Giant drill boring Seattle tunnel nears finish line

SEATTLE  — Twenty-nine months late, the massive drill boring a new Highway 99 tunnel below Seattle is almost done with its work.

The Seattle Times reports that the drill, known as "Bertha," is expected to chew through a concrete retaining wall in the next few days and emerge into daylight, ending a 1.75-mile dig that's part of a project to replace the elevated, earthquake-prone Alaskan Way Viaduct along the city's waterfront.

The tunnel ranks among the trickiest megaprojects in history: Bertha was the largest drill on Earth when it entered the ground nearly four years ago, and it pushed through tricky glacial soils beneath downtown Seattle.

The drill began overheating in late 2013, prompting long delays as it was repaired. Litigation is underway to determine who will pay for close to $500 million in cost overruns.