Rational cutting height for large cutting height fully mechanized top-coal caving

Mining Science and Technology( China)21(2011)457-462Contents lists available at Science DirectMining Science and Technology( china)ELSEVIERjournalhomepagewww.elsevier.com/locate/mstcRational cutting height for large cutting height fully mechanized top-coal cavingHuang Bingxiang Li Hongtao, Liu Changyou Xing Shijun Xue Weichao aSchool of mines, China University of Mining 6 Technology, Xuzhou 221116, chinaCollege of Safery Engineering, North China Universiry of Science and Technology, Beijing 101601. ChinaXinglongzhuang Coal Mine, Yankuang Coal Group, Zoucheng 273500, ChinaARTICLE INFOABSTRACTLarge cutting height fully mechanized top-coal caving is a new mining method that improves recoveryReceived 30 August 2010atio and single-pass production. It also allows safe and efficient mining. a rational cutting height isReceived in revised form 12 october 2010Accepted 27 December 2010one key parameter of this technique. Numerical simulation and a granular-media model experiment wereAvailable online 15 June 2011used to analyze the effect of cutting height on the rock pressure of a fully mechanized top-coal cavingwork face. The recovery ratio was also studied. As the cutting height increases the top-coal thicknessis reduced. Changing the ratio of cutting to drawing height intensifies the face pressure and the top-coaLarge cutting height fully mechanizedshattering. a maximum cutting height exists under a given set of conditions due to issues with surround-ing rock-mass control. An increase in cutting height makes the top-coal cave better and the recovery ratiowhen drawing top-coal is then improved. a method of adjusting the face rock pressure is presentedhe ratio of cutting height to drawing heightChanging the cutting to drawing height ratio is the technique used to control face rock pressure. TheGround pressurerecovery ratio when cutting coal exceeds that when caving top-coal so the face recovery ratio may be:covery ratIoimproved by over sizing the cutting height and increasing the top-coal drawing ratio. An optimum ratioof cutting to drawing height exists that maximizes the face recovery ratio. a rational cutting height isdetermined by comprehensively considering the surrounding rock -mass control and the recovery ratioAt the same time increasing the cutting height can improve single pass mining during fully mechanizedtop-coal caving.e 2011 Published by Elsevier B V. on behalf of China University of Mining Technology(6)Improved recovery ratios and productivity. therefore this isa new path for fully mechanized top-coal caving that willUsing a cutting height greater than 3. 5 m during top- coal fullyimprove the recovery ratio and productivity and will achievemechanized caving creates conditions for safely and efficientlysafe and efficient mining.mining thick and extra thick seams. the advantages of large cuttingheight, fully mechanized top-coal caving( Fig. 1)are:Stability control at the tip-to-face area and support equipmentfor large cutting height fully mechanized caving have been much(1)Improved caving characteristicsimproved after extensive theoretical and practical research [ 1-6](2)The use of high-powered coal cutters and front and rear This technique has now made very important breakthroughs inconveyors.cutting height, cutting angle, and hardness of the coal seam, etc.(3)An increase in the number of drawing ports and a shorter For example. in December 2009, a fully mechanized working facenumber 22303 of the Bulianta Coal Mine, Shendong, china, the(4)Increased ventilation sectional area and reduced air resis- Worlds first 7 m cutting height, fully mechanized working faceprocess time for drawing.tance, which helps dilute coal gas in the drawing port and is about 25 for this device. Given an extremely soft and thick seam(5)Shorter cycle time at the working face and improved this working face achieved a 5 m cutting height by using steppedadvance ratescutting technology [7). These techniques were tested in theXinglongzhuang Coal Mine in 2006 and since then studies havebeen done related to rock pressure and the flow of coal gangue[8, 9 Today it is being promoted in a number of mines and hasbeen applied to soft and thick seams successfully [10].4 Corresponding author Tel +86 516 83885662The heightessar for this technique causes theE-mail address: huangbingxiangecumt educn(B, Huang).stability of the wal中国煤化工 e grade relative to1674-5264/S-see front matter o 2011 Published by Elsevier B V on behalf of China University of Mining TeCNMHGdai:101016/ j. mstc.201105.020B. Huang et aL/ Mining Science and Technology(China)21(2011)457-462Shortens drawinghigh-powerconveyorIncreases the numberof drawing portmproves the recovery raFig 1. Important aspects of large cutting height fully mechanized mining with sublevel caving.a general cutting height fully mechanized top-coal caving