Comprehensive evaluation of water-inrush risk from coal floors

Availableonlineatwww.sciencedirect.comSciencedirectMININGSCIENCE ANDTECHNOLOGYELSEVIERMining Science and Technology 20(2010)0121-0125www.elsevier.com/locate/jcumtComprehensive evaluation of water-inrush risk from coal floorsWEI Jiuchuan", LI Zhongjian, SHI Longqing, GUAN Yuanzhang, YIN HuiyongCollege of Geology Science and Engineering, Shandong University of Science and Technology, Qingdao 266510, ChinaYanzhou Mining Co, Ltd, Jining 272100, chinaAbstract: Lower groups of coal seams are presently being mined in the Yanzhou coal mining area. We need to evaluate the riskfrom water-inrush from coal floors in order to have safe production in the lower groups of coal seams in mines. Based on a system-atic collection of hydrogeological data and some data from mined working faces in these lower groups, we evaluated the factorsaffecting water- inrush from coal floors of the area by a method of dimensionless analysis. We obtained the order of the factors af-fecting water- inrush from coal floors and recalculated data on depths of destroyed floors by multiple linear regression analysis andobtained new empirical formulas. We also analyzed the water-inrush coefficient of mined working faces of the lower groups of coalseams and improved the evaluation standard of the water-inrush coefficient method. Finally, we made a comprehensive evaluationof water-inrush risks from coal floors by using the water-inrush coefficient method and a fuzzy clustering method. The evaluationresults provide a solid foundation for preventing and controlling the damage caused by water of an Ordovician limestone aquifer inthe lower group of coal seams in the mines of Yanzhou. It provides also important guidelines for lower groups of coal seams inother coal mineKeywords: water-inrush from floors; fuzzy clustering: factors affecting water-inrush from coal floors; lower groups of coal seams;dimensionless analysis1 Introductionwords, it could eliminate the impact of the dimen-sions of the raw data- lo. We also introduce a fuzzyThe evaluation of water-inrush from coal floors is a clustering method to address the problem of limita-complex problem, related to many factors such as tions in the evaluation of water-inrush from coalhydrogeology, engineergeology, mining condi- floors by the water-inrush coefficient method. Fuzzytions and rock mechanics. So far, many theories and clustering is a multivariate cluster method, whichmethods have been proposed to evaluate water-inrush classifies many factors according to certain criteria llfrom coal floors, such as the water-inrush coefficient It is a simple but efficient method in the evaluation ofmethod, the Down Three Zones Theory, a Four-Zone water-inrush risks from coal floors. The evaluationTheory, a Neural Network Method, a Multi-source results can provide a solid foundation for preventingInformation Fusion Method and a Vulnerable Index and controlling the damage caused by water from theMethod2-7. At present, shallow lower groups of coal Ordovician limestone aquifer at the lower groups ofeams are being mined and deep exploration is in pro- coal seam mining in the Yanzhou coal mining area. Itgress. We have to evaluate the water-inrush risk from should also provide important guidelines for lowercoal floors in order to have security of production in level groups of coal seam mining in coal mining dis-the lower groups of coal seam mining.tncsTo rank the order of the factors affecting wa-ter-inrush from coal floors is a difficult problem. We 2 General hydrogeological situation ofintroduce a dimensionless analytical method to solveminIng areathis problem. Dimensionless analysis eliminates thempact of dimensions, making this evaluation indexThe Yanzhou coal mining area, a semi circle syncomparative, additive and subtractive. It converts raw clinal basin, is located in Yanzhou city and consists ofdata into new data by a particular calculation. In other seven coal mines, including the Nantun, in-glongzhuang and Baodian mines. The Tangcun mineReceived 12 May 2009: accepted 13 August 2009closed中国煤化工 o the Carbonifer.Corresponding author. Tel: 86 13789879299CNMHude, from topE-mailaddressjcwee(126.comiferous permiandoi:10.lo16s6745264(09)60172-1and Ordovician layers. The major