Stability of submarine slopes with monopile foundations under storm conditions

Monopiles are a key foundation type for securing offshore wind turbines to the seabed. They face multiple dynamic loading conditions, especially for extreme storms. Despite much research on foundation stability, there is a lack of understanding of the interaction between monopiles and complex submarine terrains, especially regarding submarine slope stability. A coupled wave-structure-soil numerical modeling framework is used to investigate the effects of the monopile on the submarine slope stability before, during and after storms for the first time, using field data of wind and wave conditions, seabed slope, soil properties, OWT and monopile at a wind farm in the North Sea. It was found that introducing a monopile into a sloped seabed environment induces significant stress concentrations, affecting the surrounding geological strata. In addition, the installation of a monopile significantly alters the local stress-strain conditions. As storms approach, the observed peak plastic strain and displacement highlight the need to incorporate cut-off speed effects into the OWT design considerations. While soil liquefaction was not detected for the model set up of the present study, it remains a potential risk in soils with low cohesion where a thorough evaluation is required. Furthermore, increasing the diameter and depth of monopile installations was found to enhance slope stability. The present study provides new insights that submarine slope instability should be a critical consideration of OWT developers.