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Caltrans to Tackle Tunnel Corrosion

Wednesday, February 24, 2016

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Although Caltrans originally expressed that the failure to a tunnel wall in the Bay Bridge area was likely an isolated incident, further inspection shows that not to be the case.

Caltrans has since discovered 12 other areas within the Yerba Buena Island tunnel where water intrusion threatens additional concrete failure, local news site SFGate reported Sunday (Feb. 21).

A Close Call

As reported earlier, the issue came to light after a chunk of concrete wall fell into the roadway, just missing a vehicle in the travel lane, in the Bay Bridge’s Yerba Buena Island tunnel, which links the western span and the new eastern span of the San Francisco-Oakland Bay Bridge.

© / Joe_Potato

Since the Jan. 30 failure, Caltrans has discovered 12 other areas within the Yerba Buena Island tunnel where water intrusion threatens additional concrete failure, according to reports.

According to reports, the debris—a 3-inch thick semicircular piece about 2 feet in length—fell into the eastbound, lower deck of the 80-year-old tunnel on Jan. 30. The point of failure was where the ceiling of the lower deck (which also acts as the deck for the westbound deck on top) connects to the tunnel wall about one-third of the way into the south end of the structure.

Caltrans began investigating the failure, but at the time believed it to be confined to an isolated area. The structure was last inspected in July 2015, officials said, with no problems identified.

Water stains were reported to be evident at the site of the failure, and a crack was visible in the concrete near the break. More concrete cracking was said to appear to be hidden by the tunnel ceiling.

Further Investigation

Caltrans officials reported finding 12 additional points of corrosion-related failure, all within the eastbound lower tunnel, through a basic testing method: tapping the concrete with a hammer and listening for hollow sounds, according to SFGate.

Although a visual inspection had been performed as recently as July, the hammer test has not been performed since 2004, the site added.

Ken Brown, a Caltrans engineer who oversees Bay Bridge maintenance, told the news site the at-risk areas were found on both sides of the tunnel and range in size from as small as 3 by 3 inches to about 2 by 3 feet.

According to ABC 7 News, Caltrans has removed concrete in areas where it feared pieces could break away and fall on vehicles.

“We removed the unsounded concrete, and it's now exposed," Caltrans spokesperson Myeast McCauley told the station. “We looked at the rebar that is in there and discovered that there is a little bit of light corrosion on the rebar."

Because the basic test method is unable to detect “less-severe” cracks and corrosion in areas of the tunnel covered with paint, specialists with x-ray equipment will need to be brought in to determine how pervasive the damage actually is, local news site SFist reported Monday (Feb. 22).

The Federal Highway Administration will assist in this phase of the investigation.

“We brought (the agency) in to advise us, to get a feel from what they are seeing in other tunnels,” Brown said.

Rainwater Intrusion

As with the anchorages on the new East Span of the Bay Bridge, rainwater appears to be the root cause of the tunnel’s problem. According to Brown, water is making its way into the tunnel through some of the 250-plus drain openings on the upper deck to the tunnel below, SFGate wrote.

By Manfred Werner / CC BY SA 3.0 via Wikimedia Commons
By Manfred Werner / CC BY SA 3.0 via Wikimedia Commons

According to Caltrans officials, water is making its way into the tunnel through some of the 250-plus drain openings on the upper deck to the tunnel below.

According to Caltrans, the upper and lower tunnels are separated by a deck comprised of reinforced concrete sections. These sections sit on top of 12-inch-wide concrete ledges on both sides of the tunnel, where 512 half-inch-thick Masonite pads provide cushioning at contact points.

Rainwater coming in through the drain openings soaked the pads, causing them to swell downward and crack the lower tunnel’s concrete wall, Brown said. Water could then seep into the cracks and corrode the steel rebar, “popping out” the concrete from the wall.

Commenting on the Masonite pad at January’s point of failure, Brown said, “it looked like it had swelled, and that it had frayed.”

In addition to replacing the damaged concrete in the tunnel, Caltrans officials said they may have to replace hundreds of the Masonite pads with rubberized ones, which would inhibit the creation of cracks.

However, the agency said the original drawings for the tunnel deck do not make clear how the drainage system works, so it sees an obstacle in how to keep water from intruding into any pads that aren’t replaced.

“We are looking at both keeping the water out and dealing with any issues we have with the bearing pads,” Brown said. “The long-term goal is to prevent any kind of continued deterioration so we don’t have any major issues."

Danger Downplayed

Caltrans officials say that drivers are safe to use the tunnel. Dan McElhinney, deputy district chief for the agency, told SFGate the corrosion was “minor, but important” and that any imminent danger had been addressed by removing the unsound concrete.

“We have checked all the walls—there is no risk of spalling in the near term,” he said. “We don’t see anything urgent at this point.”

However, area motorists don’t feel reassured.

"It's a dangerous situation and needs to be fixed,” Marnie Moore told ABC 7. “We pay enough in taxes and tolls for that not to be happening. So it's really simple for me, there is no excuse for it."

Mike Blackman agreed, saying: "They need to fix that—they need to get right on it. All of a sudden a week goes by, someone gets killed. What are they going to do then?"

Speaking for Caltrans, McCauley took a wider view. "What this speaks to in the larger picture is the need for funding and the need for maintenance of this infrastructure that is aging," he said.

Brown told SFGate the cost of repairs will come from a fund of about $70 million a year for rehabilitation projects on the Bay Area’s seven state-owned toll bridges. “We don’t have exact costs,” he said.


Tagged categories: Caltrans; Concrete defects; Corrosion; Corrosion protection; Environmental Controls; North America; Roads/Highways; Transportation; Tunnel

Comment from Fred Wittenberg, (2/24/2016, 1:46 PM)

In this publication just days ago, I named this bridge "Boondoggle." The hits just keep on coming!

Comment from Tom Schwerdt, (2/25/2016, 1:34 PM)

Fred, It's an 80 year old tunnel. Maintenance issues will crop up, you just need to deal with them proactively. I wonder what the original "design life" of the tunnel was. Bridges at that time typically would have a 50 year design life.

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