The central waterfront section of the SR 99 Alaskan Way Viaduct in Seattle is being replaced with a 2.7 km-long bored tunnel connecting the new SR 99 roadway south of downtown with Aurora Avenue in the north.

Seattle Tunnel Partners, design and construction contractors for the tunnel, selected Hitachi Zosen Corporation of Japan to design and manufacture the 17.53 m-diameter, 99.36 m long, 5,500 t TBM. The machine will be fully assembled and tested in Japan later this year, then disassembled and shipped to Seattle in 41 pieces weighing up to 900 t in early 2013. It will be reassembled, tested and commissioned by Hitachi Zosen in a 25 m-deep pit located in the tunnel construction area west of CenturyLink Field. TBM excavation will start in summer, 2013 employing Seattle Tunnel Partners’ personnel trained by Hitachi Zosen. Excavation should be complete by late-2014, and the tunnel opened to traffic by end-2015. Click here for the SR 99 tunnel project map, here for the TBM, and us/69 for tunnelbuilder archive reports. Visit www.wsdot.wa.gov and www.alaskanwayviaduct.org. 39/12.