The Elliott Bay Seawall Replacement Project—Protecting and Enhancing Seattle’s Waterfront

Abstract

The Elliott Bay Seawall protects Seattle’s downtown waterfront from waves and the erosive forces of Puget Sound and Elliott Bay. It serves to protect the core waterfront commercial and tourist district, the Alaskan Way arterial corridor, major regional utilities, and access to the busy Colman Dock Ferry Terminal. Originally constructed in the early 1900’s, the seawall required replacement due to its deteriorating condition and seismic vulnerability. The new seawall was designed to withstand the design earthquake and be durable enough to last a minimum of 75 years. The structure is supported on a jet grout-improved cellular soil mass to mitigate soil liquefaction effects during an earthquake. Concrete mixes and reinforcing schemes were selected to enhance durability. The design also incorporated allowances for projected sea level rise and potential tsunami waves. The new structure makes extensive use of modular precast concrete components to speed construction, provide enhanced durability, reduce project costs, and minimize impacts to adjacent properties. Precast elements used on the project include custom-designed precast face panels, precast zee-shaped superstructure segments, and light penetrating sidewalk panels. Another primary goal of the project was to enhance shallow-water aquatic habitat along the face of the wall. This was accomplished in part by creating a 15-foot cantilevered sidewalk with a light penetrating surface that serves to create improved fish habitat along the wall’s 3,700 foot length. Habitat-friendly concrete surface finishes and fill materials were also used. The project work also required development of a complex construction sequence to facilitate the construction process within a confined and congested site with active adjacent properties. This presentation will provide an overview of the Elliott Bay Seawall project with a focus on the key design and construction considerations, including earthquake resistance, durability considerations, and sustainable design. An overview of related design and construction considerations and construction sequence details will also be presented.