On Monday, April 28, the first of two tunnel boring machines (TBMs) that will carve the underground portion of the Northgate Link Extension was dedicated at Sound Transit’s Maple Leaf Portal site.
This was the last close-up opportunity for Brenda as the TBM is readied to start her journey underground to Roosevelt Station in June.
Brenda is not Big Bertha’s younger sister. No. Brenda is a veteran TBM, having already carved the paths between between Capitol Hill and the downtown transit tunnel wall in 2011-12.
She looks pristine on the outside now, but…
…on the inside, you can see Brenda’s experience.
Here’s where Brenda will start her journey: The Maple Leaf Portal, where the elevated light rail track leading south from the Northgate Station will head underground.
The right side of the wall pictured above is the southbound tunnel starting point where Brenda will shortly be moved to and start boring into in June. (Here’s Brenda starting to chew on the wall at the Capitol Hill Station a few years ago.)
The TBM’s 21-foot-diameter cutter head (the large green and yellow disc on the front of the TBM) is covered with teeth and holes, turns at a rate of 0.1 to 2.5 revolutions per minute, and can excavate an average of 40 feet of tunnel per day.
It’s also great for posing with.
View inside the cutter head. Here the tailings that have passed through the openings in the cutter head will fall, be carried out by this red screw conveyor, and moved through the body of the TBM.
This is the “trailing gear” that follows behind the TBM. It carries equipment for the boring machine and helps carry the spoils away from the machine. Altogether, the TBM and the trailing gear stretch out to the length of a football field.
As the TBM and the trailing gear carve the route to Roosevelt and beyond, supply trains will ferry equipment from the outside world down into the tunnels. Chief among their cargo will be the pre-cast concrete segments that compose the finished walls of the tunnel as well as provide a surface for the TBM to propel herself forward.
It is these supply trains, running along on metal rails down in the tunnels, that were judged responsible for the noise and vibrations experienced by residents in Montlake back in November 2011.
Good news for those living and working (and attending the UW) above the Northgate Link Extension tunnels: Vehicles equipped with rubber tires will be used this time around for underground deliveries.
Worm’s perspective of the cutter head.
Sound Transit has a great little video showing how tunnel boring machines work. It includes a cross-section graphic of the machine in action, as well as footage from previous excavations.
And here’s where we pause the photo essay to share with the Roosevelt neighborhood some potentially great news.
The old plan for tunneling south was for Brenda to dig one side of the route to Roosevelt Station, be trucked back up to the Maple Leaf Portal, and begin digging the other side of the route. Then a second TBM-to-be-named-later would join her in Roosevelt, where the pair would start their journey south to the University of Washington Station. Muck from the tunneling would travel up to the Maple Leaf Portal site and be hauled away there for Brenda’s solo drilling, but would be hauled out of Roosevelt Station for the remainder of the project.
Sound Transit’s Bruce Gray tells me that this may no longer be the case. Via email:
In the new plan the Contractor has proposed two TBMs going from Maple Leaf. The performance of the tunneling and the muck haulage will be closely monitored during the initial drive from Maple Leaf to Roosevelt. If all goes well, the two machines will continue on to UW with spoils removal and haulage continuing from Maple Leaf the entire time. If the new proposal does not perform as planned there could still be muck haulage and/or a third TBM launched from Roosevelt in order to meet the project schedule.
What this would mean for the Roosevelt neighborhood is that after the dump trucks bearing away the soil from the station excavation are gone, they’d be GONE. Muck from the entire Northgate Link Extension would come out the Maple Leaf Portal and be hauled away there.
Again, this new plan is not a given. And it’s going to be a while before anyone knows the contractor’s final decision. Once Brenda gets digging in June, it will take her 10-12 months to reach Roosevelt Station (via Sound Transit’s Gray). If the second TBM launches from the Maple Leaf Portal five months later in October, the pair won’t see each other in Roosevelt until August 2015 at the earliest.
To be continued…
Hey, Roosevelt: Remember when you rallied to bring light rail closer to the neighborhood’s core at 12th Avenue NE (over a station closer to I-5 on 8th Avenue NE)? On January 27, 2005, the Sound Transit board agreed with you, and the Roosevelt Station Alignment was chosen. Here, some stickers from that campaign pose with the machine that’s making it a reality.
A fragile bottle of dedicatory Washington apple cider sits in the shade along with TBM-signing Sharpies and commemorative pins.
The assembled crowd listens to officials during the dedication.
Sound Transit Board Member and City of Everett Councilmember Paul Roberts, and 46th District Representative Jessyn Ferrell, share a laugh during the dedication speeches.
Councilmember Roberts anoints the cutter head with a refreshing non-alcoholic beverage.
Then the signing began. Gathered participants were encouraged to write on the machine.
Some just signed their names.
There were a few drawings. And more than a few children’s names.
Stephen’s self-translated message read: “wish tunnel boring success!”
Representative Farrell’s signature joins the others on Brenda’s flank.
“Go straight. Go on-line. Go safely.” writes this Sound Transit staffer, as photojournalist Josh Trujillo also takes a picture.
A selection of signatures and good wishes for Brenda’s journey.
Sound Transit workers at the site wanted to get back to work, but didn’t mind standing around for a picture or two.
Members of the Sound Transit Northgate Link team pose en masse.