Optimization of long-hole raise blasting considering drilling deviations: Theoretical and numerical approaches

Long-hole raise blasting (LHRB) is a highly efficient excavation method that is used extensively in underground mining and civil engineering. However, deviations in drilling are usually not accounted for in LHRB, which may adversely affect the efficiency and progress of raise excavation. In this paper, the effect of drilling deviation on the optimization of LHRB is investigated. The actual trajectories of the blastholes were measured, and the deviation rates between different diameters were compared. The effects of the drilling deviation on the burn-cut blasting mode (BCBM) and spherical cartridge blasting mode (SCBM) of LHRB were theoretically analyzed. Numerical models with vertical holes that consider the actual hole location at different positions of the raise were subsequently developed to simulate the raise blasting damage. The results indicated that the BCBM relied substantially on the drilling accuracy to provide free surface and compensation space for further blasting, whereas the requirements of drilling deviation for the SCBM were less strict. With increasing hole deviation in the BCBM, the height of the failure area of the raise blasting increased. Optimization designs that combine the BCBM and SCBM were proposed to strike a balance between the efficiency and reliability of LHRB. A 40 m high slot raise in a large-diameter long-hole (LDL) stope was successfully formed by multimode LHRB. The field test results reveal that the optimization of LHRB is feasible in practical engineering.