Big Dig

 

Big Dig is the unofficial name of the Central Artery/Tunnel Project (CA/T), a megaproject that rerouted 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. The project also included the construction of the Ted Williams Tunnel (extending Interstate 90 to Logan International Airport), the Zakim Bunker Hill Bridge over the Charles River, and the Rose Kennedy Greenway in the space vacated by the previous I-93 elevated roadway. Initially, the plan was also to include a rail connection between Boston's two major train terminals.

The final ramp opened 13 January 2006. The project's overall completion is at 99%.

The Big Dig has been the most expensive highway project in the U.S.^[1] Although the project was estimated at $2.8 billion in 1985 (in 1982 dollars), over $14.6 billion had been spent in federal and state tax dollars as of 2006. ^[2] The project has incurred criminal arrests, escalating costs, death, leaks, and charges of poor execution and use of substandard materials. The Massachusetts Attorney General is demanding contractors refund taxpayers $108 million for "shoddy work." ^[3]

Historical background

Main article: History of the Big Dig

Boston's historically tangled streets were laid out long before the advent of the automobile. By mid-20th century, car traffic in the inner city was extremely congested, with north-south trips especially so. Commissioner of Public Works William Callahan advanced plans for an elevated expressway which eventually was constructed (1951-59) between the downtown area and the waterfront. The Central Artery (known officially as the John F. Fitzgerald Expressway) displaced thousands of residents and businesses and physically divided the historical connection between the downtown and market areas and the waterfront. Governor John Volpe interceded in the 1950s to send the last section of the Central Artery underground, through the Dewey Square (or "South Station") Tunnel, but while traffic moved somewhat better the other problems remained.

Built before strict federal Interstate Highway standards were developed during the Eisenhower administration, the expressway was plagued by tight turns, an excessive number of entrances and exits, entrance ramps without merge lanes, and continually escalating vehicular loads. Local businesses again wanted relief, historians sought a reuniting of the waterfront with the city, and nearby residents desired removal of this "Green Monster". (Its matte green paint prompted Thomas Menino to call it Boston’s 'other Green Monster'. The original Green Monster is Fenway Park's left field wall.)^[4] MIT engineers Bill Reynolds and (eventual state Secretary of Transportation) Frederick P. Salvucci envisioned moving the whole expressway underground.^{[citation needed]}

Early planning

The project was conceived in the 1970s by the Boston Transportation Planning Review 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.^{[citation needed]}

Planning for the Big Dig as a project 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.^[5].

Obstacles

In addition to these political and financial difficulties, the project faced several environmental and engineering obstacles.

The downtown area through which the tunnels were to be dug was largely landfill, and included existing subway lines as well as innumerable pipes and utility lines that would have to be replaced or moved. Tunnel workers encountered many unexpected geological and archaeological barriers, ranging from glacial debris to foundations of buried houses and a number of sunken ships lying within the reclaimed land.

The project received approval from state environmental agencies in 1991, after satisfying concerns including release of toxins by the excavation and the possibility of disrupting the homes of millions of rats, causing them to roam the streets of Boston in search of new housing. By the time the federal environmental clearances were delivered in 1994, the process had taken some seven years, during which time inflation greatly increased the project's original cost estimates.

Reworking such a busy corridor without seriously restricting traffic flow required a number of state-of-the-art construction techniques. Because the old elevated highway (which remained in operation throughout the construction process) rested on pylons located throughout the designated dig area, engineers first utilized slurry wall techniques to create 120 ft.-deep concrete walls upon which the highway could rest. These concrete walls also stabilized the sides of the site, preventing cave-ins during the excavation process.

The multilane interstates also had to pass under South Station's 7 tracks which carried over 40,000 commuters and 400 trains per day. In order to avoid multiple relocations of the train lines while the tunnelling advanced, as had been initially planned, a specially designed jack was constructed in order to support the ground and tracks to allow the excavation to take place below. Ground freezing was also implemented in order to help stabilise the surrounding ground as the tunnel was excavated. This was the largest tunnelling project undertaken beneath railway lines anywhere in the world. The ground freezing enabled safer, more efficient excavation, and also assisted in environmental issues, as less contaminated fill needed to be exported than if a traditional cut and cover method had been applied.^[6]

Other challenges included an existing subway tunnel crossing the path of the underground highway. In order to build slurry walls past this tunnel, it was necessary to dig beneath the tunnel and build an underground concrete bridge to support the tunnel's weight.

