Downdrag Force Analysis for Seismic Soil–Pile–Structure Interaction

Earthquake can cause settlement of soil being greater than that of the pile. The pile is pulled down by the soil, and negative friction force is produced on the pile side. The carrying capacity of pile will be reduced because of the negative friction force, which may cause engineering instability. In this paper, the nonlinear and finite difference program FLAC3D was used to evaluate the mechanical behavior of soil–pile interaction under seismic dynamic loading. The response of the pile side friction force, pile axial force, and soil deformation to the seismic loading were analyzed. The distribution of the negative and positive pile side friction forces, the axial force of pile were found to be varied during the period of applying seismic loading. In addition, it was observed that seismic loading had a significant effect on the vertical and horizontal displacement of soil, and the variations of which with the duration of seismic loading were non-monotonic. An increase or a decrease in soil deformation induced by seismic loading appeared alternately due to the alternate dominant function of compression effect and stretching effect. © 2016, Springer International Publishing Switzerland.