Rate Effects Increasing Lateral Capacity of Monopiles

Lateral soil resistance is a key driver for the design of offshore wind monopile foundations but current practice does not explicitly consider the effects of loading rate. This study investigates the effect of loading rate and hence, local strain rate, on clay strength using coupled Eulerian-Lagrangian Finite Element Analyses (FEA). The effect of loading rate on monopile lateral capacity is studied for a representative Ultimate Limit State (ULS) load case at a clay dominated location in the Dogger Bank Offshore Wind Farm. Calibration and validation of the advanced strain softening rate dependent soil model is done by means of laboratory tests and full-scale spudcan penetration tests at different penetration rates. The FEA of the monopile with the rate dependent soil model showed a considerable increase in lateral resistance for the representative ULS load case when compared to a conventional analysis where the rate effect is omitted. This suggests that there may be further room for geometry optimisation if rate effects are accounted for in monopile design.