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Project Name: North Antelope Rochelle Mine

Project Location: Wyoming

Project Background:

The largest coal mine in the world by reserves is the North Antelope Rochelle coal mine in the Powder River Basin of Wyoming. Surface mining operations at the site utilize two types of haul roads—coal roads and overburden roads.

The coal roads are designed to be permanent roads, while the overburden roads are designed to provide temporary access to active surface mine areas. The coal roads incorporate scoria, a highly, vesicular, dark-colored volcanic rock commonly found in Wyoming. The overburden roads are typically constructed using on-site waste rock, however, scoria is added to the wearing course on an as-needed basis to fill in depressions, or to improve traction in areas with steep grades.

Scoria, because of its porous nature, is relatively weak compared to other common types of aggregate such as crushed limestone, basalt, or granite. Cyclic traffic loads break down the volcanic material, thereby reducing its shear resistance and increasing the risk of shear failures and rutting in the mine’s haul roads. More resistant crushed aggregate was deemed to be cost-prohibitive as the nearest source was located near the Black Hills of South Dakota—more than a two-hour trip one way.

Moreover, the truck fleet had recently been upgraded to Liebherr T282C ultra-class haul trucks with 400-ton payloads. Before the upgrade, the fleet primarily consisted of Cat 793’s with 250-ton payloads. Not surprisingly, the larger trucks resulted in an increased rate of haul road deterioration.

Whereas periodic grading cycles had been sufficient to handle the rigors of the Cat 793’s; the need for re-grading became a constant occurrence under the demands of the new ultra-class trucks, and excessive rutting in turn was resulting in reduced life for the truck tires, chassis, and suspensions.

Peabody Energy, the project owner, reached out to Presto Geosystems for support in developing a more robust and resilient haul road solution to handle the demands of the trucks. The solution would require a strategy to address the shearing and rutting problems on both the permanent coal roads and temporary overburden roads.

Product Selection & Benefits:

Based on project evaluations and on-site observations, Presto Geosystems’ design engineers recommended the GEOWEB® Load Support System to stabilize the haul roads. The solution consisted of a 12-inch scoria wearing course supported by a six-inch GEOWEB layer (also infilled with scoria), in turn underlain by an enhanced woven geotextile for separation and added strength at the base of the section.

Approximately 5,500 square feet of GEOWEB was installed to reinforce and stabilize haul road cross sections. The GEOWEB sections were secured using the integral ATRA® Keys—a turn-lock key connection device that is three times stronger, and three times faster to install, than staples or zip ties.

Project Results:

Single- (127,000 lbs.) and dual- (254,000 lbs.) tire loads were tested after the installation was complete. After 140 tire passes, an unreinforced section of the road experienced noticeable rutting—approximately six inches—while the GEOWEB-reinforced section saw minimal rutting (less than one inch).

The roads reinforced with the GEOWEB geocells experienced less degradation, resulting in extended time between grading cycles and decreased wear and tear on the haul trucks.