Monitoring and Evaluation of Alabama’s First Geosynthetic Reinforced Soil-Integrated Bridge System

Abstract

Geosynthetic reinforced soil-integrated bridge systems (GRS-IBS) use closely spaced layers of geosynthetic reinforcement and compacted granular backfill to directly support the bridge deck and blend the abutment and roadway approach for a smooth transition. These systems are designed for areas where a single span is sufficient to bridge over a gap in the roadway. GRS-IBS structures have been successfully implemented in many states. Alabama has recently completed its first GRS-IBS in Marshall County, which is located within the Sand Mountain region of the Appalachian Plateau. The robust mechanical properties of the native material provided a good location to construct the first GRS-IBS in Alabama due to the low risk of scour and excessive settlement. Two 12-ft tall by 33-ft wide GRS abutments were constructed to support the load of seven, 1.75-ft thick by 4-ft wide by 52-ft long, reinforced concrete box beams, pavement and traffic. Construction of the GRS abutments was completed in three phases: excavation of the native sandstone, forming and placement of the concrete foundation, and placement of the segmental retaining wall (SRW) masonry units and reinforced backfill. The bridge beams and integrated approach were placed after the GRS structure was completed. The integrated approach consists of four layers of biaxially woven geosynthetic wrapped around No. 89 gravel, a final layer of woven geosynthetic wrapped around dense grade base and covered with asphalt pavement. Earth and pore pressure instruments were placed within the first and second layers of the two GRS abutments. Since construction began, data have indicated that earth-pressures have increased to 1800-psf after placement of the bridge beams, while pore-pressures have remained near zero. Surveys of the abutment have shown no significant movement since completion of construction. These results indicate that the bridge is performing as expected.