports and other paraeters (Kajzar et al., 2015). Beyond these basic tasks it is also possible to use the spatio-teporal analysis, cobined with the convergence easureents to copare the tie related changes that ay include: the size variation Researcher, Institute of Geonics AS CR, v.v.i. & Institute of Clean Technologies,E-ail: kukutsch@ugn.cas.cz, Tel: +(42) , February

3 and stability of rock cavities and to identify the place and agnitude of coal pillar deforation and rib conditions or collapse of pillar corners. These tasks require repeated easureents to resolve any geoetrical changes between the scans (Kukutsch et al., 2015). In general any nuber of future scans can be perfored and processed to copare with the existing scan results taken in the sae area. MINING CONDITIONS IN THE SCANNED AREA The geological setting in the area of shaft protective pillar ČSM-North Mine is quite coplex. The targeted coal sea No. 30 used for the trials, is at the depth of approxiately 700 to 900 below the surface. Above the coal sea there is a 300 thick coplex carboniferous rock ass with the overlying tertiary sedientary rock strata 400 to 600 thick with approxiately 20 thick quaternary soil overburden. The strata dip oriented in a north-east direction ranges fro 8 to 17. Occasionally the dip of a coal sea can reach up to 20. Within the proposed ining area the thickness of sea No. 30 is very variable. In places the sea splits to several separate coal sea layers. Interchangeable layers of sandstone, siltstone and coal seas are present. Sea No. 30 occurs separately only in the south-east part of the shaft protective pillar with thickness that varies fro 1.8 up to 2.2. The seas n.n. (untitled sea), No. 31 and No. 32 erge with sea No. 30 towards the north-west. This substantial and coplex coal sea (consisting of seas 30 + n.n ) has the thickness of up to 5.2 in the northwest part of the protective pillar area. In the onitored pillar area (pillars V1 and V2) in the panel V trial area the 3 thick sea consists of the coal seas 30 and n.n. The stratigraphy of the ground above the coal sea No. 30 are shown in Figure 1. Figure 1: 3D odel of onitored pillars in panel V (locality A). Coal seas blue, siltstones green, sandstones - yellow There are several faults of regional iportance in the area of the ČSM-North shaft protective pillar (see Fig. 2). There is a wide tectonic zone of the Albrechtice Fault with total throw up to 420 located in the west area. The dip of this fault ranges 60 to 65 towards the West. In the northern area Fault A is present with a throw of up to 100 and the dip of 60 towards the North. Fault B in the south part of area has a throw of around 10 with the dip ranging 55 to 70 towards the South February 2016

4 The significant regional tectonic fault zone Eastern Thrust divides the area of the protective pillar into two separate blocks with different geotechnical conditions. According to the existing knowledge the Eastern Thrust has a very sall dip ranging fro 10 to 35. The Eastern Thrust strike is generally in the NE-SW direction with the dip towards the NW. The vertical displaceent fluctuates at around 5 ark, but the range of horizontal displaceents is usually uch greater and can exceed tens to hundreds of eters. Characteristic changes in the Eastern Thrust dip with depth have been observed and ay be correlated with the transition to interlayer slips. The experience shows that these thrust fault features have a significant effect on the geotechnical conditions within the rock ass. Inside the protective pillar area surrounded by faults of regional iportance, the rock ass is typically disturbed by a syste of sall so-called sea faults. The uplift on these sea faults is ostly greater than 0.1 but typically do not exceed 1. Figure 2: Tectonic situation and position of onitored pillars in panel V (locality A) and panel II (locality B) MONITORING DESCRIPTION Stress onitoring and the deforation state of the rock ass is an essential requireent for the design of a safe and successful roo and pillar ethod that can be applied in the Czech part of the Upper Silesian Coal Basin (USCB). The roo and pillar ining ethod is usually designed on the basis of experience and practices that are observed under different geological conditions and depths. The geology in the area and depth of cover indicate that the epirical ethods of calculating the pillar loads ay not be appropriate and could be unreliable. No experience of the roo and pillar ethod exists within the USCB area therefore the pillar onitoring had to be used to easure the capacity and the deforation characteristics of the coal pillars. An extensive onitoring syste was installed to easure the load profile across the coal pillar and the deforation characteristics of the pillars during ining. The onitoring was perfored in two coal pillars within the panel V. The pillars diaond in shape and with slightly irregular sides were approxiately and in size and 3.5 high. In the context of stress and deforation onitoring the following paraeters were easured: deforation of rock overlaying the roo and pillar roadways, pre-ining stress and stress changes in rock and coal during ining, deforation of coal pillars, February

