Abstract
Strata movement boundary is not only a parameter for the prediction of overburden strata movement and deformation but also a key index of setting shafts, roadways and protective coal pillars. Based on physical and mechanical properties of rock mass, the overburden strata are divided into bedrock and unconsolidated stratum. By means of theoretical analysis, physical simulation and numerical simulation, this paper studies the movement boundary shapes of bedrock and unconsolidated stratum, builds fitting equations of movement boundary of the two, analyzes the influence of key strata (KS) on the shape of strata movement boundary, and determines the principle of setting protective coal pillars. The results show that the movement boundaries of bedrock and unconsolidated strata are located at the outside of coal mining boundary. They are concave-upward power function curves that cannot be merged into a smooth one due to their different mechanisms of movement and deformation. The movement boundary of bedrock can approximate a straight line when lithology of the overburden is relatively uniform with thin strata in different positions; the surface movement boundary extends when the overburden has thick and stiff KS that are common in deeply buried coal seam. Therefore, the width of protective coal pillar is small if the movement boundary is regarded as a straight line. According to the curve movement boundary, the protective coal pillar for the passenger roadway of Panel 31010 of Pingdingshan No.1 mine is at least 99.4 m in width, larger than the designed one, which is the actual reason for its deformation and breakage.
Highlights
Energy resource is the basis for human survival and energy exploitation has made an important contribution to the development of national economy
To protect DingWu-3 passenger roadway in Pingdingshan No.1 mine, a 90-m-wide protective coal pillar was designed in its floor, the Wu-10 coal seam, on the basis of straight movement boundary, but severe deformation still occurred at the passenger roadway during stoping [8]
Based on second derivative of Equation (18) together with the criteria theorem of concavity and convexity [45], it can be known that the movement boundary of unconsolidated stratum is a concave-upward curve, but it may not be the parabola presented by Equaiton (18) due to its viscosity more or less
Summary
Energy resource is the basis for human survival and energy exploitation has made an important contribution to the development of national economy. The strata movement boundary is considered to be a straight line [4,5] According to this viewpoint, Shu and Bhattacharyya established the mathematical expression of the movement and deformation relationship between surface and the overburden, but their prediction results were not in line with actual measured data commendably [6]. The surface movement boundary has been deeply studied because of its close connection with the living environment, especially in densely populated mining area with villages, industrial squares, railway lines, and garbage dumps on the ground For protecting these surface structures, much research has been done on it and the width of protective coal pillars [9,10,11,12,13,14]. The principle of designing protective coal pillars is determined according to the movement boundary shape, and its reliability is proved by a case
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