A new technology for coal and gas control based on the in situ stress distribution and the roadway l

Intermational joumal of Mining Soience and Technology 22(2012)145-149Contents lists available at SciVerse Science Direct>sd International Journal of Mining Science and TechnologyELSEVIERjournathomepagewww.elsevier.com/lacatelijmstA new technology for coal and gas control based on the in situ stressdistribution and the roadway layoutYang Weia.b, Lin Baiquan. Zhai Cheng.b, Li Xianzhong ab, Sun Xin Zhang Chao. bFuculty of Safety Engineering ChiTechnology. Xuzhou 221116, Chinab state Key Laboratory of Coal Resources and Mine Safery. China University of Mining E Technoiogy. Xuzhou 221116. hinaYuxi Branch of Yunnan Provincial Tobacco Compamy. Yu 653100 ChinaARTICLE INFOABSTRACTAn auxiliary yas control technology is described that can reduce coal and gas outburst accidents whenhere is no existing protective coal seam and gas pre-draining is not effective. Numerical simulationReceived in revised fonm 22 July 2011methods were used to study the stress distribution ahead of the roadway face for different in situ stresAccepted 13 August 2011ses. The results from the simulation can then provide a new gas control technology. The results show thatAvailable online 19 March 2012a high stress concentration, high stresses, and high displacement gradients appear ahead of the roadwayce when the maximum in situ stress is aligned perpendicular to the roadway axis. The risk of gas outburst is higher when the stresses decrease rapidiydistance and when the release of more energyccurs immediately after driving the roadway. The gas outburst risk is much smaller when the in situress is aligned parallel to the roadway axis. During design of the coal mine most of the coal roadwaysCoal and gas outburstald be arranged to parallel the maximum in situ stress. This will decrease the outburst risk in generalStress direcionand may be considered a new gas outburst prevention methode 2012 Publ shed by Elsevier B V. on behalf of China University of Mining Technology1 Introduction[10-14 This paper provides insight into coal and gas outburst preention by a numerical simulation of how the in situ stress affectsCoal and gas outburst is a complex disaster that can be affected coal and gas outburst.by the in situ stress, the coal strength, and the gas pressure 11.21The State Administration of Coal Mine Safety has issued the princi- 2. Numerical simulationse of"The regional outburst prevention measures first, the localInburst prevention measures second"to reduceFLAcD. one of the most important numerical simulation agolining protective coal seams or regional gas pre-drainage are the rithms for use with rock mechanics, is widely used in mining engimain prevention technologies [3, 4l Gas pressure is a scalar value neering [15-18. Here we use it to simulate the stress distributionand will be equal in every direction but the stresses from the geolog. ahead of the roadway face given different in situ stresses. Theital structure are anisotropic. The maximum and minimum princi-pal stresses are typically along the horizontal direction and the parameter values assumed are shown in Table 1The model overall length, width, and height are all 40 m. Theintermediate principai stress is usually along the vertical direction roadway is driven along the y-direction and the roadway size is15-8). These stress differences in different directions generate dif- 4 m wide by 4 m high. The model geometry and boundaries arerent stress distributions around the roadway when it travels along shown in fig. 1different directions 9 The stress concentration ahead of the road-The in situ stress effect on gas outburst during the driving of ad by a propeof the roadway direc- roadway was studied by consitwo kinds of in sittion. Decreasing the gas outburst risk this way is appropriate states and four roadway driving cycles. The research plan followsespecially when there is no protective coal seam or the gas ptrainage results are non-existent or unsatisfactory. Stress distribu-tion and gas outburst prevention have been widely studied both at (1) The maximum principle stress is perpendicularhome and abroad but there has been little investigation into preway axis and the stresses in the x, y, and z directions are 20,venting the outburst by a proper layout of the roadway direction0.and 10 MPa, respectively. The stresses ahead of the road-way face were examined when the roadway had been drivenCorresponding author Tel: +86 516 83884401中国煤化工E-mailaddress:ywcumt@163.com(W.Yang2095-2686s- see front matter e 2012 Published by Elsevier BV. on behalf of China UniversityCNMHGdoi:10.1016/jmst201108002W. Yang et aL/intemational Joumal of Mining Science an8 MPa within 1 to 3 m in front of the roadway face. This causesParameter values used in the modela very asymmetric three dimensional stress field. These asymmet-ric stresses will break the rock mass and cause great displacementBulk modulus(GPa)Ni along the roadway axis as shown in Fig 4[20the roadway axis the rock mass 3 m in front of the roadway facemoves significantly along the roadway axis. The maximum dis-1300placement is about 11 cm at the roadway face and the displace-ment gradient is about 4 cm/m. The stress concentration peaksabout 3 m in front of the roadway face. The inner rock mass moves(2)The maximum principle stress is parallel to the roadwayalong the roadway axisand the stresses in the x, y, and z directions are now 10When the maximum stress is parallel to the roadway axis, theand 10 MPa, respectively. The stresses ahead of the roadway stress ahead of the roadway face decreases and there is almostface were examined for driving cycles of 1, 2, 3, or 4m.no stress concentration the rock mass within 10 m in front ofthe roadway face moves gradually along the roadway axis and3. Stresses and displacements around the roadway for different the maximum displacement is about 0. 