Going down to see whats up – WAY down, in the Big Pipe Project
Portland's 'Big Pipe Project' to divert sewage out of the Willamette River isn't news - the West Side part of the project has been completed, and is currently in operation. But the opportunity, before Christmas, to travel 160 feet underground to see this even-larger tunnel being dug on Portland's East Side did catch our interest.
Our tour began at the contractor's East Portland offices at the Portland Opera building, just south of the Oregon Museum of Science and Industry (OMSI) on S.E. Water Street, just north of the Ross Island Bridge.
'We are at the Opera Shaft location,' said Steve Marriott, director of Portland's Bureau of Environmental Services, as he began our orientation.
'This shaft is where we inserted 'Rosie', the Tunnel Boring Machine (TBM). It's driving north from here toward Swan Island.'
Marriott explained that Portland is among some 1,000 cities across the nation which were built with a 'combined' sewer system. The raw sewage and stormwater are collected in the same system, with any overflow sent into the Willamette River.
'When the sewage treatment plant was built in the 1950s,' Marriott went on, 'they also constructed interceptor pipes to convey the flow to the treatment plant on Columbia Boulevard in North Portland. But, they didn't size these pipes big enough to handle the runoff from the rainstorms. At the time, they considered that having a clean river only in the summer was good enough; it provided a huge improvement in water quality.'
But in the 1990s, the city committed to the federal government to begin a 20-year program to address the chronic wintertime problem of combined sewer overflows into the river. And, Portland is ahead of most cities in solving this problem, Marriott said. 'Many other cities have yet to address it.'
The underground tour begins
Our first stop on the tour was seeing the technology that supports the excavation of tons of sand, dirt, and gravel, and sealing a pipe - all 160 feet underground.
Our tour guide, Shane Yanagisawa, 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 leftover rocks and sand are barged from a conveyor belt extending over the riverbank just south of OMSI to load barges, which carry it to Ross Island, where it is used to fill in the lagoon, where once sand was dredged to make concrete.
After the TBM drilling unit 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 to lock the ring in place. A special grout is then injected into the soil around each ring 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, which for those just driving by is the most visible evidence of the construction project in Southeast Portland.
Yanagisawa continued, 'This operation is a continuous process. Everything has to be working at all times - the TBM, the slurry plant, separator, the grout plant, ventilation system, and the ring manufacturing.'
Portland City Commissioner Sam Adams, joking that he's 'The Sewer Commissioner', exited the elevator, coming up from his tour of the project, just as we members of the press were preparing to descend.
'This is the first time I've had the opportunity to tour the East Side project,' he explained. 'This is an effort to reduce, by 94%, the sewer overflows into the Willamette River. We'll have spent $1.4 billion, when all of the tunnels have been dug and pumping stations have been installed. We're now about 66% complete on the overall project.'
Our group then climbed into a construction elevator affixed to the side of the shaft for our ride to the bottom. Along the walls of the 67-foot-wide shaft are the electrical conduits that power the TMB, the incoming and outgoing slurry pipes, and the large ventilation duct.
On the bottom of the huge shaft are train tracks, on which runs a 'Loki' - a squat but powerful diesel engine and passenger cars.
Once aboard, we rumbled northbound, heading through the tunnel toward the current end of the line: The TBM rig. The tunnel was temperate and dry, and we saw segments of the concrete liner rings along the way.
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, told 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 the drilling rig inches forward, the100-foot long assembly is pulled along with it.
'The TBM has now entered the Alder Street Shaft, where the old 'Corno' building once stood,' Colzani told us. 'Standing here behind the machine, we're right below the Montage Restaurant.'
Brooklyn tunneling begins in 2010
From the Alder Street Shaft, the crew will keep mining northward to the Swan Island pumping station. 'When we reach that point,' Colzani said, 'We'll take the machine apart. Then we'll haul it back to the Opera Shaft, and reassemble it there for its trip south. It will tunnel from there about 8,000 feet to our [southernmost] shaft on the north side of S.E. McLaughlin Boulevard at S.E. 17th Avenue.'
And, when it arrives there in 2011, Colzani said, another giant crane will be built there to lift out the TBM, including its 160-ton main bearing.
A large, but smaller, tunnel will then be bored south a short distance to the intersection of S.E. 18th and Insley, where the 'Insley Collector' pipe which collects sewage from throughout Inner Southeast Portland will be connected to the 'Big Pipe' via this new, final tunnel.
That will complete a 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.'