Propagation law of non-penetrating cracks in pre-splitting blasting under synergistic guidance of shaped charge tube and empty hole

The directional pre-splitting blasting has been widely utilized in coal mines, and the synergistic of shaped charge tube and empty hole helps form directional cracks and control crack length. This study used the dynamic numerical calculation method to investigate the influences of the uncoupling coefficient, the distance between empty hole and blasting hole, and the diameter of empty hole on the effective stress and crack propagation under the synergistic effect of shaped charge tube and empty hole. The formation, propagation, and crack arresting rule of the pre-splitting blasting crack were revealed. The non-penetrating crack directional control approach was proposed and applied in the deformation control practice of the small coal pillar roadway. During double-hole blasting, with the increase in the distance between empty hole and blasting hole, along with the diameter of empty hole, the four symmetric cracks around the empty hole change to bilateral symmetric ones. It was suggested to place the empty hole in the middle of the two blasting holes, and the crack arresting hole be arranged at the junction of the penetrating zone and the non-penetrating zone. Field application results showed non-penetrating cracks formed in the roof of the small coal pillar roadway. Compared with the roadway without pre-splitting, the increase in bolt axial force was small, with an average increase rate of 32.5%. The research results provide a basis for determining parameters of non-penetrating pre-splitting blasting.