10 m at the roadway facein situ stressThe displacement gradient is about 2 cm/m within the 3 m aheadThe stress redistributes around a driven roadway so that stressThis analysis shows that when the three dimensional stresses areon the gas outburst and roadway support 119). The stress distribu- the roadway direction has a significant effect on the stress and dis-tions around the roadway for a maximum stress perpendicular orparallel to the roadway are shown in Fig. 2.to the roadway axis the great stress concentration, and displacementFig2 shows that there are great stress concentrations ahead of gradient, will cause an extremely unbalanced force that stores muchthe roadway face when the maximum stress is perpendicular tohidden elastic energy. This energy will induce an outburst. when thethe roadway axis. When the maximum stress is parallel to thenaximum stress lies along the roadway axis the stress and displace-roadway axis there are almost no stress concentrations ahead of ment in front of the roadway face change gradually and there is nothe roadway face. In this case there are only slight stress concen- stress concentration so the outburst risk is smaller, tootrations around the roadway wall. Most coal and gas outburst hap-pens in front of the roadway face so the stress distribution ahead of 4. Effect of roadway driving cycle distancethe roadway face greatly affects it. fig 3 shows the three dimen-sional stress distributions ahead of the roadway face.Roadway driving speed is one of the most important factorsWhen the maximum principle stress is perpendicular to the affecting coal and gas outburst. Different in situ stresses will gen-roadway axis, Fig 3a, the stress concentrations in the x-and z-directions appears 3 m ahead of the roadway face. The stress peaks cause different stress evolutions in front of the roadway face.Theseare 28 and 14 MPa, respectively: Note there is nearly no stress con- stresses evolve immediately after the roadway is driven. Fig. 5centration in the y-direction. When the maximum principle stress shows the stress evolution in front of the roadway face for drivingis parallel to the roadway axis, Fig. 3b, there are almost no stresscle distances of 1, 2, 3, and 4 m. The number of simulation stepsconcentrations in each direction ahead of the roadway face. The is 1500, 2000, 2500, and 3000 for these cases, respectively.Thestress in the y-direction is smaller than the stresses in the x- and maximum stress is oriented either perpendicular or parallel toZ-directions. The stresses gradually approach the original, undis- the roadway axisFig 5 shows that immediately after the roadway has been driWhen the maximum principle stress is perpendicular to the ven the three dimensional stresses decrease much faster for theroadway axis. Fig. 3a, the x-stress rapidly increases from 5 to case where the maximum principle stress is perpendicular to theroadway axis. This rapid stress drop will release much more elasticenergy, which may easily result in an outburst [21, 22 Fig. 3ashows that when the maximum stress is perpendicular to the road-way axis the stresses increase within 3 m ahead of the roadwayface. The stress concentration peaks about 3 m ahead of the road-way face so the stresses drop more as the driving distance in-creases. The stress drops the most quickly when the roadwaydriving distance is 3 m The stresses beyond the point 3 m in frontof the roadway face gradually decrease to the initial value. thestresses 4 m ahead of the roadway face are smaller than the stres-ses 3 m in front of the roadway face so the stress drop is lowerwhen the driving cycle footage is 4 m compared to 3 m. Whenhe maximum stress is parallel to the roadway axis there are nostress concentrations in front of the roadway face. The threedimensional stresses gradually increase toward the initial stateso the stress drop greatly increases with increased driving length.中国煤化工CNMHGRockyui y,,hen the difference in theFig. 1. Model geometrythree dimensional stresses exceeds one half of the shear fractureW. Yang er al/International Joumal of Mining Science and Technology 22(2012)145-149T-stessY-stress--stressFig. 2. Stress distribution around a roadway for different in situ stresses. (a) Maximum perpendicular to roadway: (b)Maximum parallel to roadway.Distance from heading face(m)Flg. 3. Three dimensional stress distributions ahead of a roadway face for different in situ stresse中国煤化工roadway:(b)Maximum stressparallel to the roarHCNMHGlimit cracks wil be generated in the rock mass and it expands(20). for the in situind the mining induced stresses. ImmediatelyThe stress on the rock mass in front of the roadway face is unbalanced after driving the roadway the newly exposed roadway face allows a148w. Yang et al/intemational Joumal of Mining Science and Technology Z2 (2012)145-149百012allel io tbe0062-10Distance from beading fac(mFig. 6. Lustration of the rock mass expanding in front of the roadway face.isplacement along the roadway axis forin situ stresses(b)20Simulaton stepFig. 