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Feds nervous about a Highway 99 tunnel beneath them
Posted by Mike Lindblom
The federal government is wondering if the historic Federal Office Building, at 909 First Avenue, would be damaged by shifting soils if the state goes ahead with boring a highway tunnel beneath the foundation.
A Dec. 13 letter from the General Services Administration conjectures that the top of the tunnel might be 75 feet below the basement, near its foundation piers; or it might be only 46 feet below the basement, and either depth would place "this historic building and its occupants in permanent jeopardy."
The letter goes on to say that "compensation grouting" -- which involves injecting concrete into the soil to fill gaps caused by excavation -- cannot completely stop the soil from settling above the tunnel tube. The issues need to be resolved before the federal government would allow the state to buy underground easement rights, GSA says.
Since then, the GSA and state DOT have discussed the issue, and expect more talks. "We anticipate we'll get answers from the [state] DOT. It's fair to say we're making good progress," GSA spokesman Ross Buffington said Tuesday.
Ron Paananen, the state Highway 99 administrator, said he's certain DOT will prove to GSA the project is safe, so he declined to talk about whether the tunnel path might change, or what it might cost to furnish GSA more engineering research or protections.
He said the top of the tunnel will be 100 feet deep there, and this diagram from DOT contracting documents shows it 95 feet below surface at the Federal Office Building.
The state just signed a $1.4 billion contract with a tunneling team led by Spanish firm Dragados and California-based Tutor Perini. Paananen said the team will soon be able to provide specific answers and strategies to prevent soil sinking. Final design is less than 15 percent complete, said Rick Conte, senior engineering manager for Parsons Brinckerhoff, the state's design consultant.
Paananen also said he's confident soil settlement will be less than 1 inch, based on Dragados' experience in Europe. The giant, cylindrical tunnel machine will be able to squirt grout into the soil around it.
The Dec. 13 letter was first reported and linked by Publicola. The Seattle Times filed a state public-records request Dec. 25 for state DOT memos and records about the building, but hasn't yet received those.
The Federal Office Building, an Art Deco structure built in 1933, is on the National Register of Historic Places.
Also on Tuesday, the state met with artists facing eviction by 2012 from the nearby Western Building, home to colorful wood lofts and popular "First Thursday" tours. The 101-year-old Western, which has been cracking and sinking for years, is not expected to withstand tunnel construction.
Overall tunnel costs are $2 billion, the largest piece of a $3.1 billion highway project from Sodo to South Lake Union to replace the 1953-vintage Alaskan Way Viaduct. The DOT currently has a $100 million cushion against cost overruns, but tunneling tends to be the financially riskiest form of construction.
Two initiative campaigns, I-101 and I-102, are underway seeking to halt the tunnel project, while the pro-tunnel City Council is expected to sign utility and right-of-way agreements with DOT next month.
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