Study on mechanism and control of space fracture instability of thick and hard roof under dip angle effect in coal mines

China currently possesses a substantial number of coal seams characterized by thick hard roofs and steep inclinations. With continuous advancements in mining mechanization, increasing mining height and working face length, as well as intensified extraction intensity, the fracture of thick hard roofs induces high-intensity dynamic disturbances and extensive impacts. During weighting periods, intense strata behaviors—such as support crushing, rib spalling, roof collapse, and coal wall spalling—occur frequently. Moreover, the inclination angle of the working face leads to recurrent accidents, including support biting and overturning, severely compromising safe and efficient mining operations. Conventional beam or thin-plate theories are inadequate for analyzing thick hard roofs, as they neglect shear effects induced by roof thickening. The post-fracture structure of thick hard roofs differs significantly from that of thin roofs, resulting in variations in support–surrounding rock interactions and overburden spatial fracture behavior, thereby exacerbating ground control challenges.   To elucidate the disaster mechanisms associated with thick hard roof fracturing and to develop corresponding stability control strategies, this study focuses on the 140502 working face of Kouzidong Coal Mine and the 0448 working face of Chunyi Coal Mine, employing a comprehensive approach that integrates theoretical analysis, numerical modeling, platform development, similar material simulation experiments, rock mechanics testing, and in-situ measurements. The research addresses five key aspects: (1) the law of mine pressure manifestation under thick hard roofs; (2) theoretical analysis of medium-thick plate deformation and failure in roof strata; (3) inclination-thickness coupling effects on roof fracturing; (4) spatial fracture patterns of overburden strata; and (5) support–surrounding rock interactions.