5. Stress evolution for different roadway driving cyde distances for different in situ stress distributions ( a) Maximum stress perpendicular to the roadway: (b)Maximumnaximum unbalanced force to develop as shown in Fig. 6. The rock they need much more effort and are very complex. These consider-mass most easily expands and breaks[23, 241ations restrIcse technologies and they are not widely usedFig 3 shows that the stress perpendicular to the roadway axis isThe analysis shown above suggests that a layout of the roadwayhigher than the stress parallel to the roadway within 3 m before the might cause great stress concentrationf the roadway face.cadway face. This is true whether the maximum in situ principle On the other hand a different layour might cause little or no stressstress is perpendicular or parallel to the roadway axis Immediatconcentration. These two different arrangements would result inafter driving the roadway the stresses perpendicular to the roadway different outburst risk so using a reasonable arrangement of theaxis are nearly the same. However, the stress along the roadway axis roadways should reduce the outburst risk, in general. This appro-ops to O MPa. The difference in the three dimensional stress is priate arrangement of the roadways can be considered an auxiliaryequal to the stress perpendicular to the roadway axis so a coal and regional gas control method along with the technologies of mininggas outburst is mainly affected by stresses perpendicular to the a protective coal seam and regional gas drainageroadway axis. Immediately after driving the roadway the differenceAlthough ground stresses are generally different in differentin the three dimensional stresses reaches a maximum and the rock locations stresses across a single geological bed at the sameis mostly broken and expanded the rock should expand towards the depth can usually be regarded as the same 16]. Thus, beforeroadway axis. This expansion should reduce the strengthof the rock designing the coal mine the in situ stress distribution shouldand release much gas. At the same time many more cracks in the be determined first. The direction of the maximum stress needsrock are generated to create much more bearing surface. When to be determined. The roadway should then be arranged in parthe residual strength of the rock mass can no longer resist the resid- allel with the maximum stress vector. This will decrease theual gas pressure an outburst should happenstress concentration ahead of the roadway face and then alsoWhen the maximum stress is parallel to the roadway axis al- reduce the outburst risk.most no stress concentration appears ahead of the roadway face.On the other hand, great stress concentration appears ahead of 6Conclusionsthe roadway face for a maximum stress that is perpendicular tothe roadway axis. Hence, the outburst risk is higher when the ma(1)The in situ stress has a significant affect on coal and gas out-imum stress is perpendicular to the roadway axis than when it isburst: When the maximum principle stress is perpendicularparallel to the axis.to the roadway axis, greater stress concentration, greaterCurrent regional gas outburst control methods consist of miningstresses, and a greater displacement gradient ahead of thea protective coal seam or regional gas drainage. Mining a protectiveroadway face will increase the likelihood of an outburst.coal seam is the fist action taken if the coal seam condition meritswhen the maximum stress is parallel with the roadway axisthis. when there isprotective coal seam, or there is only onethere is little or no stress concentration and the stress andcoal seam, a regional gas drainage technology should be applied.displacement gradient is small. In this situation the outburstowever, most coal seams have low permeability and the gasrainage has a minimal effect. Consequently, it is very difficult to (2)中国煤化工 be reduced through theine these coal seams. Current stress relief technologies like looseblasting or hydraulic punching may be used to improve the perneCN MH Ge stress direction can beability. Although these technologies do improve the permeabilityconsidered an auxiliary gas control measure. This may beYang et al/lnternational joumal of Mining Sance and Technolog 22(2012)145-149considered along win the technologies ot mining a protec- distr but ion charac则 underground coal mines in Chin删010:16(3-4}333-4controlling gas and coal outburst.Ill kang HP. jiang TM, Zhang X Yan LX Research on in 1989. 26(6).-547-8peningining the minimum in situ stress from fracture chAcknowledgmentsld in jincheng12 I Chen Q Zhu8L和uHrEof in situFinancial support prowided by the National Basic Researchx57Program of China(No. 2011CB201205), the National Natural Science [131 stafford CR KDDset F AlCD-EtMelma ionic liquid.JElectrochemund of the State Key Laboratory of Coal Resources and Mine Safety /14/NaZi: 153(4):Cc207-12undation of China(No. 51074161) the Independent Research(No. SKLCRSMO8X03) the Research Fund of the State Key Laboratorgromech Abstr igs,. 3 ina-emess ground pressure. int I RoCK Mech Min saof Coal Resources and Mine Safety, CUMT (No. 09KFo9), and the [15 Yang w Lin BC(A Stress evolution with time and space during mining ofNational Natural Science Foundation of Youth science Foundation48(7)1145-52of China(No, 50804048)are greatly appreciated.116 Yang w. 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