Crews discovered an 8-inch steel pipe protruding through one of the openings of Bertha the tunnel boring machine today. The Seattle Tunnel Partners aren't ready to say exactly what is blocking Bertha, but they think the pipe might be contributing.

The steel pipe is a casing installed by state Department of Transportation in 2002. It was installed after the 2001 Nisqually earthquake to study groundwater movement in the area.

Water pressure was low enough and enough soil had been removed for workers to inspect the top 15 feet of Bertha's excavation chamber on Thursday.

Now, STP is considering how best to remove the pipe and identify any other obstructions. A number of other factors may have halted the tunnel boring machine, including soil conditions wearing on cutting toils, other objects in front of the cutterhead, or objects in the excavation chamber that are visible yet.

Even as the boring machine is stopped, construction work continues on the north and south ends of the tunnel.

WSDOT says it's too early to know the costs or schedule implications of the stoppage.

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