Contractor: Slattery, Interbeton, J.F. White, Perini, Joint Venture
Contract Value: $400 Million
Description: Complex geometrics in support of segmental concrete bridge construction.

At more than $400 Million, and one of the largest single parts of Boston's Central Artery/Tunnel project, the C09A4 contract included a number of pre-cast segmental concrete bridges of extremely complex geometry. The sub-structure was well under way and the first segments were being erected when the contractor engaged our services to solve a geometric problem that was proving very costly.

The problem stemmed from the relationship between the pre-cast segments and the wide piers called straddle bents that carried them. When constructing these bents, it was necessary to provide various embedded items such as keyways and tendon conduits that would align properly with their counterparts in the starter segments. Because many of the roadways were skew with respect to the piers as well as on a considerable slope, the contractor had been unable to correctly establish the layout for these items on the first few piers, causing delays and requiring remedial measures.

With the spatial skills to clearly define the problem and the 3-D math skills to resolve it, Civil Geometrics was able to quickly develop the appropriate models and use them to derive the required embedment layout. The result was a set of drawings showing the exact locations of embedded items on the inside face of the straddle bent formwork. Additionally for those bents that had already been built incorrectly, we were able to revise roadway alignments and generate new erection geometry for several spans that would allow those bents to be used with minimal remedial work.