Engineering & Mining Journal

SEP 2017

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HAUL TRUCKS 34 E&MJ • SEPTEMBER 2017 creased stripping ratio and increased mining costs." Joseph agreed, saying the bigger trucks require longer ramps, which mandates the miner "set back the pit walls. The more you have to set back the pit wall, the more you have to cut into it to create what essentially for a much larger mine is a more permanent road system of ramps, the more volume you're taking out." In road and ramp planning, "most mines are going 3.5 to four times the width of a truck just because of safety issues and to be able to accommodate a safety berm on the bench going up the ramp," Joseph said. "So, the bigger the truck, the wider the roads, the more vol- ume we've got to take out. The cost of moving all that additional waste you've got to be able to balance against the abil- ity to carry more load out with one single unit." This may be the foremost concern of a miner planning on deploying ultra-class haulers, Ebrahimi said. "Ramp geometry and configuration play a big role in min- ing costs," he said. "We shouldn't forget that mine geometry also affects the way we 'selectively' mine ore." Another concern is fleet management complications that can arise with a re- duced fleet size and with increasingly expensive and technologically advanced haulers. "Having fewer trucks in a fleet reduces flexibility," Ebrahimi said. "This challenge can be addressed by purchas- ing additional or spare trucks, which can be expensive." Again, Joseph agreed, saying, "The advent of the ultra-class was mines say- ing 'we're tired of having to deal with such larger fleets, can we go to a small- er fleet and do the same or better?'" The dream of smaller fleets was one of the driving forces behind the demand for ul- tra-class haulers. "Moving in that direc- tion, we've lost some of the redundancy," Joseph said. "If we lost a 240-ton truck, no big deal. We have lots of them. You lose a 360- or 400-ton truck, it is now an additional 120 to 200 tons per cycle that we're starting to lose out of the system." Not only is production hit when one of the bigger haulers is sidelined, research revealed the bigger the truck, the costlier the repair, Joseph said. "What we found was when we got into the bigger units, there were bigger types of problems and they happen more often," he said. Auto- mation, energy recapture, and integrated digital mine tech add to the complexity of the larger haulers. "And those differ- ent things require higher levels of exper- tise," he said. "The costs of labor have gone up. The tools they require, and the diagnostic systems they use, have gone up in cost." At least for a time, another simi- lar cost and challenge was centered on tires. "When we jumped from a 40R57 tire to a 55R51 tire, we made a huge jump in size class," Joseph said. "We had the manufacturer create a tire class that didn't exist. It was literally a de- mand overnight. The manufacturers learned very hard on what would work and what didn't." Other cost considerations also enter the equation. For example, the size of the haulers used can affect processes, and thus costs, downstream, Ebrahimi said. "Employing larger trucks requires bigger benches and that means coarser ore fragmentation," he added. Combined, for some miners the above- mentioned costs and potential challeng- es are greater than the expected returns on investment. "When you consider all Ramp slope, road conditions, maintenance costs, and fleet management challenges should all be considered when planning to deploy an ultra-class truck, two mining engineering professors say. Above, a Caterpillar 794 AC tops off.

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