coal seams are theMining Science and TechnologyVol 20 No. 12nd and the 3din the higher group of coal method and drew the isoline map foor the water-inrushseams, as well as the 6h, 16 h and 17 th seams in the coefficient of the 1]th coal seam to the depth of ulower group of coal seamsOrdovician limestone, We also evaluated the risk ofThe east of Yanzhou coal mining area is cut by the water-inrush from coal floors by dividing the areaYishan fault and the south, east, north of the area are into four parts. Our standard of evaluation was: a safebordering coal seam outcrops As well, its peripheries zone where Ts<0.06 MPa; a limited danger zoneare bordering the Zouxi and Caowa water sources of where: 0.06 MPa0. 15 MPa. This last area, i.e, theis an abundance of water in the shallow Ordovician extreme danger zone where Ts>0.15 MPa, was pro-limestone and Quaternary sandstone aquifers. The jected on each isoline map of factors affecting wa-amount of water in other aquifers is not very large. In ter-inrush from coal floors. In this way, we obtainedthis mining area, most hydrological types are moder- maps with the proportion of each zone on isolineately complex, while they are simple in the Beisu maps of factors affecting water-inrush from coalmine and complicated in the Yangcun coal mine.floors(Fig. 1). We calculated each factor affectingwater-inrush from coal floors on the maps with the3 Evaluation of factors affecting water. following formulainrush from coal floorsUKUp till now, there have been many theories andmethods concerning the evaluation of water-inrush where U is the factor affecting water-inrush from coalfrom coal floors, but none of these have proposed anfloors, K, the weight assigned to each factor and S; theevaluation of the order in which the factors affect area of extreme danger zonewater-inrush from coal floors We trust our dimen. area dHead pressure=0.2*138158.7+03*3443179sionless analysis will solve this problem.+04*12645485+0.5*333893853.1 Standardization process of hydrogeological+0.6*36428599+0.7*41784488data+0.8*6561577+0.9*13793440The various dimensions of factors affecting wa-+1*22880175=47969221(m2)ter-inrush from coal floors are inconvenient forWe also obtained the factor affecting the thicknessevaluation, so we need to standardize the data. There of the aquifuge, i.e., Aquifuge thickness =30612286, Ugre many methods for standardization and we have logical structure=30092157 and Water abundance =23612721standardized the data in the range from-1 to 1 by the (Table 1). We see that Head pressure Aquifuge thicknessusual method of standard deviationsThe principle of the standard deviation method isWe easily obtained the order of the factors affecstandardize the data as followsg water-inrush from coal floors in the Yanzhou areafrom our evaluation. Therefore, the scene is domio nated by the head pressure of the Ordovician limestone aquifer.where x, are the measured values, I, the samplemean and S, the sample standard deviation3.2 Evaluation of factors affecting water-inrushfrom coal floorsWe made sure major factors affecting water-inrushfrom coal floors were based on systematic collection3926000of hydrogeological data and data from mined workingfaces in the lower group of coal seams of the Yanzhoucoal mining area. The factors were: head pressure ofthe Ordovician limestone aquifer, aquifuge thickness(distances between the 17 coal seam and the Ordo-vician limestone), the geological structure and theamount of water of the Ordovician limestone aquifery means of Eq (1), we drew isoline maps from中国煤化工the data of the factors affecting water-inrush fromcoal flooCNMHO48009200We calculated the water-inrush coefficient (Ts)ofFig. 