The Exit 17 Bridge over Vermont’s I-89 in Colchester, Vermont is an integral part of the Route 2 corridor, connecting Grand Isle County and parts of Colchester to Vermont’s interstate system. Deteriorating bridge conditions from a 1960’s-era design prompted a complete replacement and interchange traffic pattern reorganization. Foamed glass aggregate delivered the lightweight fill needed to build the bridge approach and mechanically stabilized earth walls without costly excavation or long-term settlement risks.
Many of I-89’s Vermont bridges from the 1960s were designed with 60 foot spans and center piers. While effective at the time, this design exposed expansion joints to decades of road salt and harsh winter conditions. The Exit 17 bridge was strained by structural deterioration and increasing Route 2 traffic, which made a complete bridge replacement urgent.
Adding to the complexity, much of Chittenden County sits on glacial till soils underlain by deep, soft clay layers left over from the prehistoric Champlain Sea. Traditional repair methods presented serious challenges:
These conditions created a critical need for an innovative approach that would balance geotechnical performance, construction feasibility, and long-term durability.
Faced with challenging clay soils at the bridge site, Vermont Agency of Transportation engineers turned to foamed glass aggregate as an alternative to traditional fill or sheet-pile excavation. Foamed glass aggregate minimized settlement risks without the need for extensive excavation or costly reinforcement.
To validate performance, the project team used inclinometers and piezometers to measure ground movement and
water pressure. The data confirmed that foamed glass aggregate delivered the necessary stability needed under difficult subsurface conditions.
Construction & Installation
The bridge design combined mechanically stabilized earth walls to support the roadway with H-piles carrying the bridge itself. On site, foamed glass aggregate proved both practical and efficient:
Results & Benefits
The Exit 17 project was completed on schedule, with a structure designed for a 125 year service life. By using foamed glass aggregate, Vermont Agency of Transportation:
