- gr8-geo
- Mar 4, 2024
- 1 min read
Sneak peek 📢 ! Check out our contribution to the Special Issue of Ocean Engineering: "State of Practice – Geotechnical Considerations for Offshore Wind" in the link below (limited free access until April 19th).
The paper presents the results of 3D coupled cyclic time history numerical analyses of a monopile supporting a 12Â MW Offshore Wind Turbine, installed in dense cohesionless soils and subjected to a 600-s load history corresponding to the high phase of a 35-h design storm. The goal of the study is to investigate the governing mechanisms and gauge potential conservatisms or uncertainties in approaches for monopile analysis used in practice. The Ta-Ger constitutive model, implemented in FLAC3D and calibrated against site-specific cyclic tests, is used to model the complex soil response. Emphasis is placed on the effect of drainage conditions, an aspect typically overlooked in practice, although often stated as critical. Analyses show that the drainage of the system can substantially affect the response. In low-permeability soils (e.g., cohesionless soils with low-plasticity fines) widespread liquefaction may occur inducing high rotations above allowable limits. On the contrary, systems that can drain effectively within each cycle, develop moderate excess pore pressures which do not jeopardize performance. Current design procedures are often unable to accurately capture these effects possibly leading to either conservative or unconservative outcomes. Suitably validated advanced numerical analyses can be used as complementary tools to standard methods to assess these uncertainties.