The Geosynthetic Reinforced Soil (GRS) Integrated Bridge System (IBS) is a simple bridge construction method that uses readily available, inexpensive materials and basic earthwork techniques to build bridges better, faster and cheaper.
Rather than drilling a deep foundation, the reinforced soil method builds up the substructure in a faster, simpler way. Imagine building a layer cake:
This low-tech approach continues until the abutment reaches the desired height and the bridge is placed directly on top of the GRS abutment mass. A GRS approach way is then built behind the bridge beams to transition the bridge to the approaching roadway. No joint or cast-in-place concrete is needed. Since the bridge extends naturally out of the roadway, there is no “bump at the end of the bridge” caused by differential settlement between the bridge abutment and the approaching roadway.
This simplified process radically reduces construction time. A GRS IBS is built in days or weeks, not months. There is no need to wait for cast-in-place concrete to dry; the substructure is immediately ready for the bridge. In addition, on-site changes are easy to accommodate and weather is rarely a problem, since this type of construction can occur in variable conditions.
GRS IBS is strong and durable. Bridges built with GRS IBS are stronger, more durable and generally more ductile and flexible than bridges built using traditional methods. A GRS bridge performs well in earthquakes if constructed properly, with closely spaced reinforcement. Full-scale shake table testing showed that a GRS abutment structure can withstand a 1.0 g earthquake acceleration.
GRS IBS bridges are also less expensive to build. Bridges constructed with the GRS IBS cost 25 to 60 percent less than bridges built with traditional methods, depending on the standard of construction and the method of contracting (local forces versus a private contractor).
Shortened construction time means fewer labor hours. In Defiance County, Ohio, one bridge abutment was built in just 3 days. Using traditional techniques such as cast-in-place construction, that same abutment would have required 2 to 3 weeks.
This lower-tech option also reduces material costs. Inexpensive, common materials and equipment are used.
Construction is much simpler with GRS IBS since it has fewer parts. There is no need for highly skilled labor since the method only requires basic earthwork methods and practice. Simpler construction also means simpler maintenance.
Visit FHWA’s GRS IBS website.
The website includes detailed information about GRS, including a case study of the Defiance County project.
All photos shown are examples of FHWA Geosynthetic Reinforced Soil Integrated Bridge System (GRS IBS) bridges constructed in Defiance County, Ohio.