Ground-Penetrating-Radar Profiles of Interior Alaska Highways: Interpretation of Stratified Fill, Frost Depths, Water Table, and Thaw Settlement over Ice-Rich Permafrost
Cold Regions Research and Engineering Laboratory, U.S. Army Engineer Research and Development Center Hanover
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In early spring 2014, we recorded ground-penetrating-radar GPR profiles along several highways in interior Alaska to determine present and potential damaging thaw settlement, which could help site and design infrastructure in permafrost terrains. We used GPR pulses centered near 100, 150, and 320 MHz. Comparative profiles of electrical resistivity, historical GPR profiles, and limited borehole information aided interpretations. Beneath the Elliott Highway, Goldstream Road, and the Old Steese Highway, construction fill was recognized by its stratification and frost depth and water-table horizons were recognized by phase attributes of the reflected pulse, as dictated by dielectric permittivity contrasts, relative depths, and continuity. Undulating fill stratification indicated thaw settlement, caused by melting of buried ice. We interpreted various stratigraphic folds to represent cases of active, recent, remediated and historical settlement. A section along the Tok Cutoff Road revealed the top and bottom of massive ice within glacial moraine. Signal penetration was greatly reduced beneath the water table, and the permafrost table was not detected. This information is valuable for highway maintenance and planning of new construction, especially in remote locations where information on permafrost and ice features are limited.