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What's Blocking Bertha? Mystery Object Halts Tunnel Drilling

"Survey says, 'This is one big tunnel."'

The Transportation Department and contractors building a highway tunnel under downtown Seattle are trying to find out what has blocked their tunnel boring machine.

The machine called Bertha ran into something Friday and was shut down Saturday about 1,000 feet from the start.

The $80 million machine is designed to break up boulders, so there's speculation about what it hit. Engineers are considering drilling down 60 feet to the object as one of the ways to break up or remove the obstruction.

The nearly two-mile tunnel is scheduled to be completed by the end of 2015, creating a four-lane replacement for the Alaskan Way Viaduct on Highway 99.