Dynamic subsidence basins in coal mines based on rock mass theological theory

Mining Science and Technology( China)21(2011)333-335Contents lists available at Science Direct氵Mining Science and Technology( China)ELSEVIERjournalhomepagewww.elsevier.com/locate/mstcDynamic subsidence basins in coal mines based on rock mass rheological theoryYang Yu", Gong Zhiqiang, Liang BingSchool of Civil Engineering and Transportation, Liaoning Technical University. Fuxin 123000, ChinaARTICLE INFOABSTRACTArticle histolReceived 1 October 2010In order to investigate the surface deformation caused by coal mining and to reduce environmental damform 3 November 2010age,more accurate information of dynamic subsidence basins, caused by coal mining is needed. Based onnber 201rheological theory, we discuss surface deformation mechanism of dynamic subsidence on the assumptionAvailable6 June 2011that both the roof and the coal seam are visco-elastic media, put forward the idea that the principle ofsurface deformation is similar to that of roofs, except for their parameters. therefore a surface deformation equation can be obtained. given the equation of the roof deformation derived. from using a him rheoal mining subsidenceological model. In the end, we apply the equation of surface deformation as a practical subsidenceynamic basinprediction in a coal mine. Given the rheologic properties of a rock mass, the results of our research ofRheological theoriesa dynamic subsidence basin can predict the development of surface deformation as a function of timeH M rheological modelhich is more important than the ultimate subsidence itself. The results indicate that using rheologicaltheory to calculate the deformation of a dynamic subsidence basin is suitable and provides some reference for surface deformation of dynamic subsidence basinse 2011 Published by Elsevier B V. on behalf of China University of Mining Technology1 Introductiontion of time. The dynamic subsidence problem can be consideredfrom two aspects: subsidence in the process of coal mining andWith the rapid development of our national economy. increas- creep after exploitation has stopped. Therefore, the prediction ofing amounts of energy resources have been consumed, in which dynamic subsidence should be divided into two areas: surface efcoal resources account for more than 70%. without immediate ac- fect caused by mining and the rheology of rockmass over timetion areas of subsidence, caused by mining, which are much larger [3-5). We studied the dynamic subsidence problem of rock massthan the mined areas, will be formed under the action of gravita- and surface after mining from a rheology perspective by buildingtion of rock masses. The formation of a subsidence basin not only a rheological model, deriving the dynamic displacement equationchanges the original surface terrain, but also leads to land collapse of subsidence as a function of time.and changes in horizontal positions, bringing varying degrees ofdamage within range of objects on the ground such as roads,pipe- 2. Establishment of a rheological modellines, rivers, buildings and the ecological environment. The pur-pose of studying surface movements and deformation duringNot only is the rheological theory of rock mass associated withmining processes as well as deriving a formula to model their rock mass movements under mining pressure, but it also intro-behavior is to exploit effectively and efficiently the coal resources duces the time factor into surface deformation from stress andunder buildings, rivers and rails and at the same time protect the strain in a rock mass. The form of the ground subsidence curve isstructures impacted by coal mining. Therefore, correct estimates similar to that of the roof except for their parameters[6-16].Thehe subsidence basin causedHIM rheological model( Fig. 1)reflects the instantaneous elasticby coal mining are of great importance.deformation characteristics of rheological material as well as theAt present, the main methods to predict mining subsidence in- property that rock masses tend to be stable over time. Thereforeclude a probability-integral method based on a theory of random this model can be used to derive the subsidence equation of roofsmedia, a typical curve method based on information obtained from Furthermore, this model contains few parameter, so it is suitablepractical measurements, as well as a section function method [1- for simulating the rheological properties of rock and soil. The con-2]. Each of these three methods can effectively estimate final sub- stitutive equation is shown as Eq (1)sidence and deformation for any subsidence basin. However, theycannot estimate the dynamic relationship of subsidence as a func 0+0=EE+E1+E2Corresponding author. TeL +86 418 3350654where e,,E, arenf plasticity and n is the viscositymail address: yangyu9300163 com(Y Yang).