Development of Replacement Concepts for the Alaskan Way Seawall, Seattle, Washington

The Alaskan Way Seawall is a unique structure located in Puget Sound, Washington. As the interface between the dense development of downtown Seattle and the marine waters of Elliott Bay, its purpose is to provide wave and erosion protection, as well as to retain fill for upland developments and transportation and utility corridors. While the seawall has served the city well over the past 70 years, its main structural support system, a timber relieving platform, has become vulnerable to marine borers. In addition, the design and location of the seawall make it vulnerable to liquefaction induced failure in a strong earthquake. The loss of the seawall would threaten not only the transportation facilities, the waterfront street, and the Alaskan Way Viaduct (part of the National Highway System - one of the two main north-south highway routes through Seattle), but also a regional utility corridor. Because of the importance of the structure and its vulnerabilities, many seawall replacement concepts were studied before arriving at the current concept that combines soil improvement with a new concrete face panel system. This paper briefly describes the history of the seawall and summarizes the important issues considered in the development of replacement concepts for this unique and significant marine structure.