Chabot Dam is a 100-ft high earth dam that was built in 1875. The reservoir provides approximately 10,000 acre-feet of emergency drinking water supply. In 2005, the East Bay Municipal Utility District (EBMUD or the District) prepared a report that analyzed the dynamic stability of Chabot Dam; the report concluded that under the maximum credible earthquake, the downstream toe of the dam would experience localized instability and the dam crest settlement would be less than 4 feet. Although the dam crest settlement presents no risk to public safety, the expected minor slope deformations would require timely repair. In addition, the existing tower would likely fail in a brittle fashion, potentially damaging the outlet works. In light of these findings, EBMUD plans to upgrade the dam and tower. These upgrades would also satisfy the requirements of the California Division of Safety of Dams (DSOD).
TERRA Engineers was a subconsultant to AECOM and completed the constructability and environmental review for alternative seismic upgrades to the dam embankment. The alternative remedial measures included excavation and replacement of soils susceptible to liquefaction and in-situ improvement of the soils using Cement Deep Soil Mixing. The constructability review considered alternative haul routes and temporary fill storage locations (both on-site and off-site). A model was prepared to evaluate twenty-four (24) different alternatives based on cost, schedule, construction risks, environmental impacts, and permit requirements. The outcome of the study was selection of two alternatives that were evaluated in the EIR and have been brought to the design stage.
In November 2014, the TERRA-GeoPentech joint venture was awarded the contract to complete the Design for Chabot Dam Seismic Retrofit. TERRA is the managing joint venture partner and lead a multi-disciplinary team of subconsultants that successfully complete design package in 2016. Construction was completed in October 2017.