DEM study of particle scale and penetration rate on the installation mechanisms of screw piles in sand

Screw piles are efficient anchors to sustain large uplift loads and can be installed with low noise or vibration. Screw piles dimensions are currently increasing, renewing research interest to reduce the installation requirements (torque and crowd or vertical force). The Discrete Element Method (DEM) is an ideal technique to investigate the complex soil behaviour during screw pile installation. Different techniques such as particle upscaling or increase of pile penetration rate have been used to reduce the CPU time to more acceptable durations (e.g. few days or weeks). This paper investigates how such techniques can affect the accuracy of the results and change the installation mechanisms. Results show that maintaining a low particle scaling factor is essential to reproduce the correct mechanism at low pile advancement ratio (AR, defined as the vertical displacement per rotation divided by the helix pitch). The pile overflighting (AR≤1) creates an upwards movement of particles, which in turn creates some tension in the pile. Smaller advancement ratios require smaller particles to accurately capture this effect. Results also show that the pile penetration rate must be maintained relatively low to avoid spurious inertial effects.