Study on mechanism of strong strata behavior and prevention & control technology in fully mechanized top-coal caving face with hard roof

To address the challenges of complex strata pressure behavior and frequent roof disasters in fully mechanized top-coal caving faces with hard roofs, this study takes the working face 61617 as the engineering background. By integrating theoretical analysis, numerical simulation, and field monitoring, the formation mechanism of strong strata pressure in a hard-roof fully mechanized top-coal caving face is investigated. The stress evolution path, deformation and failure characteristics, and energy accumulation and release mechanisms of the hard roof during mining are analyzed. On this basis, the energy-concentrated blasting roof cutting technology based on “key stratum energy control” is proposed, achieving a full-process investigation from key stratum identification to energy regulation. The results indicate that strong strata pressure can be categorized into two main types: the long-span suspended roof fracture type and the advanced fracture rotation type. Based on the calculation of roof fracture spacing, the 11.25 m thick coarse sandstone is identified as the main key stratum, and the 7.4 m thick coarse sandstone as the sub-key stratum. As the working face advances, strata pressure behavior is concentrated in the area ahead of the coal wall and the suspended roof above the goaf, exhibiting periodic patterns. The energy evolution follows a dynamic process of “accumulation–release–transfer,” and the sudden release of energy upon reaching the storage limit of the key stratum constitutes the dynamic essence of strong strata pressure. Accordingly, a shaped charge pipe blasting for roof cutting scheme is proposed. By optimizing the borehole layout and blasting parameters, directional pre-splitting cutting is achieved. Field monitoring shows that this technology significantly improves roof caving conditions, reduces roadway deformation rates by 40%–55%, and results in a more uniform distribution of support loads, effectively controlling strata pressure. This provides a reliable technical approach for safe and efficient mining under the conditions of thick coal seams with hard roofs.