Analysis on distribution law of the abutment pressure of the integrated coal beside the road-in pack

Analysis on distribution law of the abutment pressure ofthe integrated coal beside the road- in packing forgob-side entry retaining in fully-mechanizedcaving faceZhu Chuanqu, Liu Ze, Wang Weijun, Zhang Daobing(1. School of Energy and Safety Engineering, Hunan University of Science and TechnologyXiangtan, Hunan 411201, China; 2. School of Building, Central South University, Changsha 410075, ChinaAbstract: The three- dimensional damage constitutive relationship of coal is established and distribution law of the abutment pressure of the integrated coal beside the road-in packing for gob-side entry retaining in fully-mechanized cavingface under the effect of given deformation of the main roof is analyzed by the damage mechanics theory. And the rela-ionship between distribution of the abutment pressure and thickness of coal seam is explored. The presented result is ofgreat theoretical significance and practical value to the study on stability control of the surrounding rock of road-in pack-ing for gob-side entry retaining in fully-mechanized caving faceKey words: road-in packing for gob-side entry retaining in fully-mechanized caving face; integrated coal besideadway; abutment pressure; damage mechanicsIntroductionstate between the two formers. Because loose mediumaccounts for little of the whole study the continuousThe abutment pressure before fully-mechanized medium damage mechanics can be used to study thecaving face is one of the main factors which affect the distribution law of abutment pressure of the integrateddeformation of road-in packing for gob-side entry retai- coal beside the road-in packing for gob-side entry retai-ning in fully-mechanized caving face, its size andning in fully-mechanized caving face[2)tribution law have an immediate effect on the deforma-tion and damage of the roadway. In mining process2 Three-dimensional damage constitutivethere is a high abutment pressure acting on the inte-relationship of coalted coal beside the roadway, which includes adyCoal is a kind of natural material that it has beencing abutment pressure led by this working face and going through a long geological process; inevitablyside abutment pressure led by the side working face there are many cracks and pores of various sizes andwhere mining had finished". Because of high abut- shapes. Due to the extremely inhomogeneous innerment pressure, it is more difficult for the road-in pack- structure, there are a variety of faults in the surrounding for gob-side entry retaining in fully-mechanized ca- ing rock of road-in packing for gob-side entry retainingving face to be maintained than general roadway to be in fully-mechanized caving face, that is to say,theredone. So, it is necessary to study the distribution law are many weak points of different strength in the sur-of abutment pressure of integrated coal wall to a deerthe strength of the micro-units inextent and uncover the relationship between the quality coal is different. Considering the damage of coal inof overlying strata and the deformation of surrounding loading pressure process is continuous, and if therock, which has important guiding effect to the study strength of micro-units accords with Weibull distribuon stability control of surrounding rock in this kind of tion(3], the damage probability can be calculated byroadwayEq,(1)In the process of deforming and being damagedurrounding rock is neither continuum nor pure loosemedium but equivalently continuous medium which is aWhe中国煤化工 ogical parameteCNMHGRoccined 14 November 2008Vol 7 No 3, Sept. 2009 23of Weibull distribution respectively s is strain of thecoal micro-unit; (e)is damage probability when theWhere, is a train when the micro-unit is crackedstrain 18 8.under the uniaxial stress, it also is the strain 8 inAccording to the damage mechanics of continualmedium, damage parameter D can be defined as theatio of the area which is damaged to the undamagedAccording to three-dimensional linear elasticD= S/SpP(x)dxtropic damage constitutive equation, if u =0. 