The Effect of Initiation Time Delay and Sequencing on Rock Damage in Multi‐Hole Blasting

Rock fracturing by blasting is the most common and efficient method of rock fragmentation in mining operations. The fragmentation size affects the productivity and costs of downstream op-erations, which is influenced by the encountered rock mass and blast design. The encountered rock mass is the unmodifiable parameter in blasting. Therefore, blasting improvements can be achieved by blast design, which includes explosive selection, geometrical design, and initiation sequencing and delays. Stress wave interaction between blastholes can improve or diminish fracturing. The analysis conducted in this study through numerical modelling demonstrated the improvement in blast outcomes with appropriate delay and sequencing in some cases. The optimum delay ensures the formation of fractures on the succeeding blasthole and constructive interaction with the stress wave from the preceding blasthole, increasing the stress pulse and fracturing. While it is insig-nificant in intact rock blasting, the firing sequence is vital when blasting through the contacts of soft and hard rocks or joints, depending on the infill material. Sequential initiation and firing direction do not improve fracturing in all cases; for example, when blasting through an empty joint, the joint acts as a free face with minimum to no interaction of stress wave from adjacent charges. In such cases, simultaneous initiation can be used.