• Oct. 24 project update: Bertha passes the 5,000-foot mark

    Seattle Tunnel Partners passed the 5,000-foot mark of the SR 99 tunnel drive late last week. Crews have mined 5,085 feet of the 9,270-foot-long tunnel and built 774 concrete rings. Bertha, the SR 99 tunneling machine, is now located below First Avenue, just north of Pine Street.

    STP is currently performing routine hyperbaric maintenance on the machine, including the inspection and replacement of cutterhead tools (this post explains more about the different methods for changing tools). Previous hyperbaric stops have lasted as long as seven weeks. However, STP has indicated they may choose to do shorter and more frequent hyperbaric stops moving forward.

    Now more than 200 feet below the surface, crews are approaching the deepest point in the tunnel drive. A map and description of the tunnel route – as well as twice weekly progress updates – are available on our Follow Bertha page. You can also follow Bertha on Twitter @BerthaDigsSR99

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  • Oct. 12 project update: After a brief checkup, Bertha is back on the move

    Seattle Tunnel Partners resumed mining on Tuesday following a week of planned maintenance on Bertha, the SR 99 tunneling machine. During the stop, crews performed routine maintenance, including the inspection of cutterhead tools.
    Crews initially expected to spend several weeks changing tools in hyperbaric conditions. However, after a full day of hyperbaric work and tool inspection on Monday, STP determined the cutterhead tools were in satisfactory condition and decided to continue mining.  
    With the machine functioning well and the cutterhead tools in good condition, STP will continue mining north beneath First Avenue. They plan to make at least one more stop to perform hyperbaric work, but the timing and location of future stops will be determined by STP based on soil conditions and maintenance needs. 
    The top of the tunneling machine is located nearly 200 feet below First Avenue, approaching Pine Street. As of this morning, crews had tunneled 4,750 feet of the 9,270-foot-long tunnel drive. Progress updates are posted on Mondays and Thursdays at our Follow Bertha page. You can also follow Bertha on Twitter @BerthaDigsSR99.
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  • Oct. 6 project update: Bertha reaches planned maintenance stop

    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.


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Program Spotlight

  • There's more than one way to change a cutterhead tool

    Performing regular maintenance on Bertha, the SR 99 tunneling machine, is critical to the success of the tunnel drive. During each of Seattle Tunnel Partners’ three planned maintenance stops in 2016, crews have spent time checking and maintaining various systems throughout the machine. Specific maintenance needs vary with each stop, but one maintenance item is always on STP’s to-do list: inspection and replacement of cutterhead tools.

    Bertha’s rotating cutterhead has … more