The Music of Blasting

A common adage in the Explosives Industry goes by saying that "Blasting is not bombing". One of the key differences between the two employs of explosive energy lays in the same gap existing between the application of acoustic energy that differentiates noise from music: timing and the distribution of energization in time. While timing in blasting is widely accepted to influence blast induced vibrations, it is still not completely investigated when related to rock fragmentation and downstream benefits. This paper shows a research about this topic, developedon two phases: 1) test blasts at the Experimental Mine of the Research Center of Responsible Mining of the University of São Paulo; 2) development project for large-scale production blasts in an open-cast mine. The first phase of the research was performed attempting to increase the productivity of the experimental mine, by lowering production costs and improving the quality of the product. Some Key Performance Indicators (KPIs) were established to monitor the results. A new blast design method and a more appropriate initiation sequence were designed according to the principles of: i) decomposition of the blast; ii) taking advantage of the free surfaces to favor the movement of the blasted material; iii) simultaneous holes firing as far away as possible, to avoid undesired cooperation of charges that may induce the explosive energy to work with shear effect instead of producing fragmentation. The results show that the proper selection of delay timing leads to significant benefits for rock fragmentation, downstream processes and the quality of final walls. The second phase of the study was a research and development (R&D) project in an open-cast mine with the goal to achieve an average P80 of 300 mm (11,8”) in the run-of-mine (ROM) product without altering the existing budget. The project included several variables in the blast design that were not previously taken into account, such as the orientation of natural joint sets in the rock mass, specific energy of the explosive and firing sequence. The new blast design method considered the directions of natural joint sets and determined the drilling pattern and the firing sequence accordingly to favor the movement of the blasted rock along its preferential direction, to reduce its confinement. At the end of the project, it was achieved an average P80 of 304 mm (12”) in the ROM, 50% lower than the one at the beginning of the project. The final blast of the project showed a reduction of 3% of the drill and blast cost, employing the same powder factor and the same drill pattern size used at the beginning of the project. The results of this study show how blast performance is related to variables that are not contemplated in the most common design methods or fragmentation models: the firing sequence, the degree of freedom and the direction of movement in the blast.