Abstract: As a fully displacing pile, screw piles have been widely used in various engineering construction projects. The particle breakage behavior induced by screw pile drilling in crushable sands such as calcareous sand was simulated using discrete element method. Fragment replacement method and octahedral shear stress breakage criterion were adopted for the simulations. The distributions of soil displacement, velocity, stress, and particle fragmentation evolution during pile penetration were numerically analyzed in consideration of different initial stress levels and different penetration velocity ratios. The simulations revealed that in the process of pile drilling, soil particles crushed due to high stress; in particular, particles at the end of pile crushed more severe than those at pile side. As the pile drilled deeper, the number of crushed particles increased, and the particle gradation at pile side changed. The pile tip stress in the simulation case of breakable sand was slightly lower than that of non-broken sand. The increase of initial stress level led to more severe particle breakage, wider particle dispersion range and also significantly smaller pile tip stress. Higher penetration velocity ratio helped increasing the degree of particle crushing. Under high penetration velocity ratio, particle fragments evenly distributed surrounding the pile side, and the particle velocity and displacement near the screw threads were large; under low velocity ratio, the peak particle velocity and displacement mainly concentrated at the bottom of pile tip. The research on drilling characteristics of screw piles in crushing granular materials is of guiding significance for the study of pile foundation stability and construction safety in fragile sandy soil.

Key words: screw pile, particle breakage, DEM simulation, calcareous sand, drilling characteristics