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Feb. 7 Bertha update: Two factors contributed to tunnel stoppage PDF Print E-mail
Written by Randy Post   
Tuesday, 11 February 2014 00:40

WSDOT released an update on February 7 with some conclusions regarding the blockage that has stopped the Alaska Way Viaduct Tunnel Boring Machine, Bertha's progress since December 6. Now they don't think it was necessarily the well casing after all.

They cite two factors that contributed to the blockage. First, the cutterhead was clogged with material. You can see an cool short video of a worker unclogging the cutterhead. Not terribly dramatic, but still cool. The second factor was increased temperatures inside the equipment. STP discovered damage to a seal that protects the machine's main bearing. They are still determining how the repairs will be done.

If you want to follow the chronology of this issue, read below for summaries and links to previous updates from WSDOT. And Check out the videos too! [Source: WSDOT]

Video: Replacing a Cutting Tool Inside Bertha

[Source: YouTube. Image: YouTube]

Video: Unclogging the SR 99 TBM Cutterhead

[Source: YouTube. Image: YouTube]

  • Jan. 14 Bertha Update: Going Hyperbaric - Source: WSDOT 
    This press release by WSDOT is fascinating, you should definitely check it out. It describes the hyperbaric intervention that deep see divers performed to try and determine what has impeded the progress of the Bertha TBM on the Alaska Way Viaduct Tunnel project. They describe how a bentonite mud is injected in front of the cutterhead to create a "membrane" so they could pump air into the excavation chamber to create an air bubble that the hyperbaric divers could work in. The air pushes the bentonite membrane into the soil face and holds back the soil and water. They use the screw conveyor to remove sufficient material from the excavation chamber so that the divers can work in the top half of the excavation chamber.
  • Jan. 21 Bertha Update: Initial Results of Hyperbaric Inspections - Source: WSDOT 
    In this press release, WSDOT reported that as of January 21, STP divers had spent more than 35 hours under hyperbaric conditions inspecting the TBM cutterhead from inside the excavation chamber. They removed a piece of bent well casing, pieces of PVC pipe, and found a large boulder or piece of concrete in a cutterhead opening.
  • Jan. 23 Bertha Update: More Hyperbaric Work, No New Findings - Source: WSDOT
    In this press release, WSDOT mainly just updated the total tally of hours worked by the deep see divers in the TBM intervention at the cutterhead. As of January 23, they were up to 68 hours of work performed during 17 sessions.
  • Jan. 27 Bertha Update: Restart of tunneling machine begins this week; evaluation will follow initial mining - Source: WSDOT
    Nothing too earth shattering in this update, just an attempt to explain to the public that it will take time to review the results of the hyperbaric work and that the TBM will begin some mining to test the machine.
  • Further evaluation required before tunneling can resume - Source: WSDOT
  • Jan. 31 Bertha Update: Further evaluation required before tunneling can resume - Source: WSDOT
    Bertha moved forward about 2 feet on January 28 to test the cutterhead and build the next tunnel liner ring. STP crews observed abnormally high temperatures in some components, similar to what was observed during the original stoppage on December 6. The made adjustments, moved forward another 2 feet but the temperatures persisted. The analysis will continue.
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Last Updated on Tuesday, 11 February 2014 07:58