Banking on a Bridge

Completing the geotechnical design for the approach embankments and foundations for the Charter Oak Bridge, which crosses the Connecticut River between Hartford and East Hartford, Conn., forced the designers to handle a number of unusual problems and constraints. The soft Connecticut Valley varved clay that underlays the site was expected to settle up to 60 in. in the first year of construction and exert forces of up to 350 tons on the piles supporting the embankments. In addition to the challenge from the soil, however, engineers from Haley & Aldrich, Cambridge, Mass., also had to reconsider their original plan in light of the time it might take to receive regulatory approval. Toe berms had been planned to support the eastern embankment, but, when navigational and environmental permitting processes seemed likely to delay the project, engineers came up with a new combination of methods that, while more expensive, proved more cost-effective in the long run: preloading and surcharges on both embankments, with lightweight fill on the eastern side and wick drains and standard fill on the west. Despite the $2 million additional expense, the owners, the Connecticut DOT, considered lightweight fill the most viable option because it helped ensure the $90 million project was completed on schedule.