Failure mechanism of pump chambers and their optimized design in deep mining at Qishan Coal Mine

Availableonlineatwww.sciencedirect.com° ScienceDirectMININGSCIENCE ANDTECHNOLOGYELSEVIERMining Science and Technology 20(2010)0825-0830www.elsevier.com/locate/jcumtFailure mechanism of pump chambers and theiroptimized design in deep mining at Qishan Coal MineSUN Xiaoming WU Huangzhou, CAI FengState Key Laboratory of Deep Rock Mechanics and Engineering, Beijing 100083, ChinasChool of Mechanics and Civil Engineering, China University of mining& Technology, Beijing 100083, chinaAbstract: Pump chambers, normally used as dominant structures in mining engineering to insure the safety and production of un-ground coal mines, become generally deformed under conditions of deep mining. Given the geology and engineering conditionof Qishan Coal Mine in Xuzhou, the failure characteristics of pump chambers at the -1000 m level show that the main cause canattributed to the spatial effect induced by intersectional chambers, where one pump is constructed per well. We developed an optimized design of the pump room, in which the pump wells in the traditional design are integrated into one compoundingsuggest that the new design can limit the spatial effect of intersectional chambers during construction given our relevant nusimulation. The new design is able to simplify the structure of the pump chamber and reduce the amount ofexcavationBased on a bolt-mesh-anchor with a rigid gap coupling supporting technology, the stability of pump chamber can be improvedKeywords: deep mining: pump chambers; failure mechanism; numerical simulation; optimized design1 Introduction2 Failure characteristics of traditional, designed pump chambersGiven the complex geomechanical conditions atgreat depths, the study of stability control of underThe coal fields in Xuzhou have been exploited forground engineering has received wide attention all more than a century. At present, most coal mines haveover the world. One important underground struc- been mined to great depths. From in-situ measureture, the pump chamber, can insure safe production in ment of deformation and failure position of deepcoal mines. In its traditional design, each wellpump chambers at Qishan Coal Mine and other coalequipped with one pump, which is connected with a mines. the failure characteristics of traditional de-water sump via a complementary water tunnel and signed pump chambers under complex mechanicalforms a grade-separation structure. Simultaneously, conditions are described in the following(Fig. 1)relevant support designs fail to control large deforma- 1)Heave in the pump room floor;tions in the surrounding rock. He and Sun optimized 2)Shrinkage in both sides of pump room, subsi-the design for pump chambers in soft rock and ana- dence in rooflyzed the stability of pump chambers affected by 3)Occurrence of asymmetric deformation in pumpnon-linear mechanics processesTheir design room pascan solve the stability control problem under soft rock 4) Distortion in radial direction of draw-wellconditions. In order to develop the pump chambers5)Fractured mid-pillars of cavernability controllogy during deep mining further, the failure mechanism of pump chambers and 3 Analysis of deformation and failurethe design of stability control are discussed. Engimechanism of traditional designsneering at Qishan Coal Mine in Xuzhou is used as anexample中国煤化工 nation and failureReceived 11 March 2010, accepted 22 May 2010CNMHGcal conditions at.Corresponding author. Tel: 86 1062331294the -10uf Qishan Coal Mine.E-mailaddressxiaoming_s@263.netdoi:10.1016S1674526409%60289Mining Science and te(a) Pump room abandonment(b)Equipment base destroyed (c)Concrete supporting cracks due todue to floor heaveby floor heave of pump roomsurrounding rock deformationside wall shrinkage(e) Asymmetric deformation(f Radial distortion of draw-well (g)Damaged draw-well chamber(h) fractured rock pillar in rockump room passageand rock pillarentrance of pump roomFig. 1 Characteristic deformation of pump room chambers in traditional design3. 1 geological engineering conditionsThe geological and mechanical engineering modelThe maximum depth of the -1000 m level pump of FLAC3Dis illustrated in Fig 3, using the finite difference codechamber is 1032 m (ground elevation is +32 m)atQishan Coal Mine. According to the lithologicalcharacteristics of the exposed rock strata, the surrounding rocks consist mainly of sandy shale, mudstone, sandstone, jointly developed, where the obliquity of the fragmented rock seam is about 10-15. Interms of the results of in-situ stress tests, the maxi-Substation roommum principal stress at the -1000 m level of QishanCoal Mine is horizontal stress with 40.5 MPa, in aDrawwellNEI322° direction3.2 Simulation modelThree wells, each equipped with their own pumpwere used in the original design(Fig. 2), where theFig 2 Pump room chambers arrangement planradius of each draw-well was l1 m and the matchedin traditional designsupport pattern a bolt-mesh-shotcrete-cablea)Engineering geological model(b)Traditional design model(e) Mechanical support modelFig 3 Geological, engineering and mechanical models in traditional designThe dimensions of our model are as follows: length the40 5 MPa and the load applied35 m, widthx45 m and height 35 m. There are 78912 along中国煤化工 he low load waunits,84496 nodes, 5600 structural units and 6968 introdunit nodes. According to the geological conditions, stresC GOn Of gravityOur simulationthe initial in-situ stress acting on the upper boundary model used the Mohr-Coulomb elastic-plastic constalong the y direction is 27. 