Abstract: Multistage rotated-expanded pile carrying vertical load are simulated using DEM software PFC^2D to reveal the bearing behaviors and the interaction between pile and soil. Test results show that: (1) With the increase of load in the process of loading, the side friction of the upper part of pile, the friction of diameter-expanding segment of pile, and the pile tip resistance plays the role of bearing in turn. (2) When the load is small, load is mainly composed of side friction of pile; with the increasing of load, the diameter-expanding segment of pile undertakes a rapidly increasing rate of the load; and when the load continues to increase, the increment is mainly and increasingly undertaken by pile tip resistance. (3) With the increase of load in the process of loading, the porosity of surrounding soil, the coordination number between the levels of soil, the horizontal and vertical stresses of pile, and the soil particle displacement surrounding pile are in regular changes.

Key words: multistage rotated-expanded pile, particle flow, bearing behaviors, meso-study, 2D discrete element