Extensive environmental feasibility studies, risk assessments, and other documentation were completed prior to the project’s start. The Big Dig was led by Bechtel/Parsons Brinckerhoff, one of the largest and most experienced teams in infrastructure design and construction. Mitigation alone required 1,500 unanticipated, separate agreements. The reported reasons for the cost escalation included inflation, the failure to assess unknown subsurface conditions, environmental and mitigation costs, and expanded scope. Estimates increased to $7.74 billion in 1992, to $10.4 billion in 1994, and, finally, $14.8 billion in 2007-more than five times the original estimate.
Its initial estimated cost was $2.56 billion. The Big Dig is also famous for cost increases. Its list of engineering firsts include the deepest underwater connection and the largest slurry-wall application in North America, unprecedented ground freezing, extensive deep-soil mixing programs to stabilize Boston’s soils, the world’s widest cable-stayed bridge, and the largest tunnel-ventilation system in the world. Larger than the Panama Canal, the Hoover Dam, and the Alaska Pipeline projects, it was built through the heart of one of the nation’s oldest cities. Zakim Bunker Hill Bridge, part of the Big Dig project in Boston, is the widest cable-stayed bridge in the world.
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