YERBA BUENA ISLAND (CBS SF) — Caltrans inspection crews brought out special equipment Tuesday to get a better assessment pf the state of the 80-year-old Bay Bridge tunnel two months after a chunk of concrete fell from the ceiling, landing on a car.

The 1,800 feet span of the tunnel has been under the gun since the incident. On Tuesday, technicians put the eastbound lower-deck tunnel under the radar gun.

“It’s comparable to doing an MRI on the tunnel,” explained Caltrans spokesperson Bob Haus.

With the help of the Federal Highway Administration, Caltrans is looking for corrosion and cracks in the tunnel like the one that caused the chunk of concrete to fall onto the roadway in late January.

Caltrans said some cracks were inches long while others stretch out for several feet. Workers are concerned there could be more.

On Tuesday, crews used three types of special scanning devices to find out: sound-echoing technology, ground-penetrating radar and infrared radar.

“It gives you a good idea about what’s going on about a foot into the concrete,” said Haus. “So that way, it can tell if the concrete — that may look sound on the outside about a foot in — if a problem is developing. Then you can tell ahead of time.”

At this point, Haus said there is no cause for the cracks. Engineers believe it could be a combination of rainwater from the upper deck and vibrations from cars traveling on and over it.

“It’s an 80-year-old structure. You’re going to have some cracked and chipped concrete, said Haus. Usually on something like this, it’s never about one single bullet.”

Caltrans told KPIX the last time they did a visual inspection was last July. The agency admitted engineers have not a done a basic hammer test — which involves tapping the concrete at various spots — since 2004.

Haus assured KPIX and the public that the Bay Bridge is safe, despite the string of issues the span has had.

“Well, if it weren’t [safe] we would close it,” said Haus. “Granted, that’s a draconian measure pretty extreme measure but safety is a top priority.”

If significant damage is detected, Caltrans said repair work could lead to lane closures. Repairs could include replacing some of the tunnel wall and would be done at night and during off-peak hours to reduce the impact of lane closures on traffic, according to Caltrans.

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