SEATTLE — After sending six probes into the ground in downtown Seattle, workers are still not sure why a giant tunnel boring machine is stuck under the city.
The Seattle Times reports those probes into the soil in six locations in front of the tunnel machine haven't bumped into any huge obstructions.
Project leaders originally speculated an unusually wide bolder, deposited by ancient glaciers might be blocking the machine known affectionately as Bertha.
The machine is about 60 feet under Seattle streets and about one-tenth of the way toward completing a 1.7-mile tunnel. It will carry Highway 99 traffic and allow the demolition of the Alaskan Way Viaduct on the waterfront.
Progress on the tunnel has been halted since Dec. 6.