Alumnae facilitate lecture on Boston's 'Big Dig' project

Christine Francis Shaw '97, a structural engineer at Parsons, Brinckerhoff, Quade, and Douglas Inc., and Meghan Fehlig '02, an engineer at the firm, facilitated a lecture by Vijay Chandra, a senior vice-president at the firm.

This Princeton-based engineering firm has "college champions," who are responsible for recruiting students from their alma mater. Ms. Shaw was the Princeton champion last year and Ms. Fehlig serves in that capacity this year.

During his Feb. 27 lecture, Mr. Chandra outlined the many challenges and technical innovations of the Big Dig.

The redesign and construction of Boston's Central Artery has been an enormous undertaking since 1992. The Central Artery is a wasp's nest where I-90 and I-93 meet.

The Big Dig has been called "the largest, most complex, and technologically challenging highway project ever attempted in American history." The project aims to reduce traffic congestion and improve mobility in Boston, while improving the environment and laying the groundwork for economic growth.

"When we began this we had to remember, it's not just a highway changeover; it's rebuilding a city," Mr. Chandra said.

Before construction could begin, plans had to be agreed upon, and more plans were needed to decide how to keep the city fully functional for the duration of the project.

To accomplish this, a workshop was held, inviting decision-making officials from all interested parties: engineers, architects, urban planners, city officials, and more.

"In the entire project," Mr. Chandra said, "the biggest challenge was bringing everyone together to a consensus."

The Big Dig project features an underground expressway located beneath the existing six-lane highway, which culminates in the Leonard P. Zakim Bunker Hill Bridge and the Storrow Drive Connector Bridge (see photograph). The result is a 14-lane, two-bridge crossing of the Charles River. Following completion of the underground road, the elevated highway will be demolished and replaced by open space. I-90 will be extended through a tunnel to Logan Airport.

Mr. Chandra said The Big Dig has required many extraordinary feats of engineering.

One of the major challenges was that rail and air transport had to remain fully operational throughout construction of the new highway.

Thus, to prevent disturbance of the MTA Red Line tubes, engineers froze the surrounding land with liquid nitrogen for six months while the highway tunnel was being jacked over the rail tunnels. Since the tunnel was being built over the Red Line tubes, engineers constructed something like an underwater bridge to support the roadway. This was necessary so that the weight of the tunnel would not weigh down the Red Line tubes and collapse them. Over the three years that this structure was being built, engineers and airport officials rerouted runway traffic 26 times.

The Zakim Bridge is a composite stee l-cement structure that employs the use of new stay cable technology never before used in the United States.

Most polyethylene stay cables have a layer of grout in them. However, when the cables shake from the forces of wind and vehicles driving on the bridge, the grout in the cables breaks down and separates. The water in the grout then corrodes the strands inside the cables.

The stay cables in the Zakim Bridge do not have grout in them, thus preventing such corrosion.

For more information about the project, visit www.bigdig.com