Law of surface movement for multi-coal seam strip mining ?

December 2014Journal of Chongqing University(English Edition)[ISSN 1671-8224doi:10.11835/issn.1671-82242014.04.02To cite this article: ZHANG Li-ya, ZHANG Hong-mei. Law of surface movement for multi-coal seam strip mining [J]. J Chongqing Univ: Eng Ed [ISSN 1671-8224], 2014.13(4):1221Law of surface movement for multi-coal seam strip miningZHANG Li-ya,T, ZHANG Hong-meiHunan Provincial Key laboratory of Clean Coal ResourcesHunan University of Science and Technology, Xiangtan 41 1201, P. R. ChinaSchools of Architecture and Urban Planning, Hunan University of Science and Technology, Xiangtan 411201, P. R. ChinaReceived 27 June 2014; received in revised form 12 August 2014Abstract: It is an important part of green mining to control the disasters of coal mining which have caused irreversible damagesto buildings and ecological environment. Strip mining is one of the efficient measures to control surface subsidence and miningdamage. However, the research on the laws of the surface subsidence are still deficient in multi-coal seam strip mining at presentBased on the Fast Lagrangian Analysis of Continua(short for FLAC3D)numerical simulation software, the laws of the surfacesubsidence and horizontal movement were systematically studied for different depths, different mining widths, different distancesbetween seams, different mining thickness, different parameters between seams and the special relations of the upper pillar andthe lower pillar in the vertical direction in multi-seam strip mining. The function relation between the maximum subsidence andhe maximum horizontal movement with the depth, the mining width, the seam distance, mining thickness, different parameterbetween seams anpartial offset are summarized respectively. Finally the formula integrating the surface maximumsubsidence value and the maximum horizontal movement was deduced. The results can be used for reference theory and measurethe surface displacement in multi-coal seam stripKeywords: multi-coal seam strip mining: FLAC3D; numerical simulation; surface maximum subsidence; surface maximumhorizontal movementCLC number: TD173Document code: AIntroductionSurface subsidence and environment disasterscaused by coal mining which account for 70%o inprimary energy consumption have become increasinglyT Corresponding author, ZHANG Li-ya(张立亚)to exploit the utmost of underground resources on theFunded by the Scientific Program of Hunan Provincial Scienceeffectivelykey problem of mining underand Technology department(2014FJ3104)and Scientificbuildings is to control movement of rock strata andProgram of Hunan Provincial Education Department(13C313).surfaces. which is also one of the main research中国煤化工CNMHGL.Y. Zhang, et al.directions of subsidence issues. At present, the main 2 Simulation scheme of multi-coal seam stripmethods of controlling rock strata and surfaceminingmovement include backfill mining, partial miningabscission layer grouting, and so on. Strip mining has 2.1 Numerical simulation model and boundarybeen extensively used in China for protecting buildingsconditionincreasing production cost and simple management, The effects on the surface movement weredespite its low recovery rate compared with other systematically studied for the different depth, miningmining methodswidth, distance between seams, mining thicknessUntil now, there are plenty of theories and practical parameters between seams and the special relations ofachievements about strip mining by scholars; however, the upper pillar and the lower pillar in vertical directionmost of them discuss about single seam strip mining(up and down coal pillar alignment or not) usingThe study and applichaveFLAC3D simulationNumerical simulationed year after year recently. There still exists models were built for the simulatingwhichsome deficiency under the condition of design and were continuous medium of the overlying rock stratapractice of multi-seam strip mining First, inside, using displacement boundary condition ofpredicting model and theory of surface subsidence with limiting horizontal movement in the four sides and twomulti-seam strip mining are not constructed and thedirections'displacement at the bottom of model, andresults