中国煤化工1674-5264/s-see front matter e 2011 Published by Elsevier B.V. on behalf of China University of Mining&TeCNMHGdot:0.1016mstc201105.003334Y. Yang et aL / Mining Science and Technology( China)21(2011)333-335where i is the moment of inertia of the beam section to the neutralaxis, ieI= oz'da and M is the moment of the section of thebeam, where M=ondAAccording to material mechanicsE1q(r, t)=oM(x, t)We can obtain Eq (7)according to the equilibrium of the forcesFig. 1. HIM rheological model and creep curve.q(x, t)+o(x, t)=PEq(8)can be deduced by differentiating M in Eq 5)and com-3. Surface movement and deformation of dynamic subsidence bining it with Eq(4)basins under semi-infinite mining conditionsE2\,aW(x,r)Erat+ETW(x, t)3. 1. Establishment of a roof force bearing modeln &+E26=PIn this section, we assume that factors affecting the dynamicsubsidence of surface areas are constants and use the HM model where e is the press deformation value of the coal seam, &="h4d,to investigate surface movements and deformation of a dynamIc H the height from the bottom of the coal seam to the rock stratum.subsidence basin given semi-infinite mining conditions. We also To simplify the process of derivation, we assume: 2 =2=k.assume that the deformation at any point of the dynamic basinThe partial differential equation of roof subsidence upononly changes as the working face advances. Therefore, this problem coal seam(x>O)is:can be simplified into an analysis of subsidence and deformation ofroof stratum, located above the visco-elastic foundation. As shown KE,+E)-ar0r+Eal- ar+RErcE2c)aw(x, 2+Exw=P8w(x, t)in Fig. 2 the roof stratum can be seen as a cantilever beam andboth the underlying coal seam and the roof stratum satisfyEq.(1). When x>0, the basis of the beam is the unmined coalbed and its reaction force is gc.The partial differential equation of the roof subsidence on themined area(xo is50974070). the Doctor Initial Fund of Liaoning Provincial Scienceand Technology Department(No. 20081103)and the Key Labora-K(x, t)温哪()m+sin ax+lcos ax(1-se )(16) tory Fund of Liaoning Province (No. LS2010074)is gratefullyacknowledgedCurvature over the mined area, where x<0 isReferencesx2+22[11 He GQ Yang L Ling G, Jia T, Hong D.Xuzhou: Chinanology PrWe know the curve of e(x, t) is similar to K(x, t) curve from com- [21 Liuu YC, Zhuang YH. Model for dyynamic prurface subsidenceparing their expressions Because the surface inclination caused byue to underground mining. Rock Soiuneven subsidence is T(x, t)=wx, curve T(x, t) is similar to the [3] Liu BC. Mining rock mass mechanics introduction.Changsha: Hunan Sciencehorizontal movement curve U(x, t).lation of strata movement in mined-out area. chin j Geol Hazard Control4. An example005: 16(1): 84-9 in Chinese5] Zhang XD, Fan XL Zhao DS. Time and space process of overburden strataWe have drawn figures from observed data of 13, 14 and 15 16)Hoamen. hein Rack ech Eng 2002:21(156-9observation points in the north wing of the Qinghemen Coal Mine,Coal Science and Technology 2003: 31(2): 54-6 in Chinese].where M=1700 mm, q=0.6,I-18 m, b=0. and K-61 mm/an- 17] Luo Y chengAn influence function method based subsidence predictionprogram for longwall mining operations in inclined coal seams. Min Scinum. M is thickness of the coal seam; g the subsidence coefficientechnol 2009: 19(5 ): 592-8 [in ChI the deviation of the inflection point; b the displacement factor[8] Zhang H, Wang Y], Li YF. SVM model for estimating the parameters of theand K the settling velocity.probability-integral method of predicting mining subsidence. Min Sci TechnolThe full lines in the figures are theoretical results. Given our 19) Liu w, Jia XR. Rheological model of dynamic prediction on mining subsidenceearlier theoretical deductions, Fig 3 shows that our results fit welland its applications. J Taiyuan Univ Technol 2004: 35(4): 491-4 in Chinesel.with the measured data, so our research result can be applied in 110) Huang LT, Wang jz Research on laws and computational methods of dynamisurface subsidence deformation. J Chin Univ Min Technol 2008: 37(2): 212-5practice.[111 Peng XZ, Cui XM, Zang YQ, Wang Y, Yuan DB. Time function and prediction ofprogressive surface movements and deformations. J Univ Sci Technol Beijing5 Conclusions2004:26(4):341-4.[12] Su Z]. Liu wS, Yang L Yu GM A mechanical model of subsidence due to miningis a complex dynamic process, involving time and space factors In [13] Liu r >pplication Mech Eng 2003: 25(2): 45-7The ground movement and deformation caused by coal miningview of the rheological properties of rock masses, it is more mean-01031(3):925-31ul to study a dynamic basin than a final subsidence basin for it [14] Huang LT, Wang zhe three stages and deformation velocity ofan predict deformation of any surface as a function of time. Givendynamic surface subsidence deformation. J Chin Coal Soc 2006: 31(4): 420the dynamic displacement equation between the sunk volume and [15] Tu xH, Wangon of modifiedtime, which we derived through rheological and cantilever beam中国煤化工 n Rock Soil"Mechtheories, we analyzed the distribution of surface movements and [16]Cui XM, YangCNMHGining subsidenceChindeformation on the main section of a dynamic subsidence basin.Min Mag 1996: 54