SR 520 Bridge Replacement, Pontoon Construction Facility

Grays Harbor, WA



Kiewit General, a Joint Venture

Services/Project Type
Ports and Waterfront
Roads and Bridges
Floating Structures
Bridge Inspection and Rehabilitation

To support construction of pontoons for the SR 520 floating bridge across Lake Washington, the Kiewit-General Joint Venture team (Kiewit) was selected to construct the pontoons for the new bridge and the facility required to construct them.  This design-build project included the design and construction of a new pontoon construction facility in Grays Harbor County. KPFF was the primary structural design consultant for the 900'x200' casting basin used to construct the 33 pontoons required for the bridge. The majority of the pontoons constructed were 360 feet long, 75 feet wide and 28 feet tall. This design/build process was unique for this project in that it was advertised prior to WSDOT announcing its Record of Decision (ROD) for the casting facility.  Accordingly, close coordination was required between the design/build team, the environmental (permit) task force, and WSDOT resources to ensure that all Federal and State regulations governing the design work were met prior to the completion of the ROD.

Specific elements of work designed by KPFF included development of a 55-acre casting facility and 20-acre basin; a moveable three-tiered, trussed, stop-log gate structure; structural head and cut-off walls along the shoreline; elevated mobile crane structures; a launch channel; and a combination gravity driven and pump controlled hydraulic control structure.

Filling the basin is performed utilizing the tide cycle through large diameter fill pipes and manually controlled lift gates. The gate is set and sealed at low tide and a pump driven hydraulic control structure is utilized to drain the remaining water in the basin. Elaborate fish screening and velocity control measures are utilized in both operations including a fish sane and a fish capture and transfer box utilized during draining operations. 

Throughout this project, KPFF’s familiarity with Federal (AASHTO, FHWA), State (WSDOT) and local permit and design criteria has proven influential to both Kiewit and the Owner in expediting design and ultimately construction.