I-91 Brattleboro Bridge Improvements
Owner: Vermont Agency of Transportation
General Contractor: PCL Civil Constructors
Lead Design Firm: Figg Bridge Engineers
Civil Engineer: Sebago Technics
Geotechnical Engineer: Golder Associates
Environmental & Permitting: VT Compliance Monitoring
Dubbed “A Bridge to Nature” by the Vermont Agency of Transportation, this project delivered not only a critical piece of infrastructure, but also a gateway into the state. Every detail of the uniquely shaped superstructure, piers, viewing platform and railings compliments the natural landscape.
Bridge 8 carries the northbound and southbound lanes of I-91 over a local road using NEXT Beams. Bridge 9 is a new three-span, 1,036-ft-long arching concrete bridge soaring 100 ft above the West River and built using balanced cantilever construction. It is the largest bridge in state history.
The focal point of the bridge is the two quad-wall piers which represent stone trees emerging from the ground and support the arching concrete spans. The quad-wall system of the piers provided stability and allowed for the balanced cantilever segmental construction of the bridge superstructure to be built from above without temporary falsework in the river. The balanced cantilever method allowed the long spans to be formed in a self-supported manner during construction. The method also offered an important benefit for the unobstructed use of the river and an adjacent recreational trail. Using self-advancing formwork, segments of the bridge were cast-in-place 16 ft at a time—alternating from one side of the pier to the other—until each cantilever arm reached 257 ft. When the adjacent pier’s cantilever was completed using the same process, a small closure segment was cast to connect the two cantilever arms and form the span. For the two cantilevers to meet at a precise mid-air target, surveying and geometry control were critical. Given the total bridge length, longitudinal jacking operations were designed to mitigate the long-term effects of creep and shrinkage.
During construction, crews experienced one of the coldest winters on record, including working through the Polar Vortex of 2014 as well as record snowfall in 2015. The original contract completion date was extended through change orders and the project was completed on time. One judge said the bridge was “challenging in terms of dealing with this awful weather. They were dealing with building in the water, they were dealing with using people who don’t know how to do this work and then they built this kind of iconic bridge for the area.”