Localized erosion of an offshore wind-turbine foundation

Description of the Problem

Suction foundations for offshore wind turbines can have a significant risk of erosive failure. Nevertheless, this type of marine foundation is gaining growing relevance as an environmentally friendly alternative to monopile foundations. However, if the operating suction exceeds a critical threshold during the suction-driven installation, the large hydraulic gradients within the flow network imposed in the seabed may cause piping failure (i.e. a localized erosion of soil channels), which would negate the hydraulic seal of the bucket and prevent further installation.

Scientific Relevance and Impact

For complex marine soils with markedly layered properties and/or effective intergranular cementation, deriving simple analytical solutions for the critical suction threshold is often impossible. Instead, physical tests or predictive numerical simulations are used. Unfortunately, the local fluidization occurring during piping often occurs at the grain-scale, which is not tractable with the conventional macromechanical simulation methods employed for engineering problems. Failure-triggering events often originate micromechanically (e.g. fluidization at the soil grain scale) while the load-bearing engineering application must remain in equilibrium with the external solicitations at macroscopic spatial scales.
Thus, this LHC shall produce a demonstrator of 3D particle-resolved simulation approaches for a real-scale geotechnical application, focusing at first on model validation with available experimental results (physical model tests in reduced scale), and then on a grand application focusing on a representative cut of the full-scale foundation during the first meters of the suction-driven installation. It shall elucidate the unseen microscopic physics of localized erosive failure of large offshore foundations. Moreover, the code will be developed into an open-source tool for accurate, efficient numerical studies of particle-laden flows, so that it can also be used and extended to other applications beyond this case.