Under the conditions of high ground stress and mining disturbance, the strata breakage that is induced by mining is severe. Thus, it is critical to investigate the structural characteristics of key strata (KS) in deep thick mining. This study introduces an innovative technology, namely, directional blasting fracturing, in which an energy-gathering tube is installed in a borehole and an explosive is detonated to break the roof in a specified direction. A theory of balanced bulk filling is established based on the requirements of developing a voussoir beam structure, which can be used to effectively evaluate the percentage of bulk filling in gob and to determine to which structure the key strata belongs. Based on this theory, two types of novel structural models in the advancing and lateral directions of the longwall face are established and defined for studying the roof fracturing mechanism. Compared with a cantilever structure, Model C can develop a stable voussoir beam structure, limiting the rotation space of the KS and reducing both the peak abutment pressure and the dynamic disturbance time in the advancing of the longwall face. Model E is defined as when the technology of directional blasting fracturing effectively cuts a stress transfer path into the barrier pillar. The peak abutment pressures on the barrier pillar and auxiliary entry are smaller, and the dynamic disturbance time is shorter, which can effectively improve the stability of the auxiliary entry. The key parameters of directional blasting fracturing are designed and constructed, and they include the roof fracturing height, angle, and charge structure. The field application performance of this innovative technology at the longwall face of 3⁻¹101 in Hongqinghe coal mine was evaluated by analyzing the chock pressure stress, the pillar pressure stress, and the deformation of the auxiliary entry during mining, which lays a foundation for the application of this technology in coal mines in China.

Mining fractures are the channel of gas migration, and it is important to figure out the gas migration laws for gas control. Combined with the actual geological conditions of Shaqu No. 2 coal mine, a numerical model of no-pillar mining with automatically retained entry was built to simulate the deformation and fracture of overburden rock and the evolution laws of cracks above the goaf during mining. Subsequently, CFD software is used to theoretically stimulate the gas concentration distribution laws of non-pillar mining with the automatically retained entry in the stope under non-drainage and high-level borehole drainage conditions. The laws of gas concentration in the stope were compared and analyzed under the condition of the Y-type ventilation of non-pillar mining and U-type ventilation of coal pillar mining. The results show that Y-type ventilation of non-pillar mining reduces the gas concentration in the upper corner of the working face and the goaf, and effectively solves the gas accumulation problem in the upper corner of the working face in the mode of U-type ventilation of coal pillar mining. On this basis, the high-level borehole drainage technology is adopted to effectively reduce the gas concentration in the goaf. The research has certain guiding significance for the gas management of non-pillar mining with gob-side entry automatically retained.