Centrifuge Modeling of Integral Bridges with Varying Relative Stiffness of Soil and Structure

When designing integral bridges, it is important to consider the interaction between the bridge abutments and the backfill soil due to seasonal thermal movements of the bridge deck. The relative stiffness of the soil and the structure influences the deflected shape of the abutments during this interaction, which therefore determines the distribution of lateral earth pressures that are set up. However, this relationship is not well characterized or readily considered in existing design guidelines. To explore this, four geotechnical centrifuge tests were carried out on integral bridge models with varying structural stiffness and backfill densities, with displacement cycles applied via a novel, high precision mechanical actuator to simulate thermal movements of the deck over the design life of a bridge. The results provide insight into several facets of integral bridge behavior, including the rate of strain ratcheting, the zone of backfill redistribution, and the extent of surface settlements. In particular, reducing the stiffness of the abutment was found to cause deflection, rather than rotation, to dominate the overall structural response, which led to a 46% and 76% decrease in net soil resistance and peak bending moment, respectively. Based on this, an earth pressure distribution is proposed for flexible integral abutments, addressing the gap that exists in current design guidance. Through comparing the results of this study with others reported in the literature, it is also suggested that the extent of strain ratcheting is largely unaffected by the stiffness of soil beneath the foundation, except in extreme cases.