SEATTLE — Bertha, the SR 99 tunnel machine, moved more than three feet Tuesday night after grinding to a halt more than a year ago after overheating.
The machine must mine through 20 feet of unreinforced concrete to reach a repair access pit.
The Washington State Department of Transportation said it expected the machine to overheat, as it has during recent mining attempts, because of its damaged seal system.
If the machine becomes too hot, they will take a break for it to cool down before resuming.
Work to chip away a Bertha-sized circle on the face of the pit’s southern wall wrapped up Tuesday. The plan is to make the breakthrough easier and cleaner when it moves into the pit.
WSDOT says moving Bertha into the pit is just the beginning of the repair process. The machine must be partially disassembled before it can be lifted to the surface, a process that the contractor, Seattle Tunnel Partners, has said will likely take significant time and effort.