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Shakwak & Permafrost

The Shakwak Project on the Alaska Highway has presented some unique challenges; particularly achieving a stable road over permafrost soil continues. Many of the soils are of glacial origin and are termed “ice rich”, requiring disposal of millions of cubic meters of material because it is unsuitable for road embankments.

Anything that causes the permafrost to melt will cause the ice rich soil to liquefy. Liquid soil has little strength and will settle or subside. When it freezes, it will expand or heave. This process causes large amount of damage on road surfaces. Undulations and cracking decrease drivability.

Thawed Permafrost
Handling thawed permafrost soil is nearly impossible for equipment. Some especially problematic areas of the Shakwak Project have been reconstructed during winter to minimize such problems.
Thawing is always deeper under culverts because of air and water passing through. It can be caused by
• disturbing the soil during construction,
• soil contact with ground water, or
• simply a warmer climate.

Some work undertaken to meet this challenge

• designing and building a road embankment to minimize melting 
• excavating large volumes of affected soil to meet road alignment needs
• quarrying large amounts of rock and gravel to provide suitable construction materials
• constructing granular blankets on ice rich slopes for stabilization and allowance of melting and settling without major slope failure 
• installing culverts in thawed streambeds, or insulating these with styrofoam and granular bedding material

American and Canadian scientists and engineers continue to research techniques with potential to slow down melting beneath the roadbed and achieve a more stable highway embankment.

• 3/3/2010 |
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