1 MPa, with a load along tutive relationship. The strain softening of the sur-SUN Xiaoming et alImp chambers and theirrounding rock was taken into consideration by theThe results show that stress concentration occurs ininteraction of the plastic strain value, friction and the the roof and floor of the cavern after the excavationcohesion of the softened rock. The physical and me- of the pump room and niche. During the excavationchanical parameters of the rock mass in our model are of each small draw-well, the stress is concentrated onpresented in Table 1the rock pillar, located in the middle of the smallTable I Physical and mechanical parameters of rock massdraw-wells. The stress concentration of the rock pillarclearly increased after the formation of the system ofRockmodulus modulus strength strength Frictional pump room chambers(Fig. 4). As a result, the area of(kg/m )(GPa)(GPa)(MPa)(MPa) angle()plastic damage in the rock surrounding the pumpMudstonechambers became enlarged( Fig. 5). Our calculations560604.040of the surrounding rock displacements show that theSandy-mudstonc 2550 5.0 4.0 2.1floor heave was 297. 4 mm, the roof sinkage 306.6mm, the left wall shrinkage 217.7 mm and the right3 Results and discussionwall shrinkage 326.3 mm. These results also suggestthat the excavation of multiple small draw-wells has aSteps in the numerical simulation follow the actual serious impact on the stability of the pump roomexcavation procedures, in which excavation of the Superposition stress from the spatial effect of excava-pump room is the first step, second is the excavation tion causes large deformations in the pump roomof a niche and small draw-wells and finally, the water such as floor heave, roof sinking and side walldistribution drift is connectedshrinkage( Fig. 6)a)Excavation pump room and niche(b)Excavation draw-wellsc) water distrbution drift before excavation(d) Water distribution drift after excavationFig 4 Stress distribution during excavation of pump room chambers3.4 Failure factorsFrom the analysis above, we infer the following asthe main reasons for spatial effect in traditional pumpchambers1)High in-situ stress. Due to the great depth of thisproject, pump chambers are subjected to high gravityconditions中国煤化工CNMHGwells and waterFig. 5 Plastic zone distribution after excavationdistributedesigned in a relatively complexand TeNiche andPump hdraw.wells(a)Stress concentration caused by excavation of draw-wells (b) Asymmetric deformation and floor heave of pump roomFig 6 Effect on pump room after excavation of draw-wells3)Frequent excavation disturbance Superpositionand high concentrated stress can cause failure of com-plex underground structures, due to the depth of ex-cavationPump room4 Optimized design of pump chambers4.1 Optimized design schemeIn order to eliminate the three-dimensional spatialeffect induced by the pump room chambers, the following optimized design scheme is introduced. Thethree pump wells in the traditional design are inte-Fig 7 Pump room arrangement plan of optimizedgrated into one compounding well, divided in threedesign(unit: mm)parts by reinforced concrete partition walls, alongradial directions. This improves the stress distributionof the surrounding rock and further enhances the sta-bility of the compound well. The presence of abolt-mesh-anchor-shotcrete coupling support in each3)×1100+1+400=3000tunnel ensures the integrity and stability of the pumproom chamber 3-15)The arrangement of the pump chambers in an op where R is the radius of the compound draw-well,timized design is shown in Fig. 7In this optimized design, the size of the tunnel in traditional design, mm and d the width of the partithe pump room and the location of the pump founda- tion wall in the optimized design, mmtion are the same as in the traditional design. The ra-The cross-section figures and support parametersdius of the compound draw-well can be obtainedofthe matching bolt-mesh-anchor-shotcrete areshown in Fig. 8$18.9 anchor45° noor bol中国煤化工CNMHG(a) Cross-section of pump room support(b)Cross-section of compound draw-wellFig 8 Support design of pump room and draw-wellSUN Xiaoming et alFailure mechanism of pump chambers and their4.2 Results and discussionGiven the engineering and geological conditions inQishan Coal Mine, we established the model of anoptimized design, shown in Fig 9. The parameterscalculated are presented in Table 1(e) After formation of the pump room chambers systemFig 10 Stress distribution during pump roomexcavation of optimized design(a)Geological engineering model (b) Mechanical support modelFig 9 Geological engineering and mechanical supportmodel of optimized designThe results show that the stress becomes concen-trated in the pump room and in the top and bottom ofthe niche after excavation, due to the larger cross-section of the pump room and the niche, (Fig. 10a).with the excavation of the compound draw-well, thestress concentration of the pump room and the nichesshifted to the compound draw-well(Fig. 10b). AfterFig. 