Big Dig  is the unofficial name of the Central Artery/Tunnel Project (CA/T), a massive undertaking to reroute the Central Artery (Interstate 93), the chief controlled-access highway through the heart of Boston, Massachusetts, into a 3.5 mile (5.6km) tunnel under the city, replacing a previous elevated roadway. The project also included the construction of the Ted Williams Tunnel (extending Interstate 90 to Logan International Airport) and the Zakim Bunker Hill Bridge over the Charles River.
The Big Dig is the single most expensive highway project in American history. Although the project was estimated at $2.5 billion in 1985, when the last major highway section opened in December 2003, over $14.6 billion had been spent in federal and state tax dollars as of 2006. The project was replete with delays, arrests, escalating costs, leaks, poor execution and use of substandard materials. The Massachusetts Attorney General is demanding contractors refund taxpayers $108 million for "shoddy work...."
The project was conceived in the 1970s to replace the rusting elevated six-lane Central Artery. The expressway separated downtown from the waterfront, and was increasingly choked with bumper-to-bumper traffic. Business leaders were more concerned about access to Logan Airport, and pushed instead for a third harbor tunnel. In their second terms as governor and secretary of transportation, respectively, Michael Dukakis and Fred Salvucci, came up with the strategy of tying the two projects together—thereby combining the project that the business community supported with the project that they and the City of Boston supported.
Planning for the Big Dig officially began in 1982, with environmental impact studies starting in 1983. After years of extensive lobbying for federal dollars, a 1987 public works bill appropriating funding for the Big Dig was passed by U.S. Congress, but it was subsequently vetoed by President Ronald Reagan as being too expensive. When Congress overrode his veto, the project had its green light and ground was first broken in 1991....On August 11, 2005, it was announced that the Massachusetts State Police searched the offices of the Big Dig's largest concrete supplier in June and found evidence of faked records that hid the poor quality of concrete delivered for highway project. However, it is not believed that the low-quality concrete is connected to the hundreds of leaks discovered in the tunnels that take vehicles under Boston.
On March 19, 2006, the International Herald Tribune reported that Massachusetts "Attorney General Tom Reilly plans to sue Bechtel/Parsons Brinckerhoff and other companies if the two sides do not reach an agreement over 200 complaints of poor work in the construction of a highway system under the center of Boston, the Boston Globe reported Saturday. Reilly was said to be seeking $67 million from Bechtel and $41 million from other companies." 
On July 10, 2006, at approximately 11:00 p.m., a steel tieback that suspends the concrete ceiling inside the tunnel structure failed near the eastern portal of the eastbound I-90 Connector tunnel leading to the Ted Williams Tunnel in South Boston, causing four three-ton sections of ceiling to collapse. A section of ceiling fell on top of a car traveling through the tunnel, killing newlywed 38-year-old passenger Milena Del Valle and slightly injuring her husband Angel Del Valle, who was driving. The Boston Globe noted that similar tiebacks were in use in the Ted Williams Tunnel, as well as in 17 places on I-90. Attorney General Tom Reilly issued subpoenas to those involved in the construction and testing of the tunnels in which criminal charges may follow. Governor Mitt Romney also returned from a vacation in New Hampshire to view the condition of the tunnels.  Governor Romney and Attorney General Reilly both called for the resignation of Turnpike Authority chairman Matthew J. Amorello who provides oversight on the project. This call was supported in editorials in Boston's two major newspapers, the Boston Herald  and the Boston Globe . Romney and Reilly are taking heat from the media for accepting campaign contributions from Big Dig contractors and for not taking more action prior to the fatal accident. Modern Continental was the contractor that built this section.
On July 12, 2006, investigators began questioning on how the tunnel ceiling was constructed. The collapse of the ceiling structure began with the failure of a single steel hanger that held up the panels. The failure of that panel set off a chain reaction that caused other hangers to fail and send 12 tons of concrete smashing below. Numerous problems with this same system of bolts and glue in the Ted Williams Tunnel were revealed by the state Office of the Inspector General in a 1998 report. Not only were the bolts too short, but the epoxy used to glue the bolts into the concrete were not up to standard.