Thats dust rising from Berthas rescue pit, where the machines cutterhead broke into earlier today.
That's dust and steam rising from Bertha's rescue pit, where the machine's cutterhead began to emerge earlier today. Kelly O

Bertha's cutterhead fully broke through 20 feet of concrete in the rescue pit's south wall today. To celebrate, a few hours later the Washington State Department of Transportation gathered reporters near the entrance of the Pioneer Square pit, which was full of dust from the chewed-up concrete. We couldn't see the machine itself, but Seattle Tunnel Partners program manager Chris Dixon did give us a rare public update on how the contractor plans to proceed.

For a machine that's been stuck for more than a year, Bertha moved pretty quickly through the pit's concrete wall. That has something to do with the fact that the contractor slowed down the machine's "penetration rate" to about a foot an hour, compared to the six feet an hour the machine had been moving at before, Dixon said. The machine's contractors also kept the machine from overheating by adding plenty of grease to the machine's rubber seals.

Here's what happens next: The machine's stopped excavating, but it does have five "shoves" left to go—for a total of something like 40 feet—before its front end fully emerges in the bottom of the pit. Dixon said he expects that part to go much faster than the mining itself. At that point, the contractor is going to disassemble pieces from the front end, haul them out using a big gantry crane, and replace the damaged parts. Those damaged parts include rubber seals, which prevent metal parts of the machine from touching each other, and possibly the machine's main bearing.

STP isn't sure whether the main bearing is damaged, but they've got a spare bearing anyway.

From left: Chris Dixon, Seattle Tunnel Partners project manager, and Matt Preedy, WSDOT Alaskan Way Viaduct Replacement Program deputy project administrator.
From left: Chris Dixon, Seattle Tunnel Partners project manager, and Matt Preedy, WSDOT Alaskan Way Viaduct Replacement Program deputy project administrator. Kelly O

Getting the rest of Bertha's front end into the rescue pit is supposed to take a couple of days. Dixon wouldn't venture an estimate on how long each phase of repairing the machine would take, though he did say that the latest scheduling update shows the machine starting to tunnel again in late summer.

Does STP know what actually caused the damage yet? The contractor wouldn't say. "That's something that's still being discussed and investigated," Dixon said.

As for dewatering, Dixon wouldn't answer how much water is being drawn out of the pit, or how fast. State officials haven't picked up on any new settlement since Bertha's started mining again, and Dixon said no new settlement is expected while the machine's being repaired.

But Bertha's still got a lot of tunneling to do. When asked if WSDOT would be willing to go through another lengthy stop-repair-and-start process if Bertha got stuck again in the future, WSDOT's deputy project administrator Matt Preedy said that the job will be completed. "So that's a yes?" KIRO's Brandi Kruse pressed. Her question was met with an awkward silence and visible discomfort from Preedy and Dixon.

But Dixon did seem confident about Bertha's ability to continue excavating north at lower depths beneath downtown Seattle. "We anticipate that the progress will improve," he said. "The deeper we get, the better soils we get into, the better conditions for tunneling."

The tunnel drive, he added, should be dug out by the end of 2016, and the full project should be done by the end of 2017.