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. We describe 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 (i) analyses of monopile behaviour using detailed three dimensional
(3D) finite element analysis, and (ii) 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.