Suitable layout of gate roads related to slice mining in an ultra-thick unstable coal seam

Mining Science and Technology(China)21(2011)563-566Contents lists available at Science Directted letb tuiMining Science and Technology( China)ELSEVIERournalhomepagewww.elsevier.com/locate/mstcSuitable layout of gate roads related to slice mining in an ultra-thick unstablecoal seamFan Gangweia, b * Zhang dongsheng b, Zhou LeicSchool of Mines, China University of Mining E Technology. Xuzhou 221116, ChinaState Key laboratory of Coal Resource and Mine Safety, Xuzhou 221008, ChinaXuehu Coal Mine, Shenhuo Group, Yongcheng 476600, chinaARTICLE INFOA BSTRACT≈=We determined a suitable gate road layout in slice mining in an ultra-thick unstable coal seam, using the-oretical analysis and numerical calculations. Based on plasticity theory in terms of limiting equilibriumrevised form 25 october 201013 December 2010the width of chain pillar in the upper slice was calculated to be 18 m. The stress distribution in the chainAvailable online 20 july 2011pillar after the upper slice was mined out was described with numerical simulation. The extent of theeffect of stress on the upper chain pillar on the lower solid coal was obtained on the basis of an elasticsolution of a distributed force loaded on a half-plane. three layout designs for lower gate roads were proposed and a stability factor was introduced to analyze the stability of the lower pillar with numerical cal-Slice miningculation Gate road translation was determined as the most suitable layout method, which maximizes theGate roadextraction rate on the basis of the pillar stabilityo 2011 Published by Elsevier B V on behalf of China University of Mining TechnologyStability factor1 Introduction12.70 m. The coal seam tums thinner from northeast to southwestThe depth of the coal seam ranges from 180 to 220 m and its dipSlice mining is a major mining method used in the exploitation angle of ranges from 0 to 3. the protodyakonov coefficient ofof ultra-thick coal seams. During slice mining, stress in the lower the coal seam is 2. 5. This coal mine is a low gassy mine the roofslice is redistributed under the impact of the upper chain pillar of the #61 coal seam consists of coarse-grained sandstone orand goaf. the layout of upper gate roads will directly affect the fine-grained sandstone and mudstone appears in some areas. themaintenance of lower gate roads [1-5 the layout for slice gate floor is often of mudstone or coarse-grained sandstone. a general-roads is a problematic issue related to slice mining.ized geological column is shown in Fig. 1According to the position of slice gate roads, the layout can beOn the basis of a technical proof, the company opted for sliceclassified into the following four modes [6-9]: outward, inward, mining, where the upper slice was mined by a fully mechanizedoverlapped and translational. the inward mode, which is widely longwall method with a mining height of 4.5 m, while the lowersed in slice mining, places the lower gate roads below the upper slice was mined by a top-coal-caving fully mechanized longwallgoaf, referred to as the stress- relaxed area. However the width of method with an average mining height of 8. 2 m. the length ofthe chain pillar is relatively large [6-8 Hence, a large amount of the first longwall face was 300 m and a two-entry system wcoal resources will be left if the inward layout is used, especially used.when the panel length or/ and mining height is large. therefore,in order to maximize the extraction rate on the basis of the stabil- 2. Determination of the width of the pillar of the upper sliceity of gate roads and pillars is a problem that needs to be solvedwith some urgencyThe width of the pillar is a key factor affecting the stability ofWe used theoretical calculations and numerical simulation to the pillar and the maintenance of the gate road ( 1-5). The determidetermine a suitable layout of slice gate roads related to slice min- nation of the width is affected by many factors, such as mininging in an ultra-thick coal seam in a case study from western China.The #61 coal seam is a primary seam in the