WSDOT’s Alaskan Way Viaduct Replacement Project: SR-99 Seattle Tunnel Precast Deck

August 22, 2019 1:00 pm

Mark Gaines, P.E., State Bridge and Structures Engineer, Washington State DOT; Jim Parkins, P.E., Director of Marketing, Concrete Technology Corporation; and Tim Moore, P.E., S.E., Mega Projects Bridge Manager, WSDOT

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Featured Presentation: WSDOT’s Alaskan Way Viaduct Replacement Project: SR-99 Seattle Tunnel Precast Deck (35 Minutes)

Description: The Washington State Department of Transportation’s SR-99 tunnel under the city of Seattle replaces the Alaskan Way Viaduct structure. This 9,270-foot-long bored tunnel begins south of downtown and ends at South Lake Union. Seattle Tunnel Partners was selected as the contractor for this design-build project, which opened to traffic in February 2019. Inside the tunnel is a two-level interior structure with northbound traffic running on the lower deck. The lower deck was converted from cast-in-place to precast construction as a value engineering solution to facilitate and accelerate the construction. The lower deck consists of 1,152 pieces of 14 ½-inch-deep by 8-ft-wide precast slabs that span 30 ft across the width of the tunnel. This is the state’s first recent use of full-depth precast slabs, and it is the state’s longest precast deck project to date. The webinar features design, fabrication, and construction challenges of a prestressed deck project in a demanding tunnel project.

 Presentation Photos/Graphics: 


1) SR-99 bored tunnel under the city of Seattle

2) Precast pretensioned slabs for lower deck

3) Precast slab installation and post-tensioning application

4) Completed SR-99 tunnel project opened to traffic in February 2019

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