An Ohio county engineering department is shaving weeks and thousands of dollars off replacement of simple bridges by using geosynthetic reinforced-soil (GRS) technology in the abutments. Defiance County re-cently completed replacement of its 16th bridge in about three weeks at $80,000 using GRS—shaving off an estimated $20,000 and two weeks from the 28-ft-long reinforced-concrete structure.

Defiance County Layers of fill and geotextile fabrics create an economical and efficient method of building bridge components.

Using stockpiled components of 35-lb concrete blocks, gravel and rolls of geotextile fabric, crews built the 50-ft-wide abutments in 2.5 days, says Warren Schlatter, county engineer. “We’ll build three or four bridges a year for the foreseeable future” using GRS, he says.

The principle behind GRS is alternating layers of compacted local soil with sheets of geotextiles to create a composite-acting material, contained by concrete blocks, says Mike Adams, research engineer with the Federal Highway Administration. Adams was inspired by the U.S. Forest Service’s use of closely spaced, moderately weak geotextile fill in the 1970s on logging roads. He has tested the technology around the country, most notably on full-scale bridge piers at Turner-Fairbank Highway Research Center in McLean, Va., and in conjunction with the Colorado Dept. of Transportation.

Defiance County appears to be the only agency embracing regular use of the technology. After Adams made a presentation to an Ohio county engineers’ association several years ago, Schlatter decided to try GRS. “We were a bit skeptical,” he recalls. “No way can you put bridge beams on gravel, our crews said.” The county first tried GRS on non-critical locations like wingwalls and culverts. But in 2005, Schlatter decided to use it on abutments for a small bridge with precast concrete beams. Adams tested for stresses and settlement with instrumentation. “To date, the bridge has hardly moved at all,” says Schlatter. It was built in six weeks instead of months.

Related Links: Laser-Equipped Van Eases Atlanta Runway Inspections

According to Adams, GRS so far has worked well with simple spans of up to 120 ft, with low traffic loads and concrete superstructure. Defiance County next spring will try GRS on its first steel-girder bridge, about 125 ft long.