Study on mechanism and stability control of low-side roof-cutting entry retaining in gently inclined coal seam with extra-thick main roof

This study presents pioneering research addressing the challenge of surrounding rock control in gob-side entry retaining by roof cutting under the conditions of a gently inclined coal seam with an extra-thick main roof reaching 22 m. By integrating theoretical analysis, numerical simulation, and physical analogous modeling, the influence mechanisms of roof cutting parameters on roadway stability were systematically investigated. The study reveals the inherent limitations of traditional design methods based on the goaf filling ratio. In response, an optimization model for roof cutting parameters, grounded in fracture mechanics, was developed, and the optimal parameters (cutting height of 16 m and angle of 15°) were identified. The research findings indicate that an insufficient roof cutting height results in random roof fracturing at three characteristic locations, leading to severe roadway deformation. In contrast, a sufficient roof cutting height effectively guides the roof to rupture controllably along the predetermined pre-split surface, achieving a significant reduction in stress concentration. Physical experiments validated the underlying failure mechanism and confirmed the rationality of the optimized parameters. Based on the principle of coordinated stress and displacement control, this study proposes an integrated ''four-in-one'' technical system, combining ''pre-split roof cutting, high-strength pre-stressed bolt and cable support, unitized supports, and U36 steel arches with wire mesh.'' This comprehensive approach effectively controlled the deformation of the surrounding rock while simultaneously reducing roadway excavation, support, and maintenance costs by 50%, yielding substantial economic benefits. This research provides both a theoretical foundation and an engineering demonstration for mining operations under similar geological conditions.