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U.S. DEPARTMENT OF TRANSPORTATION, Office of the Secretary, Office of Public Affairs, Washington, DC 20590

Monday, October 2, 2000
Contact: Karen Whitney
Tel.: 202-366-0660
FHWA 61-00

FHWA Researchers Take Highway Engineering "Back to the Future"
Research Shows Ancient Construction Methods Still Hold Strong Today

Federal Highway Administration (FHWA) researchers have successfully constructed an 18-foot tall bridge pier and two full-scale bridge approachways using a technique based on construction methods developed thousands of years ago in ancient Mesopotamia. The procedure shows remarkable promise for modern highway construction and could cost millions less than current methods.

"Meeting the challenges of a 21st century transportation system requires thinking outside of the box, which sometimes means reaching into the past and building upon yesterday's successes," FHWA Administrator Kenneth R. Wykle said. "This is the kind of ingenuity that characterizes our commitment to improving every facet of our nation's highway system--from process to product."

The structures were built using a technique known as Geosynthetic Reinforced Soil (GRS) technology which is simply alternating layers of compacted soil such as gravel and thin sheets of geosynthetic reinforcements. Geosynthetic reinforcements are polymer plastic materials in the form of sheets or grids. Metal strips or wire mesh can also be used for reinforcement material.

Many geotechnical experts believe GRS will revolutionize earthwork construction as it can be applied to improve roadway drainage and support, or to construct retainment walls or bridge abutments--all at a significant savings in time and cost. There is also considerable evidence that GRS technology has seismic protection potential.

The technology can be used to build simple overpasses in parks, along scenic roads or in rural areas; however it should not be used in locations where severe flooding might occur and erode the soil beneath the GRS mass. The walls can also be constructed with decorative block patterns to enhance the aesthetics of the surroundings.

With GRS, the strength and soundness of the structure comes from proper spacing of

the reinforcement materials and the quality and compaction of the gravel soil fill. The reinforcement materials confine the soil so that the structure is internally supported.

The GRS bridge pier and approachways constructed at FHWA's Turner-Fairbank Highway Research Center in McLean, Va., have withstood rigorous testing, including record-breaking amounts of applied pressure, to demonstrate their potential for use in real-world settings. The technology has already been put to practical use in Colorado where it was recently used on a project to widen a road in steep mountain terrain, to provide bridge support on several projects, including an overpass on I-25 in Castle Rock, and to mitigate a rock slide in DeBeque Canyon along 170.

The construction process is quick and can take as little as a few days or weeks, depending on the application or project. There are six basic steps:

  • Start on a level surface
  • Lay a base structure of concrete modular blocks
  • Place a layer of gravel soil behind the block
  • Compact the gravel to the height of the block
  • Lay a sheet of reinforcement on the compacted soil and extend it over the block
  • Continue the process by alternating layers of block, compacted fill and reinforcement

GRS structures can be built without specialized equipment or material. Depending on the type block and height of the wall, GRS construction is typically about half the cost of traditional structures such as a concrete cantilever wall. When the process is used to support a simple overpass bridge, the savings can be even more significant because the bridge can be supported directly upon the GRS mass, eliminating the time, cost and complexities associated with constructing a deep foundation. GRS structures also provide smoother connections to bridge abutments, limiting the bumpy transition from roadway to bridge.

FHWA has partnered with the Colorado Department of Transportation in developing GRS technology and is currently assisting the U.S. Forest Service in the construction of GRS abutments for two bridges in the Inyo National Forest in California. In addition, the New York State Department of Transportation is testing concrete beams on the GRS abutments at the FHWA bridge testing facility in McLean, Va. An additional round of experiments is scheduled for the near future.

The FHWA is an agency of the U.S. Department of Transportation.


NOTE TO EDITORS: Transportation Secretary Rodney E. Slater and transportation ministers from more than 80 countries will participate in the U.S. Department of Transportation's historic "International Transportation Symposium: Moving to the 21st Century -- Best Practices of Today and Lessons for Tomorrow," the first global transportation planning meeting of its kind. The three-day conference runs from October 9-12 at the Marriott Wardman Park Hotel in Washington, D.C., and is open to press.

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