The Portland Experience
BES Uses Innovative Approaches for CSO Projects
By Jim Rush

On some levels, nothing is truly new. In many cases, new ideas or products are simply recycled, repackaged, reinvented. Yet, sometimes the application of existing ideas to new areas can be truly innovative. Take the case of the Portland Bureau of Environmental Services (BES), for example.

Using a combination of tried-and-true contracting methods that had been successful in other sectors, BES developed a contracting method for its combined sewer overflow (CSO) abatement program that has come to be known as the “Portland Method.” The modified fixed-fee, plus cost-reimbursable approach has helped keep the city’s CSO program on budget and on schedule to meet its mandated completion date of 2011.

As it turns out, the contracting method was just the beginning of the pioneering efforts as the East Side and West Side CSO tunnels have seen the first large-scale use of slurry tunnel boring machines in the United States, as well as a record-setting 3,055-ft microtunneling drive. However, BES wasn’t looking to set records or achieve firsts. “We had some contractual difficulties on our last tunneling project,” said Paul Gribbon, program manager for BES. “We just knew there had to be a better way of doing things.”

As the 20-year CSO abatement program winds to a close, Portland is closing another chapter on a long tunneling history that dates back to the early 1900s. Tunnels in the Portland area comprise a mix of railroad, highway, light rail and sewer tunnels.

The $1.4 billion CSO abatement program has been the driver behind the recent tunnels being built in Portland. Major tunneling projects have included the Columbia Slough Consolidation Conduit, the West Side CSO project and the East Side CSO project.

Background

Portland’s early sewers piped sewage directly into the Willamette River and Columbia Slough. Following World War II, Portland built its first sewage treatment plant and began construction of combined (stormwater and wastewater) interceptor sewers to convey flows to the plant. The sewers were designed to discharge directly into natural waterways when capacity was exceeded.

In the 1970s, Portland took the first steps toward reducing CSOs, which at its worst dumped an estimated 10 billion gal of combined sewage into the river and slough each year. Portland’s CSO reduction program comprises three elements: Cornerstone projects, Columbia Slough projects and Willamette River projects.

The Cornerstone projects involve keeping stormwater runoff out of the sewer system. This includes sewer separation, sump installation, downspout disconnection and stream diversion (Tanner Creek and West Hills streams were originally piped into the sewer systems).

The Columbia Slough projects, which were completed in 2000, involved increasing capacity of the sewer and improvements in the treatment facilities. The projects were successful in eliminating 99 percent of the overflows into the slough. Tunneling on the Columbia Slough projects included 8,360 ft of 15-ft OD soft ground tunnel driven by a modified EPB TBM.

Upon completion of the Columbia Slough projects, the Bureau turned its attention to the Willamette River program – including the West Side and East Side CSO projects. The West Side CSO Project was constructed first, finishing in 2006, followed by the East Side CSO project, which is currently 80 percent complete and on schedule for 2011 completion.

Moving Forward

While the Columbia Slough tunnel was successfully built, lingering claims from the project left BES planners looking for an alternative contracting method that would result in a more collaborative environment as planning geared up for the West Side project, according to Jacobs Associates’ Glenn Boyce, who worked at Parsons Brinckerhoff as BES’s design consultant during the development of the project.

“When the West Side project was coming up, the feeling was that it was going to be a much more difficult and complex project than the Columbia Slough, which had a number of issues and claims,” Boyce said. “The owner felt that there had to be a better way, so we looked at some of the different models that had been used and modified them to meet the needs of the project.”
Some cities are limited in the types of contracts they can employ. Luckily for BES, however,

Oregon’s public contracting statutes allow exemptions for alternative contracting methods, and Portland City Council was receptive to the Bureau’s request to seek out an alternative to low bid, so BES was granted an exemption.

Design-build was considered and quickly dismissed, Gribbon said. “From an owner’s perspective, you have the least amount of control with design-build – and we didn’t want that,” he said. “This tunnel was coming right through downtown Portland and had a lot of public involvement issues. We wanted to be fully involved.”

Also considered was the construction manager-general contractor (CMGC) approach, which the City successfully employed on a City Hall renovation and other projects. That approach, however, also had drawbacks from the Bureau’s perspective. “With CMGC, the prime contractor is generally limited with the amount of work they self-perform. In our case, we wanted to know who was going to be doing the tunneling and who was going to be building the shafts,” Gribbon said.

Portland's CSO programs are improving water quality in the Willamette River and Columbia Slough. (Photos by Sue Bednarz, Jacobs Associates)

The concept of the guaranteed maximum price in the CMGC method also didn’t translate to the underground environment. “We felt that the contractor would have to include all the possible risks into the guaranteed maximum price that would inflate the cost,” Gribbon said. “So we came up with this kind of hybrid where we had them propose a fee, and then all the labor, equipment and materials we would pay as reimbursable.”

The contractor was selected on a qualifications basis, which factored in their proposed fee as well as their approach to constructing the project. The contracting team of Impregilo and S.A. Healy was selected to build the West Side CSO project.

Building Big

The West Side CSO project included 18,162 ft of soft ground tunnel mined with two Herrenknecht slurry shield TBMs and lined with 14-ft precast bolted gasketed segments, five 39- to 59-ft diameter shafts, a 137-ft diameter by 160-ft deep pump station shaft and structure, and 10,000 ft of microtunnels with 13 access shafts. Work was completed on the West Side project in 2006.

