In an ongoing effort to clean up their main waterway, the Williamette River, the city of Portland authorized construction on three new shafts as part of the East Side Tunnel Combined Sewer Overflow (CSO) project. The goal is to reduce water and sediment pollution, improve watershed health, and restore habitat for endangered salmon and steelhead.
Work on the project began in 1993 with general improvements to the sewer system. In 1999, the CSO program 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 17th 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-mile-long, 26-foot-diameter tunnel, seven shafts will connect existing overflow pipes and provide above-ground access. The Taggart shaft, a 21,500-square-foot structure located north of the Ross Island Bridge off Southeast MLK Jr. Boulevard on SE Taggart Street, commenced in 2008 and is now complete. This shaft serves as a tunnel connection for water overflow. In addition, the 18,000-square-foot Port Center shaft located at North Port Center Way, adjacent to the new Swan Island Pump Station, is the northern terminus of the East Side CSO tunnel. This structure is one of two locations where the tunnel boring machine (TBM) named Rosie will be removed. The final shaft included in this phase of construction, the McLoughlin shaft, is a 16,000-square-foot structure located at SE 17th Avenue and McLoughlin Boulevard. The McLoughlin shaft is the southern terminus of the East Side CSO tunnel, and is the site of the second location where the TBM will be removed from the tunnel.
When complete, this project will boast a 94% reduction in the volume of combined sewage and stormwater that now overflows to the river when it rains. This not only will improve the water quality in the lower Willamette, but eliminate most combined sewer overflows into the river.
To accommodate multiple pours at different heights, contractor Kiewit Bilfinger-Berger, Portland, used approximately 40 D22 cantilever dam brackets from Doka, Baltimore, Md., with spindle struts on the bottom slab as starter blocks, and simply reconfigured for lifts to support almost 2100 square feet of Frami clamp-style panels in a chorded radius geometry. Engineers worked closely with Kiewit Bilfinger-Berger to devise a sequencing plan that not only made each lift easier to climb, but also allowed on-field operators the ease of moving panels with a consistent final finish pattern from the bottom of the shaft upward to ground surface within approximately 10 casting steps. In addition, 13-foot-high crane lifts (10 to 11 each) with the D22 cantilever system "rollback" allowed the forms to be easily retracted 30 inches for the purpose of cleaning, oiling, and attaching leading anchors for the next jump. The D22 cantilever system included a safe 8-foot nominal work platform at the bottom of the form level and a walkway at the pour level. A trailing platform on the level below was used for the purpose of retrieving the cones and performing finishing work.
According to Pietro Da Sacco, the group leader of the project for Doka, the wall-forming system was the ideal solution for this particular application because Kiewit Bilfinger-Berger had effectively used this product for a previous phase of the project in 2006-2007. The wall-forming system provided formwork geometry designed to facilitate changes and to be relocated from lift to lift, all while optimizing production of labor.
"The special anchor locations were designed for the next lifts to conform to all geometric changes, which has the project ahead of schedule at this time," says Da Sacco.
Another challenge was reacting to the design/build changes for submittal to the city before the start dates. By supplying professional engineering drawings to the contractor and the City well in advance of the formwork needs at the site, the schedule was accelerated. "Doka's engineering team worked together with Kiewit's engineering team to get all pertinent information required to perform at a maximum level of efficiency," says Da Sacco.
Safety was another concern. With knowledgeable field service technicians on the jobsite for three days, the Kiewit Bilfinger-Berger crews were trained on the safe practices of the formwork, which included working level decking with no holes or trip hazards.
According to Paul Contreras, account manager, Doka was able to provide labor savings from design and product clamp-style technology. "With quality product and site training by field service technicians and use of the wall-forming system, this project put the contractor ahead of schedule and under budget," says Contreras.
Working closely and effectively with Kiewit Bilfinger-Berger proved to be the most advantageous method to create a positive relationship and outcome. With the successful installation of the shafts complete, the project is ahead of schedule both for its completion date of 2011 and its ultimate goal of creating an even healthier city.
For more information, visit www.dokausa.com.