Unique Application of Formwork for East Side CSO Tunnel Project in PortlandIn Portland, Oregon, a major 20-year USD1.4 billion overhaul programme dedicated to cleaning up the city's Willamette River is ongoing. Work on the project began in 1993 with general improvements to the sewer system. In 1999, the combined sewer overflow (CSO) programme got underway, 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 9.65 km-long, 7.92 m-diameter 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 pressure faced TBM supplied by Herrenknecht 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. In order to prepare the shaft for its new role, contractor Kiewit-Bilfinger Berger (KBB) poured a 91 cm-thick concrete lining in the 35 m-deep, 20.4 m-diameter shaft.To accommodate multiple pours at different heights, Kiewit-Bilfinger Berger used 244.3 square metres 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 200 mm 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. 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.Frami was the ideal solution for this particular application because Kiewit-Bilfinger Berger had planned for differing pour heights (4.11, 3.65 and 2 metres), thereby requiring a modular solution. Furthermore, 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.The forming system worked very well. 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.Once work was completed this spring, a tower crane loaded "Rosie" into the bottom of the shaft on 23rd March, 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.On 13th June, nine days into the planned four-year run, the TBM shut down because of groundwater flooding inside the Opera shaft wall. A breached seal in the shaft's concrete wall led to the flooding, which workers stemmed within about four hours. The breach that caused the flooding has been grouted leaving the shaft dry. Workers prepared for a second attempt to break out of the project's starting point shaft.In July, "Rosie" successfully made her way through the Opera shaft wall and into the soil, building two to three rings a day. When about 60 metres of tunnel are built, and all the tailing gear is lowered into the shaft and attached to the TBM, mining will move faster.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. Click us/90. Read also E-News Weekly 30/2007, 10/2007, 18/2005 & 40/2004. Visit www.portlandonline.com/CSO, www.doka.com and www.herrenknecht.com 32/07.