The weakening of hard coal–rock mass is the core common problem that is involved in the top coal weakening in hard and thick coal seams, the hard roof control during the initial mining stage in the longwall mining face, and the hanging roof control in the gob of non-coal mine. Based on the characteristics of pulse hydraulic fracturing and constant pumping rate hydraulic fracturing, a weakening method for hard coal–rock mass by combining pre-pulse and constant pumping rate hydraulic fracturing is proposed. A complete set of equipment for the combined pulse and constant pumping rate hydraulic fracturing construction in the underground coal mine is developed. The pulse and constant pumping rate hydraulic fracturing technology and equipment were applied in the top coal weakening of the shallow buried thick coal seam. Compared with no weakening measures for top coal, the average block size of the top coal caving was reduced by 42% after top coal hydraulic fracturing. The recovery rate of the top coal caving mining face reached 85%, and it increased by 18% after hydraulic fracturing.

Rock directional fracturing is one of the difficult problems in deep mines. Directional fracturing controlled by hydraulic fracturing in dense linear multiboreholes is a novel directional fracturing technology of rock mass, which has been applied to the ground control in mines. In this paper, a physical model experiment was performed to study the fracture propagation process between multiboreholes. The results show that the intersecting of fractures between boreholes caused the sharp fluctuation of injecting water pressure. A directional fracturing plane was formed along with the direction of boreholes layout, and the surface of the fracturing plane is relatively flat. The dynamic initiation and propagation process of cracks between boreholes during directional hydraulic fracturing were simulated. The evolution of poroelastic stress and pore pressure between multiboreholes was analyzed. The numerical results indicated that a poroelastic stress concentration zone and pore pressure increase zone appeared between boreholes in the direction of boreholes layout. The pore pressure distribution is generally an elliptical seepage water pressure zone with the long axis along the direction of the boreholes layout. After the hydraulic fractures are initiated along the direction of the boreholes layout, the poroelastic stress on both sides of fractures decreases.