The Bowman Road Bridge project in Defiance County, Ohio, demonstrates that geosynthetic reinforced soil (GRS) technology for abutments can be used to
The Bowman Road Bridge project in Defiance County, Ohio, demonstrates that geosynthetic reinforced soil (GRS) technology for abutments can be used to build strong, stable bridges faster and for less money. Instead of supporting the span on a pile cap abutment, GRS technology uses alternating layers of compacted fill and sheets of geotextile reinforcement to buttress the bridge. Without highly skilled labor, GRS abutments can be built using common construction equipment and readily available concrete masonry units.
In addition, GRS technology provides extremely durable abutments. According to Mike Adams of the Federal Highway Administration, They can even perform well in earthquakes, if constructed properly with closely spaced reinforcement. The performance of the GRS mass is controlled by reinforcement spacing.
Early development of GRS technology was pioneered by U.S. Forest Service and the Colorado Department of Transportation (CDOT) researchers. Further refinements were implemented by FHWA in collaboration with CDOT. To that end, several full-scale GRS structures were built and tested at FHWA’s Turner-Fairbank Highway Research Center in McLean, Va.
While this type of abutment isn’t right for every bridge, the technology is well suited for single-span bridges of less than 36 m (120 ft.), Adams explains. It is not advisable for crossings where scour is a key engineering factor, he adds. Accordingly, among the 80 percent of U.S. bridges featuring a single, 21- to 27-m (70- to 90-ft.)-long span, a significant portion could be GRS supported.
In the summer and fall of 2005, FHWA provided guidance and abutment design plans to Defiance County to build the Bowman Road Bridge. Opened to traffic in October 2005, it provided the county’s first experience using GRS technology to build bridge abutments. Notes County Engineer Warren Schlatter, After seeing a presentation on the technology and meeting with FHWA’s Mike Adams to learn more, we modified our plans from traditional abutments to building with GRS.
To develop some familiarity with GRS before building the Bowman Road Bridge, the county applied the system initially to retaining wall construction, thereby reducing the cost of culverts. Using the new technology paid off handsomely, as Defiance County realized a cost savings of nearly 25 percent on its first bridge support project. Moreover, construction time for the single span was reduced to six weeks from the several months typically required for a conventional bridge. Significant savings were realized in both time and costs, Adams observes. The construction time for the bridge could have been reduced even more Û to less than three weeks Û if two separate labor crews had been used to build both abutments simultaneously.
Instead of cast-in-place concrete, split-face concrete masonry block supplied by Swanton, Ohio-based Tri-County Block and Brick was used to face the Bowman Road Bridge abutments. To build a GRS mass, three steps were repeated until the desired abutment wall height was attained: installing a row of blocks, placing a layer of compacted fill to the 20-cm (8-in.) height of the facing block, and then applying a layer of geotextile. Each geotextile layer was extended between rows of block to connect abutment walls to the GRS mass. Adams notes, There are two necessary factors to assure good GRS mass performance: good compaction with quality granular fill and close reinforcement spacing.
Precast box beams fabricated by Prestress Services of Decatur, Ind., were placed directly on the GRS abutments without a concrete footing; and, the bridge does not have an approach slab, as GRS was compacted directly behind the beams to create a gradual transition from roadway to crossing. To allow the bridge and adjacent road to settle together, providing a smooth ride for drivers traveling on and off the span, asphalt pavement was placed on the bridge and approach without a conventional joint system at the bridge ends. No cast-in-place concrete was used on the structure.
FHWA instrumented the bridge so that its performance can be monitored over the next two to three years. It is performing very well, Schlatter affirms. There has been very little movement or settling, and no pavement cracking.
Defiance County is planning to use GRS technology to build seven more abutments this year. One of the biggest advantages for us is convenience, says Schlatter. Among construction advantages over using [cast-in-place] concrete is the ability to build abutments in all weather conditions. Other states that have expressed interest in using GRS for abutments include Illinois and Massachusetts.
More data on GRS technology or the Bowman Road Bridge can be obtained by contacting Mike Adams at FHWA, 202/493-3025; [email protected]. Additional information on the Bowman Road Bridge is also available from Warren Schlatter of Defiance County, 419/782-4751; [email protected]