The Effect of Soil Damping on the Soil-Pile-Structure Interaction Analyses in Liquefiable and Non-liquefiable Soils

Preliminary design of piles is performed by considering the static loads, but the final design must include the dynamic loads, especially in earthquake-prone regions. The soil nonlinearity under seismic loading is evaluated using the modulus degradation curves in the total-stress approach. In this study, two different centrifuge tests were simulated in FLAC^3D. The nonlinear elastic method (hyper-bolic model) and the elastoplastic Mohr-Coulomb (MC) model were employed in the study. The soil-single pile-structure systems were analyzed under the specific earthquake events, and the soil-pile-structure response was compared. The analyses with the low-intensity input motions show that the superstructure accelerations and the bending moments in the single pile are estimated with reasonable accuracy. However, the superstructure accelerations might be underestimated, especially in the MC model, compared to the centrifuge test results due to the increase in the amplitude of the input motion. The low accelerations can be attributed to the high damping ratios in the perfectly plastic constitutive model. Although the nonlinear elastic model is less complex, closer results might be obtained since the more realistic damping ratios are implemented. The results show that even the less elaborate models, such as the hyperbolic model with an indefinite failure criterion, might give reasonably accurate results in the total-stress approach, thanks to the limited damping ratios. As a result, the responses of the superstructure and the pile in soil-pile-structure interaction problems are highly dependent on the soil damping; in turn, the due account must be given to the selection of the constitutive model.