5 load on the installed cable bolts, roadway convergence, repetitive 3D laser scanning of pillars and ine roadways. To onitor roof deforation, fourteen pairs of 5-level ultipoint extensoeters onitored roof displaceents and eleven strain gauged rockbolts were installed at various locations Two 3-diensional CCBO stress overcoring cells were used to easure the pre-ining stress in the area and eight 3-diensional CCBM stress change onitoring cells were installed to easure stress changes during ining. Four 1-diensional hydraulic stress onitoring cells were installed at various depths into each pillar to easure vertical stress, four 5-level ultipoint rib extensoeters easured displaceents of all sides within each onitored pillar, seven hydraulic dynaoeter load cells easured the cable bolt loads installed at the roadway intersections and the roof and rib convergence was easured at key locations. The coal rib displaceents together with the convergence easureents, changes in vertical pillar loads and the onthly 3D laser scanning of the overall roadway displaceents (roof, rib and floor heave) provided data to evaluate pillar stability. Large seisology and seiso-acoustic onitoring was also undertaken to suppleent the data. 3D LASER SCANNER MONITORING DESCRIPTION For onitoring of spatio-teporal changes to the coal pillar V2 rib profile copact pulsed terrestrial laser scanner Leica ScanStation C10 was used. It is a device with a long range laser bea (up to 300 ) which provides easureents with accuracy in space (6 / 100 ), length (4 / 100 ) and angle (±60 icro-radian) and high scanning speeds (up to 50,000 points / s) (Leica C10 Data Sheet). Since this is a site with a potentially explosive atosphere and the surveying equipent does not correspond to the safety criteria, onitoring was perfored in all cases with a special perit and the use of a coprehensive gas onitoring syste. Up-to-date the laser scanning has been carried out six ties within the approxiate tie interval of 5-6 weeks (see Table 1). The initial scan has provided geoetry of the newly developed coal pillar V2 within the roadways V and V3006 (see Fig. 3). When the pillar sides were copleted the subsequent scans established the pillar boundaries within the corridors V3005 and V (see Fig. 4). Following scans easured any subsequent changes due to strata displaceents. Scanning was perfored with a resolution of 1 c / 10, while approxiately 14.5 illion spatial points fro each scanning positions were obtained. A local coordinate syste is required to tie all surveyed results together. For the scanning instruent to locate itself, several peranent (overlaying) target locations need to be established and arked (usually on the steel bolt plates that do not ove). During each survey several agnetic targets (iniu of three) are placed onto these locations with soe overlap between the targets that were used in the adjacent scans (coon targets). The instruent can be set up anywhere at a desirable location where the targets are visible. The instruent then locates itself autoatically and tie all the surveyed points together. Table 1: Laser scanner surveys up to date. Color Scan No. Date Nuber of positions , February , March , April , June , July , Septeber February 2016

6 Figure 3: Part of the pillars V2 at the intersection of corridors V av3006 (1st scan) V3006 IV III V A II V B V3005 I Figure 4: Shape of the pillars V2 - top view (6th scan) DYNAMICS OF COAL PILLAR DISPLACEMENT Raw data were processed using Leica Cyclone, Trible RealWorks and CloudCopare software. After each survey it was necessary to erge the data (taken on the day) together (registration process). The second process consists of interconnecting the current survey with the previous surveys into a new single point cloud. Fro the resultant data clouds the relatively accurate locations of the scanned surfaces are calculated and displayed. The individual profiles of each scan can be plotted as shown in Figure 5 showing the roadway cross-sections. The readily available software can be used to study individual displaceents at the points of interest. Further visual display options of the calculated net displaceents between each scan include the colour plot of the surface displaceents as shown in Figure 7. These tools enable further study of the overall displaceents and substrate conditions of each scanned surface as they develop in tie. These surveys clearly indicate the overall pillar displaceents, roof conditions and floor heave as they develop during ining and afterwards February

