(Image from disassembly-pit camera tonight)

Four years and two days after the Highway 99 tunneling machine arrived in Seattle, in pieces, after a trans-Pacific trip from Japan, it’s scheduled to finish its part of the tunnel-building job tomorrow. WSDOT announced this afternoon that the machine is on the brink of “breakthrough”:

Crews will spend this evening making final preparations. Then, early tomorrow, the massive machine will begin mining through the wall and into the pit where it will be disassembled. Machine operators will proceed slowly through the wall, so it may take several hours for the cutterhead to emerge.

And even once it does, it won’t be done, as WSDOT’s update explains – “it will be weeks until the machine is in its final position in the disassembly pit.” Then, it will be broken apart to be removed from the pit. Live-stream and time-lapse cameras are already embedded on the “Follow Bertha” page, since the public isn’t allowed at the construction site to watch in person. The latest advisory from WSDOT suggests this will happen no sooner than midmorning, but timing is subject to change – the project Twitter account is a good place to watch for updates (and we’ll be tracking it here on WSB too).

Breakthrough will come on the north side of downtown, at the end of a 9,270-foot tunnel route along which there’s still road-building and other work to be done before the tunnel’s projected opening in early 2019 (here’s the newest progress report).