Simulation Analysis of Coal Mining with Top-Coal Caving Under Hard-and-Thick Strata

J. China Univ of Mining Tech (English Edition)VoL 16 No. 2Simulation analysis of Coal mining withTop-Coal Caving Under Hard-and-ThickStrataLIU Yu-de, ZHANG Dong-sheng", WANG Hong-sheng2, MA Li-qiang, LU Xiu-mingSchool of Mineral& Safety Engineering, China University of Mining Technology, Xuzhou, Jiang su 221008, China2 Key Laboratory of Mining and Safety of ministry of Education, China University of mining Technology, XuzhouJiangsu 221008, chinaAbstract: The top-coal falling ability is a key factor to analyze for the application of coal mining with top-coal cavingBased on a hard-and-thick strata, which acts both as the floor of the upper coal seam and as the roof of the lower coalseam, nine mining projects were put forward to examine the mining of upper and lower coal seams, and a numericalsimulation was used to study in detail the corresponding top-coal compressed volume of the lower coal seam. By thesimulation effects of different layouts of coalface, the rational mining method was determined to be the staggered layoutof coalface in the upper and the lower coal seam. This can ensure the successful use of fully-mechanized coalface withtop-coal caving in the lower coal seamKey words: hard-and-thick strata; falling ability; compressed volume; staggered layoutCLC number: TD 823.49expounds the rupture of hard-and-thick strata affect1 Introductioning the cranny expansion of the top coal seam, andanalyses some problems such as the mining of theA large amount of coal seam with hard coal and upper coal seam affecting the compressed volume ofhard roof exists in the east mining area of China, the lower coal seam, and offers design guidance tosuch as in the representative mining area of Xuzhou, the successful application of fully-mechanized coalwhere the hardness is relatively large ( >2); the roof face with top-coal caving technologyis hard and the thickness is relatively large(about 20m). Two key problems must be solved for the suc- 2 Coalface Basic Conditionscessful application of fully-mechanized coal face withtop-coal caving technology: the first is the top-coalThe main seams mined in the Zhangshuangloufalling ability and the second is the control of the mine are No. 7 and No 9 coal seams. The immediatehard-and-thick roof. This paper mainly analyzes the roof, made up of gray thin sandstone, of No 9 coalrupture feature of the hard-and-thick strata and the seam is also the immediate floor of No. 7 coal seamrational project of fully-mechanized coal face with Its thickness is from 0.95 to 46.94 m, with an averagetop-coal caving technology against the first problem. of 20.05its compression strength is 58.80 toThe main characteristics of hard-and-thick strata 151.70 MPa, with an average of 84.08 MPa; its uniengineering are"hard, " solid"and"thick"."Hard" directional tensile strength is 2. 17 to 6.23 MPa, withmeans that intensity of strata is high, generally be- an average of 4.96 MPa. The height mark of No. 9109tween 60 MPa and 150 MPa;"full"means that cran- coalface is-575 to-671 m; the overlying depth isnies of strata are not developed, so there is strong about 600 m; the whole thickness of No 9 is 2.1 toentirety;"thick"means that thickness of the strata is 4.5 m, with an average of 3.6 m. The immediate floorgreat, generally greater than 10 m The east min- is mudstone 3.0 m thick and the old floor is graying areas of China such as Zhangshuanglou mine in whi中国煤化工 k. The tilt angle ofXuzhou are different from Datong mining area in thean average of24°caving shape and weighting regularity of hard-and- theCNMHG37 Um and the ri-thick strata. Based on the conditions of the coal seam gidity of coal seam is rather large with anf value of 2in Zhangshuanglou coal mine, this paper strongly to 2.5Received 22 September 2005: accepted 10 December 2005LIU Yu-de et alSimulation Analysis of Coal Mining with Top-Coal Caving Under Hard-and-Thick StrataFig. I shows the coal-rock comprehensivedistance is 15 m with No. 7 coal seam reserving a 2gram of No. 9109 coalface. In the past, themining height fully-mechanized coal caving technolProject 4: No 9 coal seam roof periodic fractureogy was always used in the coal mine. But the coal- distance is 20 m without mining No. 7 coal seamface production was low because the roof of No9Project 5: No 9 coal seam roof periodic fractureoal seam is hard-and-thick and the hydraulic support distance is 20 m with mining No. 7 coal