Geophysical Investigation Of The Success Dam Foundation: An Overview

Success Dam is a zoned earth-fill embankment located about 70 miles northeast of Bakersfield, CA. Stability analyses indicate that there is a potential for large-scale deformation of the dam during relatively low levels of earthquake shaking. At least three earthquakes in the past 150 years, and prior to dam construction, are believed to have been large enough to create a dam failure. To better understand material behavior, the U.S. Army Corps of Engineers has been investigating properties of the dam and its foundation. This includes extensive field explorations and detailed engineering studies using a variety of analytical techniques to estimate the response of the dam and foundation to earthquake shaking. Although a large amount of data have been acquired since 1992, these data are largely point data from borings. A geophysical investigation was designed to provide a continuous image of the foundation toe. This investigation employed direct-current (DC) resistivity, seismic refraction tomography (P- and S-wave), audio-magnetotellurics (AMT), and self-potential (SP). The purpose of the DC resistivity and seismic refraction tomography was to produce 2-D imagery across the foundation to investigate depth to bedrock and the occurrence of beds potentially susceptible to liquefaction. DC resistivity was used to look at the conductivity relationships in the subsurface. The resistivity data produced a higher-resolution image relative to seismic refraction tomography, which looks at compressional and shear properties of the material. AMT was applied to look considerably deeper (several 100s of m) in order to confirm depth to bedrock and investigate for deep faults. The goal of this paper is to provide technical background on the site and to highlight how these data have been used by the engineers in redesigning the new dam. Specific details on the geophysical methods are presented by the co-authors in two other papers in this session (Asch et al., 2007; Powers et al., 2007).