But Seattle Tunnel Partners project manager Chris Dixon said that estimate is "slightly optimistic."
The machine, dubbed Bertha, stopped working in early December about 1,000 feet into the 1.7-mile Highway 99 tunnel. If the six month estimate holds, that means Bertha will be stopped for nine months.
"This isn't the time to accelerate things or take short cuts," Dixon told reporters Friday.
Dixon said the Japanese company that built Bertha will finalize a report on their options to access Bertha in about 10 days. Those options have been narrowed to three shafts of different sizes that will allow crews to reach the machine. Depending on the size of the shaft, crews will be able to take apart sections of Bertha and work on them either at the bottom of the shaft or at the street surface. Those are the details the team from Hitachi-Zosen will be exploring.
Building and designing a shaft to access Bertha will take about 2 months and then repairs would have to take place, Dixon added. The shaft will be about 120 feet deep and be located just south of Main Street.
The seals surround the main bearing are broken and have to repaired or replaced.
The completed tunnel will allow the state to tear down the Alaskan Way Viaduct, the 60-year-old double-decker highway along the Seattle waterfront that is in danger of collapsing in an earthquake.
The viaduct will be closed this weekend for a routine inspection. Monitors have already found the viaduct settled nearly half an inch near the tunnel-boring machine. The Transportation Department said that was expected and the viaduct is safe, for now.
Dixon added that the state got lucky when Bertha got stuck where it did. If it had stopped further along in downtown Seattle, building a shaft would not have been a possibility, he said.
He added that the scope of the problem is not yet fully known, so the cost of repairs has not been estimated.