Engineering & Mining Journal

APR 2018

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Page 47 of 91

BLASTING 46 E&MJ • APRIL 2018 Drilling and blasting is a complex pro- cess, which in many situations is not given the full emphasis it deserves in process development and controlling the costs throughout the mine. For example, the blasting process dictates muck pile configuration, which affects shovel and loader fill factors. The fill factor of the shovel determines how many trucks are required on-site, how fast those trucks can be loaded and the truck fill factor. The fragmentation of the blast also im- pacts the crushing costs and leaching efficiency. The overbreak of the blast in- fluences slope stability, slope steepness, pit safety and scaling costs. The blasting process affects every aspect of the opera- tion and poor blasting can lead to millions of dollars in direct costs and tens of mil- lions in indirect costs at larger operations. To begin one variable, stemming, will be considered to see how this can affect a mine. Stemming 1 , while important, is not nearly as important as other variables such as burden and stiffness ratio. How- ever, one can appreciate how just stem- ming can dramatically change a blast's function. Most engineers understand that stemming lowers the air overpressure from a blast by more than 98%, which dramatically reduces noise. Proper stem- ming, however, can also decrease the P80 of a blast by more than 10% and reduce mucking cycle times by more than 18%. Yes, a few feet of drill cuttings can really change the blast this much. Optimizing the blasting process can dramatically improve the other on-site processes and lead to major cost-savings throughout the site. There are two types of optimization processes for blasting pro- grams. The first is the design process to ensure that the way the site is blasting is the most efficient for the set goals. This is similar to a site deciding which haul truck would be better: a 240- or 400-ton truck? While this is relatively simple to calculate for a haulage situation, the dy- namic blasting process involves constant modifications to this design process, and in many cases, it needs to be addressed and altered first. Now imagine a mine running a 50-ton truck from the 1980s instead of a modern 400-ton truck because that met the oper- ation's needs when the mine first started. This is typically what has happened with drilling and blasting. The blasting process still uses methods from the 1980s or ear- lier to break rock. For example, many mines still see stemming erupt violently from the blastholes with little to no move- ment of the muck pile, large boulders mixed with fines, and tremendous flyrock. If a dozer is needed to break up a muck pile for a shovel to dig, the blasting pro- cess needs major redesign. After a proper design has been imple- mented on-site, the next part of the op- timization is process improvements. Two process improvement methods are then used in sequence, the first is correction and standardization of the current design. Once a proper design has been planned and implemented, there must be meth- ods to ensure that the proper design is sufficiently applied in the field. Let's look at an example similar to this from a manufacturing or mineral processing system. A pump is set to a specified rotation per minute (RPM) to deliver a set amount of chemical in gal- lons per minute (GPM). Now imagine that the final product comes out with an error, the engineer does not just assume that because he designed and set the pump to the correct speed that it did not misfunction and instead blame improp- er chemical preparation. The engineer knows that the pumping speed and flow rate can vary, and because of this, they use flow meters and variable frequency drives (VFDs) to ensure that the flow is correct. Unfortunately, this is what is all too common in blasting where, if a prop- er design is assumed, then any problem is blamed on geology. The isolated toe left in the pit is a classic example. The most common and Six Sigma Blasting Implementing a process improvement plan for blasting can improve downstream operations By Anthony Konya and Dr. Calvin Konya 1 Stemming is the non-explosive material that is placed on top of the explosive in a loaded borehole to help trap the explosive gas pressure in the borehole, maximizing the work of the explosive. Figure 1—Lack of proper amount of stemming or incorrect stemming material can dramatically reduce blast efficiency impacting fragmentation, throw, backbreak, ground vibration and air overpressure.

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