Removal of the Former San Francisco-Oakland Bay Bridge Foundation Caisson E3 by Mechanical Means and Explosives-Paper

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The former San Francisco–Oakland Bay Bridge caisson E3 had to be removed to clear a future shipping channel. Caltrans selected a trial method combining mechanical demolition above the waterline with an implosion of the remaining structure to the mudline, 50 feet below water. This avoided constructing a cofferdam, which was estimated to take several years and cost twice as much.<br /><br />Excavators working from the caisson, custom platforms, and barges dismantled the upper structure. Crews used strategic cuts to remove large wall sections and placed all debris inside the caisson cells, preventing it from entering the bay. They then drilled the remaining walls and installed approximately 22,000 pounds of explosives. On November 14, 2015, the implosion sent about 20 million pounds of debris into the cells below the mudline. A few small sections remained above the target elevation and were removed afterward.<br /><br />Environmental safeguards included sealing the caisson’s openings, treating displaced water, monitoring marine mammals and birds, deterring birds before blasting, and using a bubble curtain to reduce the underwater pressure spike. Traffic, nearby boat access, and the BART tube were temporarily restricted. Monitoring found no observed bird casualties, and experts assessed the environmental impact as acceptable, though the fish-cage results were not conclusive.<br /><br />The project cost about $20 million—half the estimated cofferdam alternative—and was completed more quickly with lower emissions and less prolonged environmental disturbance. The successful trial established the method for removing the remaining caissons. Lessons included ensuring stable platform support on uneven walls, planning equipment and barge movements carefully, maintaining breaker equipment, and considering prevailing winds when managing dust.

Keywords

San Francisco–Oakland Bay Bridge

caisson E3

implosion

mechanical demolition

mudline

shipping channel

cofferdam

environmental safeguards

bubble curtain

Caltrans