Diversion Solution for Concrete Drilling Water
When repairs on the new San Francisco-Oakland Bay Bridge required drilling into concrete, engineers needed to ensure that the water flow required for the drilling process would not impact the Bay below.
By Kyle Van Fleet, EIT, M.SAME
The long-anticipated opening of the new 2,047-ft eastern section of the San Francisco-Oakland Bay Bridge on Sept. 2, 2013, marks the completion of a project that has been in development for more than a decade. The construction was repeatedly challenged by a series of engineering, structural and political hurdles.
After making its debut in 1936, the San Francisco-Oakland Bay Bridge provided a permanent connection between East Bay and West Bay communities for the first time. One of the longest bridges in the world, it carries a daily load of approximately 280,000 vehicles across its dual decks. In 1989, a 50-ft section of the upper deck on the eastern span, which connects Yerba Buena Island to the City of Oakland, collapsed during the magnitude 6.9 Loma Prieta Earthquake, resulting in one fatality and a month-long closure of the bridge. More than 60 people died throughout the region as a result of the earthquake and nearly 3,800 were injured. Economic damages were significant.
SEISMIC CONCERNS FORCE REPLACEMENT OF EASTERN SPAN
Faced with the decision to retrofit or replace the outdated and damaged structure, the California Department of Transportation initiated construction in 2002 of what would be one of the largest public infrastructure projects in the state’s history. Construction on the skyway segment of the bridge was first, followed by the foundations. In 2006, the self-anchored suspension bridge project—the signature element of the eastern span replacement—was awarded to contractors American Bridge and Fluor Corp., with a final completion date set for late 2013. The 625-m-long, single-tower, self-anchored seismically sound suspension bridge was designed to withstand, for the next 150 years, the type of repeated large earthquakes that have historically hit the Northern California region.
After a series of delays and closures due to extended design and contract negotiations, ongoing repairs, and investigations into the failure of critical components, a March 2013 bolt failure threatened to push the proposed Labor Day opening to December. During a routine tightening of the high-strength steel bolts used to attach shock-absorbing devices, called shear keys, to a concrete crossbeam under the roadway, 32 of 96 steel anchor rods snapped. This quickly created concerns that the remaining rods could not withstand a seismic stress test.
FIX REQUIRES WATER CONTAINMENT
Unable to replace rods that were embedded in the concrete at one end with only 5-ft of headroom where they protruded at the top, engineers abandoned the bolts and decided to retrofit the shear keys with an external steel cable and saddle system. The repair, however, would require drilling into concrete. American Bridge/Fluor needed to ensure that the water flow required for the drilling process would be safely and effectively diverted and dispersed from the drilling site, 175-ft in the air, without impacting the Bay below.
With time running short and facing unknown and untested project dynamics, American Bridge/Fluor and sub-contractor Eco Bay Services, searched for a liquid handling partner with the expertise to tackle the complex requirements. In response to the urgent call, liquid handling specialist Rain for Rent immediately dispatched its local engineering team, including a certified engineer and a member of the company’s dedicated “Sewer and Water A Team” to the bridge site to assess the situation. Rain for Rent submitted their proposed solution within 48 hours to ensure the continued momentum of the fast-moving project.
In less than two weeks, the team had planned and designed a solution that took every possible contingency into consideration—from the physical constraints of the work site to the vertical drop onto a temporary structure. The meticulous planning process included detailed engineered drawings along with proof of concept based on prior experience and successes in comparable work environments.
It was a job that required a high degree of flexibility. The amount of water and level of debris could not be accurately calculated, making it necessary to plan for a broad set of variables. The team’s unique experience, along with engineering expertise and innovative thinking would help ensure a successful project outcome.
DRILLING WATER CAPTURED
Dispatched from a water truck on top of the bridge, a continuous flow of hundreds of gallons of water cooled the drill bits during the drilling process. With a high pH level and sediment content, it was essential that the contaminated water be fully captured, contained and transported for treatment and disposal. The Bay is considered one of California’s most critical ecological habitats. Moreover, the San Francisco Bay and Delta Estuary was identified in 1987 by the Clean Water Act as one of the nation’s 28 most critical estuaries as part of the National Estuary Program, which is overseen by the U.S. Environmental Protection Agency.
In order to meet strict regulatory requirements, the discharged water from the construction project ultimately had to be crystal clear and meet drinking water quality standards. It was a job with zero tolerance for failure. The solution had to capture and contain every single drop of water as soon as the drill was fired up. There was not a start and stop or rewind button to address any shortfall in the system.
The first step was the capture of the water beneath the drilling site, which was facilitated by a steel gutter constructed by Eco Bay Services. Rain for Rent installed a 6-in pipe into the gutter that was then run vertically 160-ft down into temporary storage tanks positioned on the floating pier end caps below.
To provide additional protection against leakage and to protect the Bay’s waters, spillguards (one-piece temporary containment berms) were installed under the tanks. The last step of this part of the process involved pumping the collected water from the pier caps to a set of tanks on a barge for transportation to the Port of Oakland. After being received in the port, the water was sent to a wastewater treatment plant for filtration and sanitary disposal.
A COLLABORATIVE EFFORT
With much fanfare, the new eastern section of the Bay Bridge, with its signature white tower, opened to the public on Labor Day, Sept. 2, 2013.
While the new bridge is built with steel and concrete, its heart lies in the collaborative efforts of the developers, planners and engineering and construction teams that have delivered a safer crossing for Bay Area residents and visitors for decades to come.