C09A4 – Boston Central Artery

The largest single construction contract ever in the Commonwealth of Massachusetts, known as C09A4, was given notice to proceed in January of 1997, with a bid price of $397M. This project features several complicated structures and construction operations including the largest frozen ground jack tube tunneling operation in the world. While segmental structures represent only approximately 10% of the total contract value, they too are very intricate.

A conventional crane and an overhead gantry, manufactured by DEAL of Udine, Italy, were utilized for the construction of the viaducts. Pier segments are typically erected by crane in advance of the gantry. This gantry is extremely versatile, having a symmetrical design allowing erection in either direction. Equipped with two segment hoists for simultaneous erection of two cantilever segments, the gantry is also capable of supporting the two simple spans during construction. Design of the viaducts was based primarily on the balanced cantilever method with the span-by-span method used for two shorter spans. Span lengths range from 105 ft to 216 ft. Instead of utilizing the typical expansion joints located at piers to separate the bridge units, four hinge-spans occur within the viaducts. These are erected in typical balanced cantilever, temporarily locked, and then released as erection of subsequent spans has been completed.

Casting of the 1,062 segments began in September 1998 utilizing four forms, with completion of the project anticipated in April of 2001.