Abstract

The multiple blasthole fragmentation (MBF) model developed by Orica can model real blast designs in three dimensions of a production blast with the actual geometry of the blasted overburden and free faces. The MBF model can explicitly model the majority of blast design parameters, including explosive loading configuration, multiple decking, delay timing of each explosive charge, and explosive properties. The model has been successfully applied to several open pit mines and quarries around the world, including Canada, the United States, and Africa. The peak particle velocity (PPV) induced in the rock from the explosive detonation is used in the MBF model as the key parameter relating to the size distribution of the rock fragmentation. Relating the PPV to the rock fragmentation is based on earlier work relating the near-field vibration particle velocity to the dynamic strain in rock. A recent publication further revealed that the PPV is related to the maximum relative displacement that induces three-dimensional strain at a point in the rock.

A case study for trim blast rock fragmentation improvement was conducted at an open pit copper/molybdenum mine in Canada in 2021, that included setup of the field data collection, data analysis, and establishment of the model for the sites, scenario modeling, field implementation and results comparisons against the modeling. The field data analysis was used to characterize the rock mass property at the site. The delay timing and burden were selected from the modeling and electronic initiations were introduced to implement the recommended timing. Modeling the effect of different blasthole diameters was also conducted. Using a target size distribution, blast pattern modifications were evaluated in the modeling. The inputs collected in the field tests for the MBF model are the near-field signature hole blast vibration unfiltered by the presplit. The parameters from the near-field signature hole vibration filtered by the presplit are input to the MSW (multiple seed waveform) blast vibration model to predict the blast vibration at the highwalls from trim blasts. The effectiveness of the current presplit design was evaluated in vibration reduction at the highwall. Optimized designs were proposed based on the blast vibration modelling.