Precast provides the backbone of the Seattle waterfront while putting in place the path to local wildlife restoration.
Founded along Elliott Bay in the 1850s, Seattle is home to one of North America’s busiest sea ports. Lining the bay is the Alaskan Seawall which runs for nearly 1.5 miles along the downtown Seattle waterfront. Completed in 1934, the original seawall was constructed of old-growth lumber pilings with a filled, level shoreline.
Problem and Challenges
The seawall was at risk of deterioration and of collapse if a large earthquake were to occur. Additionally, homes and businesses on the waterfront, and the Alaskan Way viaduct, an elevated highway which runs along the bay, could also be in danger. After the 2001 Nisqually earthquake, the Seattle Department of Transportation (SDOT) discovered that exposure to the harsh marine environment, time, and a marine isopod called a gribble had damaged many of the wooden supports in the seawall.
The City of Seattle decided to replace the failing and aging seawall as part of a larger project to redevelop the Seattle waterfront. With an original estimated cost of $350 million, the seawall needed to guard waterfront developments and serve as a pedestrian walkway. A challenge the city had was to protect, and not further hamper, existing marine life in the bay which included creating a hospitable migratory corridor for salmon.
Additional challenges for the city included construction-related factors such as working in a constrained area, arranging work based on tide levels, a tight construction schedule, and production within exacting tolerances of components for field assembly.
Oldcastle Precast in Auburn, Wash., was selected by the joint venture team of Mortenson-Manson, general contractor/construction manager, to supply concrete Z-superstructure segments, sidewalk panels, and face panels for the project.
The concrete Z-superstructure segments were an important structural component in building the seawall and would act as the backbone of the new seawall's cantilevered sidewalk. Four hundred Z-shaped precast segments, each 8-ft. wide by 9-ft. tall and that extended 13-ft., were manufactured and shipped.
Additionally, Oldcastle Precast supplied 400 20-ft. tall seawall fascia panels with various architectural finishes, each measuring 8-ft. wide by 20-ft. tall with a thickness of 15 inches. The finishes on the face panels were not only aesthetically pleasing, but they were also created with the goal of helping restore the natural characteristics of Elliot Bay. The textures were inspired by tidal zonation and where different sea life – such as barnacles, mussels and rockweed – live.
“I fully believe that much of the success of the quality precast concrete components and installation is due in part because of all the hours of planning that Oldcastle Precast invested in this project. It is very refreshing to be working with such professionals.”
LJ Godsey, Engineer for Mortenson-Manson, A JV
The Elliott Bay Seawall Project will be a success because it addresses a multi-pronged need for the city and its inhabitants: a pedestrian walkway, wildlife tunnel, and supporting wall. Oldcastle Precast contributed to the project’s success by:
- Using cutting edge design – just like the high-profile project itself – in the implementation of the Z-segments
- Accelerating an already tight construction schedule that could have been disrupted by factors such as weather and tide levels
- Meeting tight tolerance restrictions for field assembly that could cause the project to have been redone if not met
- Utilizing the expertise of the team to work around the challenges with regards to the unique geometry of the Z-segments
- Designing face panels that served a larger environmental purpose
Scheduled to be complete in 2017, the wall will be a stable, safe, and seismically sound foundation for the Seattle waterfront.
Precast concrete played a critical role in the success of the Seattle Seawall revitalization. How do you know if precast is the right choice for your project? Check out our precast benefits checklist.