Revision and application of the P-Y curves to monopile foundations in cohesionless soil

Monopiles are used as foundation for offshore wind turbines, and are open-ended steel pipe piles with large diameters. For the offshore wind energy converters of 5 MW and higher, the pile diameter may be greater than 5 m. The p-y curve method has been used extensively for the design of pile foundation design and the p-y curves for piles in cohesionless soil are determined based on field test results with a pile diameter of less than 2 m, and less than 200 cycles under cyclic loading conditions. Therefore, some modifications of p-y curves need to be considered for the monopile foundation designing of offshore wind turbine. The suitability of p-y curves for designing monopile foundation is reviewed in this study. The reduction of the subgrade reaction modulus due to pile diameter, the effect of high-cycle of cyclic lateral load and scour around the monopile are considered in the modifications of p-y curves. The deformations calculated with unmodified p-y curves seem to be under estimated.