Engineering & Mining Journal

JAN 2019

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Page 35 of 59

BLASTING 34 E&MJ • JANUARY 2019 had powder representatives from local and international companies from around the world try to help them and none had been able to make any changes, because they all used old school design approaches. The authors' goal was to reduce oversize on the ore, achieve better fragmentation on the overburden, and maintain extreme- ly low powder factors. Initially a few factors such as row-to- row timing were modified to facilitate proper borehole confinement, but the ma- jor issues this site was facing was in the breakage mechanisms of the blast and the proper design of blasts. After the proper confinement was achieved the spacing was modified to accommodate the timing, burden, and bench height. The powder factor was then lowered below the required maximum — which had never been tested on-site before — and the blasts performed much better. The authors then re-adjusted the burden to increase the stiffness ratio while updating the spacing for the new conditions to blast at the sites powder fac- tor limits. Figures 10 through 13 show the differences in fragmentation for both the ore and overburden materials where the design parameters where changed and the exact same powder factor was used. Summary As discussed throughout this article, pow- der factor is an extremely poor design tool that does not belong in a blaster's arse- nal when approaching a blast design. At best the powder factor is to be used as an economic check. Old school designs based off of powder factor and powder factor principles have falsely led opera- tors to make decisions on blasting that have not only led to poor performance of blasts, but have also led to unnecessary costs in excess drilling and explosives. Modern blast design is an outcome-based approach where the actual physics of blasting are used to determine blast de- sign parameters to meet the needs of the operator. In most cases these results can even be achieved with less explosives than old school design approaches. Under old school design the ideal stiff- ness ratio to blast under for low cost was a stiffness ratio of 2.5; however, under modern design it is understood that this is actually the most expensive stiffness ratio to blast with. It is now understood that the most economical stiffness ratio to blast is between 3.5 and 6.0 which not only gives minimal cost but also the best performance. Today's blasting indus- try is far advanced from the days of load as much explosive as can be loaded and blow the snot out of the rock. It is now understood that a skilled blaster can use much less explosive and get better results than one using a larger powder factor. Calvin Konya is the founder of Precision Blasting Services (PBS). Anthony Konya serves as project engineer for PBS. Figure 10 (left)—Overburden fragmentation before pattern modifications. Figure 11 (right)—Overburden fragmentation after pattern modifications. Figure 12 (left)—Ore fragmentation before pattern modifications. Figure 13 (right)—Ore fragmentation after pattern modifications.

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