Suancigou Coal depth, coal seam thickness, height of the gate roads and theMine. This coal seam is 7.04-20.77 m thick with an average of mechanical properties of the surrounding rock At present, thereare two theoretical methods used to calculate the width of the pillar, ie, loading estimation and plasticity theory [2].s Corresponding author teL: +86 13655203693From the point中国煤化工 the width of theE-mailaddress:fangangwei@.edu.cn(GFan).pillar is suitabless than itsCNMHG1674-5264/5-see front matter o 2011 Published by Elsevier B V on behalf of China University of Mining Teciuuugydot:101016 mstc201106017G. Fan et aL/ Mining Science and Technology( China)21(2011)563-566THicknesshology Column平*以Specifications073337[JI3.2-1539391Grey white,softMusnob) Outward lavoutCoarse.94942333Grey whteFig- 2. Schematic gate road layout related to slice mining.M十0C= 1.2 MPa is cohesion, o- 25 is the friction angle andy-25 kN/mis the average volume forceCalculated from Eq (2), the width of the plastic zone in the pil704-207127lar at the entry side, xr, was 3. 423 m.ng to Eq (1).MudstoneI 3.65BLack,medium-hardB=X+2m+x1=5.083+2×45+3423=17508m0302135From a safety point of view, we decided the width of the upperFIg 1. Generalized geological column.pillar to be 18 m3. Layout of lower gateroadsultimate strength [2 ] The load limit and the ultimate strength canbe calculated by a simple estimation or an empirical formulaGiven the position of the gate roads, three possible layoutAlthough this method is simple, the calculation error is relativelyAccording to plasticity theory, a plastic zone will appear at both(1) Inward layout: The lower gate roads are positioned below thesides of a mined-out area and the gate roads. the pillar remainsupper goaf, forming an echelon pillar(see Fig. 2a). If anstable only if an elastic core exists in the pillar after the plasticinward layout were employed, the width of the lower pillarzone is formed and the width of the elastic core is not less thanwould increase and the length of the lower longwall facetwo times the mining height, which can be expressed bydecrease. Since the gate roads are located in a stress-reliefB=x0+2m+x1rea owing to the upper goaf, a fully mechanized develop.ment method is easy to carry out the key for an inward lay-out is that the gate roads are positioned away from the effectwhere B is the minimum width of the pillar to remain stable, m: xoof the upper pillar so that the gate roads can be protected.the width of the plastic zone in the pillar at the goaf side, m; m the(2)Outward layout: The lower gate roads are positioned belowmining height, m; and xi the width of the plastic zone in the pillarthe upper pillar, forming an inverse echelon pillar(seeat the entry side, m.Fig. 2b). If an outward layout were used the width of theThe parameters xo and x, can be accurately calculated based onlower pillar would reduce and the length of the lower long-plasticity theory, the method we selected to determine a suitableall face increase Since the gate roads are located in a con-width of the upper pillarcentrated stress area because of the upper pillar, theAccording to the limit equilibrium theory, the width of the plassurrounding rock would move a considerable distance. thetic zone in the pillar at the goaf side is given by [2]key for an outward layout is to conduct a suitable and effec-m k,H+Ccot otive entry-support method5(P, +C cot P)(2)3)Translational layout: The lower gate roads are translatedbelow the upper goaf, forming a parallelogram pillar(seewhere K=3.5, is the stress concentration factor: p1-0.1 MPa is theFig. 2c). If an inward layout were used the width of theresistance force of support for ribs: m=4. 5 m is the mining heightlower pillar and the length of the longwall face wouldC-1.2 MPa is cohesion; p- 25 is the friction angle: y-25 kN/mremain the same as with the upper pillar. Since the gateis the average force of the volume force: f=0. 