(Reuters) - A massive tunnel-boring machine idled last month in Seattle due to safety issues was allowed on Tuesday to resume its work on a $3.1 billion waterfront highway replacement project beset by delays, mechanical issues and cost overruns.
The drill, known as Bertha, had been ordered by the Washington State Department of Transportation to stop digging underneath downtown Seattle on Jan. 14 after a big sinkhole opened at the construction site.
Contractor Seattle Tunnel Partners was given conditional permission to restart the drill and resume digging on Tuesday so long as it adhered to a series of new safety protocol for ground control and worker safety, state transportation officials said.
The stoppage was the latest problem to befall Bertha, the world's largest tunnel-boring machine by diameter, which has became a symbol of failure to critics of the highway replacement project who have argued it was ill-planned and expensive.
Bertha had been brought to Seattle to dig an underground expressway to replace the scenic but rickety Alaskan Way Viaduct that was damaged in a 2001 earthquake and nearing the end of its lifespan.
The $80 million drill overheated and stalled underneath the city in December 2013, just 10 percent of the way through its work. It took two years to extract and repair the 7,000 ton instrument.
The highway project had initially been slated to cost $2 billion and be completed by 2015. It's now not expected to be finished until April 2018, according to estimates before the latest suspension.
Critics of the project have drawn comparisons to Boston's "Big Dig," the costliest U.S. highway project, which took nearly a decade longer to complete than originally scheduled and was notorious for cost overruns, design flaws, worker fatalities and other problems.
Reporting by Victoria Cavaliere in Los Angeles; Editing by Richard Borsuk