Bertha prepares for viaduct undercrossing 21 Apr 2016

The Alaskan Way viaduct in Seattle will be closed to all traffic from the end of next week (April 29) while TBM Bertha mines to within 15ft of the structure’s foundation piles – the closest the 17.6m diameter EPBM will come to any structures along the entire length of its 2.7km drive.

The viaduct has been reinforced to facilitate a safe undercrossing of the roadway near Yesler Way. Closing the viaduct during tunneling will enable better monitoring of the structure and allow for immediate repairs if any ground movement from tunneling should occur. In addition to strengthening measures taken by WSDOT over the years, the SR99 Tunnel contract also directed the contractor – the Seattle Tunnel Partners joint venture of Dragados and Tutor Perini – to protect the viaduct during tunneling.

“When we closed the viaduct for nine days in 2011, we saw significant congestion on Seattle city streets and nearby highways,” said David Sowers, deputy administrator of the Alaskan Way Viaduct Replacement Program. “We’ll do everything we can to ease congestion, but unfortunately there’s no way to close a major highway without disrupting traffic.”