1 Proportion of very dangerous zones on isoline mapthe coal mining area by the water-inrush coefficientf head pressure of Ordovician limestone aquiferWEI Jiuchuan et alComprehensive evaluation of water-innfrom coal floorsTable 1 Classification areaszone. We increased the safety limit to 0.08 MPa/mgiven a normal distribution of the data. Thus, the wa-ter-inrush coefficient evaluation standards have be-936761760come:safe zone: Ts<0.08 MPa/m; limited danger0.213815870zone: 0.06 MPa/m 0.15 MPa/m053338938.53648540514399104.16425528.23.2.2 Evaluation by water-inrush coefficient methodWe used data from the 17 coal seam of the re364285993899596.1805334442134133417844885298836.65004821.80earch area. In general, this seam has been more se-riously affected by the Ordovician limestone aquifer65615771646055194166987.80towards the east than towards the west. The highest137934405853540206405280head pressure of the Ordovician limestone aquifer2288901750was near the Bu45 drilling hole in the Dongtan coalmine and reached 8.8 MPa. It was low in the south4 Evaluation of water-inrush risk from The mining depth of the I7coal seam ranged fromOrdovician limestone aquifervertical distance between the 17 h coal seam and the1 Depth of destroyed floor formulaOrdovician limestone ranged from 25.59 to 102.29 mwith an average distance of 62.61 m. We evaluatedStatistical data from national field surveys pro- data from 63 drilling holes of coal mines in the re-vided us with the following empirical formulas, in search area by the water- inrush coefficient methodcommon use, for depths of destroyed floors:Table 2 shows the evaluation results for the baodianh1=0.7007+0.1079ycoal mineh=0.0085H4+0.1665a+0.10794.3579(4Table 2 Evaluation results by water-inrush coefficientmethod( Baodian coal mine)where h, is depth of destroyed floor, m: Ly the slant-Safe drilling zoneLimited danger zoneng length of the working face, m; H the mining depth,m and a the coal seam angle,Because the mining depth, ranging from 100 to1000 m in these empirical formulas was too wide, wereclassified the statistical data with a multiple linearregression model. Thus, we obtained the followingL14-1new formulas:九1=0.003H+0.1948a+0.8775T3.3 Evaluation by fuzzy clustering method+0.l116L-49066when H>650 mMany factors in the evaluation of water-inrush riskfrom coal floors should be considered. This is a com-内2=00153H+0.3774a+3.34027plex problem, which cannot be solved by the wa+0.0028L+67207(6) ter- inrush coefficient method. But a fuzzy clusteringIn Eqs. (5)and(6)T is the thickness of the coal method can consider many factors simultaneously,which solves the problem that the critical value in theThe new formulas were applied in calculating theevaluation by the water-inrush coefficient methodwater-inrush coefficient of each coal minecannot do1)Data standardization3.2 Evaluation by water-inrush coefficient methodThere are a number of methods to standardize3.2.1 Modified limit of water-inrush coefficientdata, two of which are the standard deviation methodBased on the collection of hydrogeological data of and the other the range method. We used the firstthe Yanzhou coal mining area, we calculated the wmethodter-inrush coefficient of the 16th and 1]th coal seams2)Calibrationin mined working faces and found out that the wa-With calibrationbtain the similarity coeffiter-inrush coefficients ranged from 0.30 MPa/m to clents中国煤化工 ects in order to0.90 MPa/m. Because no accidents have ever oc-curred at these mined working faces, we could not of metCNMH Gere are a numberevaluate the water-inrush risk exactly according to thelung uie simularity coefficientsevaluation standard. ie. Ts<0.06 MPa/m for the safe ('ri), such as the similarity coefficient method, theMining Science and Technologyangle cosine method and the maximum-minimum now. The Xinglongzhuang and Dongtan coal minesmethod. We used the similarity coefficient method are essentially in the danger zone or the extreme danwhich uses the following formulager zone. We need to pay close attention in order toprevent damage or control it if it does occur, caused∑{x-x不-对by water-inrush from coal floors in the lower group(-元)1(x-x7 few danger zones, it is considered a safe mine be.cause the head pressure of the Ordovician limestoneaquifer is low and its geological structure simple. Wefa'i=lfx, m is the count of think the results are reasonable because the drillingyeach column, and i the order of dataTable 4 Evaluation results of water-inrush risk from1)Fuzzy clusteringOrdovician limestone aquifer(safe zone)Transitive closure (rR D is obtained by the squareSafe zone drilling zonesAffiliationmethod from the similarity matrix(R). Because clus-02-102-202-3.024025.02-602-7,ter analysis results are usually wrong when obtainedNantun Coal MineDing129, Ding 1 18from the similarity matrix, we need to convert thesimilar matrix into an equivalent matrix. The