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Work on new span's foundation about to enter noisy next phase

February 12, 2004 Reposted from the San Francisco Chfronicle
   By Michael Cabanatuan

Oakland -- In the year since Gov. Gray Davis donned a Caltrans hard hat and declared construction of the new eastern span of the Bay Bridge under way, it's been difficult for anyone but the most curious of commuters to spot much progress.

That is about to change. The work will soon come into full view -- and earshot.

"People will start to notice," said Jeff Weiss, a Caltrans spokesman. "They will definitely see it now."

Most of the early work on the $2.6 billion bridge involved logistics -- hiring crews, setting up construction headquarters, dredging and bulldozing. Now it's time for the heavy-duty construction, and crews toiling aboard enormous barges beneath the existing bridge, often in wind and rain, have started the lengthy task of building the foundation for the new span.

Sometime early this month, workers will begin the noisy task of pounding tubular piles as long as a football field through the muck and sand of the bay floor and into the more solid Alameda alluvia -- a firm mixture of clay and gravel so hard, says Caltrans bridge engineer Mark Woods, that most people would consider it rock.

The huge pneumatic hammers used to pound the 7 1/2-foot-diameter piles will loom just north of the bridge, about 100 feet higher than the traffic decks. If motorists somehow don't notice the towering equipment, they'll probably hear the noise. A relentless "clong-clong-clong-clong-clong" will reverberate for the two years it takes to pound the piles.

In all, 160 piles will be slammed at a slight angle into the bay floor. They will anchor the 28 columns that will hold up the 1 1/2-mile-long twin concrete viaducts of the "skyway" portion span. The viaducts will reach from the mudflats in Oakland to the new bridge's signature single-tower suspension span, which will stretch to Yerba Buena Island.

But before the bridge can begin to rise from the water, workers have to build the foundation -- a multipart process that starts by building the boxes formally known as cofferdams.

The cofferdam construction has been under way since fall, when a waterborne crew started pounding 85-foot interlocking steel sheets about 30 feet deep into the mud, outlining the site of each future pier.

The 100 or so workers building the cofferdams work in unusual conditions. They're hauled by boat to huge barges in the bay, and they labor amid passing vessels and wildlife, the roar of traffic on the bridge and the winter storms. Rain doesn't delay construction, Woods said, but gusting winds can be hazardous and force a break in the work.

"We're stopped more by wind than by the high seas," he said, noting that since the workers are already working on, and in, the water, they aren't worried about getting wet.

Once the cofferdam walls are in place, crane operators scoop out the mud from the outlined area and dump in a 6-foot layer of rock and gravel. Then a 900-ton steel "footing box" -- with holes where the piles will be driven through -- is placed atop the gravel.

After that step is done, more gravel is added between the footing box and the cofferdam walls, and huge sump pumps are installed to "de-water" the dam --

in other words, pump it dry.


The last piece to put in place inside the cofferdam before the piles can be driven is a 150-foot-tall template. The giant guide sits on top of the footing box and holds the piles in place while they're pounded.

Finally, using some of the world's largest pile-driving hammers, crews pound the tubular steel pilings through the slots of the footing box and into the bay floor. The piles are so long they arrive on barges in two sections -- one about 220 feet long, the other 110 feet. The longest segment will be pushed into the bay first, then crews will weld on the second length, and the pounding will resume.

Once the piles for each pier are pounded -- most will have six -- workers weld the connection where the piles meet the footing box, slip rebar into the piles and pour concrete into both the piles and the footing box. At that point,

the foundation will be ready to support a column rising from the bay.

Each foundation, said Woods, takes about nine months from start to finish.

"You can see why it costs so much to build a bridge," Weiss said.

The $1.04 billion contract to build the skyway -- awarded to the KFM consortium of Kiewit Pacific of Omaha, FCI Constructors of San Jose and Manson Construction of Seattle -- is the largest ever awarded by Caltrans.

Designers envisioned the eastern span as a thin white line hovering above the bay, then bursting into a grand spire of steel and cable just east of Yerba Buena Island.

A huge and complex project, it is actually two bridges -- the side-by-side viaducts of the skyway and the single-tower suspension span, which will join in the middle of the bay. Construction also includes separate structures that link the new bridge to the eastern shoreline and the tunnel at Yerba Buena. At times, crews will be at work on different sections of the new span at the same time.

The skyway, the longest stretch of the span, will emerge from the bay gradually, east to west, a few pieces at a time, and one viaduct at a time. The twin concrete viaducts will each feature five lanes with emergency shoulders.


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