West Side Big Pipe

Massive Underground Project Seeks to Clean Up Willamette

By Sheila Bacon

The Nicolai Shaft - about half a mile north of the Fremont Bridge - is one of six newly created shafts along the Big Pipe route. The two tunnel boring machines were lowered down this shaft in August. Image courtesy of City of Portland BES

Two hundred years after their journey across the United States to the Pacific Northwest, Lewis and Clark have embarked on another expedition.

These modern day explorers take the shape of two 16 ft. dia. tunnel boring machines, tasked to drill and construct a 3.4-mile long, 14 ft. dia. underground tunnel along the west side of Portland's Willamette River. Nicknamed "Lewis" and "Clark" by the project team, the machines play an integral role in the largest public works project ever undertaken by the City of Portland.

The West Side Big Pipe project, which started last November and is expected to be complete by 2006, is a $293 million phase of the City of Portland Bureau of Environmental Services' Combined Sewer Overflow program; a $1 billion, 20-year effort to drastically reduce the amount of sanitary sewage and runoff discharged into the Willamette River. The pipe will run 120 ft. below the surface and loosely follow Naito Parkway from S.W. Clay Street to N.W. Nicolai Street, where it continues under the river and meets with the new Swan Island Pump Station.

advertisement

Nearly every time it rains in Portland, stormwater quickly fills the city's combined sewers, which carry both sanitary sewage and runoff from streets, parking lots and rooftops. The high volumes back up the collection system, triggering overflow devices that are meant to keep the sewers from backing up into the streets and people's homes. The volumes - made up of approximately 80 percent rainwater and 20 percent sewage - then overflow into the Willamette River. These combined sewer overflows (CSOs) contain bacteria from untreated sewage and other pollutants in the stormwater.

In 1991, the city entered into a formal agreement with the State of Oregon to control CSOs by 2001. The Bureau of Environmental Services has made significant progress since then. It has spent $500 million on a number of CSO control projects (see related story, "Reducing CSOs") and controlled 53 percent of the volume discharged to the river. With the completion of the West Side Big Pipe project in 2006 and the similar East Side Big Pipe project (currently in design) by 2011, overflows are expected to be reduced by more than 94 percent.

Both the West Side and East Side Big Pipe will intercept 50 points where untreated sewage and stormwater currently flow into the river. Overflow will be diverted into the pipes, flow to the Swan Island Pump Station currently under construction and be pumped a few miles to the Columbia Boulevard Wastewater Treatment Plant.

Since the majority of the work takes place deep underground, it's likely few Portlanders will even be aware that the mammoth project is ongoing.

"It's the biggest public works project in the history of the city," said Dean Marriott, director of Portland's Bureau of Environmental Services, "but ironic because it's out of sight. It's not like we're building the Empire State Building where people can see it."

The Dig Begins

"Lewis," one of the two tunnel boring machines employed on the West Side Big Pipe project, will burrow underground north towards Swan Island. Pieces of the machine were lowered down the Nicolai Street shaft in August. By early January, each 35-ft.-long machine will be fully installed, trailing 200 to 300 ft. of equipment such as hydraulic pumps, hoses and ventilation systems. Image courtesy of City of Portland BES

Pieces of the first tunnel boring machine were lowered down the Nicolai Street shaft - one of six newly created shafts along the route - about half a mile north of the Fremont Bridge in late August. Once the machines start moving forward through the ground, crews will start assembling the back-up equipment that will attach to the rear of the machines. By early January, each 35-ft.-long machine will be fully installed, trailing 200 to 300 ft. of equipment such as hydraulic pumps, hoses and ventilation systems.

Then, Lewis will head north to Swan Island and Clark will head south to Clay Street. (When the tunnel reaches Clay Street, the Big Pipe will hook into the nearly completed SW Parallel Interceptor, a three- to six-ft. dia. pipe that continues three miles along the Willamette to SW Taylors Ferry Road.) Lewis' segment will take 11 months to complete, and Clark's 23 months. Clark is a brand new machine, the Lewis was used once before on a tunneling project in Paris, but both have been configured specifically for this job, said Jim McDonald, project manager for Impregilo/Healy Joint Venture of Portland.

Crews will be working in "the worst possible ground," said McDonald: loose, soft soil that must be instantly supported as the boring machines advance. Each machine has a steel shield - like a can - around it. The front of the machine bores through the soil, while the back end extrudes curved concrete pieces that are bolted together to make a ring. The machine advances by pushing off these extruded segments.

Up to 10 workers per shift are underground driving the machine, said McDonald. In a 24 hour period, the machines will advance approximately 50 ft.

Early Involvement

Impregilo/Healy is a joint venture team comprised of Impregilo - a large, multi-faceted construction firm based in Milan, Italy; and S. A. Healy, a Lombard, Ill., subsidiary of Impregilo that specializes in tunnel construction. The joint venture got involved in the project during the preconstruction phase, offering Portland engineering firm Parsons Brinckerhoff input and constructability reviews.

That early involvement has helped save time and money on the project, said McDonald. Among other savings, Impregilo/Healy crews suggested a thinner concrete wall at the Swan Island Pump Station, which helped cut costs and move the project forward.

Traffic along the route isn't likely to see much interruption, said Marriott. Lane closures at shaft locations will be brief and intermittent. This winter, some lanes on Naito Parkway will be closed while crews reinforce the ground under the Broadway, Steel and Burnside bridges as a safety precaution before Lewis and Clark rumble past.

The city will have little time to regroup once the West Side Big Pipe project is finished. Final design of the East Side Big Pipe project will wrap up in the summer of 2006, and construction of the six mile long pipeline will begin that winter. The project will serve the same purpose as its cousin to the west, intercepting CSO points on the east side of the Willamette. The Bureau of Environmental Services is expected to make tunnel alignment and shaft location decisions by April 2004.