GRS Bridge Building

Ionia County replaced an aging bridge using GRS-IBS technology, creating a faster, more cost-effective, and durable solution enhanced with Allan Block systems.

New Advancement in GRS Bridge Building

Ionia County, Michigan, faced a challenge common to many counties across the United States: aging infrastructure. The two-lane Keefer Highway Bridge spanning Sebewa Creek had deteriorated beyond repair and required replacement. With limited budgets and tight timelines, the county partnered with engineers from the Michigan Department of Transportation (MDOT) and the Federal Highway Administration (FHWA) to implement a more efficient and cost-effective bridge solution.

A Better Approach to Bridge Construction

Traditional bridge construction is often slow, expensive, and complex. Since 2005—beginning with the Bowman Road Bridge in Defiance County, Ohio—the FHWA has introduced a more efficient alternative: Geosynthetic Reinforced Soil – Integrated Bridge System (GRS-IBS). Hundreds of bridges have since been built using this method, demonstrating that structures can be constructed faster, more economically, and with excellent performance.

For the Keefer Road Bridge project, the local engineering firm Williams & Works, in collaboration with MDOT, adopted this innovative approach. While early GRS-IBS structures utilized standard split-face concrete masonry units, the team sought to enhance both durability and aesthetics. Given Michigan’s harsh northern climate, they selected Allan Block Classic SRW units for the abutment structure—providing long-term durability along with a more refined appearance.

Efficient Construction with Proven Support

Milbocker & Sons was selected as the contractor for the project. Although they were new to working with Allan Block products, support from the local manufacturer, Consumers Concrete, along with on-site training from Allan Block Corporation, allowed the team to quickly gain confidence and efficiently construct the abutments.

The project was completed successfully, resolving a critical infrastructure issue for Ionia County. MDOT was highly satisfied with the outcome and is now exploring additional opportunities to implement GRS-IBS technology on future projects. This project highlights how Allan Block solutions can adapt to a wide range of site conditions.

A National Opportunity

According to the FHWA, approximately 600,000 bridges in the United States require replacement, and nearly 70% of them could be constructed using GRS-IBS technology. In many cases, these bridges can be built for up to 50% less cost compared to traditional bridge construction methods.

Why is GRS-IBS Better?

At its core, the advantage of GRS-IBS comes down to time and cost savings, driven by a simplified construction process.

Unlike traditional bridges, GRS-IBS systems typically eliminate the need for:

• Deep foundations or piles
• Cast-in-place concrete elements such as footings, pile caps, abutments, and wing walls
• Extensive curing time associated with concrete construction

Instead, the bridge is constructed directly on a densely compacted, geosynthetic-reinforced soil mass. In rehabilitation projects, existing foundations can often remain in place, providing additional stability and scour protection.

The abutments are built by placing and compacting layers of select granular fill with closely spaced geosynthetic reinforcement—typically every 8 inches (200 mm) or less. Because of this tight reinforcement spacing, the modular block facing is not required to retain large soil loads. The FHWA has demonstrated that simple frictional connections between the reinforcement and the block facing are sufficient, eliminating the need for mechanical connectors or pins common in traditional mechanically stabilized earth (MSE) systems.

Performance Backed by Research

The benefits of closely spaced reinforcement are well established. Allan Block’s full-scale seismic testing has shown that reduced reinforcement spacing significantly improves structural performance under dynamic loading conditions.

Professor Hoe Ling of Columbia University noted:

“When properly designed and constructed, these systems are well suited for seismic conditions. The wall facing, soil mass, and geosynthetic reinforcement move together in response to applied forces. Structures that are both flexible and coherent perform best under these conditions.”

Simplified Bridge Integration

As construction progresses, additional layers of reinforcement may be placed at tighter intervals—sometimes every 4 inches (100 mm)—to support a precast concrete bearing slab. Bridge girders are then set directly on this reinforced soil structure.

Reinforced fill is placed behind the girders up to the roadway elevation, creating a fully integrated system. Because the bridge and abutments function as a single unit, traditional expansion joints are not required.

Eliminating the “Bump at the Bridge”

One of the most noticeable benefits of GRS-IBS bridges is the elimination of the familiar “bump” at bridge approaches. In conventional designs, roads settle over time while bridge structures remain rigid, creating a noticeable transition.

With GRS-IBS, the bridge and approach are fully integrated, allowing them to settle uniformly. The result is a smoother ride for drivers and reduced long-term maintenance.

FHWA project data has shown:

• Virtually no cracking at girder interfaces
• Elimination of approach bumps at abutments

Scour Protection and Durability

For bridges crossing waterways, standard scour protection methods are still applied. Riprap is commonly used, and in the Keefer Road Bridge project, articulating concrete block mats were installed to protect against erosion and undermining.

A Smarter Way to Build

Constructing a GRS-IBS bridge is significantly simpler than conventional methods, relying primarily on well-executed earthwork practices such as proper fill placement and compaction. While the process is straightforward, attention to detail and adherence to best practices are critical to ensuring long-term performance.

The Keefer Road Bridge project stands as a clear example of how innovative design, proven technology, and the right materials can deliver faster, more economical, and more durable infrastructure solutions.