Repaired tunnel machine Bertha launched the new year by boring forward 6 .5 feet Monday to the north edge of its repair vault along the Seattle waterfront.
The giant drill is expected to grind through an approximately 15-foot-thick concrete wall and escape the vault this week, according to the Washington State Department of Transportation.
At the north portal, WSDOT is warning travelers to prepare for weeks of construction blockages from Jan. 18 until early March, when sign installations in the median will force traffic into the southbound bus lane. One northbound lane with be closed in the first part of the work. Traffic slowdowns are likely.
Bertha’s progress Monday allowed Seattle Tunnel Partners to fasten the 161st ring of the future four-lane tube, behind the machine, which has traveled 1,098 feet of the 9,270-foot route from Sodo to South Lake Union. The tolled tunnel is projected by STP to open in April 2018, some 27 months later than contractors offered in their winning bid for the $1.35 billion contract.
This week’s vault breakout will bring Bertha to maybe the most precarious section of the project. The path continues through waterlogged, dense sand and clay until it reaches a concrete box for inspections, then dives beneath the Alaskan Way Viaduct, past brick buildings in Pioneer Square. That entails a two-week closure of the viaduct in March.
Bertha was launched July 30, 2013, and stalled Dec. 6, 2013, three days after it dug 52 feet, but also hit a steel pipe left from state groundwater tests and got tangled in the cutter face. WSDOT disagrees that a pipe hit could cripple Bertha, while insurers argue the 57-foot-diameter machine was inadequate to effectively turn the immense volumes of soil.
Hitachi Zosen, which built the $80 million drill, installed tougher bearing seals and added reinforcing steel last year. Contractors then lowered the 4-million-pound front end into the vault, so it could be refastened to the machine in the fall. STP and Hitachi Zosen fronted the costs to revive Bertha, expected to exceed $143 million.
WSDOT has paid builders just over $1 billion to date for work already done.
