The contractor has completed the primary mining shaft for a major tunneling system under way in Portland, using a combination of two Doka formwork products.
The Opera Shaft is the main mining shaft for the $426-million East Side Combined Sewer Overflow Tunnel Project in Portland. The tunnel — also known as the East Side Big Pipe — is being built by a Kiewit-Bilfinger Berger joint venture.
The work is one of a number of projects being carried out to reduce the sewage and stormwater that now overflows into the Willamette River when it rains. Completion in 2011 will slash the combined sewer overflow volume to the river by 94 percent.
East Side Big Pipe is a sewer tunnel with a diameter of 22 feet and a length of 6 miles. It will collect and intercept overflows from existing combined sewer outfalls, and the flows will be pumped to a treatment plant.
Seven shafts along the alignment provide construction access and they will also serve a variety of functions during the system's operation, including the provision of storm surge storage capacity.
The main project mining shaft, sited across from Portland Opera, is where the tunnel boring machine begins its drives, first by heading north. It will then be returned to the Opera Shaft to start the southern drive.
The shaft also provides the primary access for workers and equipment during tunnel construction, as well as an exit point for excavated materials. Shaft construction began in March 2006 for completion in April 2007, ready for the first tunneling drive.
Doka's Far West Branch provided Kiewit-Bilfinger Berger with wall formwork and engineering support for the shaft construction. Using Doka's Frami small-panel framed formwork and one-sided D22 climbers helped the contractor to form the final lining of the 67-foot-diameter and 115-foot-deep shaft, with a final concrete lining almost 3.3-feet thick, in just 90 days.
"The forming system worked very well for us," said Kiewit-Bilfinger Berger General Superintendent Mike Hanley. "The crews could raise and set them in five shifts."
Both Frami and D22 provided key advantages.
Frami's modularity allowed for the simple removal of upper panels to accommodate differing pour heights. The panels are light and so could be quickly assembled into gangs on the ground, while minimizing crane time.
Use of the Doka D22 system allowed higher pours, which reduced the number of lifts to just four. Another advantage was a simple transition from the A-frame starter block to the upper cantilevered brackets, as D22 consists of similar parts for both the first and subsequent lifts.
A 200-millimeter tolerance for the final lining allowed for a segmental approach to construction.
The one-sided final concrete lining of the Opera Shaft was formed by using a total of 2,000 square feet of Frami, with hinged corners, in a segmented fashion. In total, 52 D22 brackets were used to provide a working platform and to climb the Frami forms. The first lift was of 13.5 feet and used 36 D22 starter blocks. Two lifts of 12 feet followed, and the fourth was just 6.5 feet.
A tower crane was used to fly the Frami and D22 gangs into the shaft, where final positioning was carried out using a mobile crane. The biggest challenge was to coordinate the supports for the D22 climbers across the tunnel eyes and this was completed smoothly.
Kiewit-Bilfinger Berger made use of Doka's on-site service for putting together the Frami system and the D22s. The user-friendliness of both systems meant that little field service attention was required.
Doka provided on-site instruction and technical support and its attention to service was also demonstrated by the speed and efficiency with which the engineering and operations team carried out deliveries, despite long distances being involved. Sending small items by courier ensured they arrived the next day.
Other aspects praised by the contractor included the engineering detail that was provided, such as a "nicely detailed set of drawings," according to lead engineer Shane Yanagisawa.
The final lining of the Opera Shaft was completed within the scheduled time, and the last of the equipment was returned to Doka after just three months.
Story and photos courtesy of Joem Promotions on behalf of Doka Formwork Technology. For more information contact Diana Wojtaszek of Doka USA Ltd at Diana.email@example.com.