Abstract: Based on particle flow theory, the laws of soil plug formation, meso-structural changes of sand soil particles and stress field distributions of soil around pile are studied by using PFC2D to simulate and reconstruct the process for different types of open-ended pipe piles driven into sand soil. In addition, the macro-mechanical response is exposed by analyzing the variation of mesomechanical parameters. The results show that the soil plug effect is largely affected by the pipe diameter, for pipe pile of 30 mm outer diameter driven into sand soil, the value of the incremental filling ratio（IFR）is small, so the soil plug effect is significant and the height of soil plug is small, whose sinking mode is similar with close-ended pipe pile. While with the increase of pipe diameter, the plugging effect decreases rapidly, for the large diameter pipe, the sand soil in the pile is not plugged completely. The mesomechanical parameters such as porosity and sliding fraction have obvious corresponding relation with soil macro displacement; and based on this, soil around pile is divided into three regions. The horizontal stress, the vertical stress and the shear stress of soil around pile are formed the "stress nucleus" at pipe pile bottom during driving process, the stress field distributions of soil are close for different types of open-ended pipe piles.

Key words: sand soil, open-ended pipe pile, soil plug effect, particle flow, mesoscopic, stress field