25 is the friction coefroads are located in a stress-relief area because of the upperficient between coal seam and roof or floor and s is the triaxialgoaf, a fully mechanized development method would bestress factor, where 5= sin geasy to carry out. The key for a translational layout is toGiven the calculated values, we determined from Eq. (2)thedetermine a suitable translation gap so that the lower gatewidth of the plastic zone in the pillar at the goaf side, xo, to beroads are located in a stress-relief area5.083m.According to the limit equilibrium theory, the width of the plas-Given this analysis, the extent of the effect on the upper pillartic zone in the pillar at the entry side is given byneeds to be determined first.x1=21hi- k,H+Ccot cpn+cotφ4. Exten中国煤化工rthere h-4. 5 m is the entry height; a-0. 4 is the side pressurem可YHCN MH Gion of stress in the lowcoefficient: P1-0.1 MPa is the resistance force of support for ribs: er slice. The stress concentration below the pillar is a major factorG. Fan et al/ Mining Science and Technology( China) 21(2011)563-566565Table 1Mechanical parameters of overlying strata.Poissons Cohesion Friction(MPa)26000.1880ainedMudstone2450#5 Coal seam 140026555grainedHorizontal distance from the centre(m)300.22Fig 5. Contours of additional vertical stress coefficient#61 CoalMudstone5.00.18InwardSandstone→ Translational5-15-105101520Distance from the centre(m)Fle 6. Stability factor of the pillar in different layouts.x(+9)Distance from the centre(m)9 /arctan+9-arctanXx2+y+9)2x2+(y-9)The contours of the coefficient of additional vertical stress in-affecting the design of the layout and the maintenance of the lower duced by the upper pillar are shown in Fig. 5. It is generallyMohr-Coulomb model to evaluate rock failure A stress boundary 7.3 m beyond the upperpll gagate roads[2, 10, 11thought that the effect of the upper pillar is slight if the additionalA numerical simulation software FLAC, was used to analyze the vertical stress coefficient is less than 0. 1[14]. Therefore the extentof the effect on the upper pillar on the lower slice is(16.3 anddistribution of stress in the pillar. This numerical model was based 16.3)in the coordinate system as shown in Fig. 4. The effect oron the actual geological condition in the mine and we used a the upper pillar is slight ifhorizontal lower gate road iscondition was applied to the upper boundary and a displacementboundary condition to the left, right and lower boundaries. Themechanical parameters for overlying strata are shown in Table 1. 5. layout design on lower gate roadsThe modeling result for the distribution of stress in the coal pillar is shown in Fig 3. The stress concentration coefficient in the pilGiven these calculations, three different layout plans were pro-lar reached 3.6 due to the superposition of side abutment pressure, posed. (1)Inward layout: the lower gate road was 8 m beyond thepper pillar. (2)Outward layout: the lower gate road was 3 m fromof stress due to the upper pillar can be calculated from a model re- the upper pillar. (3)Translational layout: the lower gate road waslated to a half plane subjected to a uniformly distributed load (see 8 m beyond the upper pillar.Fig. 4).In order to select a suitable layout of the lower gate roads, theAccording to the elastic solution related to a uniformly distrib- stability of the three plans was compared by means of nuruted load on a half plane, the coefficient of additional vertical simulation, using the FLAC software The earlier numerical modelstress applied to the upper pillar can be expressed by [12, 131was used to calculate the stability factor of the lower pillar. TheCrosshead#1105 Headgate\#1103 Tailgate36hSetup roomossheading #1101 Tailgate #1103 Headgat中国煤化工CNMH4 Simplified model of a half plane.邮. Panel layout for the睿 11U3 panelG. Fan et al Mining Science and Technology(China)21(2011)563-5667. Conclusions(1)Based on plasticity theory, the width of the upper pillar wasdetermined as 18 m.(2)Calculated from the elastic solution for the model of uni二Fformly distributed loading on a half plane, the extent ofthe effect on the upper pillar on the lower pillar wass16. 3 m beyond the center of the lower pillar. In other words,the effect of upper pillar was slight when the lower gateoads were 7. 