Sections of the SR 99 tunnel built without Bertha

11/12/2015

Approximately 20 percent of the SR 99 tunnel was designed to be built without Bertha, the SR 99 TBM. Seattle Tunnel Partners had bored more than 305 m of tunnel before they stopped to repair Bertha. Since then, they have built an additional 366 m of tunnel using cut-and-cover tunnel construction. Using cut-and-cover construction at both ends of the bored tunnel is the best way for Seattle Tunnel Partners to gradually connect the northbound and southbound lanes of SR 99. They run side-by-side on the surface up until Bertha’s part of the tunnel, where the roadway becomes a double-decker. Click here for a video and click here and us/69 for the tunnelbuilder archive. Visit http://www.wsdot.wa.gov/. 50/15.