In March 2006, construction began on the East Side Big Pipe Project, the largest sewer construction project in the history of Portland, Ore.
The East Side Big Pipe Project is the last in a series of projects to be undertaken by the City of Portland in an effort to control combined sewer overflows (CSOs) into the Willamette River and Columbia Slough.
Before the CSO projects began, overflows occurred nearly every time it rained, due to Portland’s antiquated sewer system, which could not contain the volume of mixed sewage and stormwater.
When all the CSO projects are completed in 2011, the system will overflow an average of four times each winter and once every three summers. The city will have spent an estimated $1.4 billion on the 20-year program.
So far, the CSO program had not missed a major deadline since construction began in 1993, according to Paul Gribbon, chief engineer of the Willamette CSO Tunnel Program.
As an employee of the city’s Environmental Services department, Gribbon had been working on different phases of the sewage overflow program for 16 years. He remembered the CSO program’s pre-construction planning phase, which he described as “very intensive.” In fact, he credited that comprehensive early planning as part of the reason that the project has gone so smoothly to date.
CSO projects included the Columbia Slough Big Pipe, completed in October 2000, which collected sewage and stormwater that previously overflowed into the slough. The Columbia Slough pipe and related improvements had cost $164 million.
Another project was the construction of a pipeline that diverts Tanner Creek and other streams away from the combined sewer system. The six-phase Tanner Creek Stream Diversion Project, which was finished last year, keeps 165 million gal. (624 million L) of stormwater out of the CSOs, annually.
There also was the $390 million West Side CSO Project, which included the West Side Big Pipe. This CSO tunnel — 3.5 mi. (5.6 km) long and 14 ft. (4.2 m) in diameter — became operational in 2006. The pipe now conveys sewage through the Swan Island Pump Station to the Columbia Boulevard Wastewater Treatment Plant.
The CSO projects completed to date have cut annual overflow volume by two-thirds, equal to approximately 4 billion gal. (15 billion L).
Portion Has Begun
Scheduled for completion in 2011, the East Side Big Pipe Project has a budget of $464 million. Of that, $45 million is budgeted for inflation, and $38 million is contingency funds. The contract is for $381,291,149.
The project is funded by capital bonds, which the city will pay with residential and commercial sewer fees; over the next five years, the average residential sewer bill is expected to increase by $14.17 per month.
The construction contractor for the East Side Big Pipe is Kiewit-Bilfinger Berger (KBB), a joint venture between U.S.-based Kiewit Construction and the German company Bilfinger Berger.
KBB is building a 6 mi. (9.6 km), 22-ft. (6.7 m) diameter CSO tunnel running parallel to the east bank of the Willamette River. The tunnel lining will be comprised of 8.3 million lbs. (3.7 million kg) of steel and 100,000 cu. yds. (76,455 cu m) of concrete.
There also are 7,000 ft. (2,133 m) of connecting pipelines to be constructed.
When it is finished, the East Side Big Pipe will convey sewage to the Swan Island Pump Station, which will have the capacity to pump 220 million gal. (832 million L) per day to the Columbia Boulevard Wastewater Treatment Plant.
To construct the tunnel, KBB purchased a 220-ft.-long (67 m) tunnel boring machine (TBM) manufactured by the German firm Herrenknecht, for $12 million. When the tunneling is complete, the manufacturer will buy back the TBM for a pre-negotiated salvage value.
According to Gribbon, there are no American manufacturers who build this sort of machine.
In fact, Gribbon’s team had never heard of anyone using a slurry-pressured, faced tunnel boring machine in the United States, though he said they are common in Europe.
As part of the purchase agreement, the manufacturer sent representatives to help train local workers to operate the TBM, which was dubbed “Rosie” through a public naming contest.
Rosie weighed 1,000 tons (907 t); the cutterhead alone weighed 88 tons (79 t), and is 25 ft. (7.6 m) in diameter.
When the TBM was in action, slurry was pumped into the front of the machine under pressure, keeping the soil and groundwater back.
