Glue 'creep' cause of tunnel collapse, NTSB says

BOSTON--A fatal ceiling collapse of Boston's "Big Dig" tunnel one year ago was caused by a certain type of glue used in the tunnel's construction, the National Transportation Safety Board has concluded.

In July 2006, a Boston woman traveling through the Interstate 90 tunnel was crushed when the vehicle in which she was a passenger was hit by a section of concrete panels weighing about 26 tons that had detached from the tunnel roof.

The NTSB's full report on its investigation into the accident is slated for release in a matter of weeks.

In a synopsis of its report released Tuesday, though, the Washington-based agency stated that the probable cause for the ceiling collapse was "an inappropriate use of an epoxy anchor adhesive," which over time deformed in a process called "creep" to the point where several of the tunnel's ceiling support anchors pulled free and caused a portion of the roof to collapse.

Blame for the accident rests upon a number of companies involved in the construction of the tunnel, including Bechtel/Parsons Brinckerhoff, Gannett Fleming Inc., Modern Continental Construction Co. and Powers Fasteners Inc., the NTSB said.

"The Massachusetts Turnpike Authority also contributed to the accident by failing to implement a timely tunnel inspection program that would likely have revealed the ongoing anchor creep in time to correct the deficiencies before an accident occurred," the NTSB said. The accident further stemmed from "a general lack of understanding and knowledge in the construction community about creep in adhesive anchoring systems," it said.

In a statement, San Francisco-based Bechtel said: "NTSB has performed a thorough and objective investigation of this tragic accident. We look forward to reviewing its final report."

Brewster, N.Y.-based Powers Fasteners said in a statement that while the events that led to the collapse of the ceiling panels and Ms. Milena Del Valle's death "cry out for explanation and accountability," the company believes that "it would be an untenable conclusion if the federal investigators were to consider Powers Fasteners in any way responsible, since there is overwhelming evidence that fault lies elsewhere."

Cambridge, Mass.-based Modern Continental Construction Co. declined to comment, and a representative for Harrisburg, Pa.-based Gannett Fleming, could not be reached.