of traditional prediction method is greatly the top of it is free boundary. The stress caused bydifferent from the reality value. Second, prediction gravity, which is a hydrostatic state of stress, can onlyparameter system of multi-seam strip miningbe considered in the process of calculation analysis,established too and the way of choosing prediction and the effects of tectonic stress on in-situ stress, rockparameters is in lack of reliable theory in surface initial stress depending on the load and property ofmovement calculated for multi-seam strip miningoverlying strata were neglected(See Fig. 1)Last, the research of optimal design theory and layoutnodel of multi-seam strip mining should be alsoimproved 0-ll. Based on the Fast Lagrangian Analysisof Continuum (short for FLAC3D) numericalsimulation software, we studied in this work the lawsof the surface subsidence and horizontal movementyere systematically studied for the different depth,different mining width, different distance betweenFig. I Mechanical model of numerical simulation in stripbetween seams and the special relations of the upperminingpillar and the lower pillar in vertical direction in multiThe chosen geological mining conditions forseam strip mining, and built function relations between simulation purposes were as follows: mining depththese factors and surface movement, which can be used from 200 m to 500 m, mining thickness between I mfor reference theory and measure in forecasting the and 5 m distance between seams from 10 m to 50 msurface displacement in multi-coal seam strip miningmining width ranging from 20 mmaximum change of parameters between seams being中国煤化工J Chongqing Univ. Eng. Ed. [IsSN 1671-8224, 2014,CNMHGL.Y. Zhang, et al.Multi-coal seam10 times, the thickness of floor being 40 m, coal seam varied in every simulation model and the others werebeing near horizontal and the extraction rate of design the same as the basic quantity. (See Table 2)being 50%0. The design mining district was 200 m by400 m according to the strip width to make sure full 3 Results and analysis of numerical simulationmining of surface. The dimensions of designed basicmodel were 1 200 m by 1 000 m by 286 m to avoid 3.1 Law of surface subsidence with multi-coal seamedge effects, and the grids of strike, dip, and verticalsTrip Miningdirection were divided ranging from 5 m to 40 m in thelight of simulating purpose, which had almost 35 882 3. 1.1 Effects of mining depth on surface subsidenceunits of each model. Mohr-Coulomb yield criterionwas applied according to the mechanical property ofThe law of the maximum ground subsidence ofoverlying rock strata whose parameters were selected mining depth was analyzed in the case of upper andbased on experiments in laboratory and work field (See lower coal pillars alignment and complete staggerTable 1)Relationshubsidence and its coefficient with mining depth were2.2 Numerical simulation schemesobtained by regression analysis according to simulationThe effects of changes of mining depth, widthAlignmentthickness, distance between seams and parametersW=0.718H-24.8R2=0.9648between seams on surface subsidence and horizontaldisplacement were simulated respectively under thewhere wo is the maximum ground subsidence, mm; H iscondition of the same recovery rate(50%)and up and the mining depth, m; and R is the correlation coefficientdown coal pillars alignment or complete stagger. OnComplete staggerthe basis of mining depth of 200 m, thickness of 3 m,distance of 40 m and width of 20 m one variable was W=0.781H-371, R=0.9814Table 1 Rock parameters of simulation modelStrata√GPaG/GPC/MPaT/MPa0.0020.0004Mudstone/sandstone 0.88Siltstone0.83Main roof0.51Immediate roof0.041.5Coal seam0.21323Coal seam floo0.5224.63.0Notes: Mis the bulk modulus: a-the shear modulus: a-the cohesion: the angle of friction; and a the tensile strength中国煤化工J Chongqing Univ. Eng. Ed [IsSN 1671-8224, 2014, 13THCNMHGL.Y. Zhang, et al.Table 2 Schemes of mining depth, width, thickness, interlayer spacing and lithology of alignment with upper and lower coal pillarsSchemeInterlayer ThicknessAlignmentWidth /mDepth/mLithologyMining depth ofModel 1Constantalignment andModel 2300Constantmplete staggerModel 3ConsModel 4503ConstantMining width ofModel 