seam;emerged deflection, etc. Therefore the coal mine isProject 6: No 9 coal seam roof periodic fracturetrying to use the fully-mechanized coal face with top- distance is 20 m with No. 7 coal seam reserving a 25coal caving technology under the condition of hard- m coal pillarand-thick strataProject 7: No 9 coal seam roof periodic fracturedistance is 25 m without mining No. 7 coal seam;ThicknessRock nameHisProject 8: No 9 coal seam roof periodic frac214里H聞gmhdistance is 25 m with mining No. 7 coal seam;Project 9: No9 coal seam roof periodic fracturemudstoneDeep grey. mainly made up ofuarts and feldspardistance is 25 m with No. 7 coal seam reserving a 25m coal pillarGrey. massive,18. Thin sandstone3.2 Strata mechanical parametersTable I shows the strata mechanical parameterscondensation, massive, full of plantand corresponding thickness of the numerical simulaA fossil, with sononF Black, greNo. 7 coal sebric, ATable 1 Mechanical parameters of the stratae. mainly made up ofOrdeRock GrayBulk Shear Friction Cohen- Thickrtz and feldspar. with 0number name (KN/m) modulus modulus angleGPa)(GPa)(°)(MPa)20.05Thin sandstone3.826.51.231.51.13.10Grey black, condensationMudstoneplant fos336201898.56Thin sandstonemade up of quartz and feldsparNo, 7 coal 13.7311.16.300.298404396Mudstonecondensation, massive, fragile6 sandstone 27 3.8200Fig. 1 Comprehensive column of No. 9109 coalface7 No. 7 coal0.2280.43.608 Mudstone 26.5 1.33.003 Numerical SimulationsThin273.82036208.56The mining of No. 7 coal seam induces the10 Mudstone 26.5 1.31.1porting pressure around the stope to pass to thein addition to the moving and rupture of hard-and- 3.3 Layout of monitoring pointsthick strata. The superimposed influence of both willTo analyze and study the influence of the differcracking. The influence of the different layout pro- ent mining projects of No. 7 coal seam on No 9 coalthick strata on the compressed volume of No 9 coaseam was analyzed with the numerical software coal compressed volume of No 9 coal seam(Fig. 2)UDEC 3. 0 6-913.1 Numerical simulation projects9 simulation projects arYHt中国煤化工NMHGProject 1: No 9 coal seam roof periodic breakageUs iwv., coal seamdistance is 15 m without mining No. 7 coal seam;No9c图Project 2: No 9 coal seam roof periodic fracturedistance is 15 m with mining No. 7 coal seam;Project 3: No 9 coal seam roof periodic fractureFig. 2 Layout of monitoring points.China Univof Mining&Tech(English Edition)l.16No.23.4 Analysis of the numerical simulation results calculated using the UDEC Fig 3 shows the top-coal1) Effect of different layout schemescompression of No. 9 coal seam in each monitoringDifferent simulation projects were numericallyoint of the project 6-885-75-6.5-5.5-4.5-3.5-55-4.5-3.5-25-1.5051.52.53.54.5(a) point I(b)Point 2(e)Point 3450.51.5(d)point 4(e) pointFig 3 Top-coal compression of NO 9 coal seam in monitoring pointsThrough simulation, Fig. 4a shows top-coal coal seam for project. 4 to project 6: Fig. 4ccompression of No 9 coal seam for project 1 to prop-coal compression of No 9 coal seam for project 7ject 3; Fig. 4b shows top-coal compression of No 9 to project 9502×Monitoring pointsMonitoring points)Projects 1, 2 and 3(b) Projects 4, 5 and 6(c) Projects 7, 8 and 9Fig. 4 Top-coal compression of No 9 coal seamNo.7 coal seam not mined; No 7 coal seam mined; -t No. 7 coal seam reserves coal pillarRegarding the top-coal compression of No 9 corresponding to its different roof breakage dicoal seam, the different projects show that the after No. 7 coal seam is mined. Fig. 5c shows thetop-coal compression of No 9 coal seam is much lar- topinn nf No 9 coal seam correspondger when the No. 7 coal seam is mined than when ing中国煤化工 distance under theNo. 7 coal seam isnt mined, and is the largest when coalCNMHGthe No. 7 coal seam reserves a coal pillar.der the same con-2) Effect of different fault distancesditions, the longer the roof breaking distance is, corFig. 