Geophysical and cryostratigraphic investigations for road design in northern Alaska

• DCR-ERT transects identified areas of permafrost; location and depth of ground ice; and changes in ice content.
• Geophysical results and cryostratigraphic information correlated with terrain units observed at the surface.
• Cold region highway design may benefit from geospatial analysis and geophysical investigations preceding borehole drilling.

This study used combined geophysical and cryostratigraphic methods for permafrost characterization in Arctic road design and engineering. Two major study areas located in the continuous permafrost zone represented a range of terrain conditions including yedoma (syngenetically frozen ice-rich silts with large ice wedges) plateaus and hills, thaw-lake basins, river terraces, and modern floodplains. Direct-current resistivity - electrical resistivity tomography (DCR-ERT) using a Wenner array was applied over transects. Complementary site data including the results of drilling and active layer depths measurements were also obtained. The boreholes provided cryostratigraphic information on soil texture, cryostructures, ground ice, and gravimetric moisture content of frozen soils. The resistivity data supported evaluation of the presence/absence of permafrost; location and depth of the active and intermediate layers; and in some conditions changes in ice content. In contrast, the cryostratigraphic interpretation generally offered more nuanced analysis of the subsurface, but was limited in its ability to detect unconformities and the depth of drilling. Both techniques were enhanced by the availability of high-resolution geospatial information and can be used to optimize the location and density of the boreholes for road construction.