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Seattle, Washington

Elliott Bay Seawall Project

Foundation of Downtown Seattle’s Waterfront

For more than 75 years, the original Seattle seawall—built between 1916 and 1934 using 20,000 old-growth timber piles—protected the city’s waterfront, but due to seismic vulnerability, aging, and the harsh marine environment, the structure had deteriorated and needed replacing.

In 2012, the City of Seattle hired Parsons to deliver the replacement seawall. As the prime consultant for this important project, Parsons provides overall program management and serves as the engineer of record. When completed in 2017, the new seawall will:

  • Protect critical city infrastructure
  • Reduce risk of seismic damage
  • Improve the salmon migration corridor
  • Last more than 75 years
  • Act as the foundation of Seattle’s future waterfront

Providing Overall Program Management

Parsons’ scope of work includes environmental clearances and permits for 6,800 linear feet of seawall replacement and full design and construction support services of 3,400 linear feet of seawall replacement. The project also includes design and construction of ecological features, a habitat beach, the new seawall, a restored roadway, and a promenade along the waterfront. Parsons provides extensive coordination with stakeholders, adjacent business owners, historic pier owners, the Colman Dock Ferry Terminal, the Seattle Aquarium, partner agencies, third-party utilities, and regulatory agencies.

Coordination on the project during design required hands-on management by each technical discipline lead as well as the right tracking tools. To accomplish this task, Parsons used a tiered meeting approach to closely coordinate all elements of the project and keep it moving forward by maintaining a 6-week look-ahead schedule, issues and action item log, and risk register. This approach actively involved the design team, environmental team, outreach team, right-of-way team, and procurement team, many of which had concurrent and overlapping milestones.

In addition, the design solution had to meet the habitat goals and design-life criteria while addressing many other interests along the waterfront, including pier access, urban design elements, compatibility with future phases, ongoing maintenance and operational requirements, emergency access, and construction. Through extensive coordination and collaboration, our team incorporated a typical wall design application with 8-foot wall segments that will accommodate the varying existing and future needs. This method provides flexibility to meet temporary and permanent construction needs such as utilities, pier access, pre-cast construction elements offsite, and modular elements that can be inspected.

Removing sheet piles used to separate construction activity from Elliott Bay

Project Innovations

The new seawall is a gravity structure that combines a soil-cement improvement and seawall superstructure into a single structural system. Soil-cement, constructed using jet grout to stabilize liquefiable soils that are vulnerable to seismic events, was designed and built in a cellular pattern to stabilize the ground and serve as the foundation of the new seawall. The seawall was designed in pre-cast units and cast-in-place slab; together, the soil improvements and seawall elements behave as a single structural system. The habitat improvements incorporate light-penetrating sidewalk panels that allow sunlight to reach the marine mattresses constructed below. Together, the elevated mattresses and the light will provide for enhanced salmon migration and nearshore habitat for Elliott Bay.

In addition to the innovative, single-structure system, the project design deliberately ensures that the replacement is a sustainable asset with flexibility to accommodate future phases. This feature provides the city with agility to make additional changes to a waterfront that offers a harsh and unyielding environment and is often prone to change, while enhancing the marine wildlife habitat.

Specific innovations of the structure include:

  • Use of pre-cast structural elements
  • Regulatory approval for beneficial reuse of jet grout spoils
  • Enhanced corrosion protection measures
  • Service-life modeling of the seawall structure

Red clamshell bucket removing rip rap at Seattle Aquarium

Meeting Seattle’s Needs

 

The seawall project construction is taking place in downtown Seattle along the waterfront, parallel to Alaskan Way and the historic piers near Pike Place Market. The new seawall will act as a buffer for these city landmarks and will protect critical city infrastructure from deterioration. The project is roughly 65% complete. This includes about 80% completion of jet grout activities or treatment of 195,000 cubic yards of liquefiable soils (top three in size for jet grout use in the world). Approximately 1,000 linear feet of new seawall have been constructed out of the 3,400 linear feet being replaced.

To meet the aggressive schedule for this one-of-a-kind waterfront project, Parsons is using our self-perform construction resources to inform design decisions, means and methods, construction sequencing and staging, and estimating and risk evaluation. This method provides Seattle with quick access to independent construction expertise and a team focused on providing a full suite of services to ensure that all project elements are closely coordinated and delivered on schedule.