Major work has been completed for the SR 520 Pontoon Construction Project. Crews built a massive pontoon construction facility in Aberdeen, and constructed, inspected, repaired and floated out the first six pontoons for the new SR 520 floating bridge.
WSDOT is proud of the pontoon construction work completed to date. These are the largest pontoons the agency has ever built and we have complete confidence they will meet the 75-year design life called for in the Pontoon Construction Project design-build contract.
We've developed the below timeline to help clarify how pontoons built in Aberdeen have been constructed, inspected, repaired, and towed to Lake Washington.
Note: Click each graphic to open as a larger PDF file.
Pontoon construction, inspection and repairs timeline
Construction continues on cycle 2 pontoons. View a video update about this work from WSDOT project managers, as well as photos from the Aberdeen construction site on our Flickr page.
Crews are implementing recommendations from the pontoon peer review panel, modifying their plans as show below:
Click the graphic below to open as a PDF (328 kb)
Other modifications include:
- Adding additional quality verification staff to the pontoon construction office.
- Increasing material testing of the cement and concrete mix.
- Implementing additional independent peer review of design.
On Aug. 22, inspections found ballast water leaking between two cells in Pontoon V. This leak was repaired almost immediately.
Click the graphic below to open as a PDF (660 kb)
Inspections also found moisture on the inside of an end wall in Pontoon W. WSDOT and the contractor are continuing to look into the cause of this moisture, and are developing repair plans as necessary to meet contract requirements.
A YouTube video from inside the pontoon shows these issues in full detail.
On Aug. 17, the pontoon expert review panel submitted its report to WSDOT. The report includes a review of repairs made on cycle 1 pontoons and findings that address the causes of, and recommendations to correct, two key issues: pontoon spalling and cracking. You can read the panel's report (pdf 74 kb) and WSDOT's response (pdf 72 kb).
The panel indentified three key factors of spalling and cracking:
1. The placement and location of post-tensioning ducts contributed to concrete spalling.
2. Resistance to post-tensioning from interior precast walls caused end walls to crack.
3. Finally, all quality assurance practices need to be fully implemented to monitor a variety of concrete properties, including: concrete shrinkage, curing and thermal controls, and water/cement ratios, as well as length of wall pours.
All repairs complete and endorsed by the pontoon peer review panel.
On July 30, all six Cycle 1 pontoons were floated out of the casting basin.
Watch our time-lapse YouTube video.
WSDOT convened a panel of experts to review WSDOT's repairs, analyze the cause of pontoon cracking, and make recommendations for future pontoon construction cycles.
Watch WSDOT engineer Mike Cotten explain WSDOT's pontoon inspection and repair process.
Crews found cracking and spalling after completing post-tensioning on a longitudinal pontoon. At that time we began repairs on the affected pontoon and pre-emptive modifications on the other longitudinal pontoons.
Click the graphic below to open as a PDF (809 kb)
September 2011-May 2012
Major construction under way on the first cycle of SR 520 bridge pontoons.
Cycle 1 included six total pontoons:
• Three longitudinal pontoons (360 ft. x 75 ft. x 29 ft.)
• One cross pontoon (270 ft. x 75 ft. x 33 ft.)
• Two supplemental stability pontoons (98 ft. x 60 ft. x 28 ft.)