The Transportation Department said Wednesday the 326-foot long machine it calls Bertha has drilled 359 feet.
Spokeswoman KaDeena Yerkan said the trailing gear has disappeared into the tunnel.
Yerkan says Bertha is operating well but is still in the initial phase with about 9,000 feet to go.
The world's largest tunnel boring machine is creating a tunnel nearly 58 feet in diameter as part of the $3.1 billion project to replace the Alaskan Way Viaduct, the double deck highway along the downtown Seattle waterfront.
Digging began July 30 but soon shut down for about a month in a labor dispute before it resumed Sept. 23.
More Northwest Headlines
Expansion of gun sale background checks in Oregon takes effect Sunday Evacuation order lifted for town of Roosevelt State Board of Education sets lower bar for Common Core tests Oregon warns marijuana growers against illegal pesticides $1 million bail for man accused of shooting at Fife police Cattle becomes Oregonís top agricultural commodity Yakima guaranteed at least 1 Latino council member Christian school in Oregon sued over firing pregnant, unwed educator
Our new comment system is not supported in IE 7. Please upgrade your browser here.