The Bulyanhulu Mine, Tanzania is constantly trialing ideas for improvements in the drill and blast process. The project work has resulted in a large number of choices in explosive type and charging methods being available for blast design. Interestingly, though booster sensitive bulk emulsion had been introduced to the site to reduce dilution, better results were being obtained from reduced charge columns (decoupled columns of poured anfo in 50mm pvc pipe) and pneumatically loaded anfo upholes, which had been traced. In order to compare the explosive type and charge up-methods, an explosives comparison trial was performed.rnThree tests were performed; recorded VOD, D'Autriche Method VOD and a site modified Two-Pipes Test. During the trial 126 pipes (42 trials of 3 pipes each) were blasted, with PVC casings representing hole sizes of 40mm, 57mm, 65mm, and 70mm. The resulting pipes showed six identifiable stages of failure. The pipes were measured at 200mm locations along the 1800mm witness pipe and classified by their failure stage.rnAnalysis of the pipe measurements failed to produce any correlation when analyzed statistically despite similarities being identifiable visually. Plots were then generated of the pipes considered representative of their test set. The y-axis was set up as discrete failure stages and the average recorded failure stage at each measuring point plotted. The resulting failure mode profiles were then compared.rnThree important outcomes were identifiable. These were that none of the 65mm anfo, the 65mm bulk emulsion, or the 57mm bulk emulsion tests had similar failure mode profiles to those of the reduced charge columns or the traced upholes tests. This indicated that the emulsion had too much energy. It also indicated that a shift to a 57mm hole using the same bulk emulsion would be ineffective.rnDiscussions with the explosives supplier lead to the development of a low energy bulk emulsion, known as the Buly Blend. The new energy, which can range from a relative bulk strength of 67% to 114% of the energy of poured anfo, is soon to be trialed on site at Bulyanhulu.
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