When a heavy equipment maintenance facility was built in Prudhoe Bay, special measures were taken to keep the frozen ground frozen. Otherwise, when the building was completed and the heat turned on inside, heat loss through the footings and slab would have thawed the underlying ground, causing the building foundation to settle. To prevent this, a network of steel culverts was permanently installed in the 6-foot-deep gravel subbase beneath the footings and floor slab. Afterward, cold outside air was constantly circulated through the culverts, preventing the ice lenses in the soil from thawing and thus keeping the building from settling. When the weather outside turns "warm," the thermostatically controlled circulation system automatically shuts off, enabling the ground beneath to stay frozen. Covering a 25,000-square-foot floor area, this unusual refrigeration system required over 4000 lineal feet of 12-inch-diameter steel culvert.
To reduce the amount of heat loss into the ground, closed cell extruded polystyrene foam insulation was also placed under the slab and footings, a 6-inch layer of 30-psi foam under the slab and 6-inch layers of 60-psi foam under the footings and grade beams. The bearing capacity of the polystyrene itself exceeds that of the 6-foot-thick, compacted gravel subbase.
Four hundred thirty yards of 3000-psi concrete was needed for footings and grade beams. However, to withstand the severe Alaskan cold, a 7-sack mix with an effective 4000-psi strength was used. Maximum aggregate size was 1 « inches. During placement of the footings, a makeshift tent of plastic, parachute fabric and old tarps was erected over the site and heated by portable, diesel-fueled heaters to +40 degrees F. After the footings were cast, the building shell was erected, heated by the same heaters, and the floor slabs were cast.