Ceiling Collapse in the Interstate 90 Connector Tunnel
July 10, 2006
NTSB Number HAR-07/02
NTIS Number PB2007-916203
PDF Document (3.5 MB)
About 11:01 p.m. eastern daylight time on Monday, July 10, 2006, a 1991 Buick passenger car occupied by a 46-year-old driver and his 38-year-old wife was traveling eastbound in the Interstate 90 connector tunnel in Boston, Massachusetts, en route to Logan International Airport. As the car approached the end of the Interstate 90 connector tunnel, a section of the tunnel’s suspended concrete ceiling became detached from the tunnel roof and fell onto the vehicle. Concrete panels from the ceiling crushed the right side of the vehicle roof as the car came to rest against the north wall of the tunnel. A total of about 26 tons of concrete and associated suspension hardware fell onto the vehicle and the roadway. The driver’s wife, occupying the right-front seat, was fatally injured; the driver was able to escape with minor injuries.
The National Transportation Safety Board determines that the probable cause of the July 10, 2006, ceiling collapse in the D Street portal of the Interstate 90 connector tunnel in Boston, Massachusetts, was the use of an epoxy anchor adhesive with poor creep resistance, that is, an epoxy formulation that was not capable of sustaining long-term loads. Over time, the epoxy deformed and fractured until several ceiling support anchors pulled free and allowed a portion of the ceiling to collapse. Use of an inappropriate epoxy formulation resulted from the failure of Gannett Fleming, Inc., and Bechtel/Parsons Brinckerhoff to identify potential creep in the anchor adhesive as a critical long-term failure mode and to account for possible anchor creep in the design, specifications, and approval process for the epoxy anchors used in the tunnel. The use of an inappropriate epoxy formulation also resulted from a general lack of understanding and knowledge in the construction community about creep in adhesive anchoring systems. In addition, Powers Fasteners, Inc., failed to provide the Central Artery/Tunnel project with sufficiently complete, accurate, and detailed information about the suitability of the company’s Fast Set epoxy for sustaining long-term tensile loads. Contributing to the accident was the failure of Powers Fasteners, Inc., to determine that the anchor displacement that was found in the high‑occupancy vehicle tunnel in 1999 was a result of anchor creep due to the use of the company’s Power‑Fast Fast Set epoxy, which was known by the company to have poor long-term load characteristics. Also contributing to the accident was the failure of Modern Continental Construction Company, Inc., and Bechtel/Parsons Brinckerhoff, subsequent to the 1999 anchor displacement, to continue to monitor anchor performance in light of the uncertainty as to the cause of the failures. 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 safety issues identified during this investigation are as follows:
• Insufficient understanding among designers and builders of the nature of adhesive anchoring systems;
• Lack of standards for the testing of adhesive anchors in sustained tensile‑load applications;
• Inadequate regulatory requirements for tunnel inspections; and
• Lack of national standards for the design of tunnel finishes.
As a result of its investigation of this accident, the National Transportation Safety Board makes safety recommendations to the Federal Highway Administration; the American Association of State Highway and Transportation Officials; the departments of transportation of the 50 States and the District of Columbia; the International Code Council; ICC Evaluation Service, Inc.; Powers Fasteners, Inc.; Sika Corporation; the American Concrete Institute; the American Society of Civil Engineers; and the Associated General Contractors of America.