A numerical investigation of the effect of blasthole delay in rock fragmentation

One of the main objectives of all blasting operations is good fragmentation. Rock fragmentation by blasting is a complicated process which involves consecutive loading phases. Additionally the initiation of multiple holes in a blasting operation adds complexity to the process. The intention of this study is to investigate the effect of delay between blastholes in a qualitative manner and in an actual bench scale. The 3D finite difference code (FLAC ^3D) was used to model multiple blasthole initiation in a typical bench. The blast loading history was simplified and applied to the blasthole walls. Accordingly, the interaction of explosive energy transferred to rock from each hole was examined as a function of blast-hole delay. A Mohr-Coulomb material model was used for host rock to allow for plastic failure calculations. The conducted numerical study describes the role of delay time in blasting in a qualitative manner. The obtained results show that, at the end of stress wave loading phase, long delays cause the burden to be under a higher stress state and closer to the rock mass failure envelope. In the case of 0 ms delay, in spite of high and fast delivery of energy to the rock mass, the final stress state in the burden is fairly lower than the 7 ms delay case. In other words, in this case, the burden material has a longer stress path to reach the rock mass failure envelope.