Dive Brief:

• After making very good progress in chewing a 1,019.5-foot tunnel for Seattle's Alaskan Viaduct replacement highway, the boring machine known as Bertha slowed drastically, and controllers are baffled.
• The solution will be for divers to go into the high-pressure atmosphere underground, climb inside the machine and try to determine what is gumming up the works.
• The divers will go into the area behind the 57.5-foot cutting head to see if there have been any equipment failures in moving debris through the machine, or if there is something unexpected or especially difficult about the material it has encountered at this point.

Dive Insight:

Lots of geotechnical exploration showed that Bertha would have to dig through a variety of soils on its 1.7-mile route and could always encounter cobbles and boulders. The machine is supposed to be able to break apart boulders into pieces of 3 feet or less so they can pass through, but one theory is that maybe the machine has encountered a boulder that is turning in the soil rather than being held in place for the cutting head to bust it up.