Engineering Inc. - July/August 2007 - (Page 15)

Massachusetts turnpike authority of the most difficult conditions highway engineers could ever face,” explains Michael Bertoulin, vice president of Parsons Brinckerhoff, part of the construction management team on the Big Dig. “The challenges associated with keeping the city running during the height of construction were enormous.” Deep Thinking he project has made Boston a more viable city with a great future.” richard diMino a Better city t 1998: Peak construction years begin. construction begins on the charles river crossing. 1999: Overall construction 50 percent complete. New Broadway Bridge opens. Leverett circle connector Bridge opens. 2000: Nearly 5,000 workers employed on the Big Dig. 2001: Overall construction 70 percent complete. 2002: Leonard P. Zakim Bunker Hill Bridge completed. The first phase of the project involved tunneling under Boston Harbor using the immersed tube tunnel (ITT) method. In 1991, a dredger known as the “Super Scoop” began dredging 900,000 cubic yards of earth. This enabled work crews to begin laying steel ITT sections across the harbor. Each of the ITTs consisted of a 15,000-ton composite structure composed primarily of concrete and a pair of 40-foot steel tubes joined side by side and extending 330 feet. By 1992, the 12 tunnel sections—built by Maryland-based Bethlehem Shipbuilding—began arriving at the site. Crews then added concrete to transform the steel hulks into structures that would serve as the highway’s foundation. In 1993, a catamaran barge began towing the tunnel sections into position. Each of the tubes had to be lowered within a fraction of an inch from their designated location in order to ensure a watertight seal. Workers used global positioning devices and lasers to position pieces of the tunnel within the murky waters of Boston Harbor. Working 100 feet below the surface—the Big Dig was the deepest tunneling project in the history of North America—workers finished connecting I t is a terrific example of engineering excellence and innovation. It will be a case study for building large public projects.” aBBie r. GoodMan acec/Massachusetts the 33-ton sections in 1995. By December of that year, the newly christened Ted Williams Tunnel opened on budget and on schedule. But the Big Dig had only just begun. In order to connect the tunnel to I-90, engineers had to build another tunnel under Boston’s 400-foot-wide Fort Point Channel. The eight-lane highway would have to cross over a subway line, run adjacent to a manufacturing plant and large post office and run beneath commuter rail lines. To extend I-90 under the tracks and across the channel, engineers were forced to push the limits of existing technologies. The process involved a combination of imaginative concrete box ITTs, massive ground modification and “jacked” highway tunnel boxes underneath an operating rail corridor. Engineers turned to soil mixing—a Japanese technique—to modify the pudding-like soil on the bank of the Fort Point Channel. Using heavy blades and rotors, construction workers drilled down approximately 130 feet and mixed in cement to create a material that would support 300 to 1,000 pounds per square inch (PSI). After solidifying an area and creating a mass gravity wall, excavation commenced adjacent to existing commuter rail lines at the channel edge. The area became the interface between the ITTs and jacked tunnels. However, low bridges in the channel prevented crews from building the ITTs off-site. Instead, engineers created a 60-foot-deep and 1,000-footlong dry dock, otherwise known as a casting basin. The basin held six different concrete sections during construction. The challenges didn’t stop there. Crews had to float the 27-foot-high sections (which measured up to 414 feet long and 174 feet wide) into place. Construction teams also couldn’t build all the structures at the same time—meaning the basin had to be filled and drained more than once. Two of the sections served as the foundation for ventilation structures on their roof—thus making the 2003: I-90 connector from South Boston to rt. 1A in East Boston opens in January. I-93 Northbound opens in March. I-93 Southbound opens in December. 2004: Dismantling of the elevated central Artery (I-93). Opening of the tunnel from Storrow Drive to Leverett circle connector, which provides access to I-93 North and Tobin Bridge. 2005: Full opening of I-93 South. The opening of the completely renovated Dewey Square Tunnel, including new exit and entrance ramps. Opening of the two cantilevered lanes on Leonard P. Zakim Bunker Hill Bridge. Opening of permanent ramps and roadways at I-90/I-93 interchange and in other areas. 2006: reached substantial completion of the central Artery/Tunnel Project in January. Spectacle Island Park opens to the public. 2007: restoration of Boston city streets. continued construction of the rose Kennedy Greenway and other parks. construction on development parcels continue after the central Artery/Tunnel Project is finished. SOUrcE: Massachusetts Turnpike Authority. DArrEN MccOLLESTEr/GETTy IMAGES July / AuGust 2007 ENGINEERING INC. 15

Table of Contents for the Digital Edition of Engineering Inc. - July/August 2007

Call for Entries
Contents
From ACEC to You
News & Notes
Market Watch
Legislative Action
The Big Dig
Risky Engineering
2007 Professional Liability Survey
Institute For Business Management Fall 2007 Course Catalog
Roadside Technology
2007 Convention Wrap-Up
2007-2008 Excom
2007 Fall Conference Primer
Business Insights
Technology
Members in the News
One on One

Engineering Inc. - July/August 2007

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