transi15Bao3202102202-3L141,L104Baodian Coal Minetive closure is the equivalent matrixD71, 192, Ding87, ShuilBeisu Coal Mine2)Drawing a dynamic clustering figure from thequivalent matrix(r(R))o-1,YS0L.03.05,YS02Yangcun Coal MineAfter completing these steps, we evaluated thefactors affecting water-inrush from coal floors( in thisase from the I7 coal seam), i. e, the distances be- 4 Conclusionstween the 17 h coal seam and the Ordovician lime-stone and the head pressure of the Ordovician lime-1)We evaluated the factors affecting water-inrushalso e aquifer. Table 3 shows the evaluation results,from coal floors in the lower group of coal sealso for the Baodian coal minemines of the Yanzhou coal mining area by dimen-ionless analysis. We obtained the following order ofTable 3 Evaluation results by fuzzy clustering methodBaodian coal minethe factors affecting water-inrush from coal floorsi.e.: head pressure of Ordovician limestone aqui-Limited danger zone drillingsferaquifuge thickness>geological structure>amountof water of Ordovician limestone aquifer. The head15Baoshuilpressure of the Ordovician limestone aquifer is domiBao32nanto212)We recalculated the statistical data of depth of023estroyed floors by using multiple linear regressionanalysis and obtained new empirical formulas. Theseprovided a solid foundation for the evaluation of wa-02-2ter-inrush risk from coal floors. We also analyzed thewater-inrush coefficient of mined working faces ofthe lower group of coal seams and improved the3.4 Comprehensive evaluation of water-inrush evaluation standard of the water-inrush coefficientrisk from Ordovician limestone aquifermethodWe know that the head pressure of the Ordovician 3)Our comprehensive evaluation of the risk oflimestone aquifer is dominant among the factors af. water-inrush from coal floors by the water-inrushfecting water-inrush from coal floors. We made a coefficient and fuzzy clustering methods, improvedof the water-inrush coefficient the objectivity and accuracy of the evaluation of wa-evaluation results and from the fuzzy clustering ter-inrush risk. These evaluation results provide avaluation results. Finally, we obtained the evaluationsolid foundation for preventing and controlling theresults of water-inrush risk from the Ordovician lime- damage caused by the water from the Ordovicianstone aquifer(Table 4), again for the Baodian coal limesin the lower groups of coal seamsmine. The results show that the Nantun , Beisu and中国煤化工 uld also provideYangcun coal mines are basically in the safe zone, not mpgCNMHGatuon of the lowerin the danger zone nor in the extreme danger zone. So, grothere is no risk of water-inrush in these three minesnone of which had any water-inrush accidents untilWEI Jiuchuan et alComprehensive evaluation of water-inrush risk from coal floors[4] Shi L Q, Han J. Theory and practice of dividinning areaAcknowledgementsUniversity of Mining &Technology,(nWe gratefully acknowledged thesupports from the[5] Liao w, Zhou Y, Li s Q. Study on theatural Science Foundation of Shandong Provincewavelet neural network, China Safery Science(No. Y2007F46), the Doctor Disciplines Special Sci2006,l6(l):24-28.( in Chinese)entific Research Foundation of Ministry of Education [6] Zhang X B, Cheng L, Li L. Multi-sources(No. 20070424005), China Coal Industry AssociationinrushScience and Technology Research Instructive PlanScience of Surveying and Mapping, 2006(6)x( No. MTKJ2009-290) and the National Natural Science Foundation of China(No.50539080)[7] Wu Q, Zhang Z L, Zhang SY. A new practical methodo-logy of the coal floor water brd. Journal of China Coal SocieryReferences2007,32(ll):1121-1126. (n ChinesT, Zhang wQ, LiJ X An evaluation of the safetyof cor,2000,25(3):278-282.( In Chinese)Evaluation. Beijing: Publishing House of ElectronicsIndustry, 2003. (In Chinese)[2] Wei J C, Li B Y. Security evaluation of coal mining[10] Liu YY, Wang X D, Zai J M. Dimensionless analysis foruifers. Coal Geology explorationnonlinear behavior of single pile in heterogeneous soil.20004):57-59Building Science, 2009, 25(1): 48-51[3]Li B Y "Down three zones"in the prediction of the water [11] Cao B Y. Application of Fuzzy Mathematics and Systemsand applicatio. Journal of Shandong Institute of Miningand Technology, 1999, 18 (4): 11-18. (In Chinese中国煤化工CNMHG