Engineering & Mining Journal

JUL 2019

Engineering and Mining Journal - Whether the market is copper, gold, nickel, iron ore, lead/zinc, PGM, diamonds or other commodities, E&MJ takes the lead in projecting trends, following development and reporting on the most efficient operating pr

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Page 45 of 67

HAUL ROAD MANAGEMENT 44 E&MJ • JULY 2019 The condition of a haul road can significantly affect the perfor- mance of a mine from both a cost and productivity perspective. Determining the frequency of haul road maintenance and when to take one out of service to rebuild it can be difficult. Mine en- gineers walk a fine between squandering money on too frequent service and not enough, which could cause road conditions to deteriorate more quickly. Another important aspect of haul road management is deter- mining which segments of the haul require the most attention. Looking at several factors such as distance, grade, rolling re- sistance, the hauler itself along with the desired tonnage, engi- neers can create models that let them determine were best to make that investment. For most mines, the haul road's surface is not paved and con- sists of unsealed gravel. Below that wearing course is several layers of material of different qualities and strength that support the wheel loads and protect the subgrade material. Haul road conditions deteriorate due to traffic-induced damage to the wear- ing course, environmental degradation and weathering, routine road maintenance and spillage. "If nothing is done to improve it, a haul road's wearing course will degrade over time," said Roger Thompson, principal, Mineravia. "Routine road maintenance can return the road to close to its original condition, but it can also damage the wearing course as well and reduce its operating life." Deterioration can be minimized through fit-for-purpose structural design. In other words, it doesn't matter how good the sheeting material or wearing course is on top, Thompson explained. "If we are not supporting it correctly, it's not going to work," Thompson said. "Structural design is really import- ant. When we are looking at this fit-for-purpose design, we first look at the structural design to support the wearing course. Then we select the wearing course material that minimizes the rate of degradation. There are also several quality-control prac- tices to consider during the construction process. Once the haul road is constructed, we want to look at optimizing road management practices, particularly how to manage the degra- dation of the material." Understanding Rolling Resistance Rolling resistance is defined as an additional gradient that results from the resistance to motion. Some of the resistance to motion the truck feels is likely due to defects on the road. Common road defects include potholing, rutting, corrugations, loose material or rocks on the road, all of which contribute to rolling resistance. "When rolling resistance changes, it never goes from bad to good unless we properly maintain the road," Thompson said. "It normally goes from pretty good to awful." The effective resistance (grade +/- rolling resistance) of a haul road is a good starting point. The effective resistance of a flat unpaved road (0% grade) is 2%. A haul truck would only be able to achieve 92% of the maximum speed on this surface (See Figure 1). "If we let that flat haul road deteriorate over time, where the rolling resistance increases to 4%, that 2% increase in rolling resistance equates to a 26% loss in speed," Thompson said. "Small changes in rolling resistance are quite significant in terms of the impact on loss of speed or increase in cycle time." Where's the Value? Evaluating the costs of haul road maintenance and rebuilds Figure 1 — A 2% increase in rolling resistance equates to a 26% loss in speed. Figure 2 — An increase from 2% to 3% in rolling resistance leads to a cycle time increase of 7% for the ramp haul and 20% for the flat haul.

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