Roof-breaking mechanism and stress-evolution characteristics in partial backfill mining of steeply inclined seams

Abstract

Steeply inclined seams buried at dip angles of 35–55° are considered hard-excavated seams in the mining industry. A partial backfilling method based on sub-regional features of surrounding rock deformations and failure and support stability was proposed to realize safe, efficient production, to promote sustainable development of coal mining and disaster prevention in western China. Through experiments, calculations, and theoretical analysis, a mechanical model was established, and governing equations for the deflection curve, bending moment, and rotation were deduced. Results reveal the filling percentage, filling ratio, and working-face dip angle as major factors causing roof failure. The degree of roof deformation decreases with increasing filling percentage, filling ratio, and working-face dip angle. With an increase in filling percentage and filling ratio, the range and magnitude of the stress-concentration zone at a T-junction increase, whereas those pertaining to the stress-release zone in the roof decrease. The stress-arch profile of the roof changes from a single peak to double peaks with reduction arch height. Additionally, the maximum arch height shifts towards the centre with increasing moderation of asymmetric features of stress arches. With an increase in working-face dip angle, stress concentration at the coal-wall head T-junction decreases, and a double-peak stress arch develops. Therefore, in order to obtain the best backfill mining effect, a higher filling percentage is preferred; with a maximum filling value of 0.93, the reasonable range for the filling ratio is 1/3 to 1/2 and the reasonable dip angle of the working face is approximately 35°.