Seattle has been rough on Bertha. Literally.

The world’s largest boring machine tunneling underneath the city had to make a stop recently to perform maintenance on its cutterhead. It is currently located about 170 feet underneath First Avenue and Union Street.

Related: Where Bertha is currently located under Seattle

The idea is to inspect and potentially replace cutter tools at the front of the machine. A total of 12 have been inspected; 10 of those have been replaced. Over the next week, four more could be replaced as inspections continue.

And Bertha could be looking at similar maintenance in the future. The machine has moved away from soft material and into more dense, gravel and sand. That mixture wears down the cutting tools a lot faster than sand or clay.

The Washington State Department of Transportation expects the tool replacement job to be completed by next week. Bertha could begin boring soon after that.