West Side Big Pipe
Massive Underground Project
Seeks to Clean Up Willamette
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.
Two hundred years after their journey across the United States
to the Pacific Northwest, Lewis and Clark have embarked on
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.
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
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
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
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.
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.
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
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.