Application of the PISA design model to monopiles embedded in layered soils

Abstract

The PISA design model is a procedure for the analysis of monopile foundations for offshore wind turbine applications. This design model has been previously calibrated for homogeneous soils; this paper extends the modelling approach to the analysis of monopiles installed at sites where the soil profile is layered. The paper describes a computational study on monopiles embedded in layered soil configurations comprising selected combinations of soft and stiff clay and sand at a range of relative densities. The study comprises (a) analyses of monopile behaviour using detailed three-dimensional (3D) finite-element analysis, and (b) calculations employing the PISA design model. Results from the 3D analyses are used to explore the various influences that soil layering has on the performance of the monopile. The fidelity of the PISA design model is assessed by comparisons with data obtained from equivalent 3D finite-element analyses, demonstrating a good agreement in most cases. This comparative study demonstrates that the PISA design model can be applied successfully to layered soil configurations, except in certain cases involving combinations of very soft clay and very dense sand.

Simplified Method for the Lateral, Rotational, and Torsional Static Stiffness of Circular Footings on a Nonhomogeneous Elastic Half-Space Based on a Work-Equivalent Framework

“…The first two soil profiles correspond to multi-layered clay soil profiles that are representative of realistic ground conditions for offshore wind farm sites (Burd et al 2020). The first soil profile The remaining eight soil profiles correspond to three-layered soil profiles similar to those investigated by Poulos (1979) for his comparisons of solutions for settlement of piles in layered soil.…”

Zur Anwendung der Erdwiderstandsmodelle von p‐y‐Kurven und nach DIN 4085 zur lateralen Pfahlbemessung in geschichteten Böden

“…Diese Differenzen traten dann auf, wenn der Baugrund aus einem Profil aus sowohl tragfähigen als auch nicht tragfähigen Böden bestand. Die Autoren [24] fassen zusammen, dass in fünf Fällen nach der FEM durch einen tieferliegenden dicht gelagerten Sand eine Zunahme der Bettungsspannung des aufliegenden weichen bindigen Bodens festgestellt wird, was durch das PISA-Verfahren nicht abgebildet wird. In vier weiteren Fällen wird dagegen eine Überschätzung der durch das PISA-Verfahren prognostizierten Bettungsspannungen festgestellt.…”

Editorial: geotechnical design for offshore wind turbine monopiles

“…The key research achievement from the project was the development of new methods to capture accurately the detailed monopile soil-structure interaction behaviour, facilitating site-specific and turbine support structure-specific optimisation. These developments were achieved by a wide range of connected activities: (a) site investigation and soil characterisation (Zdravković et al, 2020a), (b) numerical modelling, employing sophisticated three-dimensional finite element analysis (Zdravković et al, 2020b;Taborda et al, 2020), (c) theoretical developments including simplified design procedures (Byrne et al, 2020b;Burd et al, 2020bBurd et al, , 2020c, and (d) a comprehensive medium scale field pile testing campaign to validate the new design methods (Burd et al, 2020a;Byrne et al, 2020a;McAdam et al, 2020).…”

“…The 1D PISA design model, which is an extension of the p-y approach in which the additional soil reaction curves are applied (Byrne et al, 2020b;Burd et al, 2020bBurd et al, , 2020c, is regarded as a key advance. The model is ideally suited to computational requirements for monopile optimisation and offshore wind farm design.…”

“…The PISA design model can be applied to a range of common soil types found in the offshore environment. It is demonstrated firstly for homogeneous clay and sand soils (Byrne et al, 2020b;Burd et al, 2020b) and then further developed to account for typically-encountered layered soil profiles (Burd et al, 2020c). In the form presented in the current issue the model is applicable to monotonic loading only, though future extensions to cyclic loading are planned.…”