Piles Preserve Permafrost

Keeping it cold at Kotzebue - Veco/Nana, J.V. install passive refrigeration piles to keep the new Kotzebue hospital on frozen-solid ground 

Pacific Builder & Engineer (Alaska Edition); April 5, 1993

Anchorage-based Veco Inc., in a joint venture with Nana Regional Corp. of Kotzebue, has completed what may be the largest building-foundation job in the Unites States using passive-refrigeration piles. The $4.1 million project, for the U.S. Public Health Service, is phase one of a $40 million new hospital in Kotzebue, Alaska, that is now under way.

The contract for the second, structural phase of the project was awarded last fall to Hoffman Construction Co. of Portland. That work will get under way in early

Since 1984, the PHS has been developing its plans to replace an existing, older hospital that can no longer meet the needs of northwestem Alaska. The existing structure has also experienced foundation problems,due to the permafrost in the area.

Passive-refrigeration piles
Dealing with permafrost under the new hospital is the most challenging part of the project, said John Delapp, PHS director of facilities for the area. The building's foundation involves using a passive-refrigeration system to help keep the permanently frozen ground under the building in a cold and stable condition. It is believed to be the largest application of that technique in the U.S.

The job involved piles manufactured by Arctic Foundations Inc., an Anchorage company specializing in cold-climate foundation work. This passive-refrigeration technology is a system invented by Erv Long, who started Arctic Foundations in 1971.

'Dealing with permafrost under the new hospital is the most challenging part of the project.'   - Delapp

Veco/Nana completed the first phase of the project Dec. 19. The gravel pad was built last summer, with 360 refrigerated piles installed in November and December, according to Dave Hopkinson, Veco's project manager.

The piles, frozen in place in the permafrost, provide the real support for the 80,000-sq.-ft. building. The pad, built with the variable-quality beach gravel that is available locally, is sufficient for vehicle access, but not as the support structure for a major building, Hopkinson said.

PHS opted to go for the passive-refrigerated pile system because poor soil conditions and permafrost in the area would have made conventional piles much more expensive. If conventional piles were to be used, they would probably have been driven as deep as 75 ft. to 120 ft. Even at those depths, the piles might not have found stable soils. The passive-refrigeration piles contain a freon-gas system to maintain freezing temperatures. By using these piles to keep the ground frozen, shallower piles could be used.

The pile system involved units 32 ft. long by 20 in. in diameter, charged with a gas on the inside. The system is passive, because it uses changes in air temperatures to help keep soil cold. Piles with active-refrigeration systems require an energy source.

The piles used in Kotzebue, however, are manufactured so that they could be retrofitted with an active-refrigeration system. Arctic Foundations, which is the onIy company in the U.S. making passive-refrigeration units, manufactured the piles in Anchorage last year, according to the company's chief engineer, Ed Yarmak. They were shipped to Kotzebue by barge.

Containing the cold
Kotzebue has continuous permafrost, with the thaw reaching the 5-ft. depth in summer, but deeper frozen-soil temperatures are somewhat warmer than on the NorthSlope, where Veco has done most of its work. This makes the local permafrost potentially more unstable.

Also, deeper soils in the area contain high-salinity pockets that require lower temperatures to maintain a frozen state. Shallow methane pockets are also known in the area.

Studies had shown that the only real integrity in the soil was in the top 25 ft. - as long as it could be kept frozen. Using the shallow refrigerated piles allows the foundation to be anchored in the shallow soils.

What was tricky about the foundation job was scheduling the work so that frozen material would be trapped under an insulation layer in the gravel pad while the pad was completed last summer, according to Hopkinson. Had the schedule been off, pockets of thaw might have been trapped, requiringa casing to seal off water seepage during the drilling operations, which would have been costly.

Veco/Nana was able to keep the material cold by minimizing disturbance of the tundra, which is a natural insulation, and by getting started early last summer, before the annual thaw in Kotzebue. Byairfreighting in a geotextile fabric and laying it over the first several lifts of gravel fill, they were able to maintain cold temperatures until the arrival by barge, later in the summer, of the 4-in. polyurethanefoam boards to be used as permanent insulation in the pad. In addition, the geotextile fabric also served to keep the gravel pad from being contaminated by the organics and silt below.

The pad itself is an average of 2 ft. thick, covering eight acres and requiring 30,000 cu. yd. of material. Veco/Nana laid the gravel right on the tundra, in a technique similar to that used on the North Slope. The gravel had been stockpiled onsite the year before, by the federal government.

Veco/Nana are under strict performance specifications laid down by PHS on temperature levels to be maintained in the pad. The minimum requirements were, byMarch 15, that 22 F be maintained at the 5-ft. depth, 23 F at the 12-ft. depth, and 24 F at the 20-ft. depth. These temperatures were already being maintained several weeks ahead of the contract deadline, Hopkinson said.

'The nature of the job, with various tasks completed over a long duration, allowed us to better evaluate each work task and fine-tune every step.'    - Hopkinson

Equipped for the job
He said Veco had first contemplated bringing in all of its own equipment. But to get an early start, which was essential to success of the foundation phase, the company decided to lease equipment – a Caterpillar D-8, John Deere JD-850 and three 12-yard Mack trucks - from a local contractor. Fifteen people were on the job in the pad construction phase, which lasted six weeks. Most were hired locally, recruited through Nana, the regional native corporation for northwest Alaska.

In the piling phase of the job, Veco/Nana had a crew of 20 on the job, and used Wayne Drake General Contractor, a local firm, to subcontract the pile setting and slurry placement. The subcontractor made use of a mid-1940s-era, 30-ton cable crane, 966 and 935 Caterpillar loaders, two 12 yard Mack trucks and skid-mounted batch equipment. Like all government jobs, Veco/Nana paid wages on the federal Davis-Bacon scale, which typically allows contractors to attract the best local workers, Hopkinson said.

An arctic edge
Veco's real competitive advantage on the job, which allowed it to underbid competitors by some $400,000,was its use of a large Watson 3000 truck-mounted drill rig, barged in from the North Slope. This unit was able to drill the 30-in.-by27-ft.-deep hole and simultaneously remove the drilling spoil with high volume, low-pressure air flow. This was much faster than the conventional flighted auger-drilling method other companies would have used, which would have been slower, increasing equipment and labor costs.

Veco/Nana was happy about the way the job turned out. "The nature of the job, with various tasks completed over a long duration, allowed us to better evaluate each work task and fine-tune every step. "Because of this, we were able to really get smart and make some good decisions," said Hopkinson.

Veco's main business is oilfield services, with operations on the North Slope, the Cook Inlet region in southern Alaska, southern California and in other continental U.S., oil-producing regions. The company started doing Arctic construction in other parts of Alaska as a sideline to its North Slope oil construction work, in which the company has considerable expertise.

Hoffman Construction will start work in early May on the $35 million structural phase of the project. Apartf rom the piling, the building involves fairly conventional construction, with a structural steel frame and insulated wall panels. There will be one main floor with a second level for utilities. The project will last some 23 to 24 months, and will involve a workforce of 50 to 60 at the peak.

Text by Tim Bradner
Photos courtesy of Veco Inc.