Bay Bridge Leaks Get Low-Cost Fix
Water leaking into support structures of the San Francisco-Oakland Bay Bridge has been a concern for engineers as early as the construction phase. Now, they have hit upon a relatively inexpensive solution for plugging those leaks.
Since late 2015, workers have been applying an industrial-grade caulk that costs about $40 per tube, SFGate reported Friday (Jan. 22), which has stopped nearly all water leakage affecting the structure’s anchorages.
Caltrans structures maintenance engineer Ken Brown told the news site that the sealant has resolved about 90 percent of the leaks in the $6.4 billion two-and-a-half-year-old bridge.
The Source of the Problem
As reported earlier, the risk of corrosion from the infiltration of rainwater was raised by lead designer Marwan Nader from design firm T.Y. Lin International, the engineering and design firm responsible for designing the new Bay Bridge, in October.
The main cable of the Self-Anchored Suspension span is protected by a “steel jacket” everywhere but in the anchorages, where the 137 steel strands spread out and are exposed, making them susceptible to the elements and potentially threatening the strength of the structure.
Nader warned that if rainwater collects in the 90- by 120- by 25-foot steel boxes where the cable is anchored, the cable is at risk of corroding at its base unless some action is taken.
At that time, Caltrans indicated the leakage could be the result of a design flaw in the guardrail: holes drilled into and through the deck to affix the guardrails were allowing rainwater to infiltrate the hollow space where the cable is anchored.
Then, Caltrans was looking to existing and possible additions to dehumidification systems to deal with any rainwater entering the anchor area; however, Nader indicated the equipment would not be sufficient for the amount of water with which the anchor areas contend.
“The dehumidification is not effective if rainwater is allowed to seep into the east anchorage,” Nader told Caltrans officials at the time.
Adding Protection from Weather
Having first thought the leakage resulted from a design change that removed metal plates meant to halt the collection of rainwater, Caltrans spent $1.4 million on a complex sealant job as a fix—but the leakage continued.
Caltrans signed a work order with Benicia, CA-based contractor Golden State Bridge Inc. for assistance in repairs related to weather protection, which are expected to be complete by midyear 2016.
A new round of tests showed that there was no connection to the lack of metal plates; rather, water was coming in through gaps on the roadway side of the guardrails.
This led to the much cheaper solution of applying a $40-a-tube industrial-grade sealant to the joint between the asphalt road surface and the guardrails, the news site said. The total cost for this fix would be $100,000.
While not designed to be watertight, Brown indicated they are “getting a lot closer to where we want” with the bridge.
“In the last couple of storms, we have not seen any water coming,” Brown said. “We are trying to go out after every storm to see what more leaks.”
According to Brown, the sealant will have to be replaced about every seven years, but this is still expected to be much simpler and cheaper than some of the proposals that looked at protecting the cable and reengineering how the guardrails are anchored.
However, he also indicated his engineers are still investigating a longer-term fix for the problem.
Weathering the Storms
Caltrans sped up efforts to solve the rainwater leakage with the anticipation of heavy rains from El Nino, the agency announced in a statement.
It signed a maximum $3 million order with Benicia, CA-based contractor Golden State Bridge Inc. for assistance in repairs related to weather protection, which are expected to be complete by midyear 2016.
The scope of work includes refilling or replacing grease caps, adding weep holes and caulking steel elements and reinforcement within the bridge's concrete structure where needed for weather protection.
Existing Bay Area Toll Authority funds are supporting the current work.