Special Reports

Bridge caisson falls behind

Construction of the Tacoma caisson of the new Tacoma Narrows bridge is five weeks behind schedule, according to a report released Monday by the state Department of Transportation.

But bridge builders say they will have no trouble making up the time and will not miss deadlines set forth in their contract with the state.

"We're talking about a matter of a few weeks in a five-year project," said Claudia Cornish, a Transportation Department spokeswoman. "When you put this into perspective, it is really insignificant at this point."

The $849 million suspension bridge, being built by a Bechtel/Kiewitt partnership called Tacoma Narrows Constructors, will use two submerged caissons, or foundations, one for each of the 510-foot towers.

Each caisson is the size of a high-rise building and will drop through about 150 feet of water and about 60 feet of the sea floor.

Construction of the west caisson on the Gig Harbor side of the channel is on schedule, Cornish said, even though it started a month later than the Tacoma-side caisson.

The east caisson has been delayed in part because, being first, it was where contractors figured out how to deal with problems.

"It's been the one that had the learning curve, and the Gig Harbor caisson benefited from that," Cornish said.

Also, the channel is deeper on the Tacoma side, and the currents and winds are stronger there.

Weather was a big factor in the delay, Cornish said. High winds forced workers off the caisson several times, she said, and recent cold weather dropped temperatures too low for concrete to cure.

Hooking up anchors to the caisson took longer than expected, she said, and some anchor cables had to be reinforced to withstand the stress put on them by currents.

In October, caisson crews went from working two eight-hour shifts on the caissons to two 10-hour shifts. They'll make up more time, Cornish said, by using a more efficient method of sinking the caissons into the Narrows floor.

Both caissons are expected to be finished in June, at which point the Tacoma caisson will be about one week behind schedule, Cornish said.

Information about the bridge schedule was included in a monthly summary of the Narrows Project prepared by the Transportation Department.

Rob Carson: 253-597-8693

rob.carson@mail.tribnet.com





SIDEBAR: The work in brief

Through December:

• Bridge workers had worked 576,061 hours without an accident serious enough to force an employee to take time off.

• Construction was 26.3 percent finished.

• Design was 99.5 percent finished.

• The project had spent $266.9 million of the $615 million in its contract.

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