methodOn both sides the model has coal rocks. These are simplified as a[11-17]. In a given seam the drawing height decreases in propor- displacement boundary that allows movement in the y directiontion to the increase in cutting height. The cutting recovery ratio while the x direction acts as a fixed hinge bearing, that is to sayis larger than the top-coal drawing ratio, which makes the recoveryratio of a large cutting height working face larger than normal. But u=0is the larger cutting height better from the standpoint of increasingthe recovery ratio at the face?The effect of cutting to drawing height ratio on stope pressureAt the same time, stability control requirements of the rock model(Fig. 2).for the same thickness coal seam was analyzed by two kinds ofsurrounding the working face limits the maximum cutting height.Therefore, it is necessary to determine a rational cutting height forfully mechanized top-coal caving.Model 1: The machine cutting height is 2.5 m, the top-coalthickness is 6.0 mModel 2: The machine cutting height is 4.0 m, the top-coal2. Ratio of cutting height to drawing height: the impactthickness is 4.5 mmining pressure of fully mechanized top-coal cavingThe model predicts changes in the front abutment pressure2. 1. Simulation mode.within 190-250 m of the mining horizon of Seam 3. A simulatedmonitoring point was also used to monitor sloughing of the wallThe numerical calculation model was founded with UDEc at 190 m in the vicinity of the coal wallUniversal Distinct Element Code) software. This model is relatedto working face number 1308 of the Xinglongzhuang Coal MineThe model was designed on the principle that it should include 2. 2. analysis of simulation resultsthe key overlying strata and that the left and right edges shouldbe more than one working-face-width from the wall. The heightFor an identical coal seam thickness increasing the machineof the model is 49 m. The strike range is 250 m with a 60 m stump cutting height reduces the top-coal thickness. the increase in theon each side while the advancing distance of the working face was top-coal breaking-caving space and increased roof activity increase130 m. Table 1 gives the physical and mechanical properties of the top-coal breaking angle. The displacement increases after theworking face number 1308. Joint characteristics and a Mohr- top coal caves. Fragmentation of the top coal is also smaller andCoulomb constitutive model are also includedthe mining-induced rock mass structure shifts up. The axis dimenc The upper boundary of the model is a stress boundary where sion of pressure arch induced by mining in the overlying strataself-gravity of the overlying strata is given asaugments, and the arch springing ahead wall forwards, namelyq=∑h=13MPathe peak of abutment pressure forwards.And if the machine cutting height increases from 2.5 m to 4.0 mThe lower boundary can move in the x direction but the y direc- the width of the plastic zone at the front of the wall increases fromion is a fixed hinge bearing, that is to say16 m to 20 m(Fig 3). Therefore, for a given coal seam thickness thesize of the plastic zone depends on changes in machine cuttingheight and adjustment of the cutting to drawing height ratiohanical parameters of coal and strata for the UDEC simulation.Thickness(m) Elastic modulus( MPa) Cohesion(MPa) Inner friction angle() Density(kg/m) Poisson ratioRock Medium-sandstone20.0Medium-sandstone/siltstone 11.52.253· Coal seamSiltstone中国煤化工027Joint True joint288TH020False jointCNMHGB Huang et aL/ Mining Science and Technology(China )21(2011)457-462400350250Cutting height 4.0 m→ Cutting height25m100Distance to the wall(m8509010501150125.01350900100.010.012010014004. Abutment pressure distribution of top coal under different cutting height(a) Cutting height 2.5 m(b) Cutting height 4.0mFig 2. Numerical UDEC models.spot of resultant force for the roof pressure location on hydraulicsupport tends to the wall. therefore although it is necessary toFor identical seam thickness a change in cutting height by using increase the cutting height to increase the degree of top-coala different ratio of cutting to drawing height influences the breaking it is also necessary to prevent an excessive cutting heightabutment pressure distribution in front of the working face. The from causing the tensile shear-failure zone and the pressure sheartop coal thickness is reduced and the stiffness of the top coal failure zone in the lower top-coal located above the miningincreases as the cutting height increases. The abutment pressure machine from joining. This is needed to prevent premature caving.in the top- coal equilibrium zone with a cutting height of 4.0 m is The top-coal should meet a basic requirement of"complete in fronthigher than with a cutting height of 2.5 m( Fig 4). This is conducive of the support but breaking behind. "This paper proposes a methodto breaking of the top coal. the