Abstract: The performance of small-scale model piles embedded into red clay and tested under cyclic axial loadings is presented in this paper. The influences of cyclic loading levels and rates on long-term dynamic behaviors of pile are observed, and the mechanics of accumulated settlement is analyzed from the views of shear stiffness softening and skin friction degradation. Furthermore, the modified Hardin-Drnevich (H-D) model, being capable of reflecting the fatigue degradation of shear stiffness, is achieved in the FLAC3D, and the behavior of shear resistance degradation during quasi-static cyclic shearing under constant normal stiffness (CNS) condition is numerically investigated. Results indicate that the growth pattern of the permanent deformation is significantly affected by the cyclic loading amplitude; and the pile dynamic stiffness experiences a significant decrease in a short transition period, after which it remains invariable with cycles. The excess pore pressure caused by the shaft vibration is rather small; and the induced effective stress reduction can not sufficiently result in large friction degradation. The dynamic stiffness and acceleration of pile top increase simultaneously with the loading rates. With the modified H-D model re-developed in FLAC3D, the hysteresis curve of an easy case is well consistent with the theoretical result, which verifies the credibility of the program.

Key words: single pile, clay, dynamic model testing, cyclic behavior, pile-soil interface, fatigue degradation