Constructed between 1915 and 1934 hundreds of feet seaward of the natural shoreline, the original wall consisted of various timber-pile supported relieving platforms and concrete bulkheads.  Non-engineered fill (including debris from sawmills along the waterfront and debris from 1889 Great Seattle Fire) and hydraulic fill placed for original seawall construction fill the tideland behind the wall-making these fills highly susceptible to liquefaction.  The seawall was in urgent need of repair/replacement because of its deteriorated condition, seismic vulnerability, and the consequence of failure to adjacent buildings and infrastructure.

The new seawall project replaces or repairs 3,700 feet of the most vulnerable and critical seawall sections. The replacement/repair consists of an improved soil mass (ISM) of various width and height, which supports existing or new seawall superstructure, sidewalks, view areas, and marine habitat enhancements.

Since 2001, Shannon & Wilson has provided all geotechnical work for this project, including explorations, analyses, and design from the initial seawall condition and vulnerability assessment through final plans and specifications. Construction support includes evaluation of ISM test sections and production jet grouting.  We also performed a comprehensive regional seismicity assessment and a site-specific probabilistic seismic hazard analysis.