at 5:02pm by David Kroman
Bertha, the tunnel boring machine (TBM) that has not seen daylight for a year and two months, broke through the walls of her access pit around noon on Thursday. Some critics were concerned the broken machine would not be able to bore through the 20-foot-thick concrete walls of the pit built to excavate Bertha’s cutterhead. But Chris Dixon of contractor Seattle Tunnel Partners said she did admirably. “We were willing to run it until the internal temperature reached 60 degrees celsius. It never got higher than 30.”
Earlier in the troll, we mentioned hearing a boom before noon. Although it wasn’t confirmed, officials said the noise was likely the falling of the final layer of concrete between the machine and the pit, as can be seen in the video from WSDOT below.
Dixon spoke with media in front of the cauldron-like repair pit, which was still spewing dust. He said that once the concrete is removed from the pit, crews will move Bertha an additional 40 feet into the open air. Once Bertha is there, they will be able to extract the busted cutterhead with a massive crane, turn the 2,000 ton piece of metal horizontally and replace the rubber seals.
They will also replace the main bearing behind the cutterhead, even though they’re not sure it’s actually broken.
Dixon, although unwilling to hold onto any particular timeline, said the tunnel’s completion date was late 2017, the same date WSDOT has previously provided.
Crew moral? “They were very happy to operate the TBM again,” said Dixon, “even if for only 20 feet.” As they go deeper, said Dixon, the hope is that better, cleaner soils will make for faster progress.