Vertical and Lateral Capacity of a Monopile in Layered Soils Using 3D Finite Element Analyses

During the initial design phase of a monopile foundation for offshore wind turbines it is necessary to estimate its vertical capacity and more importantly the lateral one, together with its initial stiffness from the relevant response curves. In this paper, the vertical and lateral capacities of a large diameter monopile passing through a loose sand layer and penetrating a dense one are evaluated. 3D Finite Element (FE) pushover analyses were conducted using two different constitutive models, namely the advanced SANISAND and the standard linear-elastic perfectly-plastic model with a Mohr-Coulomb failure criterion. Soil properties like the shear modulus and friction angle were matched in both sets of analyses, while additional parameters required for SANISAND were adopted from previous literature. It is shown that the vertical and horizontal response obtained with the constitutive models above were in a fair agreement, thanks to the proper calibration of the constitutive parameters. Nonetheless, some discrepancies arose in the vertical response of the soil-monopile system, which may be attributed to the different formulation of the plastic volumetric strains in the constitutive models.