The Marine Foundations Removal Project (project) (as part of the San Francisco-Oakland Bay Bridge [SFOBB] East Span Seismic Safety Project) successfully completed removal of the SFOBB original east span in 2018. The initial vision for the project in 2001 considered marine foundation removal by mechanical methods inside large cofferdams. This method was anticipated to take multiple years for each pier. In 2015, a pilot project to remove the largest marine foundation (Pier E3) via controlled blasting successfully removed that structure in a matter of seconds with reduced environmental impacts. The project addressed the remaining 17 piers beginning in 2016 and was originally scoped to remove them over three years by blasting one pier at a time, after removal of the suspended steel truss spans. Removal of the high steel of the original SFOBB east span was completed early in 2015, and the project capitalized on an opportunity to advance pier removal with exceptional efficiency by sequentially imploding one, two, or three piers during single blast events and finished removing all 18 piers over one year ahead of schedule. Thirteen of these piers were removed during three months in 2017.
To reduce impacts from underwater overpressures, improved controlled blasting methods using hundreds of small microcharges detonated sequentially, and a blast attenuation system (BAS) surrounding each pier was used. An attenuation system introduces a volume of air into the water column to absorb and scatter the energy waves that are created. The project necessitated a novel and robust design for a BAS to achieve an attenuation level consistent with the project's environmental permits and authorizations. The design surpassed regulatory requirements and allowed for a much greater volume of air and wider curtain of bubbles than normally achieved. Noise and pressure waves from the implosion were monitored using state of the art equipment and methods. Results showed the BAS reduced overpressures by approximately 80%. Effects on fish and other marine life were successfully reduced beyond estimated and accepted levels.
Collaborative planning and execution across the design, construction, environmental permitting, and monitoring teams were critical to meet an aggressive project schedule. In addition, the project resulted in no additional impacts to the environmental, no safety incidents, minimal impacts to traffic, and increased public access to the area. The use of highly controlled charges with a BAS was endorsed as a method for removing marine foundations. The result was a rare combination of considerable civil, environmental, and economic benefits to the community. This high project profile, with its technical advancements and expedited permitting, has served as a model example of how to deliver high-profile key transportation projects in sensitive habitats that balances environmental stewardship, stakeholder and regulatory input, cost, and schedule.