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HAUL TRUCKS SEPTEMBER 2017 • E&MJ; 33 www.e-mj.com the University of British Columbia, said those side effects can prompt some min- ers to deploy mixed fleets, limiting the use, routes, and value of the loads of the bigger haulers. Both said that while ultra-class haulers may haul more using less fuel, they place specific demands on mines and operations that some cannot meet. Breaking that statement down, Joseph said under the right conditions, the big- ger haulers live up to expectations when it comes to fuel consumption. "In terms of fuel consumption, the larger trucks are doing better," Joseph said. "As pay- load size increases, fuel consumption went down per ton." Ebrahimi agreed, saying "the basic data shows that larger trucks burn less fuel per tonnages moved." Both said ideal fuel economy occurs under ideal conditions. Ideal conditions for ultra-class haul- ers, Joseph said, were large mines with gently sloping, wide ramps and roads made of hard rock. If the slope is more pronounced or if the roads turn to mud, a number of new calculations are re- quired to determine the point of dimin- ishing returns. First, he said research reveals the ideal ramp gradient is below 8%. "If you have a mine with a fairly shallow pit and 4% to 6% ramp grades in your mine, you could probably say bigger is better," he said. As for mud, the ideal rolling resistance was that found at hard rock mines, which in research conducted in Australia averaged between 3.5 and 4.5%, he added. Ebrahimi said that while roads and ramps might typically have limited rolling resistance problem spots, "the ground conditions at the face are a com- pletely different issue." The larger the truck, the more the potential problems could arise from "issues with soft ground conditions," he said. If the ramp is too steep and the road too soft, among the first noteworthy prob- lems to arise is that of emissions. "We were starting to get down this path of the rising tier engines, which was supposed to give us better fuel consumption and better control," Joseph said. "Looking at those vehicles that operate on ramps or ground that is really soft with high roll- ing resistance, like the oil sand compa- nies, we really have struggled to see any improvement at all. The reason for that is, when the engine has to work hard when the rolling resistance gets higher when the road deterioration is higher, then you not only are having a bad fuel burn, but what goes out of your exhaust is not just NOx, carbon monoxide and car- bon dioxide, it is also the hydrocarbon it- self. It is the fuel." Emissions and failing to meet legislated standards are among "the first and foremost things we are be- ing dinged on in the industry by govern- ment," Joseph said. Worse, a problem spot causing heightened rolling resistance repeatedly traversed by ultra-class haulers could set off a negative feedback loop. "If you have a higher pressure from your tires, you are going to get more ground deformation. The ground is going to deteriorate more. That means more road maintenance. That means higher rolling resistance," Joseph said. "Higher rolling resistance means longer cycle times, more fuel burn, higher emissions. This could ac- tually cost us a lot because we've got a larger truck putting down more load on the running surface." Knowing this, miners are forced to plan for it, widening roads that must be constructed with better materials. All that represents additional costs and impacts the stripping ratio. "The fun- damentals never change, but mining methods change," Ebrahimi said. "Larg- er trucks need wider ramps, which re- sults in shallower wall slope angle, in- Bigger is still better, but only in certain circumstances. Komatsu's 980E-4, above, offers a 400-short-ton payload.