An alternative p-y model for the simulation of large diameter offshore monopiles for wind turbines founded on granular soils under monotonic and cyclic loading

Abstract

The offshore wind energy industry has exponentially grown during the past decades. Monopiles with large diameters and reduced slenderness ratios are the most common foundation solutions for Offshore Wind Turbines. Such monopile foundations behave differently from the long slender piles with small diameters, for which the current design standards were developed. Therefore, further investigation on the behavior of monopiles needs to be conducted, so new design and modelling methods are proposed and applied in the engineering practice. In the present work, the behavior of laterally loaded monopiles in sands is investigated using a numerical approach based on three-dimensional (3D) Finite Element (FE) modelling and one-dimensional (1D) finite difference modelling. A series of 3D FE simulations of laterally loaded monopiles were conducted accounting for variations of pile geometry, soil properties and loading cases. Hypoplastic constitutive models were used to simulate the behavior of the soil supporting the monopiles. The simulations results were used to propose and calibrate a novel p-y model for large diameter monopiles based on the 1D Beam on a Non-linear Winkler Foundation approach. The model was formulated considering new distributions for the ultimate soil resistance and the initial subgrade modulus along depth, as well as a base shear force and a factor that accounts for the effects of soil density and loading amplitude on the accumulation of pile displacements under cyclic lateral loading conditions. At the end, the performance of the proposed model was evaluated through comparisons with a field test and a centrifuge test.