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December 10, 2013 at 11:38 AM

Highway 99 tunnel stoppage: drill brought to the rescue

Workers at the Highway 99 tunnel project are bringing a crane and drilling equipment to the waterfront this morning, to try to remove the mystery object blocking the deep-boring machine, some 60-feet underground.

The crane was unloading steel cylinders from a flatbed truck, at South Main Street and Alaskan Way South, where tunnel machine “Bertha” has been stymied since Friday evening.  Floodlights, generators, a tall drill, and a green tank for possible wastewater storage were all being staged or unloaded at nearby Terminal 46 — an indication that work may proceed into the night.

Seattle Tunnel Partners (STP) and the state Department of Transportation have yet to identify what’s in the way.

The vertical drilling equipment is similar to what STP used to install concrete pilings, to fortify the launch pit in Sodo. An auger rotates and descends vertically through temporary steel cylinders, as shown in this Seattle Times file photo.

Drilling at the Sodo launch pit. (Seattle Times file photo by Ellen Banner)

Drilling at the Sodo launch pit. (Seattle Times file photo by Ellen Banner)

There’s more to the task than simply finding and removing the clog. After that happens, crews will probably have to inject concrete grout or some other hard substance into the earth to fill the resulting gap. Bertha, known as an “earth pressure balance” machine, requires firm surroundings when it drills ahead, so that it can stay on a precise path.  So a restart might take several days.

A state DOT spokeswoman said Monday that vertical drilling was one option, to help locate or remove the object.  The tunnel team hasn’t replied yet to a request for an update Tuesday morning.

So far, about 1,000 feet of tunnel tube has been installed, close to one-eighth of the total path to South Lake Union. Contractors have been paid at least $730 million to date, of the $1.44 billion contract to build the tube, road decks, and electronic systems by the end of 2015.

Comments | Topics: Highway 99 tunnel


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