Snow Going

Low-ground-pressure ATVs carry heavy payloads across Alaska’s fragile tundra with minimal impact.
Snow Going
A low-ground-pressure ATV, built by Busby Marine and owned by Peak Oilfield Service Co., hauls an 85,000-pound articulated water truck to a remote project near Cape Simpson, Alaska. The water truck is used for ice-road construction.

It’s difficult to imagine vehicles that can transport up to 100,000 pounds of payload on Alaska’s North Slope oilfields while putting a mere 14 psi of pressure on the environmentally sensitive tundra below its “bags,” or wheels. But that’s exactly what the two low-ground-pressure ATVs owned by Peak Oilfield Service Co. do while hauling cargo cross-country on the mostly roadless Alaskan tundra.

Custom-built by Busby Marine and delivered in 2005, the two machines have played an instrumental role in transporting everything from fuel (up to 8,000 gallons per load), large trucks and construction equipment to a prefabricated office building, modular drill-rig sections and miscellaneous freight without damaging the tundra.

“They carry everything but the kitchen sink – and sometimes the kitchen sink, for that matter,” says Eric Wieman, the project manager for North Slope operations at Peak, headquartered in Anchorage and with divisions on the North Slope, at Cook Inlet and in Valdez and North Dakota.

Two key features drive the ATV’s eco-friendly performance. The first is the vehicle’s 16 large rubber bags, inflated to anywhere from 8 to 16 psi and each measuring 54 inches in diameter and 68 inches wide. The second is a unique roller-drive system that eschews a conventional drive system with axles and a transmission in favor of mechanically driven rollers atop each wheel that propel them forward or backward, Wieman explains.

Two different engines – 425 hp Caterpillar diesels – drive the rollers. One is located behind the cab; it propels the four bags under the cab and the six under its rear carriage. The second engine is mounted under a fifth-wheel trailer; it drives the six wheels beneath the trailer.

“It relies on rollers because if a vehicle like this used a conventional drive system and got stuck, the bags would spin and potentially cause tundra damage,” Wieman explains. “If these ATVs get stuck, the roller just spins on top of the bag itself, but the bag won’t turn and damage the tundra.”

While the machines look stuck-proof, they can get bogged down in deep snowdrifts. That’s why they travel in groups of two or three; if one unit gets stuck, another one pulls it backward out of a jam, after snow is shoveled away from the affected bags, Wieman says.

Controls in the cab allow the operator to control the air pressure for each tire. It’s not unusual for an operator to put more pressure in the bags on one side or the other to either balance loads or improve traction and ride stability, he notes.

In summer, the ATVs can operate at a lower pressure; reduced pressure means each tire will have a correspondingly larger contact area atop the tundra – but at a lower force on the surface. In general, the pressure in each tire results in the same amount of pressure on the tundra, so tires filled to 12 psi, for example, exert 12 pounds of pressure on the tundra, Wieman explains.

In all, Peak owns 31 tractor-trailer ATVs made by Busby, Bechtel Engineering and Rimpull Corp. and nine low-ground-pressure ATVs made by Busby and Bechtel. The two Busby Marine ATVs weigh 82,000 pounds and feature a Freightliner tractor cab; a 50-foot-long, 16-foot-wide deck; and 900-gallon fuel capacity (with an optional extra 600 gallons available).

“We used to sub that [cargo transportation] work out to a contractor who owned low-ground-pressure ATVs, but we wanted better control over our resources and the ability to get work done on our own timetable,” Wieman notes.

In Alaska, the tundra on the North Slope is closed to general tundra travel from roughly the first couple weeks of May through the middle to end of December, when the tundra travel requirements are met and the Alaska Department of Natural Resources (ADNR) deems it possible to travel without damaging the tundra. The general requirements are at least 6 inches of snow on the ground and frost depths that reach 1 foot deep.

However, Peak’s ATVs are approved for summer tundra travel by the ADNR. From July 15 until a general tundra opening, and under certain conditions – such as when the tundra is relatively dry and the loads aren’t too heavy – summer-approved vehicles are allowed to drive on the tundra, Wieman says.

As such, the ATVs offer companies like Peak a critical advantage: a head-start on building ice roads for winter travel. “They allow us to get out on the tundra prior to the general tundra opening,” Wieman says. “We can gain four to six weeks, if not more, depending on the particular winter. That’s huge because the end date [May 1] is usually fixed from a planning perspective, so the only way to gain time is on the front end.”

The ATVs are used to prepack snow for ice roads – pack it down along the route, which effectively produces a protective, less-insulating layer much faster than nature would do on its own via a natural freeze. This allows the ice-road route to meet the conditions necessary for earlier opening of the tundra for construction. Sometimes the road-building work includes sidecasting, or spraying water from a water tank atop an ATV, to create a frozen layer of protective ice, Wieman says.

In general, Wieman lauds the ATVs for their versatility. “For remote exploration projects, they’re a lifeline to all the different services and materials we need to supply and haul to support a winter operation – things such as equipment, food, workers, drilling products, potable water and sewage, if the man camps can’t treat it on their own. They’re extremely critical to establishing and then supporting remote drilling projects.

“They’re the most specialized pieces of equipment that we have,” he adds. “In terms of importance within our company, they’re right up there with our other critical pieces of equipment.”


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