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January 12, 2015 at 11:07 AM

City taking its own look at viaduct safety, as relations with WSDOT fray

December 8, 2014 photo of the deep pit that crews will use to repair Bertha, the SR 99 tunneling machine. The white pipes are part of the system designed to keep groundwater out of the pit. Excavation of the pit is more than halfway done and will be 120-feet deep when finished. http://www.wsdot.wa.gov/projects/viaduct/traffic/constructioncam

Crews use a deep pit to repair Bertha, the Highway 99 tunneling machine. (WSDOT)

The city of Seattle says it has hired its own engineering consultants to take an independent look at the Alaskan Way Viaduct, to see whether groundwater removal and other Highway 99 tunnel work poses a hazard.

The $155,000 study by CH2M Hill will start by reviewing state modeling of the 61-year-old viaduct and may go more in depth, said Scott Kubly, director of the Seattle Department of Transportation (SDOT).

The move reflects growing scrutiny and skepticism by officials from city departments, who say in letters that the flow of information from the state Department of Transportation (WSDOT) hasn’t been good enough.

Kubly and Seattle Public Utilities director Ray Hoffman say the city didn’t get sufficient notice about a Dec. 11 draft report by Brierley Associates (engineer of record for a tunnel-repair pit now under way) that warned of an elevated risk of  “catastrophic failure” in the access vault to reach stalled tunnel machine Bertha, unless Seattle Tunnel Partners (STP) changed its “repair as we go” digging tactics in the 120-foot-deep pit.  Actually, STP responded in late December and earlier this month by scraping away some nonessential concrete pillars and injecting more grout, to fortify the walls against groundwater leaks.  Nonetheless, the Jan. 6 letter was given to City Council members Friday night, made its way to The Stranger by Monday morning, and provoked nervous questions from council members.

Todd Trepanier, WSDOT’s Highway 99 administrator, said he was “disappointed” that the city was taking the information “out of context.”  Specifically, he said the Kubly-Hoffman letter omitted the next sentence, in which Brierley halted the dig at 90 feet, until STP could fill the gaps and suspected gaps between vertical concrete columns.  Otherwise, engineers feared the ring might tilt inward or spring leaks, as digging continued. At no time was there an actual threat of failure, nor a safety risk to drivers on the viaduct, Trepanier said. The vault has now been excavated to 98 of its eventual 120 feet.

Trepanier threatened to cut off city staffers’ access to real-time technical documents on a shared website.  That led Councilmember Mike O’Brien, a longtime skeptic, to say he was disappointed with WSDOT, and call for more transparency, not less.  Council President Tim Burgess, a tunnel backer, hoped “the adults in the room” would solve their differences.

City staff letters, and other records released to The Seattle Times last week, show frustration that the tunnel team canceled some weekly meetings about soil conditions in the fall, at about the time Pioneer Square soil was settling an inch.

“Obviously there are problems in communication between SDOT and WSDOT,” said Councilmember Tom Rasmussen. “We’re all concerned it’s undermining public safety, or at least public confidence in safety. Clearly the relationship is strained.”

A snippet from the Dec. 11 draft of a tunnel-team technical report.

A snippet from the Dec. 11 draft  of a tunnel-team technical report. The ring begins about 16 feet above sea level.

Also:

  • City departments are updating their emergency transportation plan in case the viaduct must be closed, noting that eventually Bertha is supposed to pass below the viaduct. Among other changes, SDOT will write a plan to keep freight moving.
  • Direct measurements by SPU found that a 20-inch water main on Western Avenue sank 1.25 inches and is considered damaged, with the suspected cause being groundwater pumping at the tunnel site. But sinking at other mains, including one on First Avenue, was less than SPU’s damage thresholds. An intergovernmental contract says WSDOT would replace any damaged cast-iron water mains.
  • The latest schedule by contractors pushed out the completion estimate to September 2017 for the four-lane highway tube, a month longer than an August 2017 date announced last month. WSDOT notified lawmakers of that change but cautions that until Bertha’s front end undergoes repairs, the state can’t vouch for schedule estimates.

For the past month, state engineers have said settlement of the viaduct has occurred evenly, there are no cracks or stresses, and it remains safe to drive. Soil sinking hasn’t worsened since the losses of just over an inch in late November, said David Sowers, a senior WSDOT geotechnical engineer.

Comments | More in Government, Traffic & Transit | Topics: Alaska Way Viaduct, bertha, Seattle Tunnel Partners

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