CLIENT: Government of the Northwest Territories, Department of Transportation
LOCATION: Yellowknife, NWT, Canada
Highway 3 is located between Rae and Yellowknife in Canada’s Northwest Territories (NWT) in an area with warm and discontinuous permafrost and variable ground ice contents. Originally constructed as a gravel road in 1968, it was realigned and the surface chip-sealed between 1999 and 2006 to accommodate higher traffic speeds. Since reconstruction, many locations within this section of highway have experienced severe differential settlement and considerable maintenance efforts have been required to keep the road in a safe driving condition.
BGC was commissioned to investigate the causes of road instability along the highway and to develop rehabilitation techniques for roads constructed on warm, ice-rich permafrost. Site investigations found the most acute areas of road instability resulted from melting of ice-rich permafrost in areas of sub-surface transition (i.e. soil-rock, unfrozen-frozen, warm-cold permafrost), where the road was constructed adjacent to a water body and where the road crossed over the old alignment.
BGC designed and constructed four test sections to address these problems. The test sections involved varying levels of embankment reconstruction including reconstruction of the road embankment as a textile-reinforced embankment (geogrid or geotextile), installation of a layer of foamed cellular concrete, reconstruction of the shoulder as a ventilated shoulder and the installation of geosynthetic-reinforced open arch culverts to replace a dysfunctional steel pipe culvert and an existing rock drain. During construction, thermistor cables were installed within the embankment to measure embankment temperatures. The test sections have been monitored since construction was completed in 2012 and will continue to be monitored through 2015 to determine the potential for these techniques to be adopted in future practices for road construction on warm, ice-rich permafrost.