Mechanism of mining-induced slope movement for gullies overlaying shallow coal seams

This paper provides an improved understanding of the movement mechanisms of both bed-rock gully and sandy soil gully when underground mining occurs underneath, followed by systematic analysis of the contributing factors such as mining advance direction, gully slope angle, gully erosion coefficient and mining height. This paper presents the results from monitoring, theoretical analyses and up to date modeling based on the geological features in the gully affected area, and the implications of these results to the success of roof support trial. It was observed that when mining occurred towards the gully, sliding of slope block along the fracture surface occurred, which resulted in unstable roof condition; when mining progressed away from the gully, polygon blocks developed in the gully slope and rotated in reversed direction forming hinged structure; within the bed-rock slope, the hinged structure was unstable due to shear failure of the polygon block; however, within the sandy soil slope, the structure was relatively stable due to the gradual rotating and subsiding of the polygon block. The increase of the value of slope angle and mining height lead to a faster and more intensive fracture development within the gully slope, which had a pronounced effect on gully slope stability and underground pressure. Various remediation approaches are hence proposed in this paper including introducing more powerful support and reasonable mining height, setting up working face along or away from gullies, using room and pillar, strip mining and backfill instead of longwall mining.