Impacts of permafrost degradation on a road embankment at Umiujaq in Nunavik (Quebec), Canada

Differential subsidence of as much as 0.85 m is affecting the access road to Umiujaq Airport in Nunavik (Quebec), Canada, located in the discontinuous permafrost zone. A geotechnical and geophysical investigation including piezo-cone test, ground-penetrating radar profiling, electrical resistivity tomography, and numerical modeling of the thermal regime of the road embankment and subgrade is presented to characterize the ground stratigraphy and permafrost conditions and to assess the exact causes and effects of permafrost degradation on the road embankment. The subsidence is due to thaw consolidation taking place in a layer of ice-rich silt underneath a superficial sand layer. While the seasonal freeze-thaw cycles were initially restricted to the sand layer, the thawing front has now reached the thaw-unstable ice-rich silt layer. According to our numerical modeling, the increase in air temperature recently observed in Nunavik cannot be the sole cause of the observed subsidence affecting this engineering structure. The thick embankment also acts as a snow fence favoring the accumulation of snow on the embankment shoulders. The permafrost degradation is also due to the thermal insulation of the snow cover reducing heat loss in the embankment shoulders and toes.