A numerical methodology to predict the lateral load response of monopiles installed in SAND considering soil stiffness degradation

Abstract

Most of the routine work concerning the design of laterally loaded monopile foundations is conducted using simplified one-dimensional (1D) models based on p-y curves. However, many of these curves have been derived from slender piles typically used in the oil and gas industry, which behave differently than rigid monopiles used as offshore wind turbine foundations. Moreover, these curves usually represent the soil response without considering its degradation, which may significantly modify the monopile lateral response. Hence, this work proposes a numerical methodology based on the finite element method to derive suitable curves for 1D models of monopiles installed in sand. First, a three-dimensional (3D) finite element model (FEM) of the monopile and the surrounding soil was constructed. In this model, the monopile had an elastic and linear material behavior. The soil response was addressed using the Mohr-Coulomb criterion combined with three different soil stiffness degradation models. For extracting the p-y curves from the 3D FEM, a 10th-order polynomial was used to fit the bending moment profiles; consequently, an 8th-order polynomial described the soil reaction profiles. Results obtained using the proposed 3D FEM and a 1D model based on the derived p-y curves were then verified against experimental results obtained through centrifuge modeling. Furthermore, the proposed 1D model adequately matched the experimental results, especially for small displacement conditions.