The state Transportation Department says the contractor, Seattle Tunnel Partners, plans to inject a material that will be inflated with pressurized air to create a "bubble" at the cutting head. That will give workers space to fix the problem.
The workers will have to spend time in high-pressure chambers to adjust to the conditions.
Drilling stopped Dec. 6 after Bertha ran into a pipe. Officials aren't sure that's the only problem.
The new Highway 99 tunnel is part of the project to replace the Alaskan Way Viaduct on the Seattle waterfront.