BOSTON, Aug. 11 (UPI) -- Ground under Boston's "Big Dig" tunnel has settled more than expected, creating a large sinkhole, transportation officials say.
Frank DePaola, acting highway administrator for the Massachusetts Department of Transportation, revealed the problem Wednesday at a meeting of the agency's board. He said the sinkhole is not an immediate safety threat, although it will be expensive to fill, a cost estimated by MassDOT at $17 million.
DePaola described the sinkhole as an underground pond believed to be about 190 feet long and 4 feet deep.
The big dig, which removed an elevated highway that had cut across central Boston for decades and replaced it with an underground tunnel, was one of the biggest and most expensive construction projects in history. Since the project was completed, a woman has been killed by a falling roof panel and other engineering problems have developed.
The sinkhole developed under a connector tunnel running under eight sets of tracks used by Amtrak and local trains. Settling above the tunnel also has been greater than predicted, requiring ballasting under the tracks.
