Research on fracturing behavior and mechanism of multi-empty-hole directional blasting in deep hard rock

The rock mass in deep metal mines is typically hard and subjected to combined dynamic and static loading, making directional fracturing difficult in deep hard rocks. In mineral-geothermal co-mining of mines, empty-hole directional blasting is an important way to achieve effective fracturing of deep hard rock. For this purpose, this paper systematically conducts the multi-hole blasting study of granite specimens with empty-holes under two-dimensional pre-stress conditions by means of experiments, numerical simulations and theories to reveal the fracturing behaviors and mechanisms of multi-empty-hole directional blasting in deep hard rock. The results show that the empty-hole generates maximum tensile stress in the direction of the incident stress wave and maximum compressive stress perpendicular to it, leading to the propagation of blast cracks along the empty-hole. However, the complexity of the fracture network decreases increasing pre-stress, and cracks propagate in the direction of the maximum pre-stress, which leads to a significant reduction of the empty-hole effect. In addition, with the increase of pre-stress level and lateral pressure coefficient, the longitudinal wave velocity, the maximum internal energy, and the maximum volume fraction of the damage element of the sample increase, while the maximum kinetic energy decreases. Finally, decreasing the hole spacing leads to easier connection of cracks, as well as adequate free surface, a reasonable blasting sequence, and increasing the blasting delay improves the complexity of the rock blasting fracture network. The results indicate that pre-stress is the primary factor limiting the formation of complex fracture networks in deep rock blasting. However, the impact of pre-stress on crack propagation is mitigated by adjusting the parameters of the empty-hole directional blasting scheme, thereby enabling controlled blasting fracturing of deep hard rock.