The Alaskan Way Viaduct tunneling project was in the news late last year when settlement of the Viaduct was reported during the dewatering efforts for the Bertha TBM rescue shaft. A recent post by WSDOT makes it clear that the settlement of the viaduct has been a problem for many years before the start of construction. The most recent round of monitoring by WSDOT began in 2001 after the completion of repairs to the the Viaduct following the Nisqually Earthquake. By 2006, a total of 4 3/4 inches of settlement had been recorded at one location. It appears that the rate of settlement is on the order of about 1/8 inch to 1/4 inch per year. I am sure the dewatering around the access pit didn’t help the problem, but it looks like it didn’t create it by itself either. This information just underscores the importance of the tunnel project to replace this aging structure. [Source: WSDOT Alaskan Way Viaduct. Image: WSDOT and STP via KPLU]
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Feb. 7 Bertha update: Two factors contributed to tunnel stoppage
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]
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