100ConstantModel 22003Constantcomplete staggerModel 3200Constant200onstantInterlayer spacing of Model10Model 2Constantcomplete staggModel 3200ConstantModel 4200ConstantModel 52003ConstantCMining thickness of Model IModel 22000Constantcomplete staggerModel 3ConstantModel 4Model 5Interlayer lithologyModel 1of alignment andModel 2omplete staggerModel 31.00Model 42000The depth is made up of 20 m alluvium, 90 m sandstone, and 90 m siltstorlepth is made up of 30 m alluvium, 135 m sandstone, and 135 m siltstone.he depth is made up of 40 m alluvium, 180 m sandstone, and 180 m siltstoneThe depth is made up of 50 m alluvium, 225 m sandstone, and 225 m siltstone.中国煤化工ChongqingUniv.Eng.Ed.[(SSN 1671-8224, 2014, 13CNMHGet alMulti-coal seamAlignment:enlarged too. Therefore the larger the mining width, theR2=0.9637more effects of stagger extent on settlement on accountq=0.0001H-0.0039,(3)of the longer roof exposurewhere q is the subsidence factorComple3.1.3 Effects of distance between up and down coaleams on surface subsidenceq=0.00015H-0.0063,R=0.9802Increase in the stress of coal pillars and roof leads toFunctional relations between the maximum groundsubsidence and the distance between up and down coalhe enlargement of the maximum surface subsidenceseams were obtained by regression analysis accordingalong with mining depth expanding from above resultsto simulation dataWith the extent of stagger of upper and lower coalAlignmentpIdded caused by the larger stress of upper coal pillar W=18466h., R=0.885 2,mpacting on the lower goaf which brought about alarger curvature of the roof of lower coal seam and thewhere is h the distance between up and down coalelationships between the value of subsidence and theseams,mining depth were linear.Complete stagger1n=-39.597ln(h)+370.89,R2=0.98843.1.2 Effects of mining width on surface subsidenceRelationship between the maximum ground increment along with the augmenting of distsubsidence and the mining width was obtained bbetween up and down coal pillars under the conditionregression analysis according to simulation dataof alignment according to regression analysis ofAlignment:different interlayer spacing. However, when upper andwn=34.784c0b,R2=0.9920.lower coal pillars completely stagger, the law of(5)surface movement was opposite because bendingwhere b is the mining width mrigidity of the rock beam increased, leading to smallComplete staggerbending value of lower roof and decreased surfacesubsidence0=3.106c24°,R2=0.9951The relationship between stagger extent andmaximum subsidence under the same interlayCurvature value of the roof increased along with theacing showed that a smaller spacing a larger effecaugmenting of mining width under the same stresson stagger extent of upper and lower coal pillar-andwhich caused a larger ground subsidence according tovice versa. There was less effects of stagger extent onregression analysis of different mining width. Underthe maximum settlement until the interlayer spacingthe condition of the same width, the ground subsidencereaching at 40m. at this time the effects of distance onspatial relationship between upper and lower coalextent of upper and lower coal pillars which caused thepillars can be neglectedstress of lower roof increased and its bending value中国煤化工J Chongqing Univ. Eng. Ed. [IsSN 1671-8224, 2014,CNMHGL.Y. Zhang, et al.3.1.4 Effects of mining thickness on surface subsidence where is E the elasticity modulus of interlayer lithology,PaRelationship of the maxiground subsidenceThe maximum surface subsidence was powerwith mining thickness was obtained by regression functional relation of interlayer lithology. The value ofanalysis according to simulation datasettlement decreased and tended to be constant with theAlignmentlithology increased because the harder lithology ofmedium rock. the lower height of immediate roofvn=70.509e33m,R2=0.9932,(9)where is m the mining thickness, m.lower mining had less effect on the stability of upperComplete staggcoal pillars and it will benefit preventing surfacese74.633e04035m,R2=0.9928(10)Synthesizing the effects of above five facsurface subsidence, a comprehensive expression can beThe value of subsidence became larger with a largerfollomining thickness in alignment and complete stagger. ItAlignment:increased faster after the mining thickness was greaterthan 3 m. Subsidence factor presenting upward q=-1.455x10+7.13x10 Ln(h)+3. 