Oct. 6 project update: Bertha reaches planned maintenance stop

Posted on Oct 6 2016 2:51 PM
Seattle Tunnel Partners has paused mining to begin planned maintenance on Bertha, the SR 99 tunneling machine. Crews stopped tunneling approximately 190 feet beneath First Avenue, just north of Pike Street, on Tuesday, Oct. 4. STP chose the location of the stop in advance because dense soils in the area are suitable for hyperbaric work – a process this post explains in detail.
Crews will spend several days preparing the hyperbaric work environment. They will then begin the difficult task of inspecting and changing cutterhead tools. There are more than 700 tools on Bertha’s rotating cutterhead, some of which can be accessed and changed from within the cutterhead spokes during the course of STP’s regular weekend maintenance. The cutting tools that crews will focus on during the upcoming maintenance period can only be accessed in hyperbaric conditions. 
Replacing cutting tools and performing other maintenance is crucial to maintaining the tunneling machine and ensuring it performs well for the remainder of the tunnel drive. This is STP’s third planned maintenance stop in 2016. The machine was stopped from March 12 to April 29 as crews prepared to tunnel beneath the Alaskan Way Viaduct. A second maintenance stop occurred beneath Spring Street from June 23 to July 18. STP expects the current maintenance period to last approximately one month, but the length of the stop will depend on the extent of the needed work.
Crews have mined a total of 4,721 feet and installed 717 concrete rings since tunneling began. They are now more than halfway through the tunnel drive. We’ll continue to provide updates on hyperbaric work and other progress around the viaduct program as STP’s machine maintenance continues.
Recent tunneling updates 


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