11 Plastic zone distribution after pump roomexcavation ofthe system of pump room chambers was formed, thetially eliminated, which clearly reduced the stress 5 Engineering applicationconcentration(Fig. 10c). Since the application of theThe new design was applied in engineering thebolt-mesh-anchor-shotcreteling support tech- pump chambers at the -1000 m level in Qishan Coalnology, the stability of the pump room chambers Minegreatly improved and the plastic zone was signifi- The components of the entire construction of thecantly reduced(Fig. 11). The results of our calcula- pump chamber consist of the pump room passage,tions of surrounding rock displacement show that the pump room, niche and compound draw-wellfloor heave is 75.1 mm, the roof sinkage 128.8 mmBy working parallel on these various components,the left wall shrinkage 110.4 mm and the right wall the construction can be accelerated. In detail, the con-shrinkage 126.8 mm.struction process is as follows1)Enlarging the section according to the design2)Erecting a lead beam for adva3)Anchor-mesh support4)First 60 mm thick shotcrete5) Installation of anchor and floor bolt according to囊the allotted spacing and row spacing of the design30o000076)Digging bottom and pouring concrete floor7)Observation of mine pressureto 1946]+08)Second 100 mm thick shotcrete to designed(a)After excavation of pump room and nichethickness, forming permanent supportFrom the displacement-time curve of the rock surrounding the pump room( Fig. 12)during the con-struction process, it is seen that the rate of deforma-tion of the surrounding rock tends to decrease afterthe ipstallation of anchors in the 12 days of excava-tion中国煤化工 of the pump roomCN MH Ability. Simultaneously, the bolt-mesh-anchor support was put in placeThe total sink displacements of the pump room roofMining Science and TechnologyVoL 20 No 6was 118 mm. The total shrinkage displacements of sic Research and Operating Expenses of the Chinathe two side walls was 255 mm, of which the left side University of Mining Technology, Beijing and thewall accounted for 125 mm and the right side wall for Academician workstation in enterprise of Jiangsu130 mm. The total heave displacements of the floor Province(No BM2009563). We gratefully acknowlwas 42 mmedge this supportSlowdeformation Right wallReferences[1] He M C, Xie H P, Peng S P, Jiang Y D Study on rockmechanics in deep mining engineering. ChineseRock Mechanicsinstalled2803-2813.(In Chinese)[2] He M C. Rock mechanics and hazard control in deepmining engineering in China. In: Proceeding of ISRM1020ternational Symposium. 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Effect of pre-tensioned rock bolts2)The numerical results indicate that an integra-on stress redistribution around a roadway -insight fromtion of several wells into one circular compound wellnumerical modeling. Journal of China Universiry ofcan be beneficial for reduction of the spatial effeMining Technology, 2008, 18(4): 509-515[10] He M C, Sun X M. Support Design and Constructioninduced by the disturbance of repetitive excavation.Guide for Roadway within Soft Rock in China. Beijing:3)The results of a practical application show thatScience Press, 2004. (In Chinese)an optimized pump chamber not only simplifies its [11] He M C, LiG F. Ren A w, Wang J. Analysis of t he stastructure. but also can reduce the amount of excavation required and can greatly improve the stability ofchamber groupsTechnology,2008,37(2):167-170Optimized designs for deep pump chambers have[12]Ren A w. Alternative Integrated Design of the PumHouse and Absorption Well System at Liuhai Coal Minealso been successfully applied in typical deep pump[Master dissertation]. Beijing: China University of Geo-gineering, such as in Xing an Coal Minesciences, 2006. (In Chinese)in Hegang and Liuhai Coal Mine in Longkou, where [13] Sun X M, HeMC. Yang x J. Research onit has been beneficial for the development of the localsupport for deep soft rock tunnel. Rock andor couplingchanics,2006,27(7):1061-1065.( n Chinese)Acknowledgements[14] Sun X M, He M C Numerical simulation research oncoupling support theory of roadway with in soft rock atThe authors thank prof. he manchao for his self-depth. Journal of China University of Mining Techless guidance in this research, which was partially [15]中国煤某supported by the Major Project of the National Basic某化二g Support Theory ofResearch Program of China(No. 2006CB202200), theCNMH Gand Development可fProgram for New Century Excellent Talents in Uni-China University of Mining Technology, 2002.(Inversity(No. NCETo7-0800), the Special Fund for Ba