From Tech Transfer Newsletter, Fall 2010
Every Day Counts
Geosynthetic Reinforced Soil Integrated Bridge System
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
Rather than drilling a deep foundation, the reinforced soil method builds up
the substructure in a faster, simpler way. Imagine building a layer cake:
- Step 1. Lay a row of facing blocks.
- Step 2. Place a layer of compacted fill (soil, etc.) behind the facing blocks.
- Step 3. Top with a sheet of geosynthetic fabric.
- Repeat from Step 1 until the desired height is achieved.
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
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
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.
To Learn More
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.
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