Dive Brief:
- The world's largest tunnel boring machine, dubbed Bertha, finished its $2.1 billion, four-year journey drilling a 1.75-mile path under Seattle when it broke through to daylight on Tuesday, according to The Seattle Times.
- The remainder of the nearly $3.2 billion Alaskan Way Viaduct replacement tunnel project includes highway decks, lights, connection of tunnel ramps to existing ramps and a testing period — all of which should take another year and a half.
- Tunneling operations were initially scheduled for completion in October 2014, putting this phase of the project 29 months behind schedule. The delay is primarily attributable to about two years of repairs after Bertha broke down in December 2013.
Dive Insight:
The cause of the breakdown remains a point of contention between tunneling contractor Seattle Tunnel Partners (STP) and the Washington State Department of Transportation. According to a report from Q13 Fox TV, STP has filed suit against the soil testing contractor that allegedly left an 8-inch steel pipe behind, the same one that sidelined Bertha back in 2014. Decisions regarding the legal responsibility of all three parties are pending.
After crews repaired Bertha, it returned to service in December 2015. However, about a month later, WSDOT and Gov. Jay Inslee stopped tunneling operations after a sinkhole developed above Bertha. Around the same time, a barge carrying excavated soil tipped over and dumped its load into the water near the spot where Bertha was operating. This prompted WSDOT to declare the site a potential hazard to both employees and the public.
STP — a joint venture that includes California–based construction giant Tutor Perini and New York–based Dragados USA — filled the sinkhole with concrete and was given the go-ahead to resume operations after a third-party study found the sinkhole was "a pre-existing void, a ground loss in the face of the (tunnel-boring machine), or a combination of both." In addition, WSDOT required STP to formulate a soil monitoring and removal plan and truck all future excavated material from the site instead of removing it by barge.