abutment pressure in the elastic to meet the requirements for fully mechanized top-coal caving inregion with a cutting height of 2.5 m is higher than with a cutting hard and soft coal conditions that uses this principle by adjustingheight of 4.0m. For these two cutting height conditions the the working face ground pressure. This is to be done by changingpressure distribution has the same phase.the ratio of cutting height to drawing height.In the plastic zone the abutment pressure distribution in frontof the working face will inevitably lead to stability of the tip-to- 3. Influence of the cutting to drawing height ratio on theface surrounding rock. That affects the extent of face rib spalling. recovery ratioThe horizontal displacement of the coal wall reflects the difficulty.or the probability, of rib spalling. When machine cutting height inEq. (1)can be used to calculate the recovery ratio for toof the coal wall increases twofold(Fig. 5). Hence, increasing the widths are equal. This allows the determination of themachine cutting height increases the horizontal displacement of height and drawing interval that gives the highest recovery ratiothe coal wall and the extent of rib spalling. For a given conditionas the cutting height increases coal wall rib spalling and roof k.h1×f1+h2×flaking in the tip-to-face area would seriously affect normalproduction due to issues with control of the surrounding rock.where k is the face recovery ratio; h, the cutting height: i theTherefore there is a caving cutting height limit(see Table 2)machine mining recovery ratio, and takes 98%: h2 the drawingField observations of ground pressure via the roof weight at height; and f2 the top-coal drawing ratioworking face number 1308(a large cutting height fully mecha-Given a fixed coal seam thickness an analysis of cutting heightnized top-coal caving working face)show that it is 10.66% larger (cutting to drawing height ratio)effects on the drawing ratio wasthan at working face number 1370(a general cutting height fully obtained from a granular media model. This experiment involvedmechanized top-coal caving working face). The influence from drawing top-coal under different conditions to get the coal-gangueadvance at working face number 1380 is increased along with layer boundary shapes after advance. Fig. 6 shows the results forthe width of the plastic zone. Higher cutting heights(measured different cutting height conditions. These experimental resultsas the ratio of cutting height to drawing height)make it easier and Eq ( 1) gives the face recovery ratio for different cutting heightfor a coal mass in the upper position of the wall to slab. The action conditions shown in Table 3. It appears that a cutting height higher405250500170.019002100550165017501850H中国煤化工CNMHGFig 3. Plastic zone distribution at the working face for different cusInsB Huang et aL/Mining Science and Technology( China)21(2011)457-462000440801201601201602.5ight 4.0 mFig. 5. Horizontal displacement of the coal wall for different cutting heightsTable 2Ground pressure parameters for different cutting heightstting height(m)idth of theRange of influenceMaaximum hequilibrium area(m)2.51122144O Cutting height 3.0 m(b)Cutting height 3.5 m (c)Cutting height 4.0 m (d)Cutting height 4.5 m (e)Cutting height 50mFig. 6. Demarcation lines between coal-gangue and the horizon after advance for different cutting heights [8]Table 3Working face recovery ratio for different cutting heightsheight(m) height(m) drawing height ight to Best drawingProgram CuttingRatio of cutting heangue content inFace recoveryinterval(m)yy ratoawing coal(%)drawing rati3.023450693.3008793.161.87162918139644932Note: A drawing interval of 0. 8 m is one cutting and one drawing: a drawing interval 1.6 m is two cuttings and one drawing.than, or equal to, 3.0 m when using the best drawing interval gives The increased machine cutting height during large cuttinga face recovery ratio greater than 90.0%. The recovery ratio for a height fully mechanized top-coal caving will reduce the thickness4.0 m cutting height is 97.5% and for a 3.0 m cutting height the of the top-coal. The ratio of cutting to drawing height changeslowest recovery ratio is 90.3%. It appears that large cutting height the ground pressure at the face and the way the top coal breaksfully mechanized top-coal caving methods at working face number This makes top-coal breaking and caving easier and thereby in1308, whose machine cutting height is 4.0 m, will be the highest at creases top-coal recovery. The cutting recovery ratio of a mine ma97.5% when using a one cutting one drawing method. the chine is greater than the drawing ratio of the top-coal so we cancorresponding gangue content when drawing top-coal is 3. 