MARYSVILLE — In the first few months of work on a new span across Ebey Slough, many passers-by asked crews what they were doing, because there was little visual evidence of anything that looked like a bridge.
That’s no longer the case.
Crews working for the state this month are instal
ling the last few steel girders across Ebey Slough, on top of which the roadway for the new bridge will be laid.
“It’s all just concrete after this,” said Janice Fahning, a project engineer for the state Department of Transportation. “Concrete and rebar.”
The new $42.3 million bridge is expected to start carrying cars and trucks on Highway 529 between Marysville and Everett next April. The project is on time and on budget, officials said.
The current swivel bridge is 86 years old, does not meet modern earthquake standards and can’t handle all the traffic during busy times.
In the early months of work on the new span, starting in July, crews were driving steel pilings 240 feet into the soil beneath Ebey Slough — not easy for the public to see. Then crews built concrete pillars around the piles above the surface, and platforms atop the pillars to serve as a base for the girders.
To do the work, crews put together a temporary steel and wood platform on the southern bank of the slough. It’s a modular structure that is custom assembled for each job, said Joe Rooney, a chief inspector for the transportation department.
The main contractor, Granite Construction of Everett, is using the platform to support cranes being used to lift the girders into place.
The longest of the girders, at 135 feet, weigh 31 tons each — (that’s 540 pounds per linear foot) — and take two cranes to lift. Altogether the bridge will contain about 2.5 million pounds of steel, Rooney said.
It’s increasingly rare for steel girders to be used in bridge construction, he said. Girders can be made more cheaply and economically from concrete.
Concrete girders are heavier, though, and would have forced the state to build a more elaborate, and probably more expensive, construction platform on the slough, Rooney said. This would have run into more environmental regulations and likely would have offset any cost savings from using concrete girders, he said.
Once girders are in place, two layers of wooden floors are built to provide a temporary base for the roadway. Rebar is installed over the wood, concrete is poured over that, and the wood is removed, leaving the concrete and steel.
The new road will have four lanes, compared with two across the current bridge. Plus, the new bridge will have bike lanes and sidewalks running in each direction. The current bridge has a walkway but no bike lanes.
Once the roadway is installed, crews will spend the winter installing sidewalks and wiring for lighting and drainage. They’ll also realign Highway 529 to meet the new bridge. The new span is just east of the old one, so the new alignment won’t be drastically different.
Next spring, traffic will use both bridges while realignment work is finished. In August 2012, all traffic will move to the new bridge, though only two of the four lanes will be open at first, because crews will need the other two lanes as a work area to dismantle the old bridge.
This will take another six months or so, with all four lanes of the new bridge open to traffic in early 2013.
The contractor will be responsible for disposal of the old steel bridge, Rooney said. They’ll likely separate it from its moorings, lift it out in one or two sections and load it onto barges. From there it will probably be taken to Seattle and transported by train to a landfill. The old pilings will be cut off below the surface and capped.
The old bridge is coated with lead paint, and to safely remove the paint to salvage the steel would probably be more trouble than it’s worth, Rooney said.
The new bridge will be able to move twice as much traffic as the current one. An average of 17,000 cars a day use the roadway, but this amount swells when there’s an accident on I-5, overloading the bridge, officials say.
Plus, the new bridge is a fixed span, meaning it won’t have to open for boats. It will have roughly a 28 foot clearance over the slough, compared with 15 feet for the current bridge, which swivels open to let boats pass.
When this happens, about five or six times a month, traffic is delayed for 10 minutes or more.
“It’s just not adequate for the traffic volume,” Rooney said.
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By the numbers
Bike lanes: 2
Girder height: 7 feet
Girder weight: 31 tons
Number of pilings: 32
Number of girders: 49
Girder length: 100 to 135 feet
People employed on project: 150
Total bridge length: 680 feet