December 11, 2013
(AP) — Diagnosing what has blocked a boring machine working on a
highway tunnel under downtown Seattle, and figuring out what to do,
could take about two weeks, the project director for Seattle Tunnel Partners said Wednesday.
Chris Dixon said specially trained workers could be sent to the site next week, The Seattle Times reported (http://is.gd/aLaJol ). They would peek outside the tunnel machine's cutter head to see what's in the way.
machine can retreat about 18 inches and compressed air would be forced
into the small space in front of the cutter head to allow workers to get
a look at the problem.
the top of the tunneling machine is about 60 feet below ground,
professional divers used to working below the surface would be needed.
leading theory is that the machine called Bertha hit a boulder last
Friday and that the soil around it is too soft to hold it firmly and
allow the cutter head to crack it apart. The machine was shut down
Saturday about 1,000 feet into the 1.7 mile project.
quickest way to remove whatever it is would seem to involve divers
breaking it up with power drills and hammers, along with Bertha's
drills, Dixon said.
contractors could drill down from above and break up the object or lift
it out. That probably would require building a protective wall or pit
to hold back sand and groundwater.
"It would take several weeks to build that," Dixon told a news conference.
58-foot diameter tunnel is scheduled to be completed by the end of
2015, creating a four-lane route for Highway 99 traffic between South Lake Union and the area south of downtown.
$1.4 billion tunnel contract is part of the $3.1 billion project to
replace the Alaskan Way Viaduct along the downtown Seattle waterfront.