Geophysical Methods Commonly Employed for Geotechnical Site Characterization: Fid-Bau Portal

Geophysical Methods Commonly Employed for Geotechnical Site Characterization

N. Anderson / N. Croxton / R. Hoover / P. Sirles

Preface he purpose of this Transportation Research Board circular is to provide highway engineers with a basic understanding of how geotechnical geophysical tools are used to image or characterize the shallow subsurface of the Earth, typically to depths of less than several hundred feet. Geotechnical geophysical tools, by design, measure specific parameters that can be used to generate physical property models of the Earth. Gravity meters, for example, measure spatial variations in the gravitational field of the Earth, and are used to generate density models of the shallow subsurface. These density models, if properly constrained, can often be transformed into geologic models with varying degrees of sophistication. T Geotechnical geophysics is not a substitute for boring or testing, but it is often a very cost-effective and reliable means of imaging the subsurface between and below boreholes and for determining the in situ bulk properties of soil and rock. Reconnaissance geophysical investigations can also be used as the basis for making better selection of borehole locations. Geotechnical geophysical investigations, in many instances, enhance the reliability and speed of geotechnical investigations, and reduce the cost of the investigation. However, geophysical tools are not always capable of meeting the objectivesrequirements of highway engineers. The subsurface targets of interest may be too small or deep to resolve, or impossible to effectively image because its physical properties are too similar to those of the encompassing data. Moreover, if constraints (generally borehole control) are not available, geophysical interpretations may be inaccurate because of their inherent nonuniqueness.