Drill Pattern Optimisation for Large Complex Blasts to Improve Fragmentation and Dig Efficiency

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Abstract At large-scale open-pit metallic mines, drill-and-blast designs can reach over 1,000 drill holes per blast. A critical input to the design of a blast is the location of sensitive zones where ground vibration, air overpressure or flyrock needs to be constrained. The other critical input is the hardness profile of the ground. Often, the hardness across such large blasts varies significantly from soft to extra hard. Traditional approaches for pattern design use constant distance (burden and spacing) between the production drill holes and vary the explosive product strength and amount in each hole to account for variation in hardness and to adhere to blast constraints. Although this approach is operationally easier to execute, it is challenging to meet fragmentation and diggability objectives. To better address these objectives, this work provides a nonlinear mathematical model for optimising drill hole locations in conjunction with explosive amounts. The model optimises the design using a three-stage methodology. In the first stage, a novel heuristic method is used to perform local optimisation to determine the number of holes. In the second stage, the precise hole locations are determined, and in the third stage the energy intensity in each hole is optimised. In a study of 10 blasts from a Pilbara iron ore mine, for the dig efficiency objective, results indicate that variable designs achieve $$\sim $$ ∼ 2% better dig efficiency, with $$\sim $$ ∼ 11% fewer holes. For the fragmentation objective, variable designs achieve $$\sim $$ ∼ 9% better adherence to the target mean particle size, with $$\sim $$ ∼ 5% less standard deviation and $$\sim $$ ∼ 13% fewer holes.