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Geophysical Characterization Of A Levee With Dc Resistivity And Electromagnetic MeasurementsNormal access

Authors: Theodore H. Asch, Maryla Deszcz-Pan, Bethany Burton, Lyndsay Ball, Wade Kress, Joseph Vrabel and Lewis E. Hunter
Event name: 21st EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
Session: Levees and Dams
Publication date: 06 April 2008
Organisations: EEGS
Language: English
Info: Extended abstract, PDF ( 3.32Mb )

Summary:
A geophysical characterization of a portion of American River levees in Sacramento, California was conducted in May 2007. Targets of interest included sand lenses that
underlay the levees and the depth to a clay unit that underlies the sand. The concern is that the erosion of these sand lenses can lead to levee failure in highly populated areas of
Sacramento. DC resistivity and electromagnetic surveys were conducted over a 6 mile length of the levee on roads and bicycle and horse trails. 2-D inversions were conducted
on all the geophysical data. The OhmMapper and SuperSting surveys produced consistent inversion results that characterized the targets of interest. GEM-2 apparent resistivity data were consistent with the DC inversion results. However, the GEM-2 data could not be inverted due to large system drifts. While this would not be as large a problem in conductive terrains, it is a problem for a small induction number electromagnetic profiling system such as the GEM-2 in a resistive terrain (the sand lenses). Despite issues with the GEM-2 inversion, this geophysical investigation was successful in detection of the sand lenses and the depth to the clay zone of interest.

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