Electrical Geophysics for Assessing Permafrost Conditions along Highway Infrastructure

The Yellowknife region, part of the Slave Geological Province, falls within the extensive discontinuous permafrost zone in Canada. A large degree of economic development is routed through Yellowknife from the mineral-rich North Slave. Despite the mineral-rich nature of this region, surficial sediment maps and knowledge of permafrost conditions are only now being established in detail. Permafrost and associated ground ice can significantly affect land-based infrastructure through influence on ground stability and drainage patterns. As such, geoscience information contributing to permafrost characterization is critical for understanding risks to roads which are vital to Northern economic development. The 100 km stretch of the chip-sealed Highway 3, west of Yellowknife, presently experiences instabilities including settlement, heave, and rotations related to transitions between differing terrain and drainage conditions within the discontinuous permafrost. Electrical resistivity data were collected over identified terrain types, and across potential terrain transitions and thaw fronts based on the hypothesis that permafrost distribution and conditions vary with terrain type. Processed resistivity models indicate distinct electrical signatures for most of the terrain types which would allow for extensive geophysical characterization complimentary to landscape mapping, temperature data and shallow boreholes. The resistivity models also exhibit features indicative of the base of ice-bonded permafrost, ice-rich sediment and thaw zones, which can be correlated with terrain features of sediment type and drainage. Observed resistivity anomalies indicate thaw zones related to existing and past road infrastructure, which help in understanding conditions causing highway subsidence.