19xparabola was at the bottom when the mining thickness103(m-3.056)2+Eas 3m because rock fracture of above goaf could140×10-H,R2=0.939reach a certain height and stopped for the existing keyhen the area of strip mining was small, which Complete staggercaused the goaf unable to be filled fully. For this reason,the height of mining had less effect on the surfaceq=1.825×102+h2504+3474×103(msubsidence. However. the subsidence coefficient29304)2+E211+e3190b-1.48×10H,decreased when the mining thickness was more than3 m (such as 4 m and 5 m)3.2 Law of surface hori罗 placement with3.1.5 Effects of interlayer lithology on surfacemulti-coal seam strigsubsidenceTaking the strike as an example, the functionalns between individual factors with theRelationship between the maximum groundsubsidence and interlayer lithology was obtaineregression analysis according to simulation datalength of paper, but the comprehensiveexpressions were given at lasAlignment:Wn=1122E3,R2=09932(11) 3.2./ Effects of mining depth on surface horizontaldisplacementn=1426.6E2,R2=0.9705The maximum horizontal displacement had anapproximately linear relation with the mining depth by中国煤化工J Chongqing Univ. Eng. Ed [IsSN 1671-8224, 2014, 13CNMHGet alMulti-coal seamregression results of simulation, which showed that the displacement caused by upper coal seam miningsurface displacement increased along with the adding overlaid the lower one, which decreased theof depth leading to the thickness of beam bending comprehensive movement after both coal seams wereThe maximum surface horizontal displacemenextent of upper and lower coal pillars; and vice versabecame larger with the stagger extent of upper and The simulation results showed that effects of staggerlower coal pillars increasing at the constant depth. It extent on the maximum displacement could beincreased faster when the stress of coal pillars and roof neglected until the interlayer spacing reaching a certainincreased leading to a larger curvature of the roof of thedistancelower coal seam3. 2. 4 Effects of mining thickness on surface horizontal3.2.2 Efects of mining width on surface horizontaldisplacementdisplacementThe relation between mining width and surface mining thickness adding when alignment and completehorizontal displacement was exponential and the stagger. The increment became lager after miningdisplacement increased with the increase of width in thickness greater than 3m and the mining thickness isthe upper and lower coal pillars alexponential relation with the maximum horizontalcomplete stagger, as shown from the regression displacement. When the mining thickness is small, theanalysis, Because the curvature of the roof increasing effects of mining cant transfer to surface for thealong with the augmenting of mining width causeexisting of key stratum. However, the rock fractureground subsidence.height become large while mining thickness increasing,Under the condition of the same width, the which will destroy the stability of pillarsmaximum surface displacement became large displacement becomes enhancement quicklylower coal pillars which caused the stress of lower re3.2.5 Effects of interlayer lithology on surfaceIcreased and its bending value enlarged too. Therefoheextent on settlement on account of longer roof exposureThe maximum horizontal displacement was a linearrelation of interlayer lithology. The value of3.2.3 Effects of distance between up and down coal displacement decreased with the lithology increasinseams on surface horizontal displacementbut the variation is a little away from alignment toBecause the variable litholosGround horizontal displnt tended to increase concentrating in the interlayer rock strata, the loweralong with the augmenting of the distance between up coal mining did not affect the stability of upper coalaccording to regression functions of different interlayerSynthesizing the effects of above five factors onspacing. However, when the upper and lower coal surface subsidence, a comprehensive expression can bepillars completely stagger, the law of surface horizontal as followsdisplacement was opposite because the horizontal Alignment中国煤化工J Chongqing Univ. Eng. Ed [IsSN 1671-8224, 2014, 13CNMHGL.Y. Zhang, et al.b=-3.1×102-5053×1031n(h)+[2] Hai L, Liang B. A method for determining the overal1.9773×10(m-2.1346)2+1.577×10-In(E)+safety factor of stripe mining [J]. China Safety Science387×10(B-22.1429)2+2.167×102ln(H)Journal, 2010, 20(10): 41-46.