Laying a strong foundation

Bridge: The pouring of concrete marks the first major stage of the new $2.5 billion Woodrow Wilson span.

February 02, 2003|By Stephen Kiehl | Stephen Kiehl,SUN STAFF

OXON HILL -- Construction crews lowered a thick black hose through a green latticework of reinforcing steel 16 feet beneath the surface of the frozen Potomac River, then began a continuous pour of the high-grade concrete that will form the foundation of the new Woodrow Wilson Bridge.

That two-day pour came to an end yesterday afternoon and with it came the first major stage of the $2.5 billion bridge project.

Crews have now finished building the portion of the bridge that is under water -- the 1,069 steel and concrete piles that plunge through the river bottom into the earth and the 64 thick concrete slabs that sit atop them.

"This is our last big pour," said construction manager George Ryland as he stood on a barge yesterday and watched a crew guide the concrete-spewing hose pouring the foundation that would support the draw span on the outer loop of the Capital Beltway.

Hamstrung for years by neighborhood protests and disputes over union labor, construction of the new Woodrow Wilson Bridge is now well under way.

It is the costliest public works project in Maryland history -- a 12-lane, 1.1-mile twin span that is designed to stand for a century and relieve a maddening bottleneck.

The first step is the foundation. The concrete is hot and fluid when first poured, malleable for 45 crucial minutes before it hardens.

Workers used rakes, shovels and vibrating machines to spread the concrete evenly and to force out air bubbles. They wore heavy layers of clothing coated with concrete splatter and worked in 12-hour shifts.

The pour began Friday morning and continued through the night and all day yesterday. It had to be done all at once because stopping and restarting could create cracks in the concrete.

"One monolithic piece -- that's what you're after," said Mike Bonin, a chief engineer on the project. "In the water, in the footing, you don't want to have a joint. It's an opportunity for water to get in and corrosion to start."

The foundation must be strong enough to withstand floods, earthquakes, hurricanes and even an errant ship. It must also, of course, withstand the steady drumbeat of the 295,000 cars and trucks expected to cross the bridge daily by 2020. The current six-lane bridge, which crosses the Potomac River south of Washington, was built in 1961 to handle 75,000 vehicles a day. It is now much busier than that, carrying about 200,000 vehicles a day.

The work zone for the new bridge is just south of the current span. It is a sprawling construction site consisting of dozens of barges connected by gangplanks and 10 cranes that rise into the gray sky. Yesterday, the highest crane was adorned with an American flag.

Workers, who get to the site by taking a short boat ride from the river's Maryland shore, focused during the past two days on pouring 6,500 cubic yards of concrete -- enough to fill a school gymnasium from the floor to the ceiling.

Each of the four foundations for the draw span is 16 feet thick, 87 feet wide and 120 feet long. The 60 foundations for the fixed spans of the bridge are somewhat smaller.

A tremendous task

"The magnitude is tremendous," said Bonin, who has built bridges across the country. "This is a big one because of all the machinery for the draw span, because of the size of the bridge. You're going to have 12 lanes of traffic overhead. Most bridges are two or four lanes."

Work on the bridge foundation -- itself a $125 million contract -- began in May 2001 with the driving of steel piles. The piles were up to 225 feet long and five feet in diameter -- so large that the contractor, Tidewater Kiewit Clark, had to bring in a 300-foot crane usually reserved for building offshore oil platforms.

Then, for each footing of the bridge, workers lowered into the river a huge basin with holes cut in the bottom. The piles came up through the holes, divers sealed the gaps, and concrete was poured through the water to create the floor. Then the green river water was pumped out of the basin to create a dry work area.

A green lattice of reinforcing steel was assembled inside the basin. Yesterday, concrete filled in through the latticework, which workers stood on while guiding the black hose that spat out the concrete.

The concrete is made in a plant set up on the Maryland shore of the river just for the bridge construction.

The plant can make about 140 cubic yards of concrete per hour, which is loaded into hoppers on barges that take the concrete out to the work site.

Conveyor belts move the concrete from the hoppers to the crane with the black hose on the end.

Then, it's poured.

Weather-friendly

Yesterday was just about ideal for pouring concrete. The cold weather helps cool the concrete, which generates its own heat as it settles.

To prevent cracks, the difference in temperature between the outer edge of the foundation and the inner core must not exceed 35 degrees. And yesterday's misty skies helped keep the concrete fluid.

"This is a great day for concrete because the moisture in the air keeps the concrete wet and there's more time to work it," said Ryland, the construction manager.

Now that the final foundation is poured, crews will complete work on the huge pedestals that sit atop the foundation. The V-shaped arms that support the bridge will branch out from those pedestals. And then the bridge will take shape.

The first span of the bridge, which will be the outer loop of the Capital Beltway, is scheduled to open in early 2006, with the inner loop span to follow two years later.

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