Deformation effect of lateral roof roadway in close coal seams after repeated mining

International Journal of Mining Science and Technology 24(2014)597-601Contents lists available at Science DirectInternational Journal of Mining Science and TechnologyELSEVIERurnalhomepagewww.elsevier.com/locate/ijmstDeformation effect of lateral roof roadway in close coal seams afterrepeated miningXie Jianlin Xu Jialin Wang Feng Guo Jiekai Liu donglintate Key laboratory of Coal Resources and Safety Mining, China University of Mining and Technology, Xuzhou 221008, Chinab School of Mines, China University of Mining and Technology, Xuzhou 221008, ChinacNo. 1 Coal Mine of Pingdingshan Tian' an Coal Industry CO Ltd, Pingdingshan 467011, chinaARTICLE INFOABSTRACTArticle historThis paper analyzed the deformation mechanism in lateral roof roadway of the ding Wu-3 roadwayReceived 12 December 2013hich was disturbed by repeated mining of close coal seams Wu-8 and Wu-10 in Pingdingshan No. 1Received in revised form 13 January 2014Mine. To determine the strata disturbance scope, the strata displacement angle was used to calculatepted 10Available online 18 August 2014the protection pillar width. a numerical model was built considering the field geological conditionssimulation, the mining stress borderline was defined as the contour where the induced stress is 1.5 timesKeywordsof the original stress. Simulation results show the mining stress borderline of the lateral roadwayxtended 91.7 m outward after repeated mining. Then the original stress increased, deforming the road-ng stress borderlineway of interest. This deformation agreed with the in situ observations. Moreover, the strata displacementStrata displacement angleangle changed due to repeated mining. Therefore, reselection of the displacement angle was required tolesign the protective pillar width. Since a constant strata displacement angle was used in traditionalProtective pillardesign, the proposed method was beneficial in field caseso 2014 Published by Elsevier B V on behalf of China University of Mining TechnologyIntroductionwas used to calculate the width of a protective pillar. The analyticalresults indicated that the roadway would not distort or fail when itUnderground roadways are often deformed when they are was out of the strata displacement scope after mining. The actualaffected by nearby working faces. Thus, a reasonable location is field results showed that the roadway didn ' t distort after miningan important precondition for guaranteeing the stability of a Wu 8-31010 working face. However, serious distortion occurredroadway [1-7. The roadway could be protected by coal pillars. after mining Wu 10-31010 working face in close distance seamsThe traditional way is to calculate the protective pillar width with Affected by repeated mining, the roof roadway has more complexthe strata displacement angle as a main design parameter, combin- influencing factors on deformation than that in single coal seaming geological conditions and empirical data. Many geologic and mining [11-15 It is inadequate to make judgments merely onmining factors are related to strata displacement angle, such as the traditional strata displacement angle. The width of a protectivethe upper layer rock stress characteristics, mining method, mining pillar based on traditional methods cannot satisfy practicaldepth, mining height of coal seams and repeated mining [8, 9 The requirements, This study will further research on the deformationstrata displacement angles used in protective pillar design are effects in lateral roof roadways in close coal seams after repeatedcommonly acquired from observation data within 300 m mining mining by employing mining stress evolution as well as stratadepth. It seems that the strata displacement angle in the same displacement.mining area is consistent. However, whether the strata displace-ment angle is dependent on the mining depth remains unknown2. Engineering situationIn order to protect the Ding wu-san chengren roadway in theroofs of Wu 8-31010 and Wu 10-31010 working faces(miningWu 8 and wu 10 coal seams are close seams of no. 1 Mine indepth was about 600 m in each case)of No. 1 Mine of Pingding- Pingdingshan Tianan Coal Industry Limited Company.Theirhan, the strata displacement angle selected from statistical data vertical distances are about 10 m on average. Mining on the Wu8-31010 working faAnril 2.009 and stopped in January.Corresponding author. Tel. +86 138520831422010. Mining the中国煤化工 began in January2012 and stoppedCNMHGhttp://dx.doiorg/10.1016/j.ijmst.2014.04.0032095-2686 2014 Published by Elsevier B V on behalf of China University of Mining TechnologyJ. Xie et al/ International Journal of mining Science and Technology 24(2014)597-601200mface. For each of the 20 observation points, deformation of theDing wchengren roadwayroadway roof and floor as well as two brackets was measured by240mcross measurement. The initial data were measured on January280m21,2012.280mWu 8-31010 working facField measurements were carried out on the ding wu-san320m320mhengren roadway on February 12, March 10, April 6, April 30, June48 Wu 10-31010 working face9 and july 7 in 2012 respectively. table 1 shows the results. Thedata show the difference between measured data and initial data-400mSome positive values were obtained because of field measurementerror due to manual measurement by tape.Fig. 1. Relationship between location of Ding wu-san chengren roadway alThe positions of large deformation in the roof and floor causedworking facesby mining were from the 5th observation point to the 14th one(Table 1). The maximum relative displacement value of roof andig. 