Energies, Vol. 12, Pages 4665: Directional Blasting Fracturing Technology for the Stability Control of Key Strata in Deep Thick Coal Mining (Energies)

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 item are smaller, and the dynamic disturbance time is shorter, which can effectively improve the stability of the auxiliary item. 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 item during mining, which lays a foundation for the application of this technology in coal mines in China.