Steel overruns unlikely on Stilly Bridge construction

Mowat Construction crews remove slabs of the concrete deck of the I-5 southbound Stillaguamish Bridge Aug. 15. - Kirk Boxleitner
Mowat Construction crews remove slabs of the concrete deck of the I-5 southbound Stillaguamish Bridge Aug. 15.
— image credit: Kirk Boxleitner

ARLINGTON — Mowat Construction has already removed more than half the deck of the I-5 southbound Stillaguamish Bridge, with more than 90 days of its 120-day window left to replace the bridge deck.

Although the state Department of Transportation allowed for as much of 20 percent of the steel beneath the concrete deck to be replaced, construction crews encountered the first of the steel stringers in need of replacement Aug. 15.

WSDOT Assistant Project Engineer Polly Brooks noted that Mowat has 120 calendar days, including holidays and weekends, to complete its work. She added that the only way this window can be extended, without Mowat being financially penalized, if the construction requires more steel work than WSDOT originally estimated.

"So far, we've had to replace one stringer and a rivet, and do some minor steel repairs," Brooks said. "Until now, almost all the steel we've seen has been in good shape, so we don't foresee any overruns."

Even with relatively few steel replacements to date, construction crews have taken care to avoid any risk of contaminating the river below.

"All of the equipment has multiple containment barriers to catch any runoff," Brooks said. "There are tarps above the deck to catch the rain before it can hit the cut concrete, and there's a deck that's been added below the bridge to catch even dust and other fragments."

Brooks explained that, while cured concrete poses no environmental risks, freshly cut concrete can affect the pH levels of water.

"Even the temporary access that we've created, from Gulhagen Road to the portion of I-5 southbound that we've cordoned off, was evaluated beforehand to make sure it would have no negative impacts on any wetlands or the flood plain," Brooks said.

She reported that Mowat has adopted a 24-hour-a day, six-days-a-week construction schedule for the $8.7 million project, setting aside Sundays as "catch-up days" to compensate in case inclement weather delays parts of their work.

"The rain has slowed it down a little bit, but not too badly," Brooks said. "It's coming along well."

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