Numerous airports pavements built in the North 50 or 60 years ago were constructed on
permafrost. When the active layer that thaws and freezes again under the pavement was relatively
shallow, the permafrost provided good support and the pavements performed well. However, due
to climate change/global warming, the depth of the active layer became larger and the permafrost
started to melt.
The airport in Yellowknife is located in a discontinuous permafrost zone. The asphalt pavement
on Runway 10-28 was built in the 50s. The pavement includes 175 mm of asphalt and 0.6 m of
granular materials. Soils are variable but typically include silts that are very frost susceptible. The
soil is particularly poor at the location of an old water course. The surface drainage consists of
two ditches at a significant distance from the runway and there are no subdrains. The permafrost
is melting and the depth of the active layer is increasing. This in turn causes settlements and
bumps in the pavement at a number of locations. At the same time, since the soils are frost
susceptible, there are also frost heaves.
The airport in Hay River is located in a scattered discontinuous permafrost zone. The asphalt
pavement on Runway 14-32 was built in 1966. It consists of 150 mm of asphalt and 1.1 m of
granular materials. Similar to the Yellowknife Airport, the subgrade soils are frost susceptible.
There are subdrains along both edges of the runway pavement; however, the subdrains have
failed and the pavement over them has cracked severely. The investigation showed that the
permafrost has almost melted. There are locations where the pavement has settled and bumps
have formed. These locations are primarily in the non-keel zones, outside quarter of the pavement
width immediately adjacent to the pavement edge.
The previous pavement rehabilitation designs by others included full or partial depth
reconstruction and installation of thermal insulation. Unfortunately, both these alternatives are
cost prohibitive. Construction costs in the North are very high compared to other areas of Canada
and there are significant budgetary constraints. There is also concern about the long term
performance of thermal insulation within the pavement structure.
The new pavement design recommendations were based on the assumption that the permafrost
is melted or may come and go in the future. The pavements were designed similar to the ones
located in non-permafrost zones, where significant frost heaving and spring seasonal thawing
occurs. Emphasis was placed on drainage, surface and subsurface where necessary.