The East Side CSO project, currently under construction, is even larger. It involves constructing 29,260 ft of tunnel using one 25-ft diameter Herrenknecht slurry shield TBM. A joint venture of Kiewit and Bilfinger-Berger was selected for this project. The East Side project also included a microtunnel drive of 3,055 lf, which established a new U.S. record for the longest microtunnel. The previous record was 1,625 ft.

Originally designed as two drives with an intermediate shaft, the record-breaking drive was a direct result of teamwork between all project parties. The contracting approach allowed the contractor, designer and owner to discuss options. The feeling was that the contractor could do the drive without the intermediate shaft, so it was evaluated and decided to move forward with contingency plans in place.

Another example of teamwork occurred during construction of the Swan Island Pump Station as part of the West Side contract. The project involved a 137-ft diameter, 160-ft deep shaft, with slurry walls and jet grout columns for groundwater cutoff. However, groundwater flows were higher than anticipated, causing a delay of about six months. The contractor came up with a solution of moving the operations center, which was to be constructed on top of the completed pump station, off to the side so it could be built concurrently with the station. “That allowed us to make up three or four months of the time we lost,” Gribbon said. “If that had been a low bid contract we would have been facing a big differing site conditions claim.”

Winding Down

BES has gained a lot of tunneling experience over the past decade and a half, but when crews put the finishing touches on the East Side tunnel next year, it will mark the end of the 20-year consent decree program. In hindsight, Gribbon believes that the modified fixed-fee, plus cost-reimbursable contracting approach applied on the West Side and East Side projects was the best way forward.

“We had some contractual issues related to subcontract management and contractor rework that could be improved, but from our perspective I don’t think we could have come up with a better way,” Gribbon said. “There is never a one-size-fits-all solution, but as an owner the more flexibility you have in how you contract, the better off you are. Sometimes design-build is the best way to go. Sometimes low bid is the best way to go.

“For us, this method worked because whenever we had a technical problem – and we had some big ones on the West Side – we went straight into brainstorming solutions. We didn’t waste our energies fighting over money.”

Jim Rush is Editor of TBM.

Revisiting the Tri-Met Tunnel Construction By Joe Gildner Passing through the underground sections of Tri-Met’s Blue Line you can be forgiven for not admiring the unassuming tunnels and deep station surrounding your 5 p.m. light rail train bound for Beaverton/Hillsboro. From 1993-1997, this was the theater of construction operations for Tri-Met, its contractor (Frontier Kemper/Traylor Brothers (FT)) and the design team led by Parsons Brinckerhoff. In 1993, Tri-Met awarded a contract for $103.7 million to excavate twin tunnels (each three miles long and 21 ft in diameter) and construct the deepest transit station in North America, which was built 260 to 270 ft below the ground surface in a twin-bore, binocular configuration. The tunnel alignment traverses Portland’s West Hills, crossing underneath Washington Park, numerous residential structures and approximately 1,100 graves. The massive underground station is situated beneath a parking lot serving Metro Washington Park Zoo and nearby attractions. The West Hills is composed of a diverse range of hydro-geologic conditions consisting primarily of uplifted, layered basalt flows. To handle these conditions, FT used different excavation methods in the headings advanced from each portal. The running tunnels were divided into three sections (labeled Reaches A, B and C) each representing roughly one-third of the total alignment length. In the western third (Reach C), the geologic conditions are highly variable, ranging from high-strength basalt to stiff to hard clayey-silt. Consequently, the design team recommended drilling and blasting for hard rock and earth excavation for soft ground. This included blasting 80 ft under the grave sites. The contract documents allowed nighttime blasting (10 p.m. to 6 a.m.) provided the impulse noise from blasting did not exceed 93 dBC as measured at the nearest residential structure. Nighttime blasting generated a number of complaints from people living over 1,000 ft down-range. For the most part the complaints were triggered by the concussion of the lower frequency of the airblast. Noise levels of 100 to 115 dBC were measured at these distances. The contractor tried a number of techniques to mitigate the problem and the only plausible solution was achieved when the team designed and constructed an oversized cross passage between the tunnels to effectively “muffle” the airblast. At the opposite end (Reach A), FT launched a rotary gripper shield tunnel boring machine (TBM) designed to cut medium high to high strength basalt. The geotechnical documentation described the basalt as having low rock quality designation (RQD), however the standup time was considered adequate for TBM operations. The TBM began mining and immediately encountered problems. The basic problem was the short stand-up time of the rock (raveling) which prevented the TBM from mining a full face. The team came up with a number of modifications to address the situation including: a) reversing drive configuration for the cutterhead, b) modified gripper configuration for improved steering, c) additional drive to boost torque, and, d) slurry at the cutterhead face, creating a poor man’s earth pressure balance machine. Although progress was slow, the TBM exhibited improved steering and ground penetration. The major surprise was that with the slurry, the TBM operated best in reverse! Finally, the deep-mined station was constructed in basalts using the drill-and-blast method. Given the proximity of zoo facilities to the construction site, zoo officials became concerned about the physiological stress on the animals from the construction noise and vibration. The team conducted a complete assessment of the situation, including fecal, urine and blood assays on selected species (elephants, rhinoceros, penguins and lemurs) before, during and after blasting work. To our knowledge, there was no evidence of unacceptable stress levels for the zoo inhabitants. Nevertheless, it’s difficult to say with certainty if humans either working on the project or living near the project experience episodes of physiological stress. Joe Gildner served as Project Manager for Tri-Met during the design and construction of the Westside Light Rail tunnel contract. He is currently the Executive Project Director for Seattle Sound Transit on active tunnel work for the Agency’s University Link Project.