Analysis and application of fracture evolution law of overburden compacted area on fully-mechanized mining face under multiple factors

In this work, the physical similarity simulation test and theoretical analysis were used to study the compacted area of fully mechanized mining face under multiple factors. These factors include different mining heights (2，4，6 m), different advancing speeds (3 m/d,5 m/d,7 m/d), and different dip angles of coal seam (0°,15°,30°). The evolution law of the shape of compacted area with the change of the above factors was obtained. The results showed that the height of "three zones" in goaf increased linearly with the increase of mining height, the decrease of advancing speed and the increase of dip angle of coal seam. The farther away from the roof of coal seam, the smaller the permeability of the overlying strata was. The penetration decreased rapidly after reaching a certain height. The separation rate of overlying strata was squeezed by the higher strata and supported by the coal wall, showing a saddle shape on both sides higher than that in the middle. Based on the sudden decrease of strata permeability, the sudden increase of strata separation rate and the development height of fracture zone, a criterion for determining the boundary of overburden compacted area was constructed. The overall development morphology of compacted area under different conditions was obtained, and it was found that the mining height has a great influence on the height of compacted zone, the dip angle of coal seam has a great influence on the width and symmetry of compacted area, and the influence of advancing speed on the height and width of compacted area is relatively balanced. Finally, based on the theory of mining fissure elliptic paraboloid zone, combined with the experimental results, the mathematical equation of the compacted area of the mining fracture elliptical belt affected by the above factors was established. The engineering practice has proved that it effectively improves the effect of field gas control and ensures the safe mining of working face.