16%, increase the face recovery ratio by increasing the cutting heightWorkers usually follow the practice of closing the drawing coal and the top-coal drawing ratio. an optimum ratio of cutting towindow once gangue appears. This terminates caving and so thedrawing heights exists where the recovery ratio of the face is thegangue content when drawing top-coal will be lower than the highest(Fig.predicted 3. 16%. In practice there is a drawing way loss in additionThe coal中国煤化工 angue nearby the drawto the drawing interval loss. The actual recovery ratio is then a bit ing coal winlower than what the test results would predict.when theCNMH Gourse of drawing coalBecause the gangue isB Huang et aL/ Mining Science and Technology( China)21(2011)457-462bFace recovery890Optimal ratio of cuttingheight to drawing heightRatio of cutting height to drawing heightRatio of cutting height to drawing heighFig. 7. Relationship between recovery ratio and cutting to drawing height ratio.nearer the coal drawing window than the upper top-coal it willarrive at the drawing coal window ahead of the upper top-coalFollowing a"close the drawing coal window once seeing gangue"approach causes the upper top-coal to be drawn incompletely.Gradually reducing the thickness of the top-coal makes the loss1244of the upper top-coal smaller and the top-coal drawing ratio will756increase. But thin top-coal causes the slope of the coal-gangue lineto be to steep and the distance between the coal-gangue line andthe end of the hydraulic support upper beam will be reducedThe mixing of coal and gangue will increase as the distancebetween the coal-gangue line and the end of hydraulic supportupper beam is reduced. The mixing of coal and gangue willCutting height(m)low top-coal drawing raFig,&Frequency distribution of cutting heightTheoretical and experimental results show that increasedcutting height and appropriately reduced thickness of the top- coalwill help improve the top-coal recovery ratio. The top-coal recov-ery ratio will decrease if the top-coal is too thin. the highest faceThe current cutting height of a general fully mechanizedrecovery ratio for large cutting height fully mechanized top-coal coal caving face is around 2. 5 m. According to the new version ofcaving can be determined. a ratio of cutting to drawing height of China's Coal Mine Safety Regulations the drawing height is to be1: (1. 1-1.3)is reasonable. Face rib spalling and roof flaking in the not more than three times the cutting height. The single cuttingtip-to-face area will not have too much impact during normal pro- and drawing height of the large cutting height fully mechanizedduction and the overall performance of the hydraulic support posi- top-coal caving method can be increased by 2-3 mtion is good when the cutting height is 4 m high.In the Xinglongzhuang Coal Mine the reasonable upper limit forcutting height is 4 m. Considering the optimum ratio of cutting to 5.Application of large cutting height fully mechanized top-coaldrawing heights and the problems of surrounding rock control we caving in the Xinglongahuang Coal Mineconclude that the maximum height of the hydraulic support shouldbe 4 m and that a reasonable upper limit for cutting height isSome basic parameters of the working face number 1308 are a3.8-4m.cover depth of 354. 7-503.5 m and a face length of 207 m. Workingface number 1307 has been mined to the west side and facenumber 1309 has not been mined to its east side. the coal sean4. Relationship between cutting height and the mining height thickness is 7. 85-9.9 m with an average thickness of 8.60 m andlimit for fully mechanized top-coal cavingthe coal seam dip is from 2 to 10 with an average of 6. About3.3 m from the bottom layer there is a layer of carbonaceousWhen the coal seam thickness varies a cutting height increase is mudstone partings from 0 to 1. 1 m thick. The coal Protodyakonovconducive to breaking and caving of the top-coal. For given physi- hardness coefficient, f, is 2.3: the parting hardness, is 2.5.Thecal and mechanical properties of the coal and rock strata, and a components of the immediate roof are siltstone 3. 20 m thick withfixed ground pressure, a reasonable minimum ratio of cutting to an f of 5.7. The components of the immediate floor are siltstonedrawing heights for fully mechanized top-coal caving exists. When 7.04 m thick and f is 3. 