Opera Shaft Completed on East Side Tunnel Project

Wed January 23, 2008 - West Edition
CEG



In a city as committed to a healthy lifestyle as Portland, Ore., a major overhaul dedicated to cleaning up the city’s main waterway (the Willamette River) is practically a given. In any other city, a 20-year, $1.4 billion program designed to reduce combined sewage and storm water overflow by 94 percent might appear overly ambitious. But in Portland, it just seems to come with the territory.

Work on the project began in 1993 with general improvements to the sewer system. In 1999, the Combined Sewer Overflow (CSO) program got under way, diverting streams that once flowed into the sewer system back into the Willamette River, upgrading pumping stations and installing a CSO tunnel on the western side of the river from the Marquam Bridge to the Swan Island pump station.

Now in its 16th year, the project has reached its final stage: the construction of an East Side CSO tunnel, which will mirror its western counterpart, running from the intersection of Southeast 17th Street and McLoughlin Boulevard to the Swan Island pump station.

To service the 6-mi.-long (9 km), 26-ft.-diameter (7.9 m) tunnel, seven shafts will connect existing overflow pipes and provide above ground access. One shaft, the Opera Shaft (so named because it sits on the property of Portland’s Hampton Opera Center), will serve as the main mining shaft for the tunnel construction. Not only will the shaft be the entry point for “Rosie,” the slurry-pressured, faced tunnel-boring machine (TBM) that will dig the CSO tunnel, but it will also be the exit point for excavated materials, which will be loaded onto a barge and taken to the Ross Island lagoon.

To prepare the shaft for its new role, contractor Kiewit-Bilfinger Berger poured a 3-ft.-thick (.9 m) concrete lining in the 115-ft.-deep (35 m), 67-ft.-diameter (20 m) shaft.

To accommodate multiple pours at different heights, Kiewit-Bilfinger Berger used 2,630-sq.-ft. (244 sq m) of segmented Doka Frami formwork to form the one-sided final concrete lining of the Opera Shaft. Initially, Doka’s Top 50 system was proposed for this project. However, since there were only four lifts, it was important to have a system that could be assembled quickly.

The 7.8 in. (20 cm) tolerance for the final concrete lining allowed for the segmental (or chorded) approach required of the Frami system, which is the fastest assembling wall system in the market, according to the company.

Doka also provided 52 D22 brackets, which also served as climbers for the Frami forms. Because the panels are light-weight, they could be easily hand-assembled into gangs on the ground, thereby reducing crane time. In addition, the forms’ modularity allowed different pour heights to be accommodated easily with the simple removal of upper panels.

According to Jon Colinares, Doka’s account manager, Frami was the ideal solution for this particular application because Kiewit-Bilfinger Berger had planned for differing pour heights at 13.5, 12 and 6.5-ft. (4.1, 3.6 and 1.9 m), thereby requiring a modular solution. Furthermore, he said, because there were only four lifts, it was important to utilize a system that would be quick to assemble, allowing Kiewit-Bilfinger Berger to begin the sequence of lifts as soon as possible.

“Kiewit needed a solution that was quick to assemble, yet provided the required strength for one-sided cantilevered pours of varying heights,” said Colinares. “Doka provided Kiewit with Frami, the fastest assembling wall system in the market. In addition, Doka’s D22 system provided Kiewit with a light-weight system capable of withstanding the relatively high one-sided pour pressures.”

According to Mike Hanley, Kiewit’s general superintendent, the fast assembly proved extremely beneficial, proving to have immeasurable time-saving benefits.

“The forming system worked very well for us,” said Hanley. “The crews could raise and set them in five shifts. Overall, this meant that it took only 90 days to form the final lining of the huge shaft.”

Another challenge was coordination of the design of the support members and loads imposed by Doka’s D22 brackets within the tunnel eye, which is composed of steel beams with spacers to account for the radius of the D22 supports. Doka’s engineering team worked together with Kiewit’s engineering team to come up with an efficient solution around the tunnel eye.

“Typically, to climb forms, we have concrete to bear on from the previous lifts. Since there was no concrete at the opening of the tunnel eye, we suggested placing horizontal beams that went across the tunnel eye so that our D22 brackets could have something to bear against for the second climbing lift. Doka USA provided Kiewit with the imposed point loads needed to support the D22 brackets,” stated Doka’s Project Manager Pietro Da Sacco.

Once work was completed this spring, a tower crane loaded “Rosie” into the bottom of the shaft, where the machine was assembled and began working to clear the tunnel north toward the Port Center Shaft. There, it will be retrieved and refurbished before being lowered again through the Opera Shaft to begin moving south toward the McLoughlin Shaft.

Colinares stated that key to success on this project was close collaboration and the effort Kiewit and Doka made from the very beginning to establish requirements. With a clear set of requirements, Doka was able to provide the most suitable and efficient system for the job without much re-engineering. With the successful renovation of the Opera Shaft completed, the project remains on schedule both for its completion date of 2011 and its ultimate goal of creating an even healthier city.

For more information, call 877/365-2872 or visit www.dokausa.com. CEG