State replacing faulty nuts in Big Dig tunnel system
Highway officials have found a widespread problem of cracked construction nuts within the Big Dig tunnel system, leading workers to inspect more than 100,000 nuts, Highway Administrator Tom Tinlin said Wednesday.
Hundreds of deficient nuts have been identified through the system, though officials said there are no safety concerns.
The nuts are part of the engineering system holding up lights weighing roughly 100 to 130 pounds, but redundancies built-in to the support system mean the lights will not fall, highway officials said.
"At no time was anything in danger of falling," Tinlin told the Massachusetts Department of Transportation Board of Directors on Wednesday.
Tinlin said he and senior electrical engineer Dan Mullaly tested the safety by hanging off one of the lights with a faulty nut looking for "any type of give at all," and Mullaly also went to work on the equipment with tools.
"We tried to break it, and we weren't able to," Mullaly said in an interview. The lights have six nuts and a wiring system holding it up, Tinlin said. He said, "Even if all six bolts went, the wires themselves would hold the thing up."
A nut that Tinlin brought in to show officials and the public had a thin crack in it.
The first cracked nut was discovered in the Ted Williams Tunnel by a Michael Baker International inspector in mid-September during a routine inspection, according to the Massachusetts Department of Transportation.
Working at night without full shutdowns of the highway, workers have inspected 70 percent of the 30,000 nuts in the Ted Williams Tunnel, where 878 − or 4 percent − were found to need replacement.
So far, far fewer cracked nuts have been found in the Interstate 90 Connector and Interstate 93 tunnels. Workers have inspected 14 percent of the 107,550 nuts in those tunnels and only found 49 needed replacement.
Tinlin aims to finish the Ted Williams Tunnel inspections by the end of October and the remaining checks by the end of November.
"I'm very confident with their approach," MassDOT board member Ruth Bonsignore said in an interview, contrasting it with "some of the maintenance issues that have surprised people in the past." She said, "I think the department is really in earnest applying the lessons learned from the first years out from the project to make sure that they stay ahead of maintenance issues and needs."
In March 2011, Frank Tramontozzi resigned from his top highway position over his handling of an incident where a 110-pound light crashed onto the roadway in February of that year.
In July 2007, the National Transportation Safety Board determined that faulty epoxy was to blame for a fatal incident a year earlier when a three-ton-ceiling panel fell in the Interstate 90 Connector Tunnel, killing Milena del Valle.
Transportation Secretary Stephanie Pollack told the board transportation officials are working to spend money from a trust fund financed by construction companies that improperly performed work on the massive tunnel system.
The Big Dig replaced the Interstate 93 overpass that ran through the heart of Boston with an underground tunnel that stretches out to Logan Airport.
It is possible that the nuts were screwed in too hard decades ago and have been cracked since they were first installed, or minor cracks caused by over-torqueing the nuts during installation could have worsened during the wear and tear of the heavily used tunnel, Tinlin said.
Tinlin said he could not estimate the cost of the inspection and replacement work being undertaken nightly in the tunnels. The cost would vary depending on the amount of new nuts needed, said Tinlin, who said the work is being done in-house and through existing contracts.
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