For a mine to decide on its optimal level of fragmentation is not always straightforward; once decided, however, achieving it requires reconciling blasts-as-designed against blasts-as-fired.According to BME’s global manager for blasting science, D. Scott Scovira, BME has the necessary tools on both the blast design and blast operations side of the blasting equation to deliver optimal fragmentation. “We are also working with partners in total mine design software systems to seamlessly integrate our blasting tools into their system,” said Scovira. “The goal is to integrate blast design, blast recording, and blast delivery systems; this allows for easier interrogation of results, to guide the drilling and blasting process to produce consistent, quality blasts.” He highlighted that rock fragmentation distribution is often a key performance indicator of blast performance, with each mine targeting a fragmentation distribution that is optimal for their total mining cost. “Agreeing on an optimal mine fragmentation distribution can be a challenge,” he said. “A mining operation department may want fine fragmentation distributions for maximum excavation productivity and minimal oversize handling. Others may opt for coarser fragmentation to achieve better economy in input costs, while crushing and milling departments may have their own target fragmentation distributions – different from the mining department.” Fragmentation assessment At the end of the day, though, mines need accurate fragmentation assessment tools to understand site-specific conditions and to optimise blast explosives loading and initiation designs. This includes being able to ensure that the designed blast is accurately translated into the actual fired blast. “On the blast design side of the equation, BME’s BLASTMAP is a powerful blast design software tool to specify explosive hole loads and assign hole firing times,” said Scovira. “The latest version of BLASTMAP includes a new design tool to heat-map initiation burden relief times.” Burden relief times can strongly influence rock fragmentation and displacement. Understanding and managing burden relief times allows the blast designer to target specific blast outcomes. BLASTMAP can also estimate blast fragmentation outcomes, based on standard geomechanical rock properties specific to any given blast design. With data from in-field fragmentation distribution measurements, the fragmentation distribution prediction tool can be calibrated to site-specific conditions and results.
“BME also offers solutions on the blasting operations side – where the BLASTMAP‑designed hole charge can be downloaded into BME’s XPLOLOG data recorder,” he said. “On the bench, the XPLOLOG can be used by blasters to capture as‑drilled hole depths and compare these to the design depths.”He noted that XPLOLOG can be used by the bulk explosives truck operators to target the as‑designed bulk explosive hole loads and stemming columns, and capture the actual loads placed. “For blast initiation, the design hole firing times can then be downloaded from BLASTMAP into BME’s AXXIS Logger, for electronic detonator programming,” he said. “After the blast is complete, the AXXIS Logger can be downloaded to compare as-designed versus as-fired initiation information.” Ground reactivity Another key element of good blasting practice is being aware of reactive ground, and selecting the appropriate product for safe blasting and good results. “Ammonium nitrate-based explosives can undergo rapid exothermic reaction in the presence of certain sulphide-bearing ground,” he said. “At best, this jeopardises the quality of the blast, while at worst creates life-threatening conditions on site.” He noted that BME has a long track record of safe blasting applications in reactive ground conditions at several mine sites in countries including Zambia, Mauritania and South Africa. If reactive ground is suspected at a site, isothermal laboratory tests are conducted to assess the degree of ground reactivity. The amount of chemical inhibitor required to retard reaction can be determined, as well as the safe operating window to charge, tie-up and blast. BME Zambia has a plant-based laboratory in Zambia which is fully equipped to test ground for reactivity – in line with the globally recognised AESIG Code of Practice. “The ground reactivity lab in Zambia includes a small rock crusher to test fresh rock; this gives more accurate results than testing drill cuttings, which may have already oxidised out,” said Scovira. “BME Zambia worked closely with our laboratory in Losberg, South Africa, to formulate our specialised reactive ground-inhibited bulk product INNOVEX 100 RG.” This product is matched up with compatible non-electric and electronic blasting systems to achieve safe and quality results.