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.
GUIDANCE SYSTEM
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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