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SR 520 - Innovative pontoon construction complete in 2010


WSDOT completed the first of several steps to replacing the SR 520 floating bridge with innovative pontoon construction tests.  

Aug. 24, 2009, WSDOT awarded Advanced Construction Methods and Engineering for Pontoons to Quigg Bros., Inc. for their low bid of $2.8 million.

Construction of the test pontoon was completed in May 2010 and tests provided WSDOT engineers a number of lessons, concrete mixes, forming methods and construction techniques that will save time and money as work progresses to replace pontoons for the new SR 520 bridge.

See photos of the progress
at the Advanced Construction Methods and Engineering site.

A new approach to bridge pontoon building 

SR 520 Bridge pontoon concept image
This is a preliminary graphic of a future SR 520 bridge pontoon, compared to a football field.  See photos of the work on the test pontoon.

  • The shaded area represents the mock-up section WSDOT constructed as part of the testing work.
  • The white area represents the cells and walls of a finished SR 520 bridge pontoon.

The pontoons for the SR 520 floating bridge are the largest we’ve designed and need to be built on a fast schedule in order to replace the vulnerable SR 520 floating bridge. Previous pontoon construction projects, like the Hood Canal Bridge, help inform our work, but each bridge design is different and presents a different set of challenges. 

This work helps us address possible challenges and avoid delays by:

  • Testing mix designs for strength and durability. Using several different concrete mixes and types of aggregates help us ensure the materials are watertight, resistant to cracking, and the new SR 520 bridge pontoons will be durable.
  • Testing forming methods for efficiency. Employing different forming and pouring methods help us identify a preferred system that is efficient and constructible.
  • Expediting pontoon construction. Identifying preapproved mix designs and forming methods make certain that Kiewit-General is able to begin pontoon production as quickly as possible.

Key dates

  • April/May 2009: Identify the testing location.
  • August 2009: Advertise the testing effort to contractors.
  • August 2009: WSDOT awards project to Quigg Bros. Inc. 
  • September 2009 to April 2010: Project under way.
  • May 2010: Testing efforts are complete; publish findings.


WSDOT Aberdeen Project Office
Scott Ireland, Project Engineer
4801 Olympic Highway
Aberdeen, WA 98520
Phone: 360-533-9352