SEATTLE — On Friday state officials provided the most complete answer yet about what's wrong with the tunnel machine known as Bertha.
Project leaders announced the cutterhead became clogged, forcing the machine to slow in December.
They also revealed there is damage to a key piece of the machine, the rubberized seal around the main bearing.
Engineers discovered that problem while investigating high temperature readings.
Matt Preedy of the Washington State Department of Transportation said the seal will likely need to be replaced but it's not yet clear how long that will take or what it will require.
"That could be very complex or it could be very easy," he said.
The seal protects the main bearing, which turns the cutterhead.
"I'd say at this point it's very unlikely there's anything wrong with the main bearing," Preedy said.
Preedy said the contract included a spare main bearing, just in case, which is in Europe.
Bertha remains under warranty and representatives of the manufacturer, Hitachi-Zosen, are actively engaged in resolving the problem.
Preedy said a problem with the main bearing seal appeared during testing of Bertha in Japan.
As for the cutterhead, Preedy said it is not yet clear exactly why it became clogged in December after working fine.
"The combination of maybe ground conditioning, maybe the way the machine was being operated, were among the possibilities," Preedy said.
The clogged cutterhead forced the machine to slow in a way that first made engineers think Bertha had encountered an obstruction.
Subsequent inspections of a pressurized area around the cutterhead found nothing significant blocking Bertha.
During 158 hours of hyperbaric interventions last month, workers cleaned muck off the cutterhead and replaced cutting tools.
Bertha is digging a two-deck tunnel for State Route 99 to replace the Alaskan Way Viaduct, which is vulnerable to earthquakes.
The state has not yet provided an estimate for when tunneling will resume.
KIRO
