Multislice Longwalling for Thick Seam Extraction - Properties of Goaf in the Roof and Gate Roads Behaviour Presenter: Stanisław Prusek Authors: Prusek S.,¹ Lubosik Z¹., Płonka M 1., and Syrek B² ¹ Główny Instytut Górnictwa (GIG), Poland ² Katowicki Holding Węglowy SA (KHW), Poland AusRock 2014: Third Australasian Ground Control in Mining Conference 5 6 November 2014, Sydney, Australia
PRESENTATION OUTLINE Some information on Central Mining Institute (GIG). Some data on Polish hard coal mining industry. General information concerning Thick Coal Seams Extraction. Properties of Goaf in the Roof and Gate Roads Behaviour underground measurements. 2
Some information on Central Mining Institute (GIG) 3
The Central Mining Institute (in Polish: Główny Instytut Górnictwa, in brief: GIG) Research institute, established 1945, Subordinates to the Minister of Economy of Poland, Employees (2013) 578 people, including 14 professors and 15 Assoc. Prof., Notifying Body No. 1453 of the European Union within the range of the directives:94/9/we (ATEX),98/37/WE (machinery), 93/15/WE (explosives for the civil use), and explosion-proof safety according to the world certification system IECEx, The Scientific Council holds full academic authorizations to grant the degree of doctor and doctor habil., and to apply for the title of professor in mining (since 1961) and environmental engineering (since 1998). 4
Basic areas of GIG activity MINING AND GEOENGINEERING OCCUPATIONAL SAFETY IN THE INDUSTRY ENVIRONMENTAL ENGINNERING MATERIAL ENGINEERING SOCIO-ECONOMIC STUDIES CERTIFICATION, ATTESTATION, INTEGRATED MANAGEMENT SYSTEMS TRAINING AND EDUCATION 5
Experimental Mine Barbara An unique place for mining investigations in a real scale COAL DUST EXPLOSION IN EXPERIMENTAL GALLERY 6
Some data on Polish hard coal mining industry 7
Coal is the major fuel used for generating electricity in Poland. About 86 % of electricity is produced in coal-fired power plants. 8
Location of Polish coal basins and coal production in Poland in 2013 Total 142.3 Mt Hard coal 76.5 Mt Lignite (brown coal) 65.8 Mt 9
Polish hard coal mining industry in 2013 Production 76.5 Mt, (64.4 Steam coal, 12.1 Coking coal) Number of underground mines 30, Employees about 107 000 workers, Extraction system 107 single entry retreat longwalls were employed, 101 longwalls with natural roof caving and 6 with hydraulic backfilling Average extraction depth - 713 m. 10
The coal seams are mined in conditions of natural hazards: Gas hazard Fire hazard Dust hazard Seismic and rock burst hazard Water hazard Climatic hazard Such mining conditions negatively affect the costs of mining activity of Polish companies Radiation hazard 11
General information concerning Thick Coal Seams Extraction 12
Among the methods commonly used for thick coal seams extraction the following can be mentioned: Single pass longwall (SPL) Multi-slice longwall (MSL) Longwall top coal caving (LTCC). B.Hebblewhite, Morgantown 2013 13
In Poland Multi-slice longwalling (MSL) is employed the coal seams are extracted in slices with: roof caving, extraction from top to bottom (descending order), hydraulic backfilling, extraction from bottom to top (ascending order), combination of the above two systems (hybrid). Underlying slice is mostly mined after 2-3 years 14
Properties of Goaf in the Roof and Gate Roads Behaviour underground measurements 15
IMPREX PROJECT Realized in years 2008-2011 16
Multi-slice longwalling in KHW Company data collected from 24 longwalls 17
Average values of coal beam thickness and coal UCS in the longwalls operated under previously extracted upper slice of the seam 18
Underground measurements were carried out in three longwall panels located in slices of seam 510 Longwall Name 02a seam 510 slice II 04a seam 510 slice I XVII seam 510 slice II depth, m 815-865 795-850 700-765 seam inclination, 0 4 4-6 4-6 longwall height (seam thickness), m 3.6 (5.5 7.95) 3.0 (6.6 7.95) 2.7 (4.0-4.47) longwall length, m 220 270 140-170 longwall panel length, m 860 610 720 coal beam thickness, m 0.4-0.8 0.4-0.8 0.4 19
Scope of underground measurements Location of measurement stations in longwall panel 02a, seam 510, slice II Ø96 mm borehole 10 m long 20
Assessment of the strength parameters and goaf structure - employed devices Hydraulic pump Head with a needle Assessment of the strength parameters of the caving goaf by means of the borehole hydraulic penetrometer. Console for measuring and storing the pressure data Determination of the caving goaf structure by means of the borehole endoscope (endoscopic methods). 21
Results of measurements of goaf compressive strength The average values of goaf compressive strength obtained from the boreholes drilled in : longwall panel 02a: test no 1-36.53 MPa test no 2-13.17 MPa test no 3-28.2 MPa longwall panel 04a: test no 4-22.7 MPa test no 5-28.4 MPa longwall panel XVII: test no 6-4.14 MPa test no 7-24.3 MPa Raise 3 a Raise 4a Example of the strength parameters of the caving goaf measured by means of the borehole hydraulic penetrometer longwall 02a 22
Assessment of the structure of goaf in longwall panels 02a, 04a and XVII performed by means of endoscopic method In most investigated boreholes the goaf was intensively cracked 23
Vertical and horizontal convergence and floor heave in Raises: 3 a, 5a and 19 - values and trend lines 24
Load exerted on steel arches in Raises 3 a, 5a and 19 - values and trend lines 25
CONCLUSIONS 1. In the Polish hard coal mines in seams to be extracted in slices, i.e. ones with a thickness of 4.5 m and more there are around 952.6Mt of coal which constitute that part of the resources which may be economically extracted. 2. The Multi Slice Longwall System (MSLS) is already a commonly used method for thick seam extraction in Poland. 3. In order to design a longwall under a previously extracted upper slice of the seam it is necessary to determine the compressive strength of the caving goaf at the roof, its quality and the load on the support. 4. High variability (from 0 to 80MPa) of the caving goaf compressive strength assessments obtained by means of a borehole penetrometer led to the conclusion that the results do not describe the caving goaf parameters but the parameters of rocks, which form the caving goaf only. Hence the use of a borehole penetrometer to assess caving goaf UCS is not recommended. 26
CONCLUSIONS 5. The most promising way to determine the roof conditions in longwalls under a caved goaf seemed to be an assessment of the equivalent compressive strength and degree of reconsolidation. 6. All boreholes into the goafs examined by means of the borehole endoscope were cracked, some of them practically the whole length, but others in some zones only. It can be concluded that the density of fissures reduces with the distance from the roof to the gateroad. 7. The results of the gateroad stability measurements confirmed that in the workings located under the goaf no large convergence or load were observed in comparison with the workings located below the natural roof. 27
Thank you for your attention Stanisław PRUSEK, Associate Professor Head of Department of Extraction Technologies and Mining Support GIG plac Gwarków 1 40-166 Katowice Poland s.prusek@gig.eu phone: +48 32 2592423 fax: +48 32 2584425 mobile: +48 512293839 28