UC San Diego

Geosynthetic reinforced soil (GRS) bridge abutments are becoming widely used in transportation infrastructure and provide many advantages over traditional pile-supported designs, including lower cost, faster and easier construction, and smoother transition between the bridge and approach roadway. Seismic events represent a severe loading condition and experimental testing and evaluation are needed to understand the potential issues and performance characteristics. This study involves a comprehensive evaluation of the performance of GRS bridge abutments for the service limit state, the strength limit state, and an extreme event limit state (i.e., seismic loading conditions) using both numerical simulations and physical modeling experiments.

A numerical model was developed for GRS bridge abutments under service loading conditions and was validated using field measurements. Simulation results indicate that the horizontal restraining forces generated from the bridge structure can have an important effect on reducing lateral facing displacements and bridge seat settlements of GRS bridge abutments. Parametric studies were conducted to investigate the effects of various design parameters on the performance of GRS bridge abutments for service loading conditions, and the results indicate that reinforcement spacing, reinforcement stiffness, bridge load, and abutment height have the most significant effects on the lateral facing displacements and bridge seat settlements.

The numerical model was enhanced by incorporating the strain softening behavior for backfill soil and the rate-dependent behavior for geosynthetic reinforcement to simulate the load-deformation behavior of GRS bridge abutments up to failure condition. A linearly elastic reinforcement model can capture the deformation behavior of GRS bridge abutments for service loads, but not for larger applied loads approaching failure. The geometry parameters for GRS bridge abutments have important effects on the internal failure surface of the GRS bridge abutments, and the internal failure surface manifests as a bilinear surface that starts at the heel of the bridge footing, moves vertically downward to mid-height of the GRS bridge abutment, and then linearly to the toe of the GRS bridge abutment.

The seismic response of GRS bridge abutments was evaluated using an experimental testing program. Shaking table tests were conducted on six half-scale GRS bridge abutments by application of a series of shaking events in the directions longitudinal and transverse to the bridge beam. Experimental design of the model specimen followed established similitude relationships for shaking table testing of reduced-scale models in a 1g gravitational field, including scaling of model geometry, geosynthetic reinforcement stiffness, backfill soil modulus, bridge load, and characteristics of the earthquake motions. Experimental results indicate that the seismic facing displacements and bridge seat settlements for GRS bridge abutments are small and will likely not have a major effect on the bridge performance. Reinforcement spacing and stiffness have the most important effects on the seismic performance of GRS bridge abutments.