#7 Alaska Pipeline $ 8 billion
The Trans-Alaska Pipeline is one of the most expensive oil pipeline construction works that cost 8 billion dollars to the government of United States. The pipeline was built between the years 1974 and 1977. The only reason behind this Trans-Alaska Oil Pipeline was the 1973 oil crisis which raised the prices of oil in the United States. This rise made an exploration of Prudhoe Bay oil field which was economically feasible. The oil field in the Prudhoe Bay was discovered in the year 1968 and the crisis provided a reason to extract the oil to the surface. The oil travelling started in the year 1977, few oil spillages have also been recorded, and the accounts suggested that the pipeline has successfully transferred almost 16 million barrels of oil. The construction began in the year 1974. The few reasons made the task delayed, the cold weather, workers and the construction of Dalton Highway. Thousands workers were employed with the attraction of high paying jobs. More than 8 billion dollars was spent to build the 800 miles of long pipeline. Conditions were extreme, extremely cold climate, difficult terrain and in Atigun Pass the river forced the workers to face unseen difficulties and problems. Hence the construction was not less than a challenge. 
[youtube]http://www.youtube.com/watch?v=KcjdrEBSH14[/youtube]
#6 CVN-78 class aircraft carrier $ 9 billion / unit
Construction on components of CVN-78 began in spring of 2007. It is planned to be complete in 2015. It is under construction at Newport News Shipbuilding, a division of Huntington Ingalls Industries (formerly known as Northrop Grumman Shipbuilding) in Newport News, Virginia. It is the only shipyard in the US capable of building nuclear-powered aircraft carriers. In 2005 it was estimated to cost at least $8 billion excluding the $5 billion spent on research and development. A report published in 2009 said that the Ford would cost $14 billion including research and development, and the actual cost of the carrier itself would be $9 billion. Construction of the CVN-21 project began on August 11, 2005 with the beveling of a 15-ton metal plate. This metal plate will be used in the construction of CVN-78. Advance construction will take an estimated two years before construction can begin on the actual ship herself. This gives technicians and engineers the time needed to test and design the ship, and all the new technologies that will be used for CVN-78.
[youtube]http://www.youtube.com/watch?v=lXLDGPbWfIg[/youtube]
#5 James Bay Project $ 14 billion
The project was to build a series of Dams, dikes, reservoir and power stations. Three major rivers Caniapiscau, Eastmain and Opinaca were diverted into it in order to increase its potential power. The project was executed in Hydro-Quebec, the main concept behind the construction was to produce maximum amount of hydroelectric power. Four power houses, 215 dikes and dams and a 4800 kilometer network of 735 kilovolt transmission lines to transmit the power south to Montreal and Quebec. The construction got completed in the year 1985; the total cost of development was approximately 14 billion dollars with a generation of 10,300 megawatts of electricity. The project has raised controversies for its effect on the native people and environment; it also flooded 11,500 km2 areas that are home to Cree and Inuit.
[youtube]http://www.youtube.com/watch?v=8nJ5NpHWqWs[/youtube]
#4 Big Dig $ 22 billion
The Project was developed in an answer to the increasing traffic over crowding on Boston’s historically tangled streets, which were made in early times before the advent of automobiles and mechanical vehicles. This urged a cause to expand or build something new so that they can avoid traffic jams and traffic congestions. The, then Commissioner of Public Works William Callahan pushed through plans and provided a very inimitable idea for an elevated expressway, which was finally completed between downtown and waterfront. The project was executed and accomplished by the Massachusetts Turnpike Authority with the Big Dig and the Turnpike’s Boston Extension from the 1960s being financially and legally joined by the legislature as the Metropolitan Highway System. Since the project was too big and enormous to handle that’s why it was broken into many small sub projects with well defined interfaces between contractors. The Project was supervised by two different corporations Bechtel Corporation and PB. The Charles River crossing had been a source of major controversy, the design was not complete because of that river some serious steps were suggested to resolve the issue some of them were very expensive and some were practically instable but then an idea came to work separately on another project that would ultimately connect the Tobin Bridge to Charles River crossing. Swiss Engineer Christian Menn took over to the development of the bridge; he gave nice and sleek design of the bridge that have the capability to withstand many tons of traffic. The project was completed in the year 2007 and about 22 billion dollars was spent on this huge project.
