May 25, 2023

Replacing a Movable Bridge Over Vermont’s Lake Champlain

In 2018, the Cianbro team began construction to replace the nearly 70-year-old bridge over Lake Champlain connecting North Hero and Grand Isle, Vermont. The North Hero-Grand Isle bridge had recently required several costly repairs, and the Vermont Agency of Transportation (VTrans) determined that the best course of action would be to update it with an entirely new structure that will last for roughly 100 years.

The North Hero-Grand Isle bridge is vital to commuters coming to and from southern Vermont and is the only vehicular movable bridge in the state. The bridge also sees frequent boat traffic on the lake throughout the summer. With a potential detour of more than 70 miles for vehicular traffic, the project team needed to build a temporary movable bridge using an Acrow bridge and trestle approach. However, as the project moved on to demolishing the existing bridge in 2019, the team discovered contaminated soil, setting the timeline back by a year.

Once the team addressed the soil issue and the COVID pandemic had subsided, construction on the new bridge began in late 2020. The new bridge consists of two bascule piers constructed of concrete that make up the main structures on the project. Each pier is essentially a three-story building with electrical, mechanical, and storage rooms; and a control house for the bridge operator and bathroom.

Work on the new bridge began with an estimated 1,200 cubic yards of tremie placements and rock anchors for these piers. As the concrete came up, 3-foot-thick exterior walls soared out of the cofferdams built by the Cianbro team. Once the roofs of the piers were cast in place, the structural steel for the bridge, provided by Cianbro Fabrication & Coating and G&G Steel, began to be erected. This was no small feat, as the team had to ensure boats could pass through the channel unimpeded by a restricted channel width. The team worked six days a week and multiple night shifts to complete the work. pay

One unique feature of the new North Hero-Grand Isle bridge is the hydraulic cylinders, four on each leaf, which make the bridge operate smoothly. The hydraulic piping and electrical work took place from 2021 through 2022. Many bridges contain a submarine cable, however, due to the site’s contaminated soil, the team installed a wireless system to operate both leaves of the bridge from the control house. Both bascule decks are half-filled concrete grid deck systems and were completed in the summer of 2022. The project progressed through earthwork and paving with a fall opening of the bridge in 2022.

Many of the team members on the North Hero-Grand Isle project were on the project from the beginning of construction. Our team has had a tremendous impact on the surrounding communities, and the dedication to the project throughout the years was impressive. Our team members and trade partners on this project are part of history for the state of Vermont, and we are proud of the team who made this bridge come to life.

Click the link to read more about Cianbro’s recent projects.


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