5a shows the top-coal compression of No9 respondingly the larger the top-coal compression ofcoal seam corresponding to its different roof breakage No9 coal seam is; when the coalface is located diwhen No. 7 coal seam is not mined. Fig 5b rectly under the coal pillar, the compression of No9p-coal compression of No 9 coal seam coal seam is the largest for each of the monitoringLIU Yu-de ct alSimulation Analysis of Coal Mining with Top-Coal Caving Under Hard-and-Thick Stratapoints with different roof breakage distances40Monitoring pointsMonitoring pointsFig 5 Top-coal compression of No 9 coal seamBreakage distance 15 m: Breakage distance 20 m: -t Breakage distance 25m4 Simulation Effect of Seam Stagger of 4.2 Simulation projectsNo.7 and No. Coalface layoutThere are three projectsIn order to confirm the best layout fashion, theProject 1: First No.7 coal seam is mined; finallysoftware RFPA2000 was applied to analyze the min- No9 coal seam is mineding effectProject 2: No. 7 coal seam is temporally notmined and No 9 coal seam is mined first4.1 Numerical simulation modelProject 3: First No. 7 coal seam is mined, reservFig. 6 shows the numerical simulation model. ing the coal pillar in No.7 coal seam; finally No 9coal seam is mined4.3 Analysis of simulation resultsFig. 7 shows the final result of each project. It isobvious that the staggered layout of fully-mechanizedtop caving coalface of both No. 7 coal seam and No 9coal seam is most beneficial to the lower coal seamsfal(a) Project 1(No 9 coalface advanced 120 m) (b)Project 2 (No 9 coalface advanced 150 m)(c)Project 3(No, 9 coalface advanced 130 m)Fig 7 Roof movement features5 Field Application Effectig. 8 is the staggered layout of No. 9109 fullmechanized coal face with top-coal caving and No. 7109 coalface of Zhangshuanglou mine in Xuzhou. In2003. it took the coalface 8 months to advance, andproduced 664 kilotons of raw coal, with a maximumnIno中国煤化工daily production of 4600 ton, with an average of 3265tons daily and a maximum monthly production of 83 1-DCNMHGo9 coal seam: 3-Sumpkt. The results with this technology were more satis- 6-8coalface: 5-Cut hole of No, 9109 coalface7-No. 7109 coalfacegy of great mining height, and the technology hasFig 8 Staggered layout of coalface in No. 7and No9 coal seamsbeen popularized and practiced in the whole mineJ. China Univ of Mining Tech (English Edition)Vol 16 No. 2coal pillar of No 9 coal seam, is larger, and a lot of6 Conclusionstiny crannies will be induced. It can benefit the cav-ing of the top-coal of No 9 coal seam.1)Under the mining effect of No. 7 coal seam2) The numerical simulations and field applicacoalface, tiny crannies of definite magnitude will tion indicate that the staggered layout of coalface ofcome into being in No 9 coal seam. Consequently, No 9 coal seam just under coalface of No. 7 coal seamcoal seam is mined directly, the striking load is in- coal seam, the successful mining of No 9 coal seamduced; the partial top-coal of No9 coal seam is frac- with fully-mechanized coal face with top-coal cavingtured, and the partial size of some zones of top-coal is can be ensured, and the effect of satisfactory and eco-arge. This does not benefit the falling of the top-coal nomical technology can be achievedof No 9 coal seam. When No. 7 reserves a coal pillar,the pressure of top-coal, which is the correspondingReferencesI Qian M G Shi P W. Rock Pressure and Strata Control. Xuzhou: China University of Mining Technology Press, 2003. (InChinese)Wei J P, Jin Z G Yang Y F, et al. Numerical simulation of hard roof control. Chinese Journal of Rock Mechanics and Engi-neering, 2002, 21(supp 2): 2488-2491.(In Chinese[3] Wei J P, Jin Z M, Niu Y H. The experimental studies of rock pressure during fully mechanized mining with sublevel cavingJournal of Taiyuan University of Techanolog, 1999, 30(3): 331-335 (In Chinese)[4]GuQZ, Shi Y w, QiQ X Rules of roof movement in sub-level caving workings. Jourmal of China Coal Society, 1996, 21(1)45-50. (In Chinese[5] Qian M G Miao XX, Xu J L, et al. Key Strata Theory in Ground Control. Xuzhou: China University of Mining TechnologyPress, 2000.(In Chinese)Lin C D. Procedure analysis of numerical simulation for the failure mechanism of laminate roof. Chinese Joumal of RockMechanics and Engineering, 1999, 18 (4): 392-396.(In Chinese)[7] Wang Y J, Xing J B. Discreet Element Method and Its Application in Geotechnical Mechanics. Shengyang: Northeast IndusCollege Press, 1999.(In Chinese)[8] Zhu H C, Brummer R, Andrieux P. Numerical modeling methods and applifor jointed rock mass, part 2: applicationengineering practice. Chinese Journal of rock Mechanics and Engineering,23(20:3444349.( In Chinese)[91 Jiang FX, Yang S H, Xun L. Spatial fracturing progresses of surroundirasses in long wall face monitored by microseismic monitoring techniques. Journal of China Coal Society, 2003, 28 (4): 357-360.(In Chinese[10] Ma Q Y, Zhao X D, Song Z Q. Break of main roof ahead of workface and ground pressure Joumal of China Coal Society,2001,26(5):473-477.( In Chinese)中国煤化工CNMHG