Frequency effects in the dynamic lateral stiffness of monopiles in sand: insight from field tests and 3D FE modelling

With the offshore wind industry rapidly expanding worldwide, geotechnical research is being devoted to foundation optimisation - most intensively for large-diameter monopiles. The analysis and design of monopiles still suffers from significant uncertainties in relation to cyclic/dynamic loading conditions. The aim of this work is to shed new...

Seismic inversion of soil damping and stiffness using multichannel analysis of surface wave measurements in the marine environment

Determination of soil material damping is known to be difficult and uncertain, especially in the offshore environment. Using an advanced inversion methodology based on multichannel spectral analysis, Scholte and Love wave measurements are used to characterize subsea soil from a North Sea site. After normalization, a determinant-based objective...

Dynamic soil stiffness for foundation piles: Capturing 3D continuum effects in an effective, non-local 1D model

A method is presented to accurately capture the 3D interaction phenomena of a foundation pile embedded in soil, in a computationally efficient non-local 1D model. It is shown how to extract the global stiffness kernels from simulations with the 3D inhomogeneous continuum, and implement them in a 1D non-local Winkler-type model that can...

Effective soil-stiffness validation: Shaker excitation of an in-situ monopile foundation

In an attempt to decrease the modelling uncertainty associated with the soil-structure interaction of large-diameter monopile foundations, a hydraulic shaker was used to excite a real-sized, in-situ monopile foundation in stiff, sandy soil in a near-shore wind farm. The response in terms of natural frequency and damping of a pile-only system...

Effective stiffness method for rigid monopile foundations of offshore wind turbines and in-situ validation

It is widely accepted that the initial stiffness derived with the p-y methodology as prescribed by the American Petroleum Institute does not capture the true small-strain stiffness for rigidly behaving piles. We present an alternative method, capturing the 3D effects in the soil-pile interaction, in which the soil is characterized with in-situ...

A method for identification of an effective Winkler foundation for largediameter offshore wind turbine support structures based on in-situ measured small-strain soil response and 3D modelling

A procedure is presented for the derivation of an effective small-strain soil stiffness governing the soil– structure interaction of large-diameter monopiles. As a first step, geophysical measurements are used to estimate the depth-dependent shear modulus G of the soil stratum. The second step is to use this modulus and an estimated Poisson’s...

Method for extracting an equivalent Winkler model of the 3D dynamic soil-structure interaction of large-diameter offshore monopile foundations

The motivation for this work stems from the offshore wind industry, where designers are faced with a discrepancy between the available design methods and the typical dimensions of the offshore wind foundations that call for other design approaches. Throughout the years, much valuable work has been performed in the prediction of long, slender,...

Assessing the small-strain soil stiffness for offshore wind turbines based on in situ seismic measurements

In this contribution, in situ seismic measurements are used to derive the small-strain shear modulus of soil as input for two soil-structure interaction (SSI) models to assess the initial soil stiffness for offshore wind turbine foundations. This stiffness has a defining influence on the first natural frequency of offshore wind turbines (OWTs),...

Estimation of the vibration decrement of an offshore wind turbine support structure caused by its interaction with soil