7 Fro the coparison in Table 2 it is clear that: Varying degrees of rib displaceent rate change in tie (Figure 6) occur in the whole profile of the pillar. Significant coal pillar deforation, accopanied by a continuous coal rib spall into the roadway area were encountered in the roadways V3006, V and V Rib displaceents of up to 50 c were easured in the coal pillars. These results correlate with the outcoes and findings fro the convergence and extensoeter easureents. Within the belt roadway V3006 the pillar deforation was uch lower. The reinforceent perforance and functionality can also be assessed fro the scanned roof or rib bolt oveents and the overall roof convergence. As in the case of rib displaceents it is possible to detect significant changes in floor deforation. However these changes are difficult to asses as they are affected by a cobination of different factors such as floor heave, floor brushing and oving ining equipent. The 3D laser scanning technology also enables the long ter onitoring of strata conditions and thus proved to be beneficial for this project where pillar creep ay occur. C1 C2 C3 C4 Figure 5: Cross-sections of the roadways V and V3006 1st scan (black) to 6th scan (red) Table 2: Cross-sections of V and V3006 roadway coparison between 1 st and 6 th scan Cut No. Width 1st scan () Width 6th scan () Difference () Change (%) Height 1st scan () Height 6th scan () Difference () Change (%) C C C C In Figure 7, parts A and B show the dynaics of the rib in a tiefrae of approxiately 7 onths (6 scans) during and after the V2 pillar developent. The part A shows the rib displaceents ranging c in five weeks after the pillar was fored. In the following five weeks the rib displaceents increased by 5-7 c to approxiately 20 to 27c. These were the axiu changes easured in the tiefrae of seven onths. It appears that the botto of the rib side displaced ore than the top. This phenoenon ay be related to the large floor heave, which partially affected the botto half of the pillar February 2016

8 where the displaceents of ore than 40 c can be seen. Another reason ay be the uneven cut in the V roadway (see Fig. 4). Thus this cut ay have a negative effect on the adjacent rib oveent. This can be investigated further by plotting horizontal oveent together with the rib geoetry in a plan view. Figure 6: Dynaic of coal pillar / decrease in displaceent/tie rate over tie Part A of Figure 7 corresponds to the location of the pillar extensoeter VeH2 (Figure 7, iddle of cuts in part A). The extensoetry results and the colours obtained fro Figure 7 are copared in Table 3. It should be noted that the colour range in Figure 7 and Table 3 can be changed to enable ore accurate coparison for interpretation. Figure 7 clearly shows that the rib displaceent rate is decreasing over tie as shown in Figure 6. Further easureents will be conducted in the future to establish whether the pillar will stabilise. Copared to Part B (Figure 7 and Table 3) there are no significant rib displaceents in Part A. Much larger displaceents can be clearly seen in Part B. This ethod of displaceent reading by colour range shows the strength of the laser scanning. The tie dependent displaceents in space can be easily obtained and interpreted providing a quick and safe ethod to enable geotechnical assessent of strata conditions underground. Table 3: Extensoeter VeH2 data corresponding to Fig. 7, part A and B 1st onth 2nd onth 3rd onth 4th onth 5th onth 6th onth 7th onth 8th onth VeH2 rib displaceent () Increase in VeH2 displaceent () Correspondi ng color scale (used in Fig 7 Part A) Correspondi ng color scale (used in Fig 7 Part B) not easure d not easure d Blue Blue Blue Green Blue Green Green Yellow Green Orange Green Red to be easure d to be easure d February

