Report: Collapsed Big Dig ceiling had smaller safety margin than other U.S. tunnel ceilings
Wednesday, November 1st 2006, 6:15 am
By: News On 6
BOSTON (AP) _ Federal inspectors have found that a Big Dig tunnel ceiling that collapsed in July and killed a motorist was designed with a smaller margin of safety than other tunnel ceilings in America, according to a report obtained by the Boston Globe.
The Interstate 90 connector tunnel's drop ceiling panels were held in place by steel hangers suspended from bolts that were glued into the tunnel ceiling with epoxy. But there were no beams attaching the ceiling to the walls, and there were half as many bolts used as called for in the original design.
``No redundancy was built into the ceiling in the event the hangers failed,'' according to a preliminary report by the National Transportation Safety Board obtained by the Globe.
``The NTSB has researched other tunnels throughout the country and has found that significant redundancy is built into the ceiling design'' so that the ceilings would not collapse when bolts fall out, the report said. The Globe account appeared in Wednesday's editions.
The report does not reach conclusions about the cause of the ceiling collapse because the investigation is not finished. The July 10 accident has resulted in a civil lawsuit and other federal and state criminal investigations of the $14.6 billion highway project.
The preliminary NTSB report said the joint venture company overseeing Big Dig construction, Bechtel/Parsons Brinckerhoff, decided to use epoxy bolts, rarely used for heavy objects, even after switching to heavier concrete ceiling panels to save money.
The NTSB report also suggests that flaws in construction by Modern Continental Construction Co. may have made the design more hazardous, the Globe said.
Federal investigators also have found no evidence the Massachusetts Turnpike Authority, the agency overseeing the Big Dig, rechecked the ceiling bolts after the I-90 connector opened in 2003, the report said. A similar finding was announced in October by the state's inspector general.
Modern Continental and Bechtel/Parsons Brinckerhoff have previously said they stand by their work on the Big Dig, and are cooperating with investigators.