Analysis of Dynamic Evolution of Surrounding Rock Movement and Stress-Fracture in the Upward and Repeated Mining of Close-Distance Coal Seams

The distribution of mining-induced stress and the resulting rock fractures are two crucial factors affecting mineral extraction in protective layer mining. This research establishes a correlation between the vertical fracture aperture and the second derivative of the rock layer’s subsidence curve equation. The article explores the span requirement for a simply supported beam to fracture. This condition is relevant to understanding the dynamic evolution of rock movement and stress fractures during repeated mining of close-distance coal seams. Our study investigates alterations in rock stress and fractures resulting from repeated upward mining of coal seams, using the nearby coal seam cluster in Jincheng Mine as a case study. The research findings indicate that during the mining of the upper coal seam, the roof experiences significant but brief periodic loading intervals, as well as severe and moderate periodic loading. As mining progresses to the lower coal seam, pressure relief of the upper coal seam gradually increases in both degree and range. In the upper coal seam, the vertical stress distribution follows a sequence of “V,” “U,” and “W” forms. The upper coal seam undergoes five stages of expansion deformation: compression, expansion, increased expansion, decreased expansion, and stable expansion.