3 m beyond the upper pillar in a horizontalDistance to the working face(m)(3) The translational layout was selected as the final plan in a(a)Roof-to-floor convergencecomparison of pillar stability and that of the width of the pil-lar of three different layout plans, i. e inward, outward andtranslational. For the translational layout, pillar stability isthe best and coal recovery is at a medium level.(4)Field observations proved that the designed layout was suit-2oable and the calculation method used applicable for slicemining related to ultra-thick coal seams.AcknowledgmentsDistance to the working face(mFinancial support for this work, provided by the Research Fundof the Fundamental Research Funds for the Central Universities ofFIg&. Deformation in surrounding rock during mining operationsChina University of Mining Technology(No. 2010ZDPO2B02),theState Key Laboratory of Coal Resources and Mine Safety (NoSKLCRSMO8X2), the Jiangsu 333"High Qualified Talents, the Na-stability factor was derived from the Mohr-Columb criterion and is tional Natural Science Foundation of China(Nos. 50904063 anddefined as15】」51004101), and the Scientific Research Foundation of China Uni-versity of Mining Technology(Nos. 2008A003 and 2009A001)Is g9x+-m9eferenceswhere o, is the major principal stress; o3 the minor principal stress1]u YQ. Underground mining, Xuzhou: China University of Mining andchnology Press 2003: 220-1o the internal friction angle and c the cohesion[2] Qian MG, Mine pressure and ground control. Xuzhou: China University ofThe stability factors of the pillars for three different layouts arelining and Technology Press 2003: 194-217(In Chinese).shown in Fig. 6. For the inward layout, the stability factor in most [31 Baryshnikov V D. Cakhova, L N, Kramskov N P Stress state of ore mass in theof the lower pillar is around 1. For the outward layout, the stabilityfactor in the entire pillar is less than 1. For the translational layout, 14] Shen SH. Development of slice mining in china. World Mining Equipmentthe stability factor in the pillar is significantly greater than 1, whichmeans the stability of the lower pillar in this layout is the best of15] islam MR, Hayashi D. Kamruzzaman ABM. Finite element modeling of stressdistributions and problems for multi-slice longwall mining in Bangladesh.these three plans.with special reference to the Barapukuria coal mine. Intemational JoumalIn the translational layout, the stability of the pillar was the best(61 Guo YH, Duan JG, Li LH Support mechanism of side bolts in lower slicingand the width of the pillar was less than that for the inward layoutroadway. Joumal of Mining Safety Engineering 2007: 2(4): 465-8(InTherefore, the translational layout was selected as the final plan sothat coal recovery could be maximized on the basis of pilla[71 Yang JH, Cai MF, Guo YH. Study on the technique of sparklet-inboard-typeyout of gateroad in the bottom slicings. Chinese Journal of Rock Mechanicsstability18) Zhai YD. Li BF. The theory and practice of outward staggered entnes arrangingrsity of Technology[9] Tian ZQ, Deng SG, Zhang Z]. Zhao HY. Research on translation layout of mining6. Field observationpal with closed distance to other seam Coal ScienceTechnology 2008: 36(4): 20-4( In ChinesAn active panel, #1103, in the #61 coal seam of the Suancigou 110] Zhang BS. Yang SS, Kang LX. Zhai YD. Discussion on method for determininCoal mine was selected to monitor the deformation in the sur-Rock Mechanics and Engineenng 2008: 27 (1): 97-101(In Chinese).rounding rock in order to validate the selected design. The panel (111 Ma OL L H Bai Jz Close range sub-coal seam roadway[13] Zhu SY, Jiang ZQ, Yao P Xiao WG. Application of analytic method in calculatingFig8 shows that the deformation of the crossheading entries infloor stress of a working face. Joumal of Mining Safety Engineeringthe surrounding rock were, in general, quite similar. The maximum [14] Huang n, 92-4(In Chinese)I Iu F An n Reasonable layout of gateroads in closeobserved roof-to-floor convergence was 35.5 mm and the maxi-中国煤化工 In Chinese).lum rib-to-rib convergence 40 mm, which is not very large in [15] Peng ss.West Virginia Universityengineering projects in mines. Therefore, the designed layout wasCNMHGto