Effect of Backfill Soil Type on Stiffness and Ultimate Capacity of Bridge Abutments

Bridge abutments are earth-retaining structures which support the superstructure at the ends of a bridge and provide resistance to deformation and earthquake induced inertial forces from the bridge deck. Current design practice in California makes use of bi-linear load-deformation curve and does not account for the structure backfill properties. An experimental and an analytical research program were conducted at UCSD to further investigate such structure backfill interaction characteristics. In order to meet the objectives of this research project, a field investigation was conducted to develop a proper characterization of the soil types used for abutment structure backfills. The experimental program included five large-scale tests to examine the effect of structure backfill soil type, backfill height, vertical movement of the wall, and pre-existing cut slope in backfilling on stiffness and capacity of the abutments in the longitudinal direction. The study indicated that the response of bridge abutments in the longitudinal direction is nonlinear and a function of several influential factors which need to be considered. The passive resistance of the structure backfill is controlled by the soil shear strength and interface friction. It was shown that the vertical movement of the wall has a significant effect on the amount of maximum passive pressure.