The California Department of Transportation (Caltrans) is using cutting-edge technology to remove the marine foundations of the former East Span of the San Francisco-Oakland Bay Bridge while protecting area wildlife and reducing project cost and schedule.
The technology controls the blast sequence down to microseconds by using a computer system to precisely detonate hundreds of small individual charges to implode the foundations, thus greatly reducing impacts. At the same time, Caltrans is implementing a blast attenuation system that creates a shield of air bubbles to abate resulting sound waves and pressure.
“By employing leading edge technology, we have reduced the temporal environmental impact of our demolition work from years to seconds,” said Stefan Galvez-Abadia, Chief, Office of Environmental Analysis and San Francisco-Oakland Bay Bridge Environmental Manager. “Simultaneously, we are working more safely and efficiently and saving money.”
The agency’s other option would have been to build a cofferdam, he said, which is an enclosure around each foundation pumped dry to enable loud, heavy machinery to carry out the demolition work. With a limited construction window each year, it could have taken up to four construction years to remove each foundation, a very expensive undertaking. In addition, this approach can result in continuous environmental impacts and safety risks.
“Real-time results have exceeded those anticipated by the model,” Galvez-Abadia said. “Both in-water noise and pressure as well as water quality impacts were significantly less than anticipated. We view this cutting-edge technology as another valuable tool in our toolbox.”
Caltrans’ implosion technology supplements additional steps it routinely takes to protect wildlife. The marine foundations are located in a portion of the San Francisco Bay that contains several fish species protected by the Endangered Species Act as well as marine mammals protected by the Marine Mammal Protection Act. Caltrans avoids impacts to most of these species through seasonal work windows. However some species are present in the Bay year round and the agency has developed specific work windows to avoid impacts to these species to the greatest extent practicable.
History of Project
The reason for removal dates back to 1989, when a segment of the bridge partially collapsed during the Loma Prieta earthquake. Although it reopened later that year after extensive retrofitting, experts decided that the East Span needed to be more earthquake-resistant than would be possible by retrofitting the existing bridge. Construction of a replacement span began in 2002 and was opened to traffic in 2013. After beginning to dismantle the original span’s superstructure in 2013, Caltrans began to remove its foundations as stipulated in the final Environmental Impact Statement (EIS) for the replacement span.
The first of the former East Span’s 21 foundations, called Pier E3, was imploded in November 2015. Two more foundations followed suit in 2016, and an additional six to thirteen are slated for demolition in 2017 and 2018, when the project is slated for completion.
Caltrans’ engineers and environmental team spent years working closely with a variety of resource agencies to determine how best to minimize potential environmental impacts to area wildlife and habitat.
Before beginning the project, the agency received federal permits from the National Marine Fisheries Service (NMFS), the U.S. Army Corps of Engineers, the U.S. Coast Guard, and the U.S. Fish and Wildlife Service (USFWS). State agencies granting permits included the California Regional Water Quality Control Board, the California Department of Fish and Wildlife, and the San Francisco Bay Conservation and Development Commission. These permits covered the building of the new bridge as well as the removal of the original bridge by mechanical means.
As the implosion work advances, Caltrans will continue to implement its impact avoidance and minimization measures. In addition, marine mammal species in the area will be protected via monitoring of pre-established exclusion zones around each foundation. If marine mammal species such as harbor seal, sea lion, or harbor porpoise, are spotted, the implosion will be delayed until the individual has moved outside the zone. Water quality and air quality monitoring also will continue to be conducted.
Perhaps the most powerful piece of the protection arsenal is Caltran’s air bubble curtain. To activate the system, a compressor pumps air through a manifold of perforated pipes set in a steel frame. Multiple frames contiguously surround the foundation and are activated just before the implosion process begins. The escaping air bubbles create a continuous shield, or wall, that provides a robust acoustic barrier.
Lessons Learned and Advice
Caltrans has tweaked several of its procedures along the way, said Galvez-Abadia. For example, after analyzing the results of the Pier E3 Demonstration Project, then determining that potential impact areas were less than modeled and subsequently consulting with associated resource agencies, the expanse of the wildlife exclusion zone was reduced to reflect the minimized impacts.
He recommends that other state departments of transportation consider adopting a similar approach for their own underwater implosion work provided they adhere to the following guidelines:
- Allow sufficient time to develop and tailor the technology and time of year to the particular locale and scenario – in Caltrans’ case, it took about two years;
- Ensure that those carrying out the work possess a high level of expertise and will not cut corners;
- Identify appropriate work windows when the least number of species may be affected;
- Reach out early to local environmental stakeholder groups as well as resource agencies, and continue the dialogue throughout the process.
The technology behind the air curtain will be added to Caltrans’ Technical Guidance for Assessment and Mitigation of the Hydroacoustic Effects of Pile Driving on Fish. The current version provides guidance on the environmental permitting of in- and near-water pile driving projects. It includes an extensive collection of data on pile driving under a variety of conditions that can be used as an empirical reference for the permitting process.
For more information on Caltrans’ bridge marine foundation implosion work, contact Stefan Galvez-Abadia, Chief, Office of Environmental Analysis and San Francisco-Oakland Bay Bridge Environmental Manager, at [email protected]. Information also is available from Dr. Brian Maroney, SFOBB Project Manager and Chief Engineer, at [email protected].
A video describing the environmental monitoring efforts is available here.