Cracks have formed in some walls of a condominium building next to Lake Washington, and the homeowners blame pile-driving work for the new Highway 520 floating bridge.
The cracks appeared early last month on the top floor of the four-story Canterbury Shores in the Madison Park neighborhood, so close to the Seattle shoreline that a statue of a dog was erected to scare geese off the lawn.
Four units have shown damage, all on the top floor, said Don Morgan, the building’s resident manager. The wood-framed, 91-unit building was constructed in 1967, and sits 560 feet from the nearest pile-driving.
Paint has split where ceilings meet walls. In some interior hallways, cracks spread outward from the window frames.
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It’s not obvious whether these cracks, which manifest as 2 to 5 feet long on the painted surfaces, are superficial or structural.
Residents have hired an engineering firm to investigate; three independent experts and two state transportation officials visited the building Wednesday, said Bill Mundy, a third-floor resident who for years has watchdogged the 520 project.
The state Department of Transportation (DOT) says it has been monitoring the vibrations, and will investigate damage claims when residents file those, as expected later this year.
Pile-driving is a possible cause, spokeswoman Suanne Pelley said. An email to homeowner representatives, from 520 engineer John Chi, raised other possibilities including pre-existing damage, normal wear and tear, or even that the soft soil near the lake is gradually settling.
On a recent day, as bridge workers were hammering a pile — at 41 strikes in a minute — the outdoor balcony floors quivered slightly with every smack.
“It’s just a huge ‘kabang’ every few seconds. There’s nothing you can do,” said resident Joan Byrne, whose unit hasn’t shown damage.
Just to the east, the 316-unit Edgewater Apartments, just 340 feet from the nearest pile-driving, are also at risk for vibration and noise.
The steel piles are temporary, allowing workers and machinery to be stationed on platforms to build the upcoming West Connection Bridge, part of the new 520.
That roadway will join
the new six-lane bridge to the 1963 four-lane bridge, until the state can build farther west, to reach land in Seattle.
A new $4.3 billion Highway 520 replaces an old bridge that’s vulnerable to collapse in a severe windstorm or earthquake. The new bridge adds a bike trail and transit-carpool lanes across the water and on the Eastside.
The episode serves as a reminder that long after politicians make their speeches and hoist their gold-painted shovels to get construction started, the real work of delivering infrastructure can stress the neighbors.
The Brightwater sewer tunnel caused a sinkhole and other damage in Bothell in 2010. Sound Transit tunnel construction below Montlake sent tremors from a supply train into houses, so Sound Transit modified its track designs in 2012 to absorb the vibrations.
The state two years ago inspected the buildings, and conducted further inspections last spring just before the piledriving, so it could better compare the conditions before and after all 300 piles are driven.
DOT previously installed seven monitors in the two properties, and added two more monitors last week,
said spokeswoman Suanne Pelley. So far, she said, the shaking has stayed below federal thresholds, but damage is still possible in vulnerable buildings.
“We’re continuing to work with the neighborhood,” Pelley said.
Mundy said the top floor is most vulnerable, because any shaking in the foundation would be amplified as the motion transmits to upper levels. Mundy, a professional land-valuation expert, is part of the Coalition for a Sustainable 520, a group of neighborhood advocates who seek protections from noise and traffic, and to reduce the bulk of the new bridge’s design.
Munday said a law firm has been hired to examine multiple impacts at Canterbury Shores, including noise, and flashing lights during night construction,
The permanent columns for the new bridge are being installed by drilling deep into the lake bottom, then pouring concrete down a tube, a process that doesn’t require noisy hammering.
But future bridge segments near Foster Island will need piles to be driven.
Mike Lindblom: 206-515-5631 or firstname.lastname@example.org. On Twitter @mikelindblom