San Pablo Dam Seismic Upgrades

El Sobrante, California


East Bay Minucipal Utility District

TERRA led a multi-disciplinary team of subconsultants that was responsible for the design of the seismic improvements of this 170-foot high hydraulic fill embankment dam that was constructed in 1920. TERRA also provided engineering support during construction of the seismic upgrades.
The improvements consisted of the in-situ treatment of 137,000 cubic yards of the alluvium underlying the dam using Cement Deep Soil Mixing (CDSM) and the reconstruction of a downstream buttress.
Through a comprehensive and innovative characterization of the 1920 hydraulic fill (core and shells) as well as of the alluvium beneath the dam, and extensive discussion and detailed presentations of the data, we were able to show to the satisfaction of the Division of Safety of Dams (DSOD) that the performance of the dam during the Maximum Credible Earthquake would be significantly better than estimated by previous studies completed in 2004. As a result, our design considerably reduced the size of the required seismic upgrades from what had been anticipated at the preliminary design stage of the project. This significantly reduced the necessary volume of CDSM and avoided the need to use a borrow area that would have imposed major environmental and logistics constraints along a tortuous access road, and other constructability issues to the project.
The cost savings associated with our design were on the order of $40 million; a significant amount given the overall construction cost of $60 million.
The project was recognized by the American Society of Civil Engineers as the Outstanding Geotechnical Project in the State of California in 2009 and the award was accepted by EBMUD and TERRA as the design team leader.

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