The large machine dug 64 feet between Sept. 23 and Oct. 1, averaging about 11 feet of excavation per day of work, the Washington State Department of Transportation said. The tunneling comes after a month-long stoppage following labor disputes and technical problems.
Bertha has dug out 88 feet of tunnel space since it started work. A permanent tunnel ring has also been installed and the tunneling shield is now underground, which allows for faster drilling, WSDOT officials said.
Crews hope to speed production and recover distance lost during the stoppage, officials said.
Bertha will average a rate of about 35 feet a day at high speed, officials said.