Deep-hole directional blasting for roof cutting and pressure relief in coal mines and its applications

This study proposes a deep-hole directional blasting technology based on polymer energy charge packages for roof cutting and pressure relief as a solution to difficult roadway support and poor stability of coal pillars due to high pressure of composite roof plate in thick coal seams. Specifically, we probed into the control mechanism of polymer energy charge packages on the redistribution of stress field in surrounding rocks through theoretical analysis and analyzed how varying blasting parameters affect fracture penetration through LS-DYNA numerical modelling. The 15115 working face of a mine was taken for analysis to optimize key parameters such as borehole depth, spacing, roof cutting height, charge volume and charge structure, coupled with on-site industrial experiments and evaluation of pressure relief. After the blasting of polymer energy charge packages on the roof of the mining area, explosive energy was preferentially released in the direction of polymer energy. With identical charges, it generated main fractures that were significantly longer compared to that in the non-polymer energy direction, with a length ratio of 4.2∶1.0. The maximum displacement of the top and bottom plates in the adjacent roadway was reduced by 82% in the pressure-relieved section than that in the non-pressure-relieved ones. In the roof cutting roadway, the average compressive strength of the rock mass was reduced by 27% in the direction of polymer energy compared with that in the direction perpendicular to the polymer energy. Results verified the validity of the proposed technology for its effective directing of fracture expansion along the preset path, which significant reduced the length of the roof plate overhanging the roof and the collapse of the rotary extrusion on the coal column pressure. This study therefore offers references for controlling roadway stability under complex, high-stress geological conditions in deep mines.