Use Of Geophysical Surveys For Fill Characterization And Quantity Estimation At Brownfield Sites – A Case History

New building construction planning typically includes site characterization with standard<br>geotechnical drilling and sampling methods under the direction of a professional engineer. For project<br>sites with the potential for variable types and thicknesses of fill materials, including contaminated<br>wastes that pose a possible environmental hazard, this traditional site characterization approach can<br>result in under sampling and lead to an unrepresentative site characterization. This can also result in<br>significant cost overruns and other surprises. In recent years, as reuse of ‘brownfield’ properties has<br>increased, the need for better, more reliable site characterization methodologies has grown. The<br>combined use of geophysical surveys and standard drilling and sampling methods during the project<br>planning phase has been shown to be a valuable approach to meet these needs.<br>This paper presents a case history of an actual construction project in which geophysics was<br>combined with traditional drilling and sampling at a brownfield location where a 70,000 cubic yard<br>excavation for two commercial building basements was planned. Historical information combined with<br>the initial drilling results and geophysical testing revealed a potential two-dimensional bias to the fill<br>distribution. Closely-spaced, 2-dimensional resistivity profiles were independently acquired and<br>inverted, and then jointly interpolated in 3-dimensions to render a 3-dimensional image of the fill<br>materials. The 3-dimensional imaging allowed for the quantification of fill types and quantities for<br>proper management during excavation, and the development of estimates for transportation and disposal<br>of the materials. In addition, it also allowed the construction management team to plan for proper<br>segregation and handling of these materials to minimize total construction costs and schedule delays<br>while maintaining safe working conditions.