The refuse bin only holds 300 tons, so mine production relies completely on four Volvo A40E FS articulated dump trucks to haul coarse refuse and build the 8,000-ft long dam around the impoundment. “Our mining operations depend on those trucks to haul coarse refuse,” said Henshaw. “If one truck goes down, we can adjust. But if the trucks can’t run, the plant shuts down, and we’re in trouble.
“These trucks run 24/5 and do about 45 miles per shift,” said Henshaw. “So in three shifts, that’s 135 miles per day. We’ve owned three of the Volvo trucks for two years. We don’t calculate their availability, but it’s very good.” The fourth truck was purchased recently.
“Each truck hauls about 145 tph,” said Henshaw. At 40 tons per load, that’s about three loads per hour, or a 16-minute cycle time. Occasionally, cycles are reduced to five or 10 minutes.
The Volvo trucks typically dump their loads in one place, and dozers spread it out in 1-foot lifts. Regulations demand the material meet a compaction specification. Henshaw says that with 6-wheel drive, the Volvo trucks make a point of driving over virgin fill, where no other truck has tracked. That helps compaction. A roller is only needed during the rainy season, when the fill is wet.
The dam is built up in benches and each bench rises on a 2:1 slope to meet the next bench. At the top, the dam is 80-feet wide.
When trucks work the top of the dam they begin by dumping in 1-foot lifts on the downstream side. They work their way upward and over to the lake side of the fill. “When we reach the point that we’re 30-feet wide at the top, then we do our upstream push-out,” said Henshaw. “We push the coarse material out into the slurry impoundment.”
River View operators like the six-wheel lockup feature on the Volvo trucks. “We lock into 6-wheel drive for just about every load,” said Loyd Patton, who operates one of the Volvo trucks. “If we didn’t have 6-wheel drive, we would just bog right down in the wet material. Rigid-frame trucks would not perform here; they could not climb the grades. We couldn’t do without the six-wheel lockup.” Engineered ramps at the River View mine are designed at maximum 10% slopes.
If the mine had to use rigid-frame trucks, Henshaw said it would take two extra operators—and their added expense—to maintain the haul roads and an additional fill area. One operator would run a motor grader, and the other would run a dozer. “This material can be slick when it’s wet,” said Henshaw. “Running a rigid-frame truck here would be like putting a bull on ice.”
Volvo’s six-wheel lock-up feature enables River View to run during winter months, when the weather is especially rainy. “We get 42 to 48 inches of rainfall every year, and most of that falls in the winter months from November to March,” said Henshaw. “Some mines haul to a temporary refuse stockpile during the winter, but we can’t do that because we don’t have space for it.”