The largest tunnel boring machine of its kind in the world is on her way.
Bertha, the State Route 99 tunneling machine, is now tunneling in Seattle soil after breaking through the access pit wall late Wednesday. Seattle Tunnel Partners (STP) has mined 73 feet and installed 12 concrete tunnel rings since Bertha first moved forward in the pit on Dec. 22. STP has two tunneling crews of approximately 25 members each. Each crew is working six, 12-hour shifts per week.
Bertha is expected to reach a planned underground maintenance stop just south of Yesler Way in late January. Once there, crews will spend three weeks performing final maintenance before the machine tunnels beneath the Alaskan Way Viaduct.
Check the Follow Bertha page for ongoing information about conditions Bertha will face during her the tunnel drive. Below is video of tunneling crews at work this week.