Study On Maincontrol Factors And Predicting Method Of Surface Subsidence In Strip Mining Of Near-shallow Coal Seam

At present, the main method of surface subsidence prediction is the methodof empirical prediction, which is represented by probability-integral and basedon measured data, but does not involve study of overlying strata movement ruleand often does not apply to surface subsidence prediction in inadequate coalmining.Near-shallow coal seam is much closer to the surface, so it is moresusceptible to the impact of mining activities. Based on this status, this paperindicates the maincontrol factors and the effect of the maincontrol factors onoverlying strata movement rule in strip mining of near-shallow coal seam，witchis inadequate coal mining，through orthogonal experiment, numerical simulationand theory analysis and presents the mechanical model of key strata，witchcontact surface subsidence and overlying strata movement，and the predictionmethod of surface subsidence in in strip mining of near-shallow coal seam.Concrete contents and main conclusions are as follows：1) This paper defines strip mining of near-shallow coal seam: near-shallowcoal seam is refers to burial depth not over200m, ratio of bedrock thickness and soil layer thickness between1to5, one or two key strata in overlying strata andstrip mining is the mining method that the mining width is not sufficient toallow overburden to reach full mining and preserve width is enough to supportoverlying strata.2)There are too many Influence factors of overlying strata movement andsurface subsidence, so these factors are grouped to do orthogonal test. Thefactors of first orthogonal test are the properities of primary key strata. Thefactors of second orthogonal test are significant factors in the first experimentand the properities of inferior key strata and topsoil. The factors of thirdorthogonal test are the location of key strata and the properities of non-keystrata. The factors of fourth orthogonal test are the properities of coal seam. Thefactors of fifth orthogonal test are significant factors in the fourth experiment,mining dimensions and the properities of roof and floor layer.3)To do single factor experiment on the significant factors in theorthogonal experiments and analysis the influence of these significant factors onthe movement law of overlying strata, witch verifies the results of orthogonalexperiment and further defines the main controlling factors of surfacesubsidence in strip mining. The final verified main control factors of stripmining in shallow seam are the size of mining (mining width, remaining width,mining height) and the thickness of inferior critical layer. The factors witch haveless significant influence on the surface subsidence are the thickness of mainkey strata, the elastic modulus and Poisson’s ratio of inferior key strata, the Poisson’s ratio and angle of internal friction of the interlayer between keystratum and the cohesion, angle of internal friction angle and Poisson’s ratio ofthe coal pillar.4)Based on.the feature of overlying strata movement of strip mining innear-shallow coal seam, this paper presents the mechanical model of inferiorkey strata and main key strata and according to the relation between thesubsidence of inferior key strata and main key strata gets deflection curveequation of main key strata through deflection curve equation of inferior keystrata. Then to do mechanical analysis of inferior key strata and verify that themodel’s response to the main control factors is consistent with law of overlyingstrata movement, witch results show that they are consistent. At the last, thispaper through the deflection curve equation of main key strata gets thesubsidence curves of surface and presents the prediction method of surfacesubsidence in strip mining of near-shallow coal seam.