Pesky Permafrost

The Arctic-conscious U.S. Army has to keep the Frozen North frozen. The reason: beneath much of Alaska, as in other Arctic lands, lies a thick layer of "permafrost," or permanently frozen ground. It is hard and firm, but, as Russians discovered in Siberia long ago, even a trickle of heat can turn it to slithery muck. Roads and airport runways, absorbing summer sun, get as squashy as cranberry bogs. In winter, the warmth of a heated building may seep into the permafrost, allowing floors to sink and walls to wobble drunkenly. Many Alaskan villages, built in defiance of permafrost, look like modernist paintings, their streets slanting sideways and their buildings out of line.

Last week, near Fairbanks, Alaska, Army engineers were watching thermometers sunk in the icy subsoil under buildings and airports. Their job: to catch up with the Russians, leading authorities on Arctic construction problems.

When Russians build on frozen ground, they sink piles deep into the permafrost, melting the holes with steam jets. The piles are then wrapped in tar paper and greased, so that the topsoil, freezing and thawing with the seasons, cannot stick to them and heave them. But piles are scarce in much of Alaska, and Army engineers think they know something better: thick insulating mats to keep the permafrost always frozen.

Near Fairbanks, the Army has laid down 20 runway sections insulated from the permafrost by layers of cellular concrete, asphalt, foam glass, gravel, moss and spruce boughs. Under each runway are thermometers to measure heat penetration. For buildings, the trick is to rest the walls on thick mats of insulating material, or allow cold air to circulate freely under heated floors. Roads will be insulated, too, to keep foundations frozen under thundering tanks and trucks.

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