25p[-(s/s0)e& 0)oily, the relationship between axial stress andaxial strain wasWhere, S is the area which is damaged; So is wholearea before the material is damaged0=203+E(1-D)eTaking a micro-unit out from the coal in front ofFrom Eq(2), Eq(8)and Eq(9), the dam-the working face, its stress state can be shown as age constitutive relationship betweenstress andFig 1. And the stress state can be simplified, given axial strain under three-dimensionaltionthe stresses accord with linear elastic generalized can be depicted asHook’slawEElexp(10)3 Distribution of abutment pressure underthe effect of given deformation of theFig 1 Micro-unit of coalabutment pressure is the result of overlying stratamoving,and it has direct relationship with the confiσ1=(61+a2+a)+Eration and movement law of overlying strataAccording to the analSIs on surro02=A(61+62+6,)+EB (3) movement law of road-in packing for gob-side entry retaining in fully-mechanized caving face, and setting theσ;=1(61+B2+63)+163key strata over roadway as focus, mechanics model ofWhere,a,, 02, 0, are three main stresses of the mi. key rock mass of road-in packing for gob-side entrytainingin fully-mechanized caving face can be estabcro-unit respectively; 61, 62, 6, are its three main lished, which is shown as Fig.2strains respectively; E is its elastic modulus; u is itsPoisson ratio and is a constantIn order to simplify the calculation process, theKey biock ePoisson ratio is given a value, u =0. 25, thenq. (4 )can be gottenWhen the micro-unit is being damaged, its stres-ses accord with Misses yield criterion (51, that is(σ1-a2)2+(2-o3)2+(3-01)2=2o3(5)Fig 2 Mechanics model of key rock massWhere, oo is uniaxial compressive strength of theof road- in packing for gob-side entryretaining in fully-mechanized caving facemicro-unit, When 2=o3, Eq (5)can be simplified as fol-In the model thebody, and inevitably it fractures, rotates and sinks, e-03ventuoof and top coal inFrom Eq (4)and Eq(6), Eg (7)canbe gotten the fYH中国煤化工ng a unt out fromtheCNMHG, at the beginning(7) there is only initial stress acting on the unit. With the24 Engineering Sciencesunt entersancling ment under the advancing abutment pressure; a1, b,abutment pressure area, and the stress ( axial stressare undetermined constantsg)increases gradually, loading displacement andIf the thickness of immediate roof and coal is hstrain &, gradually increase too; when &, increasethe strain under advancing abutment pressure iscertain value, axial stress would increase to its ultimateEt=21h(12)strength. With mining continues, e, increases contiIn stress-state of virgin rock the confining pressureously, the unit comes into a plastic state, its carrying of coal is o,. When the working face advancing, thecapacity keeps decreasing until it has been fracturede areatment pressure acts onTherefore, the distribution law of abutment pressure in damaged at different degrees, the confining pressurefront of the working face corresponds with a whole load- goes down and it is 0 at coal wall. So, the distributiing process a sample rock is pressed on a rock test ma- of confining pressure in the region from coal wall tochine. Distribution law of side abutment pressure is where the coal is in stress-state of virgin rock is in ex-approximately the sameonential form, which isAccording to the deation of main roof in front of the working face has thea;=exp[Gr- dI(13)character of power function, and it can be depicted as: Where, d is the extent of the region influenced by thez1=a1x1+c1(11) advancing abutment pressursetting the start point of a certain abBased on the above equations, from Eq(10)toment pressure as an origin, x is the distance of a cer- Eq (13), the advancing abutment pressure isy,21al displsex2E(14)The integrated coal beside the road-in packing forz2=a2(y+D)+c215)gob-side entry retaining in fully-mechanized cavingWhere, y is the distance of a certain point alongface is influenced not only by advancing abutment pres- coal tendency: l is the distance from working face tosure but also by goaf-side abutment pressure. There the position where main roof is broken in the integratedare many factors affecting the side abutment pressure, coal; a2, b2, C2 are undetermined constantsone very important factor of them is the position whereain roof is broken. The hypothesis can be the vertical pressure the equation used to calculate side abutmentdisplacement under the effect of side abutment pressure pressure can be gottencould be calculated by Eq. (15)(y+D)(y=d)203expl11)+E(2(y+2+explC2-(16)Boof theThe thicknesses of its coal seam and immediatecoal beside the road-in packing for gob-side entry retai- roof are 6.07 m and 2. 64 m respectively, the miningning in fully-mechanized caving face can be calculated depth is 330 m. The distance from working face to theby Eq(17).position where main roof is broken is 4 m. Primary(17) rock stress is tested as 0, = 7. 8 MPa, 03=2. 5 MPa4 Experimental calculation and analysisThe elastic modulus of coal is 5. 