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March 16, 2014 at 11:27 PM

How Bertha chipped her teeth

Photos from Seattle Tunnel Partners’ winter inspections bear witness to the extremely abrasive soils that lurk below downtown Seattle, and perhaps contributed to tunnel machine Bertha’s lengthy stoppage.

Project directors have already reported that drill teeth are wearing out and being replaced faster than expected — no mean feat, given that Lynn Peterson, the Washington State Department of Transportation secretary, said in a groundbreaking ceremony speech that the machine would shed nine tons of steel particles during  its 1.7-mile journey.

Chipped scraping bits. (Seattle Tunnel Partners photo)

Chipped scraping bits. (Seattle Tunnel Partners photo)

Here is an image of chipped teeth removed during two weeks of inspections in January, after Bertha stopped making forward progress Dec. 7. Photos and other documents were released to The Seattle Times late last week under an open-records act request.

In addition, crews working under hyperbaric pressure retrieved several feet of steel pipe, wrapped around some spokes of the cutter head, a boulder more than three feet wide, and chunks of concrete that likely were part of the tunnel project. Shortly after the dig began July 30, Bertha struggled through layers of concrete grout that STP used to reinforce the weak fill soil in Sodo.  A brick and plastic also turned up.

Steel pipe scraps found in the cutterhead. (STP photo)

The records don’t contain any news bombshells, but add a few interesting details:

  • An expert review team for WSDOT noted the heavy wear on cutting blades, but says it wasn’t severe enough to prevent moving forward. Their investigation in January focused mainly on the soggy soils, and whether STP was injecting the right conditioners to make the dirt firm yet crumbly.  Clogs in the cutterhead are being blamed for the Dec. 7 stall.
  • During restart attempts Jan. 28-29, in which the machine advanced about four feet, tunnelers stopped or slowed the drill several times to prevent overheating. They also pumped in new grease to cool the main bearing. “DT (downtime) due to continuing to pump grease thru main bearing while contractors discuss a solution with Hitachi about bearing overheating,” says a notation the afternoon of Jan. 29.
  • That night, operators restarted and stopped seven times, halting whenever Bertha reached temperatures of around 150 degrees, state quality reports say. The crews skipped their meal break.

This week, STP is expected to announce details of how it will dig a 120-foot-deep, circular pit in front of the machine, to remove the cutterhead and fix the damaged bearing. Hitachi-Zosen, which built the $80 million drill, is still working out a plan for repairs. Bertha would restart Sept. 1 at the soonest.





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