STUDY ON SELECT DESIGN FACTORS IN GRS BRIDGE ABUTMENTS

Abstract

Construction of Geosynthetic Reinforced Soil (GRS) bridge abutments requires high-quality coarse-grained backfill materials. But the increasing scarcity of select fills has driven up construction costs, creating a demand for more affordable alternatives. To address this economic concern, this study examines the viability of using a marginal quality soil as backfill material for GRS bridge abutments. The marginal soil used in this study had nearly 25% fines, but it was non-plastic. Three model walls with identical designs were constructed: Model 1 with sand backfill (control case) and Models 2 and 3 with the marginal soil as the backfill, which was placed and compacted in both models at OMC+3% gravimetric water content. The strip footing, representing bridge load, was at the same location for Models 1 and 2, but it was placed closer to the abutment facing in Model 3. Each model abutment was instrumented to monitor settlements, facing displacements, reinforcement strains, and water content at selected locations within each model. Results of the study showed that Model 2 exhibited slightly larger deformation than the control model and Model 3 showed greater deformations than Model 2 due to the proximity of the strip footing load to its facing. Nevertheless, footing settlements, facing displacements and reinforcement strains in all models were significantly smaller than the FHWA serviceability requirements for a 190 kPa design load. These observations indicate that with proper design, including tightly-spaced reinforcement and strong facing-reinforcement connection, as was done in this study, marginal quality backfills of the type used in this study can serve effectively as backfill in GRS bridge abutments. The study provides valuable insight into the influences that backfill quality and footing location could have on structural stability and performance of GRS bridge abutments, offering a potential path toward cost-effective backfill alternatives for their design.