Seattle Tunnel Partners has started excavating the circular pit crews will use to access and repair Bertha, the stricken 17.5m diameter Hitachi Zosen SR 99 TBM being used to bore the 2.7km long Alaskan Way Viaduct Relacement Tunnel.On Friday evening, Oct. 17, an excavator rolled into position to the west of the Alaskan Way Viaduct near Pier 48, where STP stopped tunnelling last December after Bertha overheated. There, crews began taking the first scoops of soil from what will become a 75m deep, 50m wide pile-supported pit.
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Approximately 20,000 cubic yards of soil will be removed from the pit over the course of excavation. Because a number of other important construction activities are competing for space near the pit, there will be many days when excavation doesn’t occur. Contaminated soil will be hauled by truck or barge to a disposal facility; STP will store non-contaminated soil and use it to fill in the pit after tunneling resumes.
Meanwhile, crews are continuing to lower groundwater in enclosed areas near the machine and prepare for installation of the massive crane that will be used to hoist pieces of the machine to the surface for repair later this fall.
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