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The fatal Big Dig tunnel ceiling collapse could have been avoided if designers and construction crews had considered the possibility that the epoxy securing tons of ceiling panels could slowly pull away, federal investigators concluded Tuesday.
The "epoxy creep'' factor was among the major findings released at a hearing of the National Transportation Safety Board, which conducted a year-long investigation into the collapse that killed a Boston woman.
On the one-year anniversary of the accident, the board met to review and approve a final report on the collapse's probable cause. The board also was expected to issue a series of recommendations.
Milena Del Valle, 39, was crushed to death on July 10, 2006, when about 26 tons of concrete ceiling panels fell from the Interstate 90 connector tunnel as she and her husband drove toward Boston's Logan Airport.
"It's very difficult to re-live this tragedy,'' said Del Valle's 24-year-old daughter, Raquel Ibarra Mora, of Costa Rica, who attended the hearing and spoke to reporters through a translator. "It's a very rough time for me.''
But Mora said she was "extremely pleased'' that NTSB seemed to be doing a thorough job investigating the tragedy.
The probe found problems with the bolt-and-epoxy system used to hold the 4,600-pound concrete ceiling slabs. The investigation showed 20 anchors pulled out from the tunnel roof.
Modern Continental Construction Co., the company that constructed the I-90 connector ceiling, used "fast-set'' epoxy supplied by Powers Fasteners, Inc. to secure anchor bolts in the collapsed tunnel, investigators said.
"The design is reasonable, it's the epoxy that's the issue,'' said Bruce Magladry, director of the NTSB's Office of Highway Safety, citing the adhesive's poor resistance to "epoxy creep.''
Magladry said there was no malice among those who built and oversaw the Big Dig.
"I don't think they understood creep at all,'' he said.
Magladry described the creep as the tendency of some epoxies to slowly give way over time under constant applied pressure. He compared the creep of the epoxy used in the collapsed ceiling to adhesive used on a mailing label, which would yield to pressure over a longer period of time.
"Although the epoxy used in the tunnel had acceptable short term strength, it was incapable of supporting much lower loads over an extended period of time,'' Magladry said. "If any of the entities involved in the ceiling design and installation had considered creep as a possibility, a different epoxy or a different anchoring system would have been used.''
Similar adhesive anchors are used in tunnels in New York and Virginia, NTSB investigators said, but they hold lighter panels that are less than 500 pounds.
The $14.798 billion Big Dig, the costliest highway project in U.S. history, has been plagued by construction problems and cost overruns during the two decades it has taken to design and build it.
Last summer's accident spawned tunnel shutdowns, extensive ceiling repairs, a wrongful death lawsuit and a wave of federal, state and criminal investigations, including the NTSB probe.
Massachusetts Attorney General Martha Coakley is expected to announce soon whether she'll press criminal charges in connection with the accident.
Also pending is a wrongful death lawsuit filed by Del Valle's family against the Massachusetts Turnpike Authority, the agency overseeing the Big Dig, and several companies associated with design and construction of the project. The companies have said they stand behind their work.
Calls to the Massachusetts Turnpike Authority, Big Dig project manager Bechtel/Parsons Brinckerhoff and Modern Continental Construction were not immediately returned Tuesday.
State Transportation Secretary Bernard Cohen, who also is chairman of the Turnpike board of directors, would likely comment at the end of the hearing, a spokesman said.
This program aired on July 10, 2007. The audio for this program is not available.
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