Integrated 3-D GeoInvestigation for the San Francisco–Oakland Bay Bridge East Span Replacement

Geotechnical studies for the replacement of the 4-km-long San Francisco-Oakland Bay Bridge (SFOBB) East Span included extensive over-water and onshore geophysical surveys, geologic mapping, and geotechnical explorations. The data collected from those studies were integrated to develop a comprehensive 3-D representation of the subsurface conditions along the chosen bridge alignment. This paper summarizes the geophysical surveys, geophysical data processing techniques, and the integration of the geophysical data with marine borings and CPT soundings. By comparing the seismic reflection data with downhole P- and S-wave velocity suspension logs, it was possible to accurately convert the time sections obtained from the geophysical surveys to depth sections despite the presence of gas-charged sediments infilling an extensive paleochannel system. The combined data also documented the lack of recent activity of several faults. All of the geophysical and geotechnical data were captured in a Geographic Information System (GIS) database. The GIS was used to shorten the overall timeframe for the site characterization and allowed project design to proceed concurrently with the geotechnical study.