South Boston Interchange 80% complete
Picture yourself in the east side of Boston, one of America's oldest and most congested cities. Your job is to build a huge tunnel 1,200 feet long and 325 feet wide to help carry traffic from Logan Airport under the city. No problem - except for all the buildings, roads, a maze of utilities and as-yet-to-be-uncovered structures and objects accumulated during 350 plus years of civilization. As if these weren't enough challenges, this tunnel-building project connects to other projects in Boston's famous "Big Dig", and the projects adjacent to yours are over a year behind schedule.
The tunnel cannot be completed until another contractor finishes building the immersed tube tunnel sitting inside the partially completed tunnel constructed earlier. Essentially, joint venture crews have created a building dock for the immersed tube tunnel. They also built a temporary dam at one end of the building dock to keep water out. When the immersed tubes are completed this April, the basin will be flooded with water at sea level and the tubes will be floated one half mile into the river channel to their final resting place. The floated tubes will form the next stage of the tunnel being built by another contractor for I-90. The immersed tube tunnel units had to be constructed at this location because of obstructions in the river channel father down stream.
After the tubes are floated out, the basin will be closed and pumped dry. It then becomes the excavation for the tunnel for the South Boston Interchange. Crews will go into the basin and finish building the cut-and-cover tunnel and join it to already completed portions of the tunnel that were not used as a building dock.
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