PERFORMANCE OF GEOSYNTHETIC-REINFORCED WALLS SUPPORTING THE FOUNDERS/MEADOWS BRIDGE AND APPROACHING ROADWAY STRUCTURES. REPORT 2: ASSESSMENT OF THE PERFORMANCE AND DESIGN OF THE FRONT GRS WALLS AND RECOMMENDATIONS FOR FUTURE GRS ABUTMENTS

The Founders/Meadows structure is the first major bridge in the United States built on footings supported directly by geosynthetic-reinforced soil (GRS) walls, eliminating the traditional use of deep foundations altogether. The performance of the front GRS walls, which support the bridge structure and embankment behind the abutment wall, was investigated by collecting data for the movements of the wall facing, settlement of the bridge footing, distributions of the vertical earth pressures and geogrid tensile strains inside the front GRS walls, and lateral earth pressures against the wall facing. Monitoring data was collected during six construction stages and while the structure was in service. This report provides a summary and analysis of the collected data, assessment of the performance and design of the front wall, and recommendations for design and construction of future GRS abutments. Compaction operations created large loads in the reinforcements and against the wall facing during interim construction stages of the front wall. The front GRS walls showed excellent performance because: (i) the monitored movements were significantly smaller than those expected in design or allowed by performance requirements, (ii) post-construction movements and geogrid strains became negligible after an in-service period of 1 year, (iii) measured loads in the reinforcements, connections, and on the wall facing were less than or around 50% of those estimated in the design, (iv) there is not any potential for overturning the structure (due to the flexibility of GRS wall system, resulting in the reduction of loads developed behind and against the wall facing), and (v) the measured bearing pressures were well below the allowable soil bearing capacity. The design employs a high creep reduction factor for the geogrid reinforcements although little if any long-term creep was observed.

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