Abstract

This paper presents a holistic and cost-effective approach to finding Arctic gravel sources, which involves supplementing borehole data with a geophysical survey. When correlated with borehole data, geophysical surveys provide detailed information on organic overburden thickness, granular deposit depth and quantity, and potential geohazards, such as unbounded permafrost or ice and silt lenses within the deposit. This paper describes a traditional geotechnical drilling program on the Arctic Coastal Plain on the North Slope of Alaska that was followed by a multiple-method geophysical survey to further delineate subsurface conditions. The survey included Ground Penetrating Radar (GPR) and CapacitiveCoupled Electrical Resistivity Imaging (C-CERI) methods. C-CERI data were collected primarily to characterize the vertical and lateral extents of coarse-grained vs. fine-grained materials, while GPR data were collected primarily to identify potential subsurface ice-wedges or ice-lenses. Correlated with borehole data, the survey inferred the locations of undesirable materials: massive ice deposits, areas of higher sand and silt concentration, and potential cobble zones. Based on the combined analysis of geotechnical and geophysical data, a 31 acre source material area was identified that limited the undesirable material and maximized the quantity and quality of gravel. It is estimated that two times the number of boreholes would have been needed to identify the optimal source material area, bearing costs that would have been on the order of three times that of the geophysical survey, thus realizing significant cost savings by using a combined geotechnical and geophysical approach to the issue of exploring for Arctic gravel resources.

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