On Thursday, Bertha broke into its repair pit with a boom and a cloud of dust.
The sound of falling concrete sent Gladys Fred out of her Pioneer Square office.
Click here to see Bertha's biggest moments.
"A huge boom and everything shook, the building shook," Fred said.
The drama of the breakthrough followed successful mining through the repair pit's 20-foot wall.
Contractors had feared Bertha would overheat.
It did not.
"We're very pleased that the contractor has made this milestone," said deputy project administrator Matt Preedy of the Washington State Department of Transportation.
Since Tuesday night, the world's largest tunnel boring machine advanced more than it has since breaking down in December 2013.
It was able to limp along with injections of grease to keep it cool.
http://youtu.be/uwguAPEaRcQ
Once Bertha advances 40 feet into the repair pit, which contractors estimated would happen in a couple of days, the next step will be to disassemble the machine so a huge crane can lift the cutterhead to the surface for repairs.
Contractors will replace the vital main bearing, which turns the cutterhead.
The seals that protect the bearing got contaminated with muck in 2013, contributing to the machine overheating.
Chris Dixon of Seattle Tunnel Partners did not provide a timeline for when the repair process would begin.
He did say the most recent official estimate is for the repaired machine to resume mining the new State Route 99 tunnel at the end of the summer.
[ See video from WSDOT of Bertha breaking through. ]
Dixon described the schedule as dynamic, and said contractors hoped to dig again sooner.
In December, STP had officially estimated a restart date of April, but complications arose in building the repair pit, including ground settling nearby that might be related to the project.
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