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SNOHOMISH — There’s no quick fix for the pothole covered by a steel plate on the Bickford Bridge over state Route 9.
The asphalt failure that deepened in mid-October wasn’t the city’s fault, nor the pavement contractor’s. The Tribune was told the cause was, in part, the bridge itself.
The bridge deck under the pavement vibrates and flexes from vehicles driving over it.
It’s “not a stable surface for the asphalt. It’s why it’s failing,” city engineer Yosh Monzaki said.
The arrangement is the State Department of Transportation (WSDOT) maintains the bridge structure, and the city is responsible for the pavement on top.
Snohomish last repaved the bridge in 2021.
WSDOT constricted what Snohomish could do, city officials said. It resulted in paving the bridge with a thinner layer of asphalt than what Snohomish would normally use for a heavy-traffic road.
An arterial such as Avenue D should have 6 to 8 inches of pavement, Monzaki said. That generally goes for bridges, too.
The Bickford Bridge’s pavement is 4 inches thick, Monzaki said. The pavement previous to that repave was thicker, he said.
But even a thicker layer would eventually crack because of the flexing bridge deck underneath, Monzaki said.
Even a different material such as concrete wouldn’t work.
“There isn’t a product out that we could substitute for asphalt” that can withstand the flexing, Monzaki said.
City engineers are working to find the best solution.
When it was paved in 2021, the closure lasted more than two weeks while the city waited for state officials to inspect the bridge structure. The contractor ground down the asphalt to the bridge deck, scooping it off the deck.
As for the bridge’s wooden deck, state inspectors found no repairs were needed, WSDOT told the Tribune at the time.