1 shows the adjacent position relationship between Ding floor at the 7th observation point was 587 mm. The positions ofwu-san chengren roadway and the two working faces. The protec- two influenced brackets were from the 3rd observation point totive pillar was designed 48 as the unified strata displacement the 10th one. The maximum relative displacement value of twoangle. The protective pillar of Wu 8-31010 working face was brackets at the 6th observation point was 488 mm. According to68 m The protective pillar of Wu 10-31010 working face was 76 m. the measured data, Ding wu-san chengren roadway becameseriously distorted after mining Wu 10-31010 working face3. Analysis of field measurement data of Ding wu-san chengren4. Deformation effects in Ding wu-san chengren roadwayDing wu-san chengren roadway didnt distort after mining WuDing wu-san roadway was located in the lateral roof of Wu 8-8-31010 working face. The roadway distorted after mining Wu 10- 31010 and Wu 10-31010 working faces. Roadway deformationas related to the characteristics of the overlying strataroadway every 50 m to acquire information about the deformation working face, working face arrangements and the method ofcharacteristics following the start of operations on the working support. The material of roadway surrounding rock was sandyTable 1Field measured dataItemFeb. IMarch 10April 60-10oof floor displacementTwo brackets displacementRoof floor displacementTwo brackets displacement-557Roof floor displacementTwo brackets displacRoof floor63Two bracke45552053075100Roof flo-5-25-1301703475006Two brackets displacement120150Roof floor displacemenTwo brackets displacement-127Two brackets displacemenRoof floor displacement9Two brackets displacementRoof floor displacementTwo brackets displacementRoof floor displacementwo brackets displa106Two brackets displacement15f& floor displacementTwo brackets displacement202535Roof& floor displacementTwo brackets displacementRoof floor displacement-1Two brackets displacementwo brackets displacementTH中国煤化工Two brackets displacementCNMHGTwo brackets displacementRoof floor displacementJ Xie et al / International Journal of Mining Science and Technology 24(2014)597-6015994.2. Stress in close coal seams after repeated miningface( Fig. 3a). The large deformation of the roadway occurred aftermining both Wu 8-31010 and Wu 10 3-1010 working facesFig 3b). In order to discuss the reasons for roadway deformationin further studies, a few horizontal survey lines were set in theoverlying strata of the roof above the working face. Fig. 4 showed三Wu10scamthe horizontal stress distribution in survey lines of the correspondg overburden strata. The mining stress borderline was defined asFig. 2. Numerical simulation mode.a curve, which was made up of points where the horizontal stressvalue in different survey lines was 5% higher than the originalstress value [16]. The working face mining had a major effect onmudstone. a combined support method of bolting and shotcreting the overburden strata inside the mining stress borderline nearbywas used. The corresponding roadway protective pillars were set inboth working facesgob, while none was observed on the overburden strata outsidethe lin4. 1. Numerical model configurationAs can be seen from in Figs. 3 and 4, the roadway was in the ori-ginal stress area outside the mining stress borderline after miningu8-31010 working face. The roadway did not deform due to theIn order to study the deformation of Ding wu-san chengren limited influence of the mining. The mining stress borderline of theroadway at different periods, a numerical model( Fig. 2)is builtusing UDEC2D, by considering geological conditions of Wu 8- roadway extended outwards by 91.7 m after mining Wu 8-3101031010 and Wu 10-31010 working face as well as roadway. Theand Wu 10-31010 working face. The original stress area of themodel size(width x height)was 700 x 567 m In the model, wu roadway became an area of increased stress Deformation and failseam and Wu 10 seam were 2.0 and 3.0 m in thickness, respecure was largely affected by repeated mining on the working face.tively. The seams were nearly horizontal. The roadway section observationThe numerical stimulation result was consistent with fieldwas 4.2 x3.0 m and adopted a bolt and cable combined supportmethod. The horizontal direction was fixed in the left and rightborders of the model and the vertical direction in the bottom 4.3. Strata displacement angle in close coal seams after repeatedboundary was stationary. The