Engineering & Mining Journal

JUL 2019

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Page 47 of 67

HAUL ROAD MANAGEMENT 46 E&MJ • JULY 2019 wearing course material is sent to a civil lab and they provide a particle size density (PSD) and Atterburg limits reports. Using this information coupled with the speed and the weight of the truck, rolling resistance can be effectively modeled over time. "Practically what that means is that we are able to look much more closely at how the road deteriorates over time," Thomp- son said. "As shown in Figure 3, that deterioration is based on a maintenance interval, but at some point we will reach the stage where, no matter how much maintenance work we do, it will not improve the rolling resistance. That's when the mine should consider a re-sheeting campaign." Re-sheeting Haul Roads As the road maintenance frequency is reduced, vehicle operat- ing costs increase with rougher roads and cycle times increase as does the fuel burn. "So, what we are looking for is a sweet spot on the haul road that shows this is the maintenance interval we must apply where the maintenance costs and truck haulage costs are minimized," Thompson said. "That sweet spot will be different for the flat haul and ramp segments and there is a very different cost profile between those two." To understand how roads react to changes in wearing course resistance, mine engineers could split haulage into similar segments, in terms of geometry (width and grade), type of sheeting material, and the tonnages the roads are expected to handle (See Figure 5). Then they could use var- ious approaches to assess fuel burn as a critical cost com- ponent and cycle times. The Cooper equation, for example, developed by Alan Cooper from Snowden about 10 years ago, provides good insight into what the speed and fuel burn of a truck will be based on a few key operating parameters, Thompson explained. "The majority of the costs will be associated with fuel burn and it will give the best indicator of the value add for improving road maintenance activities," Thompson said. A case study looking at three segments of haul road provides the methodology to identify the improvement base case. Seg- ment A is 10% grade ramp out of the pit. Segment B is the flat Figure 4 — Cooper equations reliably model truck speeds and fuel burn. Figure 5 — Three base cases are modeled for 20 days hauling 125,000 t/d. Figure 6 — As far as unimproved (left) vs. improved, the red line represents the amount of material moved on a daily basis, which reduces as the rolling resistance increases, but the rate of decrease has been significantly reduced through re-sheeting. The blue line represents the amount of haulage that would have to be supplemented to maintain the 125,000-t/d target.

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