Linear Crusher ...reduce cost per mile of ­remote, rocky road construction

by Del Williams

For those in forestry, mining, oil extraction, or other professions requiring access to often remote locations, maintaining not only primary, but also secondary and even tertiary roads is often a must. But on unpaved roads, the more remote the greater the cost and challenge to maintain them with traditional commercial gravel sources or pit-based mobile rock crushers.

Instead, a growing number of industry professionals are using an innovative category of machinery called linear crushers to reduce the cost per mile of remote road construction while rehabilitating unpaved roads. They are using the existing rock that is typically found in the road subgrade, ditches, or berms, to gravel road surfaces.

In contrast to mobile rock crushers – which are only “mobile” when moved to a site but stationary when operating – linear crushers actually move along the road that is being repaired, crushing existing oversize rock along it. The result is usually mixed with existing gravel and soil to not only resurface a road, but also improve its subgrade at a fraction of the cost of traditional methods.

Low-cost, long-wear road re-surfacing

“Using a linear crusher on main and secondary roads that do not require DOT spec gravel resurfacing costs us about $10,000 per mile including spreading and rolling, which saves us about $20,000 to $25,000 per mile compared to the commercial cost of gravel,” says Nick Jones, Southeast Region Forest Engineer for the Washington State Department of Natural Resources (DNR). The DNR maintains good road access as part of its mission in managing 5.6 million acres of forest, range, agricultural, aquatic, and commercial lands for the people of Washington.

A contract was set up to demonstrate the linear crushing process after the DNR was approached by Roadtech Inc., a St. Maries, Idaho-based manufacturer and contractor of linear crushers that specializes in road reconditioning. The company’s linear crushers can pulverize native rock up to 16-inches in diameter using a chrome alloy hammer and anvil system that forces material through a restrictive crushing chamber.
“The linear crusher’s hammer-anvil type system can break up our hard fractured basalt,”

says Jones. “Typical production is approximately 1.5 miles of road per day.”

According to Jones, a mobile rock crushing-pit operation would cost the DNR about $20 to $25 per cubic yard of gravel applied or about $30,000 per mile to gravel a road, depending on factors such as permitting, rock quality, and haul distance. Rock pits, which must be permitted for environmental reasons, can take up to one acre, depending on stockpiles for a crushing operation; and rock crushers are increasingly scarce in central Washington, as the local timber industry has declined.

Even when gravel from commercial sources or pit-based mobile rock crushers is available, neither method addresses the road subgrade, where underlying rocks are often the cause of road performance problems such as drainage, drivability, or alignment.

“Too often, as a road’s gravel surface thins out, native rock comes up in the subgrade, making the road difficult to maintain,” explains Jones. “When subgrade rocks are removed, more material is needed to fill the voids.”

“Over ­­­a 10-year road maintenance cycle, the DNR estimates that about $4,000 per mile is saved using a linear crusher,” adds Jones. “Instead of having to regrade and reshape roads with a native running surface every couple years, we can do so about every five years for roads using the linear crushing process because these roads hold their shape longer and wear better. This makes for a safer, smoother ride for trucks or vehicles on the road.”

Resurfacing 17 miles of road for the price of five

When the Yankee Fork Road project in the Salmon-Challis National Forest in Salmon, Idaho finally received funding to resurface about five miles of double-lane road with a 6 inch depth of 1.5-inch minus crushed aggregate, estimates were based on using a privately-owned local pit, according to Jeff Parker, a retired USFS project engineer who supervised the project. Then the local pit owner denied use of the pit as a rock source, putting the project in jeopardy.

“There were no other approved local sources, and if you don’t have a pit that’s right along the road you’re working on, costs can skyrocket,” says Parker.

Parker contracted with Roadtech Inc. to use a linear crusher on the project. According to Parker, the savings in haul costs on the double lane road allowed for the expansion of the project to include another 12 miles of single lane road. The single lane portion of the road had sections that were very rocky with very few turnouts. “The road wasn’t constructed to have a lot of gravel hauled in because trucks couldn’t turn around, and there wasn’t much gravel left to maintain,” says Parker. “Many Forest Service roads are up where traditional resurfacing projects are not practical, and this was one of them.”

“The linear rock crusher was the only equipment we could get up there to get enough gravel on the road,” he says. “Past road maintenance could only blade larger rocks from the subgrade to make it as smooth as possible, creating rock berms lining the road. The linear crusher was able to use material in the road’s rocky subgrade and its berms to create a gravel layer that a grader could maintain.”

“In the end, what was to be five miles of resurfaced gravel road became 17 miles of resurfaced gravel road with the same funds, using the Roadtech linear crusher,” says Parker.

Because of the success of the Yankee Fork Road project, the USFS bought its own linear crusher, which is stationed on the Salmon-Challis National Forest and used on road projects in a dozen Forests in the Intermountain Region, according to Parker.

“Linear crushers make sense not only for forestry, but also for mines, logging, oil extraction, counties, and organizations like the Bureau of Land Management,” concludes Parker. “The more remote the road that needs gravel resurfacing, the more sense this equipment makes, particularly in high altitude locations where you’d never get gravel to the road.”

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