No abstract

This paper presents an experimental study of the dynamic response of a half-scale geosynthetic-reinforced soil (GRS) bridge abutment system using a shaking table. Experimental design of the model specimen followed established similitude relationships for shaking table tests 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. The 2.7 m-high GRS bridge abutment was constructed using well-graded sand backfill, modular facing blocks, and uniaxial geogrid reinforcement with a vertical spacing of 0.15 m in both the longitudinal and transverse directions. A bridge beam was placed on the GRS bridge abutment at one end and on a concrete support wall resting on a sliding platform off the shaking table at the other end. The GRS bridge abutment system was subjected to a series of input motions in the longitudinal direction. Results indicate that the testing system performed well, and that the GRS bridge abutment experienced small deformations. For two earthquake motions, the maximum incremental residual facing displacement in model scale was 1.0 mm, and the average incremental residual bridge seat settlement in model scale was 1.4 mm, which corresponds to a vertical strain of 0.7%.

Seismic compression of unsaturated soils occurs due to particle rearrangement during largestrain cyclic shearing which may be resisted by interparticle stresses that depend on the matric suction and degree of saturation. Due to the high rate of shearing in earthquakes, seismic compression is expected to be an undrained phenomenon with changes in total volume, matric suction, and degree of saturation along with an evolution in soil hydro-mechanical properties during cyclic shearing. To simplify this problem and better understand the mechanisms of seismic compression, this study seeks to isolate the effect of matric suction through a series of drained cyclic simple shear tests on unsaturated sand subjected to different shear strain amplitudes. These tests were performed in a cyclic simple shear apparatus with suction-saturation control using a hanging column and suction monitoring using an embedded tensiometer. Matric suction values in the funicular regime had the greatest effects on the magnitude and rate of development of seismic compression with cyclic shearing, and values in the capillary regime were similar to those in dry and saturated conditions. The volumetric contractions also caused the soil-water retention curve and suction stress characteristic curve to shift toward higher suctions during cyclic shearing.