Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/387031
OPERATIONS ILLUSTRATED AGGREGATES MANAGER Voices of Experience Kent Clifton Bryan Smith ▼ ▼ T here are several key factors to consider when it comes to haul roads — design, good material, and maintenance. "You have to look at what effect a haul road has on haul trucks," says Kent Clion, senior market professional – Mining Equipment Application, Caterpillar, Inc. "You need to design the road with constant grades of no more than a total effective grade of 12 percent. You have to use good material to build the road, and you have to maintain it once it's built. If you don't maintain it, the downside is going to be a reduction in tire life, an increase in fuel burn, a reduction in component life, and an increase in cycle time." Clion says it's important to eliminate water as much as possible on the haul road and to maintain excellent compaction. Haul roads should be designed with a dual cross fall of 2 to 3 percent with a slight crest at the centerline that will allow water to run into drainage ditches on both sides of the road. Bonding the materials together by adding compaction to the haul road will remove air pockets and pre- vent water from penetrating the road. If water is allowed to percolate under the road, it can provide so spots and create an opportunity for the road to come apart. "Haul road width is key," Clion continues. "Haul roads should be three times the width of your widest truck. at will allow for loaded and empty trucks, as well as motor graders or other support vehicles to work on the road at the same time. At no time do you ever want to stop a truck, loaded or empty, because the haul roads are too narrow." Clion adds that all haul roads need proper safety berms at the proper height. So, the design of the haul road should include the width of the road, the drainage ditch, and the safety berm. And when it comes to designing the curves and crowns, make sure the operator will have excellent visibility with no blind spots. Once the haul road is in place, maintenance is very important. "e best tool for maintaining the haul road is, obviously, the motor grader," Clion says, adding that the size of the haul trucks running on the road will determine the size of the motor grader. "Wheel load- ers can be used to maintain haul roads, but they don't do it as cost effectively. Ag tractors with drag boxes are sometimes used, but the one that will deliver the most value to a haul road is constant motor grader support." Focusing on the haul road can easily reduce an operation's cost per ton by 3 to 5 percent. H aul road design is important. "We create an ideal long-term mine plan that includes haul roads that have been worked many different ways in order to maximize our reserves," says Luck Stone Mine Development and Blasting Manager Bryan Smith. "However, we may choose to put a haul road in a location that makes for the shortest travel distance to get to a bulk of reserves and later relocate it to a perimeter route to respect the final mine plan." To help design haul roads, Luck Stone uses a Caterpillar soware program called Fleet Production and Cost Analysis (FPC). e program allows the company to look at numerous routes to see how each will impact productivity and cost per ton to find the optimum location for the final haul roads. "When we first design the haul road and begin shooting it, we start prey wide," Smith says. "We can always trim it down if everything is perfect, but we may need a lile more width to protect our associates from local geologic conditions." Grade is an important parameter. "A grade of 10 to 12 percent is recommended, but we typically design for 12 percent," Smith says, explain- ing that a lile bit steeper haul road gains reserves over the life of the pit. "We do our best to shoot that road to a consistent grade to reduce transmission shis in the haul truck. We try to minimize sub-drilling so we can cut a grade that's really close to solid rock, which makes the haul road easier to maintain over time." Smith would ideally like to see a motor grader maintaining the haul roads once a month, but that isn't always the case. "e local operations teams make up for that by patching and repairing the haul roads with front-end loaders," he says. "If a washout occurs, they go in immediately and patch it." Oen, it's worthwhile to construct an intentional road across the pit floor to help maintain drainage. Even though the floor may be fairly level, there are high spots and low spots, and pooling water in the low spots can cause haul trucks to slow down. "If you put a lile crown on the road, it will keep the water off," Smith explains. "A well-maintained road in the pit will allow haul trucks to maintain a greater maximum speed. It's worth it to spend extra time to create the beer road to reduce the cost per ton and increase safety and productivity in the long run. Routine use of a water truck designed with a pumped water spray can also help operators run at higher safe speeds, by reducing air-borne dust and eliminating the pooling of water that can cause ruing."