9 Figure 7 - Developent of deforations at selected parts of the coal ribs in the roadway V Differential point cloud odels aong the first and subsequent five scans A - Left side of roadway rib V300501, B - Right side of roadway rib V CONCLUSIONS The roo and pillar ethod has been trialled in the shaft protective pillar at the CSM Mine within the USCB. A coprehensive coal pillar onitoring was essential as this was the first application of the roo and pillar ining ethod in the Czech Republic at great depth. Two coal pillars located in the sea No. 30 were intensively onitored to ensure stability of the panel and safe ining procedures. Several onitoring instruents were used to easure stresses and displaceents in this trial. One of these instruents was the 3D laser scanner to easure strata surface displaceents during and after ining took place. The easureents indicate that the 3D laser scanner is a coprehensive tool enabling both nuerically and graphically the express the dynaic changes taking place in the ine roadways. The laser scan results fro several subsequent surveys indicted significant coal rib displaceents taking place shortly after ining started. The easured rib displaceents varied and ranged fro 15 to 20 c when ining took place increasing after 7 onths to 20-27c at pillar id height. Post-ining rib displaceents were also easured. The results indicate that the lower coal rib suffered greater deforation ainly due to large floor heave that occurred along all sections of ine roadways. In soe places the lateral displaceents easured ostly at the lower rib exceeded 50 c. As expected, the roof displaceents were negligible and are not discussed here. These scanned data were directly copared with the extensoetry results February 2016

10 Graphic display of the easured changes that occurred, enabled easy and iediate evaluation of the strata conditions up to the easured date. Based on these data the level of risk can be established whether to abandon the ining area in case of severe pillar deforation. Application of the 3D laser technology to easure strata displaceents in underground ines is becoing increasingly popular due to low cost of easureents its ease of use and data quality it produces. Graphic outputs of the easureents enable quick assessents of the situation at hand. Over the coing years this ethod will inevitably becoe an essential part of the safe and econoic onitoring syste used on regular basis to provide quick and reliable inforation on strata conditions in real tie ACKNOWLEDGEMENTS This article is written in connection with the Projects Institute of Clean Technologies for Mining and Utilization of Raw Materials for Energy Use (reg. no. CZ.1.05/2.1.00/ and MSMT LO1406), which is supported by the Research and Developent for Innovations Operational Prograe financed by the Structural Funds of the European Union and the Czech Republic. The presented work is also written in connection with the project Research on geotechnical aspects of the Roo and Pillar ining ethod and issues of the ethod application in the Upper Silesian Basin (02575/2014/RRC), which is supported by foundation prograe Support of science and research in Moravian-Silesian region 2014 and project for the long-ter conceptual developent of research organisations (RVO: ). REFERENCES Kajzar, V, Kukutsch, R and Heroldová, N, Verifying the possibilities of using a 3D laser scanner in the ining underground, Acta geodynaica et geoaterialia, Vol. 12, No. 1 (177), pp ISSN Kukutsch, R, Kajzar, V, Koníček, P, Waclawik, P and Ptáček, J, Possibility of convergence onitoring of gates in coal ining using terrestrial 3D laser scanner, Journal of Sustainable Mining, Vol. 14, Issue 1, pp ISSN Leica ScanStation C10 Data sheet: Link: /Leica_ScanStation_C10_DS_en.pdf. Waclawik, P, Koníček, P, Ptáček, J, Staš, L., Kajzar, V, Kukutsch, R and Souček, K, Monitoring evaluation of the stress-strain state of the rock ass during the ining of coal sea No. 30 (634) within a trial operation ining ethods roo-pillar in protective shaft pillar of CSM Mine - North (in Czech), OKD a.s Ostrava, 2015, pp. 82. Waclawik, P, Ptáček, J, Kukutsch, R, Kajzar, V, Koníček, P, Souček, K and Staš, L, Monitoring evaluation of the stress-strain state of the rock ass during the ining of coal sea No. 30 (634) within a trial operation ining ethods roo-pillar in protective shaft pillar of CSM Mine - North (in Czech), OKD, a.s. Ostrava, pp February