SEATTLE - The giant drill Bertha might reach the concrete wall at the end of the new State Route 99 tunnel before the end of March.
Chris Dixon, project manager of Seattle Tunnel Partners, told KIRO 7 on Friday that "if things go well, we should be there by the end of next week."
The next step will be to break through the five-foot headwall into daylight.
Bertha is now beneath Sixth Avenue between John and Thomas Streets, less than 300 feet from its target.
It will take three weeks to fully move the machine into what's called the reception pit. Then, it will take four or five months to remove Bertha, piece by piece.
Dixon said the plan is to "disassemble it into 20-ton pieces that can loaded directly onto trucks and transported from the site."
STP considered many options, including lifting Bertha out entirely with a giant crane, before deciding to disassemble it in place using regular cranes.
"We looked at it very hard and determined we could do it inside the pit, which is going to minimize the impact to the surrounding community and allow the streets to remain open," Dixon.
Doing the work below street level will also be quieter.
Project leaders say there will be trucks leaving the site, but they won't have a significant traffic impact.
Disassembling the 6,700-ton machine will be overseen by manufacturer Hitachi-Zosen, which is expected to reuse some pieces.
The rear section of the machine will be removed through the 1.7 mile tunnel out the south end.
After Bertha overheated and broke down in 2013, the tunnel project is about three years behind schedule.
A breakthrough as soon as next week would be well ahead of the June estimate contractors gave last summer.
That estimate has been improving in official schedule updates, with the most recent schedule posted on the WSDOT website projecting a breakthrough on April 17.
Dixon says Bertha has required fewer and shorter maintenance stops than expected and has been averaging between six and eight concrete rings per day.
Project leaders still estimate the tunnel will open to traffic in early 2019, but on Friday KIRO 7's Graham Johnson asked WSDOT project administrator Joe Hedges if that might happen in 2018.
"Our common goal is earlier is always better," Hedges said. He called a 2018 opening "possible, but there's a lot of work yet to be done."
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