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November 3, 2014 at 3:11 PM

Excavation to tunneling machine resumes; no artifacts found

Archaeologists have seen enough 19th-century shell deposits that they can let heavy excavation resume at Seattle’s Pioneer Square waterfront, where workers are digging an access pit to reach buried tunnel-boring machine Bertha.

Seattle Tunnel Partners was given permission Sunday to continue digging the 120-foot-deep vault, after stopping work Oct. 23, the state Department of Transportation announced Monday.  The pit operation was halted because of shells found about 18 feet below street level — forcing the state to investigate whether Native artifacts or human remains were buried.

None were found.  Instead, the shells are believed to be primarily small Olympia oysters, dumped by a commercial shellfish operation.

bertha_pit

When the vault is finished, Bertha will drill into open air, so a red crane can lift away the cutting head and ring-shaped bearing assembly for repairs. (WSDOT image)

The find caused 10 days’ delay to STP’s repair operation, which entails detaching Bertha’s cutting head, damaged seals, and main bearing, so the drive parts can be repaired or replaced at street level.  STP has set a goal of restarting the tunnel bore to South Lake Union in March, as described here by STP director Chris Dixon.  The contractors haven’t issued any further notice of delays.  “As far as we know, they’re still planning to lift the machine out of the ground in December,” said Laura Newborn, a DOT spokeswoman.

The giant tunneling machine remains buried 60 feet below street level, following a stall in early December.

When the deep vault is finished, Bertha will drill through the concrete about 43 feet, into open air below a crane.  The $2 billion project is at least a year behind schedule, and officials now hope to open the four-lane highway tube to traffic in late 2016.

 

 

 

 

 

Comments | More in General news, The Blotter | Topics: bertha, Highway 99 tunnel, Seattle

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