Newspaper article The Christian Science Monitor

Bolt Failure at Big Dig: An Anomaly?

Newspaper article The Christian Science Monitor

Bolt Failure at Big Dig: An Anomaly?

Article excerpt

Boston's Big Dig tunnel project doesn't have a "black box" - like a plane's flight data recorder - to pinpoint why several tons of ceiling tiles fell and fatally crushed a motorist July 10.

But even in the absence of such evidence, experts suggest that the epoxy-and-bolt system used to fasten the concrete slabs overhead is so commonly used that its failure seems unique to the Big Dig.

"That technique is used extensively," says Jerome Connor, a structural engineering professor at the Massachusetts Institute of Technology (MIT) in Cambridge. Epoxy is a high-strength adhesive that often requires mixing on-site before installation. "It's the fact that they only used a limited number of bolts - there was a very low margin of safety," says Dr. Connor, who is not personally involved in the investigation, and notes that it's premature to draw conclusions about the cause of the tragedy.

Massachusetts Gov. Mitt Romney (R) told reporters on Monday that more than 1,100 of the tunnel's bolt assemblies were installed with epoxy. Highway officials plan to reinforce all of the epoxy assemblies with non-epoxy anchors.

For a design like the Big Dig's ceiling, Connor says, engineers often add safety "redundancies," or identical, extra supports capable of holding far more weight than the structure actually demands. In other words, there should have been enough epoxy-and- bolt anchors to hold the ceiling panels in place even if a few of them failed.

In the I-90 Connector tunnel, he contends that too few anchors were used to hedge against failure. "They didn't have enough capacity to carry the load," says Connor. "It was a chain reaction, it occurred very suddenly. There was no room - no margin for error."

But the accident defies what has long been a tried-and-true method for securing panels to tunnel ceilings. Indeed, the Massachusetts Transportation Authority last week enlisted European construction firm Hilti Corp. to install a similar model of load- bearing bolt anchors - but ones that won't rely on high-strength adhesives such as epoxy.

"Obviously there are checks and balances in the construction process," says Marty Schofield, vice president of product safety at Hilti. …

Search by... Author
Show... All Results Primary Sources Peer-reviewed


An unknown error has occurred. Please click the button below to reload the page. If the problem persists, please try again in a little while.