A damaged tunnel boring machine has broken through a 6m-thick concrete wall to reach daylight for the first time in over a year.
The machine, named Bertha, spent the whole of 2014 underground after its cutterhead clogged in late 2013 while it was working on a road scheme in Seattle.
At midday local time on Thursday 19 February, the top portion of the cutterhead broke through the southern wall of the access pit.
Crews will continue to mine an additional 600mm before stopping to build another concrete tunnel ring.
Contractor Seattle Tunnel Partners and manufacturer Hitachi Zosen are leading the major recovery effort.
The machine will continue to move forward in 2m increments, stopping to build rings on its way into the pit. When the front end of the machine is fully exposed, crews will begin the disassembly process.