Precast Concrete "Z" Superstructures Used to Construct Seattle’s New Elliott Bay Seawall

New seawall structure consists of a cast-in-place support slab with custom precast concrete face panels, precast concrete Z-superstructure segments and precast sidewalk panels.

Seattle, WA, November 08, 2015 --( Oldcastle Precast, Auburn, Wash. was selected by the Joint Venture Team of Mortenson-Manson, general contractor/construction manager (GC/CM), to supply precast concrete Z-shaped superstructure segments and 20-foot tall seawall face panels for the city’s new $371 million Elliott Bay Seawall Reconstruction Project at the waterfront in downtown Seattle, Washington.

The City of Seattle Department of Transportation’s (SDOT) Elliott Bay Seawall Project, part of Seattle’s Waterfront Program, determined that the 100 year old seawall needed to be replaced. Built between 1916 and 1936, the failing wall suffered significant timber decay and deterioration of the structure from continued exposure to storm waves and tides, including damage from the magnitude 6.8 Nisqually Earthquake.

Acting as a retaining wall between Elliott Bay and the waterfront, the new seawall structure consists of a cast-in-place support slab with custom precast concrete face panels, precast concrete Z-superstructure segments, and precast sidewalk panels.

To successfully manufacture the contracted precast seawall components, Oldcastle Precast worked closely with Mortenson-Manson to customize the design and engineering of the fascia panels and specialty Z-superstructure segments essential to the seawall’s stability. The Z-superstructures were a vital structural component, acting as the concrete backbone of the new seawall’s cantilevered sidewalk.

“I fully believe that much of the success of the quality precast concrete components and installation is due, in part, because of all the hours of planning that Oldcastle Precast invested in this project. It is very refreshing to be working with such professionals,” stated LJ Godsey, Engineer for Mortenson-Manson, A JV.

In all, 400 precast concrete Z-superstructure segments (8-foot wide by 9-foot tall, that extend 13-feet) and 400 precast concrete fascia panels (8-ft-wide by 20-ft-tall with a thickness of 15 inches), with various architectural finishes, were manufactured and shipped by Oldcastle Precast-Auburn.

“Compliments on the face panels,” stated Carly R. McArdle, P.E. of Magnusson Klemencic Associates, which provided engineering services for the waterfront seawall project. “In short, we all think they turned out great! The JCFO team was very excited to see the install pictures, a few of them noting how amazing it was to see them in place. The appreciation for detail and quality has clearly translated into Oldcastle Precast products.”

Oldcastle Precast’s innovative precast solution has improved constructability, accelerated the construction schedule, and easily overcome the demanding challenges of the unique seawall project. Constructing Elliott Bay’s Seawall in this cuustomized manner provided an efficient and long-lasting solution for the City of Seattle.

Funded mostly by a 30-year $290 million bond measure that voters approved in 2012, the Elliott Bay Seawall Project, from South Washington Street to Virginia Street, is scheduled for completion in mid-2016.

View the Seawall Installation video now: to view.

Read more about this project.
Oldcastle Precast, Inc
Barbara Bogo