1. The roof support is a hydraulic supportthe cutting to drawing height ratio is fixed increasing the cutting of the type ZFS7200/ 20/40 characteristic of a large cutting heightheight brings a corresponding increase in drawing height.and low drawing position. The mining method is long wall miningTable 4Physical parameters of the hydraulic support.utting Pitch angle of the base() Dip angle of the prop(.)Pitch angle of the roof beam Dip angle af shieldheight(m) ( means elevation and -(-means forward and+ means backmeans dip)Fore-top Fore-down Back-top Back-down (+ means elevation and - (included angle withprop-5.512.51256.158Avg 3.610646.520.160.15YHa中国煤化工43.14CNMHGB. Huang et aL/ Mining Science and Technology(China)21(2011)457-462along the dip with fully mechanized top-coal caving along the full Referencesseam. This face began production in November of 2006. Itsmeasured average cutting height is 3.61 m( Fig. 8)and the drawing I1 Wang JH. Present status and development tendency of fully mechanizedheight is 4.99 m. The ratio of cutting to drawing height is 1: 1.38Technol 2006 34(1): 4-7 Iun Chinesand the cutting depth is 0.8 m. this face uses one cutting and [2] Hao H]. Wu J Zhang Y The balance structure of main roof and its action toone drawing and single round ordered drawing means coal cuttingand drawing occur in a parallel operation.2004292}137-41| in Chines13) Gong PL Jin ZM. Mechanical model study on roof control for fully-mechanizedThe bow and head hydraulic support roof beam ratios arecoal face with large mining height. Chin J Rock Mech Eng 2008: 27(1): 193-8 [in10.75% and 89.25% and the overall performance of the hydraulicsupport position is good (Table 4). The coal wall rib depth averages 14] He FL Qjan MG. Liu XF. Chen Lw. ui CF. Tilt characteristics and control200 mm during the course of roof un-weighting with a maximumof 1.0-1.5 m, and an average of 400 mm during roof weighting The 151protection of working face withchock-shield hydraulic support of the type ZFS7200/20 /40 hasgood adaptability for"sticks","protection", andstability". The4 2: 15-20 [in Chinese.[61 Yi MS Selection of mechanized working face length by great height miraverage top- coal fragmentation is 20-30 cm. The average immedi-nder shallow coal-seam in Shendong Coal District China Coalcoal and gangue is good. The average recovery ratio at working face [7 Liu CY Hung Jate roof fragmentation is 30-40 cm. The flowing property of theM, Wang J. Wei MT. Study on tip-to-face coal andmechanized stepped large cutnumber 1308 is from 89.37% to 91.97%. Compared to adjacentin extremely softMining Technol 2008: 37(6): 734-9ordinary fully mechanized caving working face number 1307 thelin chinesface recovery ratio of at number 1308 has increased by 1.36%[8] Huang BX Liu CY. Niu HW, Wang J. Research on coal-gangue flow fieldMining Safety Eng 2008: 25(4): 415-9 in Chinese.[91 Yan SH. Research on side and roof falling mechanism and control approaches6. Conclusionsfull-mechanized caving mining with large mining height. Coal MiningTechnol 2008: 13(4): 5-8 in Chinesel(1)A method of adjusting the ground pressure for fully mecha- I10 w Lu SY. Research and application of fully mechanized caving mining withnized top-coal caving based on regulating the ratio of cutting:5-8 in Chineseto drawing heights is proposed.[11] Chen YG. Qian MG. China coal mine strata control. Xuzhou: China University of(2)For given conditions a limit to the cutting height for large (12) Zhang D, He DD Roof falling mechanism of face area in fully-mechanized sub-cutting height fully mechanized top-coal caving exists.face and its controL J Xiang(3)Increased machine cutting heights of large cutting height2001;16(3):11-5| in Chinesefully mechanized top-coal caving reduce the thickness of [13] Xie Gx. Chang JC. Yang K Investigations into stress shell characteristics ofthe top-coal. Increased cutting height makes the ratio ofsurrounding rock in fully mechanized top-coving face. Int J Rock MechMin Sci 2009: 46: 172-81 in Chinesethe better. But there is an optimum ratio of cutting to draw. 114 Ataei M, Bodaghabadi S. Comprehensive analysis of slope stability andcutting to drawing height change and caving changes foretermination of stable slopes in the Chador- Malu iron ore mine usinging height that maximizes the recovery ratio of the face.cal and limit equilibrium methods. j China Univ Mining Technol08:184)488-93.(4)Surrounding rock control and recovery ratio factors lead to a [15] Ma JR, Cui GX, Qin Y Zhou CQ, Experimental research on unloading propertiesreasonable cutting height for the Xinglongzhuang coal seamclay under high stress. j China Univ Mining Technol 2008: 18(1): 122-5.conditions this height is 4 m[16] Wang EY, Liu XF, Zhao EL, Liu ZT. Study of electromagnetic characteristics ofress distnbution and sudden changes in the mining of gob-surrounded coal(5)Increasing the cutting height can increase the single passface. J China Univ Mining Technol 2008: 18(1): 1-5.ining thickness of the coal seam.strength of hard-rock pillSci2000:37:123946.[181 Liu CY, Huang BX Wu FF. Wan Z]. Yang P]. Fragment dimension theory of topcaving and drawing for fully mechanized top coal caving and itsAcknowledgments[19] Huang BX, Liu CY, Wu FZ Experimental research on drawing top-coalUniv Mining Technol 2006: 35(3): 351-5 intone roof. J ChinaFinancial support for this work, provided by the National BasicResearch Program of China(No. 2007CB209400)and the National (20 Fan KG. Zhai DY. Research on characterr of drawinNatural Science Foundation of China(No. 51004104) is gratefullyheight to d wing he ignt, Mining safe Environ rote 003:53030: 7-9 ngacknowledged中国煤化工CNMHG