Big Dig ceiling collapse

The Big Dig ceiling collapse occurred on July 10, 2006, when a concrete ceiling panel and debris weighing 26 short tons (24,000 kg) and measuring 20 by 40 feet (6.1 by 12.2 m) fell in Boston's Fort Point Channel Tunnel (which connects to the Ted Williams Tunnel). The panel fell on a car traveling on the two-lane ramp connecting northbound I-93 to eastbound I-90 in South Boston, killing a passenger and injuring the driver. Investigation and repair of the collapse caused a section of the Big Dig project to be closed for almost a full year, causing chronic traffic backups.

The east ends of the westbound and eastbound connector tunnels were designed and constructed in the same manner. Both ends of the tunnel were built sooner than the connecting section to allow the D Street bridge above to be constructed sooner. The end sections were not designed to incorporate a hanging ceiling system like that used in the connecting section.

The collapse of the ceiling structure began with the simultaneous creep-type failure of several anchors embedded in epoxy in the tunnel's roof slab. Each of the panel's intersecting connection points consists of several individual bolts anchored into the roof slab concrete. The failure of a group of anchors set off a chain reaction which caused other adjacent connection groups to creep then fail, dropping 26 short tons (24,000 kg) of concrete to the roadway below.

Numerous problems with this same system of bolts and epoxy in the Ted Williams Tunnel had been previously revealed in a 1998 (Massachusetts) Office of the Inspector General report. Not only were the bolts too short, but the epoxy used to glue the bolts into the concrete was not up to standard. The state Turnpike Authority and the Federal Highway Administration, citing the ongoing criminal investigation, refused requests received after the accident to release documents relating to the work conducted along the Seaport connector, including:

One year earlier, US House Representative Stephen Lynch also had trouble obtaining records regarding the Big Dig tunnel leaks for the Congress' Committee on Government Oversight.

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Wikipedia