This is the first time in more than a year that the Highway 99 deep-bore tunneling machine has moved.

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After more than a year,  Bertha has moved.

The deep-bore tunneling machine — stalled with a broken seal beneath downtown Seattle — dug more than 3 feet through unreinforced concrete as of 7 a.m., the state’s Department of Transporation reported Wednesday.

“Seattle Tunnel Partners is mining again,” project spokeswoman Laura Newborn said.

STP, the contractor for the $1.35 billion tunnel project, began operating Bertha Tuesday night as part of a mining effort to get the machine repaired.  Bertha must mine through 20 feet of concrete to reach the 120-foot deep SR 99 access pit, which STP constructed to repair the machine.

“The duration of this effort will depend on the machine’s ability to mine through the concrete while operating with a damaged seal system,” WSDOT said in a press release Wednesday about Bertha’s progress.  “STP anticipates the machine may overheat, as it has during their most recent attempts at mining. If the machine becomes too hot, they will take a break for it to cool down before resuming.”

As of 10 a.m., Newborn said she didn’t yet know whether the few feet of mining so far has caused any overheating problems.

Specially built as part of the project to replace the aging Alaskan Way Viaduct with a bored tunnel, Bertha — the world’s largest-diameter tunneling machine — stopped tunneling on Dec. 6, 2013, after the machine overheated about 60 feet underground between South Jackson and South Main Streets. STP later determined Bertha’s seal system was damaged and its main bearing had been contaminated.

Once Bertha reaches the access pit, repair crews are expected to partially disassemble the machine before a crane can lift it to the surface.  As part of the repair work, Bertha’s damaged parts will be removed and replaced, and “structural reinforcements” will be added to the machine, WSDOT has said.

What’s still to be determined is who will pick up the tab for Bertha’s repairs. Last year, STP requested $125 million for the repair work, but WSDOT denied that request, claiming it had “no contractual merit.”

More on WSDOT’s website.