Optimization of borehole layout in equal-diameter empty hole parallel cut blasting

Cut blasting is a critical technique in roadway excavation, where the layout of cut holes directly affects the quality of excavation blasting. Based on the engineering context of phosphate mining in Hubei Province, this study first analyzed the effects of blasting gases and stress waves according to rock blasting mechanics, derived the calculation formula for the fracture zone radius, and determined the optimal distance between cut holes and empty holes. Subsequently, based on the calculated optimal distance, two empty hole layouts were designed: a six-empty-hole pattern and an eight-empty-hole pattern. Using ANSYS/LS-DYNA software, the effectiveness of cut blasting under these different layouts was analyzed from the perspectives of surrounding rock damage, dynamic evolution of the stress field, and extent of the cut cavity, followed by validation through field experiments. The results indicate that the optimal hole spacing between cut holes and empty holes is 170 mm, and that at the same distance, empty holes arranged at 45° generate greater circumferential (hoop) stress compared to those arranged horizontally. Furthermore, when sufficient compensation space cannot be provided, it is advisable to appropriately reduce the hole spacing, thereby reducing the rock volume between cut holes and empty holes to allow adequate expansion space for the rock.