GRS-IBS

Geosynthetic Reinforced Soil (GRS)

Integrated Bridge System (IBS) Technology

What is GRS-IBS?

GRS-IBS is a form of accelerated bridge construction (ABC) that lowers cost, slashes construction time, improves durability, and increases safety—all at the same time. For budget-challenged State Transportation Agencies (STAs), that is a life-saver.

GRS-IBS technology uses alternating layers of compacted granular fill material and fabric sheets of geotextile reinforcement to provide support for the bridge. GRS-IBS also provides a smooth transition from the bridge onto the roadway, and alleviates the bump at the bridge problem caused by uneven settlement between the bridge and approaching roadway. The technology offers unique advantages in the construction of small bridges, including:

• Reduced construction time and cost, with costs reduced 25 to 60 percent from conventional construction methods.
• Easy to build with common equipment and materials; easy to maintain because of fewer parts.
• Flexible design that's easily modified in the field for unforeseen site conditions, including utilities, obstructions, existing structures, variable soil conditions, and weather.

How Does It Work?

Rather than installing a deep foundation, this reinforced soil method builds up the substructure in a faster, simpler way. It is similar to building a layer cake. First, builders lay a row of facing blocks. Second, they add a layer of compacted fill to the height of the facing blocks (8 in.). Next, they add a layer of geosynthetic fabric. The process is repeated over and over until the desired height is achieved.

Three Main GRS-IBS Components:

Case Study: The Bowman Bridge

The Bowman Road Bridge in Defiance County, Ohio, was built in just 6 weeks. Construction time could have been reduced to less than 3 weeks if two separate labor crews had been available to build both abutments simultaneously.

Many factors contributed to the time reduction. There was no need to pour concrete, which can take significant project time. Instead, precast concrete box beams were placed directly on the GRS abutments. No approach slab was needed; GRS was compacted directly behind the bridge beams to form the approach way. Materials are readily available, a benefit of the generic nature of the system.

Costs were also radically reduced. The county realized a cost savings of nearly 25 percent on its first bridge support project. These savings came from more than just the reduced labor costs that result from shorter construction time and simpler construction. GRS bridge abutments also require fewer materials.

Instead of using cast-in-place concrete for the abutment walls, the Bowman Road Bridge engineers used split-face cinder blocks (modular concrete blocks) to face the abutment. Underneath the GRS abutment, they used a Reinforced Soil Foundation (RSF) over the clay subsoil.

The RSF uses GRS to provide embedment and a larger bearing area. GRS consists of layers of compacted granular soil alternated with sheets of geotextile fabric reinforcement to provide support. With GRS-IBS, there is no need for a deep foundation. The construction is jointless and has no approach slab. This has the added benefit of eliminating the bump—typically experienced where a bridge abuts the roadway.

The performance of the Bowman Road Bridge and the other GRS-IBS bridges has been outstanding. All have performed well and have required no maintenance to date. They have also saved the county significantly on construction costs.

FHWA and Defiance County proved that this new technology works. For transportation agencies whose budgets are insufficient to meet bridge construction demands, GRS-IBS could be the long-awaited answer.

FAQs

What makes GRS strong?

What other advantages does GRS have for bridge construction?

Does GRS have other uses?

How is a GRS mass created with a modular block facing system?

Contact Information

For training or more information on this Every Day Counts Initiative, please contact your local FHWA Division Office.

To learn more about EDC, visit:

http://www.fhwa.dot.gov/everydaycounts

About Every Day Counts

Every Day Counts is designed to identify and deploy innovation aimed at shortening project delivery, enhancing the safety of our roadways, and protecting the environment.