Bertha could resume tunneling before Christmas if work stays on schedule.

Seattle Tunnel Partners Project Director Chris Dixon told the Seattle City Council that crews are in the “final stages” of testing the boring machine that is being pieced together after months of repairs.

“We may be in position to resume tunneling before Christmas,” Dixon said. Whether that happens will be determined by the events that unfold in the next week or so, he added.

Related: WSDOT ‘pretty frustrated’ with yet another Bertha delay

The machine is undergoing a no-load test, which includes rotating the cutterhead and other moving parts. Essentially, crews are making sure it operates as it should, before resuming its journey under Seattle.

Once the machine is given the OK, crews will backfill the emergency repair pit, allowing a full test of Bertha as it moves back into position.

Dixon said repairing Bertha has taken longer than anticipated.

The tunneling machine is expected to reach a planned maintenance site by January. That site will allow crews to run tests on the machine before it continues on.

Dixon said Bertha could be under the Alaskan Way Viaduct by March 2016. Tunneling is expected to be complete by January 2017.

Whether Bertha resumes digging before Christmas or not, Dixon said crews will get some time off during the holiday. The original estimate was it would be on the move Dec. 23.

So how do crews know that the repairs made to Bertha are adequate to address what caused the project to become behind schedule?

Through design and repairs, Dixon said he believes the issues have been addressed. The main repair was to the outer seals.

Dixon would not tell the council exactly what he thinks caused the machine to overheat and lead to such a long delay in the project. The tunnel was originally expected to open in 2015. It is now expected to open April 2018. Bertha broke down in December 2013, about 1,000 feet into its more than 9,000-foot journey from SoDo.

Dixon said attending the council meeting proves his faith in the project.