The Seattle Seawall was originally constructed between the years of 1916 and 1934 utilizing and estimated 20,000 old growth timbers that have been slowly eaten away from father time and gribbles (tiny marine borers that have an appetite for wood). Seattle’s Seawall supports SR 99, Alaska Way, the ferry terminal, as well as major utilities. Seismic concerns are also an issue since everything behind the seawall from Alaskan Way to Western Avenue is built on top of fill.
CJA was selected as the specialty drilling contractor to install the temporary shoring at the Seattle Central Seawall along Seattle’s downtown waterfront, as part of the $220 million Elliott Bay Seawall Replacement Project. Construction is broken up into multiple seasons due to the tourism economy along the current Seattle Seawall. Season 1 work wrapped up in May 2014 and Season 2 will begin again in September 2014.
Condon-Johnson & Associates value engineered the temporary shoring system to help minimize project costs. The final design encompassed the use of auger-casting soldier piles and lagging, with one row of tiebacks to support a 14ft cut along 3,100 lf of the seawall. In addition to allowing excavation for removal of the old deck, the shoring system will assist in supporting the Alaska Way Viaduct as well as several utilities while the existing seawall is removed and its replacement is constructed.