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Bertha resumes tunneling after course correction

Less than 1,000 feet to go


WSDOT announced late Monday that Bertha, the tunnel boring machine currently digging the State Route 99 tunnel, is back to work after a six inch course correction.

Seattle Tunnel Partners halted boring last week to check position after surveys led them to believe Bertha was “several inches” off. Adjustments like this “are common during mining,” according to WSDOT’s announcement.

Corrections to Bertha’s path are made through as guidance system, complete with lasers that move along with the machine. The system sends information to the surface that crews can use to adjust course.

The boring machine has less than 1,000 feet to go before arriving at the finish line—a disassembly pit. Seattle Tunnel Partners estimates Bertha will arrive there sometime this May.

This five-day delay went by quickly, by comparison. From December 2013 to December 2015, the machine was stalled for repair and a partial cutterhead replacement. A few smaller delays continued in 2016, including a sinkhole-related incident.

WSDOT estimates that the tunnel should be ready for traffic in early 2019.