The Washington Transportation Department says crews have completed the second of four planned exploratory 5-foot-wide shafts being dug in front of a massive machine that got stuck last month while boring a tunnel under downtown Seattle.
Spokeswoman Laura Newborn says the shafts are being dug in hopes of identifying any metal in the path of the machine known as Bertha and removing as much of any such obstruction as possible.
Crews thought they might have encountered an obstruction during drilling of the first shaft but weren't sure because the vertical drill quickly passed by on its way to a final depth of 118 feet. No objects were found while drilling the second shaft.
The machine ground to a halt on Dec. 6 after running into the 8-inch diameter pipe that had been left in the ground in 2002 after the department checked groundwater in the area.
Bertha, an $80 million equipment and the biggest boring machine in the world, can blast through rock, timber and compressed soil; however, it cannot drill through thick metal, officials said.
The machine is stopped about 60 feet underground and one-tenth of the way toward completing a 1.7-mile tunnel. It will carry Highway 99 traffic and allow the removal of the Alaskan Way Viaduct.