Global Fastener News

Epoxy Creep, Lax Oversight Blamed in Big Dig Collapse

Jason Sandefur

Federal authorities blamed “epoxy creep” for the fatal Big Dig Tunnel collapse that killed a woman in July 2006. Officials at the National Transportation Safety Board said the ceiling collapse was likely caused by the “use of an epoxy anchor adhesive with poor creep resistance” that could not sustain long-term loads.
“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,” stated Bruce Magladry, director of the NTSB’s Office of Highway Safety. “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.”
Project oversight failure was also cited by NTSB. Ceiling designer Gannett Fleming and Bechtel/ Parsons Brinckerhoff, project manager for the tunnel, failed to recognize long-term bolt slippage as a potential problem that needed to be addressed in the design and approval process for the tunnel ceiling, the board determined.
The board “also found substantial mistakes by the Massachusetts Turnpike Authority and by other contractors … (whose) failure to catch the error and to aggressively investigate when bolts started coming loose during construction, contributed to the tragedy,” the Boston Globe reported.
Epoxy creep and lax oversight were among the findings revealed at a hearing of the NTSB, which investigated the collapse. A comprehensive report is due out in several weeks.
A review of records determined that roughly 20 bolts, about 5/8 of an inch in diameter and 6″ to 8″ long, had pulled out of drilled holes. Some of the bolts had no epoxy on them, while others had an uneven distribution of epoxy or epoxy that was discolored.
In recent weeks investigators revealed that some of the 4,600 pound concrete ceiling panels had been installed with “fast-set” epoxy to anchor the bolts. Magladry said the epoxy used on the tunnel had “exceptionally poor” resistance to creep the tendency of some epoxies to slowly give way under constant pressure.
The board issued a series of recommendations, including a nationwide moratorium on the overhead use of epoxy bolts in highway construction if their failure would endanger the public. Likewise the board called for the Federal Highway Administration develop national standards for testing epoxy bolts used in this way and urged all states to identify locations where overhead anchor bolts are used and inspect them.
The findings comes days after the Globe revealed companies involved in building the tunnels are reportedly trying to hash out a settlement with the woman’s family. The family filed a multi-million lawsuit against the main tunnel contractors, along with the fastening system’s distributor, wholesaler and manufacturer. “Estimates of the potential damages the (family) could obtain from a jury have ranged from a few million up to $75 million,” wrote Scott Allen of the Globe.
Massachusetts Attorney General Martha Coakley is expected to announce soon whether she’ll press criminal charges in connection with the accident. �2007 FastenerNews.com