By David R. Butcher
http://www.thomasnet.com

November 22, 2005 – Boston, MA -- Considered the largest and most complex highway-and-tunnel project in our nation’s history, Boston’s “Big Dig,” in structural scale and scheme, is comparable to the great projects of the last century, including the Panama Canal, the “Chunnel” and the Trans-Alaska Pipeline. 

Boston’s Central Artery/Tunnel Project (CA/T), unofficially and popularly called the Big Dig, was, without exaggeration, a massive undertaking in its attempt to replace the previous elevated roadway and route the city’s chief highway into an underground tunnel.

The project garnered great bilateral debate — at its inception, throughout and still — due to its massively overblown budget and hidden costs, as well as political and environmental controversies, among other unforgiving natures of the project. (According to a Christian Science Monitor article, [http://www.csmonitor.com/2003/1219/p02s01-ussc.html] the Big Dig’s cost was more than double the Panama Canal’s in today’s dollars.) As well, its effects likely will be felt for decades both by Bostonians and beyond, as commuting habits for Boston residents have changed and 60 percent of the project’s tab was federal, meaning nearly every American taxpayer has felt the impact of the price tag.

Yet the structural-design perspective represents what ArchitectureWeek  [http://www.architectureweek.com/2001/0926/building_2-1.html] has described as “the greatest re-imagining of a cityscape since Baron Hausmann tore up medieval Paris in the 1860s and built the iconic grands boulevards that today are the city’s signature.”

Indeed, as the Christian Science Monitor [http://www.csmonitor.com/2003/1219/p02s01-ussc.html] has noted, “no one disputes that the project is an engineering marvel,” and some [http://www.architectureweek.com/2001/0926/building_2-1.html]can only describe the project as “epic.”

The Big Dig project consisted of two primary components (which in themselves involved a great deal more of technically difficult and large-in-scope components):

1. Replace the six-lane elevated highway with an eight-to-ten-lane underground expressway directly beneath the existing road; and
2. Extend I-90 (the Massachusetts Turnpike) from its previous terminus south of downtown Boston through a tunnel beneath South Boston and Boston Harbor to Logan Airport.

Further, the intention was to do all of this while the city remained undisrupted in its day-to-day life — throughout 14 years of construction. The project has been under construction since late 1991 and, though most of the major construction is complete, there remains still a number of sub-projects to conclude.

Of course, there were a number of attention-garnering engineering feats: the removal of 13-16 million cubic yards of dirt to make room for 7.5 miles of underground roads (20 percent less than the Chunnel Tunnel built to connect Britain and France); the world’s largest tunnel ventilation system; and the world’s widest cable-stayed bridge. The designers and builders of the project faced difficult soil conditions; tight working spaces; proximity to construction of huge glass, steel office towers and agedly fragile brick buildings; and the need to hold up an elevated highway while tunneling directly beneath it.

Design and construction were supervised via a joint venture of Bechtel Corporation and Parsons Brinckerhoff; due to the project’s size, the design and construction were broken up into dozens of smaller subprojects with well-defined interfaces between contractors, according to Wikipedia’s in-depth look.  According to ArchitectureWeek, the Central Artery Corridor Master Plan “divided the corridor — which constitutes only about 20 percent of the total open space that will be generated by the overall Big Dig — into districts, each with its own history, architecture, and constituency. From these broad directives, individual planners and landscape architects will be hired [sic.] to realize their visions. The other buildings fronting the square indicate the rich architectural soup that is modern Boston.”

The following are some structure- and design-related facts, provided by the Massachusetts Transportation Authority (MTA) [http://www.masspike.com/bigdig/background/facts.html#concrete]

• Whereas the elevated Central Artery had six lanes, the new underground expressway has eight to ten lanes.
  Whereas the elevated highway uncomfortably carried more than 190,000 vehicles a day in 2000, the underground Central Artery will carry about 245,000 vehicles a day by 2010. The Ted Williams Tunnel will carry about 98,000 vehicles a day.

• The project placed 3.8 million cubic yards of concrete.

• The project installed more than 26,000 linear feet of steel-reinforced concrete slurry walls, forming the underground highway’s walls (and the supports for the elevated highway during construction) — the largest application of this construction technique in North America -- all resting on bedrock 120 ft. below Boston's streets.

• Reinforcing steel used in the project would make a one-inch steel bar long enough to wrap around Earth at the equator.

• The project’s seven-building ventilation system is one of the largest highway-tunnel ventilation systems in the world.

• Traffic using the Metropolitan Highway System -- including the underground Central Artery, the Ted Williams Tunnel, and the Mass Turnpike out to Route 128 -- is monitored by the most advanced traffic management and incident response system in the world; radio and cellular phone signals are rebroadcast into the tunnels.

• All told, about 5,000 miles of fiber optic cable and 200,000 miles of copper telephone cable were installed.

• The Leonard P. Zakim Bunker Hill Bridge is the widest cable-stayed bridge in the world and the first hybrid and asymmetrical design in the U.S., using both steel (in the main span) and concrete (in the back spans).

• The cable-stayed bridge across the Charles River used 1,820 miles of steel wire to form the seven-wire strands that are in turn bound together to form the support cables — the largest, a foot in diameter.

• The project required the largest use of segmental bridge construction and the largest application of steel box girders in the U.S.

• Three hundred acres of new parks and open space are, or will be, created; more than 2,400 trees and 26,000 shrubs were planted at Spectacle Island. Another 2,400 trees and more than 7,000 shrubs will be planted downtown.

 (We realize this list is roughly as long as Carol Brady's grocery list; but it's good stuff, no?)

 Although Boston’s Big Dig project — considered the largest and most complex highway-and-tunnel project in the nation’s history — was intolerably interminable (and alluringly alliterative), its scale and scheme in structural design are truly comparable to some of the great projects of the last century.

For a photo gallery of the project...

References & Resources

Boston Reconnecting by James McCown ArchitectureWeek, Sept. 26, 2001 http://www.architectureweek.com/2001/0926/building_2-1.html

$14.6 billion later, Boston's Big Dig wraps up by Seth Stern The Christian Science Monitor, Dec. 19, 2003 http://www.csmonitor.com/2003/1219/p02s01-ussc.html

Massachusetts Turnpike Authority, The Big Dig http://www.masspike.com/bigdig/index.html

“Big Dig” Wikipedia, last modified: Oct. 24, 2005 http://en.wikipedia.org/wiki/Big_Dig

“Finishing the Big Dig,” Boston.com News http://www.boston.com/news/traffic/bigdig/