Crews are working on the final steps before Bertha, the Seattle tunnel boring machine, resumes digging next week.

Seattle Tunnel Partners began filling in the access pit on Sunday, according to the Washington State Department of Transportation.

The pit is being filled partially with sand, as is the excavation chamber behind the machine’s cutterhead. The remaining 51 feet from the sand will be filled with compact soil.

Related: Bertha on schedule to resume tunneling by Christmas

Once the pit is filled, final tests will be done on Bertha before it resumes digging.

Bertha is sitting on a concrete cradle at the bottom of the access pit, about 20 feet from the wall it will tunnel through when mining resumes.

The pit was used to haul portions of the machine out of the tunnel, after it broke down about 1,000 feet into its more than 9,000-foot journey under Seattle.

The most recent schedule for Bertha provided by STP shows the machine will be ready to resume mining by Dec. 23. Bertha could be under the Alaskan Way Viaduct by March 2016 and tunneling could be completed by January 2017.