3D numerical analysis of screw pile subjected to axial compressive and lateral load

Onshore wind turbine foundations are typically subjected to lateral wind load and axial compressive load from the superstructure. The concrete gravity type foundation and precast or cast-in-situ piles are conventionally used as a foundation for wind turbines. However, they involve higher material costs for gravity type foundation and are not environmentally friendly as they have a greater carbon footprint. They also produce greater spoil during installation for cast-in-situ piles, or noise and vibration for driven piles. In the present study, screw piles are considered to be an alternative to the existing concrete foundations for wind turbines. A three-dimensional numerical analysis is carried out to analyse the screw piles behaviour under the combined lateral and axial loading in loose sand. The screw pile is considered to be wished-in-place. The soil is modelled assuming the Mohr-Coulomb constitutive relationship and the screw pile modelled assuming the linear-elastic behaviour. The performance of the screw piles is studied in terms of their load-carrying capacity and the yield envelopes are developed. The effect of the helix spacing, helix number, and the effect of axial compressive load on lateral capacity are studied. Finally, the behaviour of screw piles is compared to the solid straight shaft concrete piles. Results show that the performance of the screw piles considered per unit weight of the foundation is much better than the conventional concrete piles. Hence, the screw piles could be used as a potential alternative foundation for the wind turbines.