6 GPa, which is theTHng face S,6 of Changcun coalmine, coalLu'an mining district, is a fully-mechanized caving rannatitutive relationship are m =2face and the technology of road- in packing of gob-side Eo中国煤化工ters are a1=a2=entry retaining was adopted there. It can be used as an 0. OlCNMHG.2.example to analyze the distribution of the abutmentut the above data into the Eq (14), Eq. (16)pressure of integrated coald Eq.(17 ), and after calculation, the distributionVol. 7 No 3, Sept. 2009 25law of advancing abutment pressure of working face canbe shown as Fig 3 and the distribution law of abipressure of integrated coal beside roadway is shown asFig. 4430505-h8 m一h10m/=12m20304050Distance/mFig 5 Relationship between advancingabutment pressureof working face andthickness of coal seamfrom the tart ponFig 3ution law of advancing abutmentessure of working face15pressure and thickness of coalDurance alona tron! mimmediate roof get bigger, not onlyofFig 4 Distribution law of abutment pressurebutment pressure would increase but also the length ofof the integrated coal beside roadwayroadway influenced by abutment pressure would increase, but the area with high stress acting on wouldIt is shown in Fig 3 that the maximum of advan- away from the roadwaycing abutment pressure is 28 MPa and about 32 m in 5 Conclusionsfront of the working face. Due to the superposition ofessure. the maximum of adva1)High abutment pressure of integrated coalbutment pressure of the integrated coal beside roadway one of main factors influencing the stability of road-inis 36 MPa and about 6-8 m in front of the working packing for gob-side entry retaining in fully-mechaface, which can be seen in Fig. 4nized caving face. The damage mechanics theory wasThe relationships between advancing abutment used to analyze the distribution law of the abutmentpressure, side abutment pressure and thickness of coal pressure of the integrated coal in this paper, it providesseam are shown in Fig. 5 and Fig. 6.scientific base for the stability control of surroundingIt can be observed in Fig. 5 that with the thickness rock of moad-in packing for gob-side entry retaining inof immediate roof and coal seam increasing the maxi- fully-mechanized caving facemum of advancing abutment pressure goes away from2)The distribution of abutment pressure of inte-working face, its value increases. When h is 8 m, the grated coal beside the road-in packing for gob-sidemaximum is 30 MPa and the distance that the maxi- try retaining in fully-mechanized caving face is relativemum away from working face is 31 m; while h is to the thickness of immediate roof and coal seam.That12 m, the two parameters are 37 MPa and 37 mis to say, the thicker they are, the higher abutmespectively. In Fig. 6, when h is 8 m the maximum ofd affected by abutside abutment pressure of integrated coal is 10.5 MPa ment中国煤化工ay is more difficultand it is 4 m away from coal wall; when h is 12 m the to beCNMHgmaller the thickness11 MPa and 8is, the lower the abutment pressure, and the roadwayTherefore, when the whole thickness of coal seam and is easier to be maintainedReferences[4] Yu Shaowen, Feng Xiqiao. Damage Mechanics [M]. Beijing: TH[1] Wang Weijun, Feng Tao, Hou Choujun, et al. Analysis on the re-inghua University Press, 1997.lationship between stress distribution on integrated coal beside[5] Chen Zhonghui, Xie Heping, Ling Zhongming. Study on falling aroadway driving along next goaf and damage of surrounding rockbility of top coal during top coal caving by damage mechanics[J][J]. Chinese Joumal of Rock Mechanics Engineering, 2002, 21Chinese Joumal of Rock Mechanics Engineering, 2002, 21(8):(11):1590-151136-140.[2] Chen Zhonghui, Xie Heping. Damage mechanics analysis on the[6] Qian Minggao, Miao Xiexing, He Fulianstribution of abutment pressure around a coal face[J].Chineseeffect between supports in the workings and the rocks[ J].JoumalJoumal of Rock Mechanics Engineering, 2000, 19(4): 436439of China Coal Socicty, 1996, 21(1): 40-44[3] Tang Chunan. Catastrophe in Rock Unstable Failure [M].BeiAuthorZhu Chuanqu, male, born in Wangcheng, Hunan in 1962, received the BS degree from Hunan UniversityScience and Technology in 1984, the MS degree from Henan Polytechnic University in 1989 and the Ph. D degreefrom China University of Mining and Technology in 2004. Being engaged in teaching and scientific research in min-ing engineering, he has won a National Prize for Progress in Science and Technology and 4 Provincial Prize for Pro-gress in Science and Technology. Besides he has published 2 monographs and 60 articles in joumals. HereachedbyE-mailcqzhu@hnust.edu.cnFoundation item: Supported by the National Science Foundation of China(50874042, 50674046), National Sci-ence Important Foundation(50634050)and Hunan Science Foundation(06JJ50092中国煤化工CNMHG