Evaluation of Geophysical Methods for Alaskan Material Sources (05-0312)**
Steve Saboundjian, Alaska Department of Transportation and Public Facilities
Robert G. Dugan, Golder Associates, Inc.
John Liu, Golder Associates, Inc.

A geophysical investigation was carried out at four material source sites in Alaska’s interior to evaluate the effectiveness of three geophysical methods for assisting in site characterization. The methods included: ground penetrating radar (GPR), seismic wave refraction, and electrical resistivity imaging (EI). Each of the three methods was used at four potential material sites for which borehole test data was available. One site was located on the Steese Highway and the others were along the Dalton Highway. The objective was to determine which method or methods can best be used to understand the geologic framework of a site under various conditions. Of particular interest was identifying the best geophysical approach, with regards to instrumentation, field procedures, analysis and presentation, for identifying and mapping materials that would be appropriate for transportation construction projects. Results showed that the success of the geophysical methods, in terms of useful results and ease of use, was very dependent on both surface and subsurface conditions of the particular site. The study found that the GPR was the most time- and cost-efficient method, however it provided the least subsurface penetration and quantitative information on the materials. Thus, at sites with thick sand/gravel layers, the GPR did not map the deeper boundaries as clearly as the seismic refraction or EI methods. However, seismic refraction, capable of significant depth of penetration, was ineffective in the presence of surface organic soils. Finally, although EI produced relatively detailed images showing lateral and vertical variations in resistivity, the interpretation of the information was, in some situations, ambiguous and could not always be correlated with the collected borehole data.