(In ChineseR2=0.900海龙梁冰煤层条带开采整体安全系数确定方法研究[中国安全科学学报,2010.20(10):41-46Complete stagger[3 Zou YF, Deng KZ, Ma WM. Mining subsideb=3.25×102+h30010+2.113×103(m-26818)2+engineering [M]. Xuzhou: China University of Miningtechnology Press, 2003: 173-180. (In Chinese157×102ln(E)+4.153×103(B-23.333邹友峰,邓喀中,马伟民.矿山开采沉陷工程[M]徐州:202×102ln(H),R2=0.885(16)中国矿业大学出版社,2003:73-180[4] Guo WB. Research on the non- linear theoretical model4 Conclusionsand application with strip mining [D]. Xuzhou: ChinaUniversity of Mining Technology Press, 2004.(Indisplacement hold an exponential relation with the郭文兵条带开采的非线性理论模型与应用研究⑩D]mining thickness. The value of subsidence and徐州:中国矿业大学,2004displacement becomes large with mining thickness[5] Zhang YB, Zou YF, LI DH, et al. Instabilityincreased. However. the relations between subsidencecharacteristics of strip mining system under dynamicloading []. Journal of China University of Minimare a quadratic polynomial function; when miningTechnology, 2013, 42(4): 567-572(In Chinese)thickness is 3 m. the values of them reach at the bottom张彦宾,邹友峰李德海,等动力扰动作用下条带开采2) The relationships between surface subsidence,系统失稳特性研究[J中国矿业大学学报,201342(4)horizontal displacement and interlayer lithology areexponential and linear respectively. The values of[6 Guo lQ, Cai QP, Peng XQ. Effect of strength criterionsubsidence and displacement become larger with theon design of strip coal pillar [J]. Rock and Soillitholodecreased. However. theMechanics, 2014, 35(3): 777-782(In Chinese)horizontal displacement is a little away from alignment郭力群,蔡奇鹏,彭兴黔.条带煤柱设计的强度准则效to complete stagger应研究[J岩土力学,201435(3:777-7823)The function relations between surface subsidence[7 An TL. Study on the laws of surface movement andand displacement with the five factors in alignment anddeformation by coal seam strip mining [D]. Tangshancomplete stagger state were givenHebei United University, 2013. (In Chinese)安铁梁煤层条带开采对地表变形规律的研究[D]唐References山:河北联合大学,2013[8] Chen SJ, Fan HD, Tan ZX, et al. Analysis on predicted[1] Guo LQ, Peng XQ, Cai QP. Design of strip coal pillarbased on the unified strength theory [J]. Journal ofunderground mine strip mining in multi Seams [JIChina Coal Society, 2013, 38(9): 1563-1567.(IrCoal Engineering, 2010, 12: 63-67. (In Chinese)陈绍杰,范洪冬,谭志祥,等多煤层条带开采地表移动郭力群彭兴黔,蔡奇鹏.基于统一强度理论的条带煤预测参数分析山J煤炭工程,2010,1263-67柱设计煤炭学报,2013,38(9):1563-1567[9] Chen SJ, Zhou H, Guo WJ, et al. Study on long-term中国煤化工J Chongqing Univ. Eng. Ed [IsSN 1671-8224, 2014, 13THCNMHGMulti-coal seamstress and deformation characteristics of strip pillar [J]principle of FLAC [M]. Beijing: China CommunicationsJournal of Mining safety Engineering, 2012, 29(3)Press, 2005: 339-522(In Chinese)376-380. (In Chinese刘波韩彦辉FLAC原理、实例与应用指南M]北京:陈绍杰,周辉,郭惟嘉,等条带煤柱长期受力变形特征人民交通出版社,2005:339-522研究[采矿与安全工程学报,2012,29(3):376-380[13] Florkowska L. Numerical modelling for underground[10] Liu Gang. Static and dynamic stability of coal pillars inmining related geotechnical issues [J]. Studiastrip mining [D]. Xi'an: Xi'an University of ScienceGeotechnica et Mechanica, 2013, 35(3): 578-588and Technology, 2011.(In Chinese[14] Trueman R, Castro R, Halim A. Study of multiple刘刚条带开采煤柱静动态稳定性研究[D].西安:西安draw-zone interaction in block caving mines means of科技大学,2011a large 3D physical model [J]. Internal Journal of Rock[11] Wang CQ, Gao LQ, Chen SJ, et al. Field research onMechanics and Mining Sciences, 2008, 45: 1044-105long-term bearing capacity of strip pillar [J] Journal of [15] Caudron M, Hor B, Emeriault F. A large 3D physicalMining Safety Engineering, 2013, 30(2): 799-804model: a tool to investigate the consequences of groundmovements on the surface structures [C]. In王春秋高立群,陈绍杰,等条带煤柱长期承载能力实marguerite D. et al. editors. 14th International测研究采矿与安全工程学报,2013,30(2):799804Conference on Experimental Mechanics(ICEM 2010)[12] Liu B, Han YH. The guide of application, example andFrance: EDP Sciences. 2010: 22001. P 1-8中国煤化工J Chongqing Univ. Eng. Ed [IsSN 1671-8224, 2014, 13CNMHG