Influence of air-deck blasting on fragmentation in jointed rocks in an open-pit manganese mine

The influence of air-deck blasting on fragmentation in jointed rock masses of a manganese open-pit mine has been investigated. It is revealed that air-deck blasting improves the degree of fragmentation and produces more uniform fragmentation compared with conventional blasting. Mean fragment size (MFS) reduces from a range of 0.36–1.0 m to a range of 0.27–0.51 m. Fragmentation index (FI) and blast-induced fragmentation increase from 1.38 to 4.34 and from 37–65% to 66–100% respectively. Empirical correlations have been developed to estimate MFS and FI from conventional and air-deck blasting on the basis of Bieniawskiʹs rock mass rating, powder factor and ratio of spacing to burden. Results indicate that air-deck blasting could be more effective in very low to low strength moderately jointed rock masses than in medium strength highly jointed rock masses.