Characterization and simulation of the coal-rock boundary equation on the upper and lower sides of the inclined coal caving opening

In order to explore the top coal release law of the fully mechanized top coal caving face under different inclination angles, taking the 0291 fully mechanized caving face of Tangshan Mine as the research background, a comprehensive research approach combining theoretical analysis, numerical simulation, and physical similarity simulation experiments was adopted to derive and obtain the representation equation for the coal-rock boundary line on the upper and lower sides of the inclined coal caving opening. Firstly, the parabolic equation of the coal-rock boundary equivalent to the area of the release ellipsoid is established for the correspondence between the top coal caving and the coal-rock boundary. Secondly, the numerical model of coal seam thickness of 7 m, coal caving opening width of 1.5 m, coal seam inclination angle of 0°, 10°, 20°, 30° and 40° is established by PFC software, and the coal-rock boundary marker layer is set up to obtain the fitting equation of the coal-rock boundary. Furthermore, the theoretically calculated equation is compared to further modify the coal- rock boundary equation. Finally, the self-designed “three controllable” electric top coal caving experimental equipment is used to carry out the physical similarity simulation experiment of the corresponding conditions, and the rationality of the correction equation is tested. According to the principle of “closing the door after seeing the waste”, a simulation of the single coal caving opening caving process in inclined coal seams is conducted.The simulation results show that: as the inclination angle of the coal seam increases, the coal-rock boundary gradually transforms from symmetric to asymmetric parabolic distribution, and the lower side of the coal-rock boundary is constantly far away from the centerline of the coal caving opening, and the upper side of the coal-rock boundary is constantly close to the centerline of the coal caving opening, and the upper side of the slope is much more gentle than the lower side of the slope. The theoretical calculation is higher than the equivalent parabolic eigenvalue of the simulation results, and the equivalent parabola correction coefficients under different inclination angles are summarized to improve the theoretical equations of the coal-rock boundary; the similar results of physical similarity simulation experiments and numerical simulation reflect that the released ellipsoid of inclined coal seam mainly comes from the top coal on the upper side of the inclined side of the coal caving opening, and the top coal on the lower side of the inclined side of the coal caving opening is easy to be piled up to form an arch in the process of releasing coal, and the reasonable results of the correction equation are verified at the same time.