ideal elastic-plastic constitutive miningmodel-Mohr Coulomb yield principle was used for the materialAccording to the field conditions, Ding wu-san chengren roadAfter mining the working face the stress change in the upperway was mined first in the numerical stimulation, and followed overburden layer had a direct effect on strata displacement. As aby Wu 8-31010 working face, and Wu 10-31010 working face result, the strata displacement angle changed correspondingly. Awas mined afterwardsfew horizontal survey lines were set out in different layers above口工工1.1301.100090100凸m0(a) After mining Wu &-31010 working face(b) After mining Wu 8-31010 and wu 10-31010 working faceFig 3. Roadway deformation characteristicslIl 3marIIiIIMIll2.5 Max MagnitudeMax Magnitude1236E+mmTTT IITITTilh-mMTMIIMIIOVu 8-31o1C6072E+07Mu8310111中国煤化工13E+07CNMHG(a) After mining wu 8-31010 working face(b) After mining Wu8-31010 and Wu 10-31010 working faceRoadway ammImmmmm(a) After mining Wu 8-31010 working face(b) After mining Wu 8-31010 and Wu 10-31010 working faceRoad身Max.M3-1.5353E52m6l45E+00-3.8353E+00(a) Alter mining wu 8-31010 working faceb) After mining wu8-31010 and wu 10-31010 working faceFig. 6. Protective pillar design after repeat mining.the working face, and subsidence value curves could be obtained Therefore the roadway did not deform when it was outside thethrough model mining. The points where the subsidence value strata displacement range. According to Fig 6b, the width of pillarwas 10 mm in surface survey lines were chosen as the border point ob after mining Wu 10-31010 working face was 99 m. The actual[17]. The corresponding strata displacement angle was obtained by width of the pillar designed is 76 m, which is less than that ofjoining the border point with the gob boundary. Fig 5a shows the ob. Consequently, the roadway deformed when it was inside thestrata displacement angle after mining Wu 8-31010 working face. strata displacement range after close coal seams repeated mining.In Fig 5a, the curvesoriginated frorhorizontal survey lines after Wu 8-31010 working face miniand the oblique line is the strata displacement angle line. Fig6. Conclusionpresents the strata displacement angle after mining Wu8-31010(1) The deformation mechanism of Ding Wu-3 roadway wasThe numerical result suggests that the strata displacementexplained in this paper. The mining stress borderline wasangle is 55 after mining Wu 8-31010 working face. The roadwayextended after repeated mining of the close coal seamsdid not deform when it was outside the strata displacement scopeThe pre-assumed original stress area was disturbed, resulat that time. Affected by mining Wu 8-31010 working face, theInts increasemining stress borderline extended a large distance after mining(2) The mining stress borderline changed after repeated miningWu 10-31010 working face. Therefore, the surface subsidence crit-of close coal seams, causing the alteration of the strataical point extended outwards, decreasing the strata displacementdisplacement angle. Therefore, it was essential to design aangle to a value at 40. Roadway deformation occurred at this timeprotective pillar of the lateral roof roadway by reselectingwhen it was within the strata displacement range.the strata displacement angle after repeated mining. Compared to the traditional way considering a single strata dis-5. Protective pillar design of lateral roof roadway based oIplacement angle, the new method provided a significantstrata displacement angle in close coal seams after repeatedimprovement in instruction for similar engineering cases.Since the strata displacement angle has changed after close coal Acknowledgmentsseams repeated mining, it was necessary to design a protective pil-lar of a lateral roof roadway by choosing a new strata displacementFinancial supports from the National Natural Science Founda-angle. Fig. 6 presents the protective pillar after repeated mining. tion of China(No中国煤化工demic ProgramFactors influencing strata displacement angles should be taken Development of Jiaitions of chinainto consideration in designing the width of the protective pillar (No. SZBF2011-6-B3CN MH Gechnology Supfor the roadways affected. According to Fig 6a, the width of pillar port Program of ChmldIwJ.2012D0nuDuu), and the Projectafter mining Wu 8-31010 working fac52 m. The actual Funded by state Key laboratory of Coal Resources and Safe Miningwidth of the pillar designed is 68 m, which outweighed oa. of China(No sKLCRSM11X03)were appreciated by the authors1. Xie et al. International Journal of Mining Science and Technology 24(2014)597-601References[10] Zhu L], Chen I.on determination displacement angle of[1] Lu SLJiang YD, Sun YL The selection of vertical distance Z between roadway [111 Zhang BS. Yang SS, Kang In on method for determining reasonableand its upper coal seam. J China Univ Min Technol 1993: 22(1): 16-9.lose multi-seam. Chin J Rock Mech Eng[2] Lu SL, Sun YL, Jiang YD. Selection of horizontal distanc2008;27(1):97-10and the edge of its upper pillar. 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