GRS-IBS Bridge
Hartland VTrans Bridge Replacement Project
Every Project Starts with a Purpose
Deterioration of the superstructure of TH 41 Bridge 37D in Hartland, Vermont, posed a risk to heavily trafficked Interstate 91, running below the bridge. State of Vermont Agency of Transportation (VTrans) inspectors warned of the potential for full-depth pop-outs and risks of concrete falling onto the interstate below. Additionally, the bridge was not wide enough for the state’s snowplows. An initial engineering study recommended replacing the superstructure, meaning everything above the piers.
The Solution
Solving for Style, Function, and Durability
Rather than replacing only the superstructure of the existing bridge, VTrans determined it was more economical to replace the entire bridge using the Geosynthetic Reinforced Soil–Integrated Bridge System (GRS-IBS) with Diamond Pro® Pin as the facing system. GRS-IBS consists of alternating layers of compacted fill and closely spaced geosynthetic reinforcement, blending the roadway into the superstructure to create a jointless interface.
For the reinforced abutments, engineers specified pinned segmental retaining wall units for their durability, ease of installation, and centering system, which helps keep courses running straight. This marked the first use of GRS-IBS technology in Vermont and the first GRS-IBS installation for Cold River Bridges LLC.
The team constructed a footing of compacted ¾-inch concrete aggregate and placed the first layer of Diamond Pro PS 8 × 18 × 12-inch blocks in Granite Gray. The Diamond Pro PS system uses pins as a location device during installation. Pins are inserted into the blocks before placing backfill, and subsequent courses are set over the centering pins to limit movement. After each course of block was laid, stone and geosynthetic fabric were installed, repeating the block, stone, and fabric sequence. More than 10,000 blocks were placed without specialized equipment.
For the Hartland Bridge, the existing structure was replaced with two single-span bridges using GRS-IBS abutments. Each bridge spans one barrel of the interstate, eliminating 190 linear feet of bridge that would have required future maintenance.
Despite COVID-related delays, construction was completed in a single six-month season from May to November. During that time, the bridge was closed and traffic was detoured along Town Highway 41 through a privately owned gravel pit.
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The Result
A Lasting Impression:
The Final Transformation
Replacing the bridge’s superstructure would have required two years of construction and extended the life of the bridge by only 40 years. In contrast, by using GRS-IBS to replace the entire bridge, construction time took only six months and extended the life of the bridge to 100 years.
The new, wider bridge was finished in one phase, before the winter season began, causing less disruption to local traffic. And perhaps best of all, using GRS-IBS technology cost $3 million less than replacing the superstructure of the previously existing bridge.
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