Rock fragmentation control in opencast blasting

The blasting operation plays a pivotal role in the overall economics of opencast mines. The blasting subsystemaffects all the other associated sub-systems, i.e. loading, transport, crushing and milling operations.Fragmentation control through effective blast design and its effect on productivity are the challengingtasks for practicing blasting engineer due to inadequate knowledge of actual explosive energyreleased in the borehole, varying initiation practice in blast design and its effect on explosive energyrelease characteristic. This paper describes the result of a systematic study on the impact of blast designparameters on rock fragmentation at three mines in India. The mines use draglines and shoveledumpercombination for removal of overburden. Despite its pivotal role in controlling the overall economics of amining operation, the expected blasting performance is often judged almost exclusively on the basis ofpoorly defined parameters such as powder factor and is often qualitative which results in very subjectiveassessment of blasting performance. Such an approach is very poor substitutes for accurate assessment ofexplosive and blasting performance. Ninety one blasts were conducted with varying blast designs andcharging patterns, and their impacts on the rock fragmentation were documented. A high-speed camerawas deployed to record the detonation sequences of the blasts. The efficiency of the loading machineswas also correlated with the mean fragment size obtained from the fragmentation analyses.