The excavated materials were separated: slurry was recycled back to the front of the machine, and the soil was discharged through pipes to a muck conveyor on the surface. The muck conveyor carried the soil to barges, which shipped it to Ross Island, where it is used as fill.
Similar, smaller TBMs, made by the same manufacturer, were utilized to construct the West Side Pipe. During that process, the construction team experienced a bit of a learning curve.
“We got some ideas about maintenance on the cutterhead, like how often it needs to be changed depending on the type of soil,” said Gribbon.
For instance, they learned that the Troutdale Formation, a geologic layer composed of cemented gravel, was highly abrasive on the TBM. However, the TBM also had the best production rate through the formation, excavating as much as 76 ft. (23 m) per day.
During the construction of the East Side Pipe, KBB was expecting the TBM to average 39 ft. (11.8 m) of tunnel per day. The machine operated 24 hours a day, in three eight-hour shifts, five days a week. All told, Rosie was expected to mine 550,000 cu. yds. (420,000 cu m) of soil from the tunnel.
The tunnel, which averaged 150 ft. (45.7 m) deep, would pass through seven tunnel shafts. As of late March, three of the shafts were under construction.
The Opera shaft, named because it’s located near the Hampton Opera Center, was the largest of the seven shafts at 67 ft. (20 m) in diameter and 115 ft. (35 m) deep. It was the main mining and access shaft for the East Side Big Pipe Project, and the entry point for the TBM.
The Opera shaft had been fully excavated and de-watered. Crews still are working on the internal walls.
A tower crane will be lower the pieces of the TBM to the bottom of the shaft, where it will be assembled and set into action along its route north to the Port Center shaft.
The shaft measures at 49 ft. (14.9 m) in diameter and 129 ft. (39 m) deep and is expected to arrive there in 2010.
At the Port Center Shaft, the machine will be retrieved and refurbished. The TBM will then be returned to the Opera shaft to start its southern progression to the McLoughlin shaft. This shaft has the same measurement as the Opera and will finish tunneling in 2011.
Gribbon said that construction of northern segment shafts are proceeding swiftly. The walls of the Alder shaft are 49 ft. in diameter and 112 ft. (34 m) deep and are installed. The crews already are preparing to de-water. The TBM will arrive there in December 2007.
The walls have been started at the Steel Bridge shaft, which is 49 ft. in diameter and 153 ft. (46 m) deep. The TBM is scheduled to break into that shaft in June 2008.
As might be expected with a project of this scale and budget, a small army of subcontractors had been involved. Major players included the construction management firm Jacobs Associates, and the design engineering firm Parsons Brinckerhoff.
In addition, it is estimated that over the course of the East Side Big Pipe Project KBB will enter into contracts with local firms to the tune of approximately $53 million. Gribbon’s list of subcontractors currently tallies up to approximately 90, and five years of work still remain.
Those subcontracts have provided economic boost to local businesses.
However, project managers nationwide might be more interested to learn about the unusual type of contract that was arranged, first with West Side Big Pipe contractor Impregilo/S.A. Healy J.V., and later with KBB for the East Side Big Pipe.
“It is not low bid, it is qualifications-based procurement,” explained Gribbon.
The contract type was cost-reimbursable with a fixed fee, meaning that the city paid the prime for labor, equipment and materials as re-imbursables, whereas all of the contractor’s overhead is one fixed fee, paid as percent complete.
The CSO team proposed this form of contract because they knew how technically challenging the jobs would be, said Gribbon.
They had surveyed other U.S. tunnel jobs, and found that it was not unusual for these projects to be a year late or 50 percent over budget. So the CSO team knew that they had to find a different way to go.
It was important that the Big Pipe Projects stay on schedule, because the City of Portland and the State of Oregon have agreed on an Amended Stipulation and Final Order (ASFO) that requires the city to control CSOs to the Willamette River by 2011.
Portland’s City Council supported the alternative contract, which Gribbon describes as “very conducive to forming a partnership with the contractor.”
As the CSO program enters its 16th year, on deadline and on budget, it appears that the unusual contract procedure has worked for everyone. CEG