Come underground and see exclusive photos of your sewer-bill dollars at work …
How far is 160 feet down? Yes, those are people standing at the bottom of this shaft!
Story and photos by David F. Ashton
Portland’s “Big Pipe Project” to divert sewage out of the Willamette River isn’t news – the West Side project has been completed, and is currently in operation. But the opportunity to travel 160 feet underground to see this giant tunnel dug on Portland’s east side caught our interest.
Our tour began at the contractor’s East Portland offices in the Portland Opera building, located just south of OMSI.
“We are at the Opera Shaft location,” Steve Marriott, director of Portland’s Bureau of Environmental Services said as he began our orientation.
“This shaft is where we inserted ‘Rosie’, the Tunnel Boring Machine (TBM). It is driving north toward Swan Island.”
Our tour guide, Shane Yanagisawa, explains the equipment used in the massive project.
Brief history of sewers
Marriott stated that about 1,000 cities across the nation were built with a “combined” sewer system. The raw sewage and stormwater were collected in the same system, and sent into the river for disposal.
“When the sewage treatment plant was built in the 1950s,” Marriott went on, “they also constructed interceptor pipes to convey a lot of that flow to the treatment in North Portland. They didn’t size these pipes big enough to handle the runoff from every single rainstorm. At the time, they considered that having a clean river in the summer was good enough; it provided a huge improvement in water quality.”
But in the 1990s the city agreed to a 20-year program to address the chronic wintertime problem of combined sewer overflows.
Portland is ahead of most cities in solving this problem Marriott said. “Many other cities have yet to address the problem.”
This machine – the separator – divides mining spoils into piles of gravel, pebbles, sand, and the mining slurry that is returned to the tunneling machine.
This conveyor belt system takes the excess sand and gravel from the tunnel to barges which remove it and dump it in Ross Island lagoon.
Tunneling support system
Our first stop on the tour was seeing the technology that supports excavating tons of sand, dirt, and gravel, and sealing a pipe – all 160 feet underground.
Our tour guide, Shane Yanagisawa, lead planning engineer with Kiewit Bilfinger-Berger, walked our group over to a three-story tall building on the project site, just east of the Opera Shaft.
“This is the separator,” Yanagisawa explained. “Everything that is cut by the mining machine is mixed with slurry made up of water and bentonite clay. It is pumped to the surface where it is separated in into big chunks, small rocks, sand, and slurry. The slurry is pumped back down to the TMB.”
The rocks and sand are barged from a conveyor belt south of OMSI to fill in the lagoons once mined at Ross Island.
The most visible portion of the project to folks in Inner SE Portland is the Opera Shaft crane. It lifts and lowers all parts and supplies for the project.
These pre-cast concrete segments form rings that stabilize the tunnel section just dug by the TBM. The disks to the left of the ring segments are some of the TMB’s cutting heads.
Paving the pipe
After the TBM pushes forward, cutting a section of tunnel, it is lined with a series of 25 identical, pre-cast concrete ring segments, and finished with one key segment that locks the ring in place. A special grout is injected into the soil around the rings to help seal the pipe.
These ring segments are made on site, using some of the spoils from the tunneling operation. They – and all other equipment and supplies – are lowered down the Opera Shaft by a huge construction crane, perhaps the most visible evidence of the construction project in East Portland.
Yanagisawa continues, “This operation is a continuous process. Everything has to be working at all times – the TBM, slurry plant, separator, grout plant, ventilation system and ring manufacturing.”
Even Portland City Commissioner Sam Adams is required to wear safety gear, including the snappy yellow toe protectors we all slipped on our boots.
Commissioner Adams endorses progress
Portland City Commissioner Sam Adams, joking that he is “The Sewer Commissioner”, exited the elevator, coming up from his tour of the project, as we were preparing to descend.
“Hopefully the calisthenics portion of the safety orientation wasn’t too strenuous for you,” he kidded.
“This is the first time I’ve had the opportunity to tour the east side project. This is an effort to reduce, by 94%, the sewer overflows into the Willamette River. We will have spent $1.4 Billion, when all of the tunnels have been dug and pumping stations have been installed. We’re about 66% complete on the overall project.”
The Loki train hauls personnel and equipment from the central shaft to the trailing end of the TBM.
When the Eastside Big Pipe goes into operation, this pipe will be carrying pressurized, raw sewerage. We prefer to tour the pipe in its pristine state!
As we speed toward the trailing end of the TBM, we pass endless sections of Big Pipe rings.
Going down
Our group gets into a construction elevator affixed to the side of the shaft for our ride to the bottom. Along the walls of the 67′ diameter shaft are the electrical conduit that powers the TMB, incoming and outgoing slurry pipes, and a large air ventilation duct.
On the bottom are train tracks, on which runs a “Loki” – a squat but powerful diesel engine and passenger cars.
Once aboard, we rumble northbound, heading toward the end of the line: the TBM rig. The tunnel is temperate and dry; we see segments of the concrete liner rings along the way.
Members of this press junket marvel at the size of a machine that cuts a 26-foot-diameter tube far underground.
This is a view of the “trailing gear” that feeds supplies and power to the TBM in the distance.
Tunnel manager Greg Colzani says today is just another day at “the office” – but much quieter, since today the machine isn’t running.
The TBM at rest
Because this was a system maintenance day, the TBM was silent when we exited the train, about a mile north of the Opera Shaft.
Greg Colzani, tunnel manager tells the group that the TBM is about 30 feet long; but the equipment behind it, including the devices used to set the ring segments in place, is about 70 feet long. As it inches forward, the 100′ long assembly is pulled along with it.
“The TBM has entered the Alder Street Shaft, where the old ‘Corno’ building once stood” Colzani comments. “Standing here behind the machine, we’re right below the Montage Restaurant.”
This is the back of the TBM. Ahead of it lies more soil and rock to bore through, 160 feet below SE Alder Street.
Southbound trip begins in 2010
From this point, the crew will keep mining north to the Swan Island pumping station. “When we reach that point,” Colzani said, “We’ll take the machine apart. We’ll haul it back to the Opera Shaft, and reassemble it for its trip south. It will tunnel about 8,000 feet to our [southernmost] shaft at SE McLaughlin Boulevard and SE 17th Avenue.”
And, when it arrives there in 2011, Colzani said, another giant crane will be built there to lift out the TBM, including the 160-ton main bearing.
A large, but smaller, tunnel will be bored south a short distance to the intersection of S.E. 18th and Insley, and the “Insley Collector” which collects sewage from Inner Southeast Portland will be connected to the “Big Pipe” with this new, final tunnel.
That will complete the project that Commissioner Adams said he considers to be a “100-year project that will prevent all but the worst overflows into the Willamette River. And keep the sewer system functioning for the next century.”
© 2007 David F. Ashton ~ East Portland News Service
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