SEATTLE -- Bertha, the world’s largest tunneling machine building the new State Route 99 tunnel under Seattle, hasn’t made much news since it successfully cleared the pilings holding up the Alaska Way Viaduct in early May.
Since then, after leaving its last maintenance stop known as “safe haven 3,” the machine has dug deeper and mined another 1,500 feet, bringing the total length of the tunnel to nearly 3,000 feet - 2,971 to be exact. The total tunnel length is 9.270 feet; that represents nearly one-third of the overall length of the SR 99 tunnel.
The bottom of the tunnel, which is 60 feet high, is approximately 200 feet below ground level. At this point, Bertha will start mining upgrade toward its planned exit between the Space Needle and the South Lake Union neighborhood.
The Washington State Department of Transportation announced Bertha would also be taking a break, as soil conditions now permit a maintenance stop lasting several weeks where workers will be able to replace cutting tools on the front of the machine and make an overall inspection of the machine’s systems. Bertha mined 675 feet in June and 722 feet in May, according to WSDOT.
WSDOT also announced a $3.5 million contract with Interwest Construction of Sequim to build a new flyover ramp to take Northbound cars off SR-99 and deliver them to Dearborn St.
Construction is expected to be confined to the current work area at the south end of the SR 99 tunnel.