Construction phase

The Central Artery/Tunnel Project was managed by the Massachusetts Turnpike Authority with design and construction supervised by a joint venture of Bechtel Corporation and Parsons Brinckerhoff. Due to the enormous size of the project—too large for any company to undertake alone—the design and construction of the Big Dig were broken up into dozens of smaller subprojects with well-defined interfaces between contractors. Major heavy-construction contractors on the project included Jay Cashman, Modern Continental, Obayashi Corporation, Perini Corporation, Peter Kiewit Sons' Incorporated, J.F. White, and the Slattery division of Skanska USA. (Of those, Modern Continental was awarded the greatest gross value of contracts, joint ventures included.)

The nature of the Charles River crossing had been a source of major controversy throughout the design phase of the project. Many environmental advocates preferred a river crossing entirely in tunnels, but this, along with 27 other plans, was rejected as too costly. Finally, with a deadline looming to begin construction on a separate project that would connect the Tobin Bridge to the Charles River crossing, Salvucci overrode the objections and chose a variant of the plan known as "Scheme Z". This plan was considered to be reasonably cost-effective, but had the drawback of requiring highway ramps stacked up as high as 100 feet (30 m) immediately adjacent to the Charles River. The city of Cambridge objected to the visual impact of the chosen Charles River crossing design. It sued to revoke the project's environmental certificate and forced the project to redesign the river crossing again. Meanwhile, construction continued on the Tobin Bridge approach. By the time all parties agreed on the I-93 design, construction of the Tobin connector (today known as the "City Square Tunnel" for a Charlestown area it bypasses) was far along, significantly adding to the cost of constructing the U.S. Route 1 interchange and retrofitting the tunnel.

Boston blue clay and other soils extracted from the path of the tunnel were used to cap many local landfills, fill in the Granite Rail Quarry in Quincy, and restore the surface of Spectacle Island in the Boston Harbor Islands National Recreation Area.

The Zakim Bunker Hill Bridge, designed by Swiss designer Christian Menn, is the terminus of the project, connecting the underground highway with I-93 and US 1. The distinctive cable-stayed bridge is supported by two forked towers connected to the span by cables and girders.

The Leverett Circle Connector, a companion bridge to the Zakim, began carrying traffic from I-93 to Storrow Drive in 1999. The project had been under consideration for years, but was opposed by the wealthy residents of the Beacon Hill neighborhood. However, it finally was accepted because it would funnel traffic bound for Storrow Drive and downtown Boston away from the mainline roadway.^[7] The Connector ultimately used a pair of ramps that had been constructed for Interstate 695, enabling the mainline I-93 to carry more traffic that would have used I-695 under the original Master Plan.

When construction began, the project cost, including the Charles River crossing, was estimated at $5.8 billion. Eventual cost overruns were so high that the chairman of the Massachusetts Turnpike Authority, James Kerasiotes, was fired in 2000. His replacement had to commit to an $8.55 billion cap on federal contributions. Total expenses eventually passed $15 billion.

Final phases

On January 17, 2003, the opening ceremony was held for the I-90 Connector Tunnel, extending the Massachusetts Turnpike (Interstate 90) east into the Ted Williams Tunnel, and onwards to Logan Airport. (The Williams tunnel had been completed and in limited use for commercial traffic and high-occupancy vehicles since late 1995.) The westbound lanes opened on the afternoon of January 18 and the eastbound lanes on January 19.

The next phase, moving the elevated Interstate 93 underground, was completed in two stages: northbound lanes opened in March 2003 and southbound lanes (in a temporary configuration) on December 20, 2003. A tunnel underneath Leverett Circle connecting eastbound Storrow Drive to I-93 North and the Tobin Bridge opened December 19, 2004, easing congestion at the circle. All southbound lanes of I-93 opened to traffic on March 5, 2005, including the left lane of the Zakim Bridge, and all of the refurbished Dewey Square Tunnel.

By the end of December 2004, 95% of the Big Dig was completed. Major construction remained on the surface, including construction of final ramp configurations in the North End and in the South Bay interchange, and reconstruction of the surface streets. Many impact-mitigation projects (transit, pedestrian, bicycle, and parks) also remain, but some are in danger of cancellation due to cost overruns on the rest of the project.

The final ramp downtown—exit 20B from I-93 south to Albany Street—opened January 13, 2006.^[8]

In 2006, the two Interstate 93 tunnels were dedicated as the Thomas P. O'Neill Jr. Tunnel, after the former Democratic speaker of the House of Representatives from Massachusetts who pushed to have the Big Dig funded by the federal government.

