Oakland, Calif. — Caltrans announced that it is meeting with key environmental regulators to discuss options for safely removing the old Bay Bridge's underwater piers. Caltrans is considering the least environmentally impacting alternative, including the potential for controlled underwater charges that would reduce impacts to the environment compared with a traditional underwater demolition.
The following video provides simulations of the underwater removal methods currently under consideration:
"Removing the old Bay Bridge is essentially an environmental project and our top priorities are efficiency, safety and environmental sustainability as we take down the old structure," said Chief Bridge Engineer Dr. Brian Maroney. "We could mechanically remove the underwater piers bit-by-bit using large saws or jackhammers over many months, but that has prolonged impacts on marine life and generates rubble that would have to be sent to a landfill. One option is to remove the underwater piers using carefully controlled underwater charges – an innovative, safe and potentially more environmentally-friendly option."
The controlled charges would simplify the underwater demolition process and spend less time potentially impacting marine life. Caltrans is meeting with a consortium of environmental agencies to start the process of obtaining permits to allow controlled charges as an effective and environmentally sensitive method of safely removing the underwater piers.
Underwater controlled implosion technology has improved considerably over the past decade. Today there are controlled charges that quickly dissipate and do not generate harmful chemicals. A quick, controlled implosion could mean that construction crews are not working underwater for many months, which means fewer disturbances to marine life.
These controlled ballistic charges would happen underwater and would likely not be heard or seen by nearby motorists. In addition, a heavy protective mat would be placed on top of the pier during the operation to prevent flying debris from being projected. Caltrans would also temporarily provide a rolling traffic stop strictly for sound to ensure motorists were not distracted.
The mechanical method for removing the pier would be to use a cofferdam, a temporary watertight structure that’s pumped dry to enclose an area underwater and allow for construction on the pier. A wire saw, ram hoe and other demolition equipment would likely be necessary with the cofferdam. Building and operating a cofferdam in the Bay, given the depth and dynamic waters, could take longer, increase risk to worker safety, as well as harm marine species over a prolonged period of time.
If environmental regulators grant the necessary permits, Caltrans is planning to remove one pier using the controlled charges in November 2015. Further removals may require additional approvals from the regulatory agencies.