The State Route 99 tunnel is now 70 percent complete, and on Tuesday Seattle Tunnel Partners installed the one-thousandth concrete ring.
Nearly a year since contractors restarted drilling after a two year breakdown, the Washington State Department of Transportation invited reporters inside to see the progress.
The machine is now beneath Belltown, having mined more than 6,550 feet from Pioneer Square.
Contractors estimate Bertha will break through near the Space Needle in June 2017 and open the tunnel to traffic in 2019, three years late.
State officials will brief legislators about the project on Thursday in Olympia.
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