Aug. 4 project update: New video highlights tunnel segments as Bertha nears First Avenue

Posted on Aug 4 2016 2:55 PM
Bertha, the SR 99 tunneling machine, is approaching the intersection of First Avenue and University Street as crews with Seattle Tunnel Partners continue mining north beneath downtown.
As of this morning, the tunneling machine had traveled a total of 3,518 feet and installed 533 concrete tunnel rings. The top of the machine is nearly 130 feet below street level. Earlier this week, crews successfully tunneled beneath the off-ramp that connects northbound SR 99 to Seneca Street. The machine passed approximately 90 feet below the the piles that support the ramp.
Crews will continue tunneling north beneath First Avenue for several blocks. Their ultimate destination is a receiving pit near Seattle Center, where Bertha will end her 9,270-foot-long journey beneath downtown.
The building blocks of the SR 99 tunnel
Crews have now installed more than 5,000 curved concrete segments in the tunnel – each one weighing an average of 36,000 pounds. Bertha takes 10 of these segments and creates a five-story-tall tunnel ring, as shown below. 

Steps of ring building

A look at how each tunnel ring is pieced together by Bertha, the SR 99 tunneling machine.

It will take 1,426 of these rings – or 14,260 concrete segments – to create the nearly two-mile-long tunnel. All the precast segments were built locally, at the Encon Washington plant in Pierce County. Segment production wrapped up in fall 2014. Every segment is checked multiple times for quality before being brought into the tunnel for installation. This video shows you exactly what the tunnel is made of – building blocks of steel and concrete.