LAUSR

Screw piles have been widely used as foundations for various types of structures. Drilling velocity ratio, the ratio of rotational velocity to driven velocity, is a critical parameter that affects the driven behaviors of screw piles. Three dimensional discrete element method, with a particle refinement method to enhance computation efficiency, is used to study the driven behaviors of screw piles to compare with the laboratory mini screw pile test results achieved by Shi et al. (Rock Soil Mech 39(6):1981–1990, 2018). The driven behaviors of a mini screw pile (900 mm long and 40 mm shaft diameter) with a variable diameter auger into loose granular assemblies under 0.5, 1 and 1.5 critical drilling velocity ratios are studied. The variation of stress distribution in the assemblies, particle movement around the piles, and evolution of void ratio in the assemblies are investigated. The results indicate that particles around the piles behave differently under different drilling velocity ratios. The reduction of driven force with the increase of drilling velocity ratio can be explained using the direction of particle movement around the piles and the vertical force acting on the screw blades. It was found that under high drilling velocity ratio, higher downward vertical force can be provided by the blades.