Problems

"Thousands of leaks"

As far back as 2001, Turnpike Authority officials and private contractors knew of thousands of leaks in the ceiling and wall fissures, extensive water damage to steel supports and fireproofing systems, and overloaded drainage systems.^[9] A $10 million contract, signed off as a cost overrun, was used to repair these leaks. Many of the leaks were a result of Modern Continental and other subcontractors failing to remove gravel and other debris before pouring concrete. This was not made publicly known to the media, but engineers at MIT (volunteer students and professors)^{[citation needed]} did several precise experiments and found a few serious problems with the tunnel. ^[10]

On September 15, 2004, a major leak in the Interstate 93 north tunnel forced the closure of the tunnel while repairs were conducted. This also forced the Turnpike Authority to release information regarding its non-disclosure of prior leaks. A follow-up reported on "extensive" leaks that were more severe than state authorities had previously acknowledged. The report went on to state that the $14.6 billion tunnel system was riddled with more than 400 leaks. A Boston Globe report, however, countered that by stating there were nearly 700 leaks in a single 1000-foot section of tunnel beneath South Station. Turnpike officials also stated that the number of leaks being investigated was down from 1000 to 500. ^[10]

Substandard materials

Massachusetts State Police searched the offices of Aggregate Industries, the largest concrete supplier for the underground portions of the project, in June 2005. They seized evidence of faked records that hid the poor quality of concrete delivered for the highway project. In May 2006, six executives of the company, including its general manager, were arrested and charged with crimes related to fraud. Immediately after the arrests, Massachusetts Governor Mitt Romney announced he would return $3,900 in political contributions from employees of Aggregate Industries.^[11]

On March 19, 2006, the International Herald Tribune reported that Massachusetts Attorney General Tom Reilly plans to sue Bechtel/Parsons Brinckerhoff and other companies because of poor work on the project. Over 200 complaints have been filed by the state of Massachusetts as a result of leaks, cost overruns, quality concerns, and safety violations. In total, the state is seeking approximately $100 million from the contractors ($1 for every $141 spent).^[3]

Fatal ceiling collapse

Main article: Big Dig ceiling collapse

A fatal accident raised safety questions and closed part of the project for most of the summer of 2006. Part of the ceiling collapsed in a tunnel segment under South Boston, connecting I-90 to the Ted Williams Tunnel. The July 11 collapse killed one person and contributed to the death of another, a heart attack victim who died en route to a hospital when his ambulance was caught in a resulting traffic jam two weeks after the collapse.^[12] On September 1, 2006, one eastbound lane of the connector tunnel was re-opened to traffic.^[13][14]

Following extensive inspections and repairs, Interstate 90 east and west bound lanes reopened in early January 2007.^[15] The final piece of the road network, a high occupancy vehicle lane connecting Interstate 93 north to the Ted Williams Tunnel, was reopened on June 1, 2007.

On July 10, 2007 after a lengthy investigation, the National Transportation Safety Board found that epoxy glue used to hold the roof in place during construction was not appropriate for long term bonding.^[16] This was determined to be the cause of the roof collapse. The Power-Fast Epoxy Adhesive from Powers Fasteners used in the installation was designed for short term loading, such as wind or earthquake loads, not long term loading such as the weight of a panel.^[17]

Powers Fasteners revised their product specifications on May 15, 2007 to increase the safety factor from 4 to 10 for any of their epoxy products which are intended for use in overhead applications. The safety factor on Power-Fast Epoxy in particular was increased from 4 to 16.^[17]

References

See also

• Boston Bypass
• Callahan Tunnel
• Conservation Law Foundation
• Dublin Port Tunnel - Similar project on smaller scale in Ireland with similar problems.
• Interstate 90
• Interstate 93
• Leonard P. Zakim Bunker Hill Bridge
• Massachusetts Turnpike
• MBTA
• Sumner Tunnel
• Ted Williams Tunnel

External links

• http://www.tsomides.com/news/downloads/Tunnel%20Design1.pdf
• Powell, Michael, "Boston's Big Dig Awash in Troubles", Washington Post, 2004-11-19, Retrieved on 2006-08-09.
• Official site
• Project map
• Boston CA/T Project History at MIT Rotch Library
• Steve Anderson's BostonRoads.com
• PBS.org – Central Artery
• Big Dig Disaster

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