Examination of the reduction in natural frequency of laterally loaded piles due to strain-dependence of soil shear modulus

Society's transition to low-carbon energy sources has resulted in significant expansion offshore wind technology. Most turbines (OWTs) are founded on large-diameter steel tubular piles driven into the seabed, termed monopiles. OWTs subjected large numbers of dynamic and cyclic environmental loads during their lifetime. To avoid fatigue or resonance issues, accurate characterisation soil-structure interaction under operating extreme conditions is paramount. There a need further improve understanding lateral response after load cycling (storm events). This paper presents results field tests with two different slenderness ratios, where natural frequency was measured series applied load-unload events. 1D numerical models were developed several parameters varied identify importance nonlinear soil-pile interaction. Approaches estimate soil shear modulus both in-situ post trialled, five subgrade reaction used couple pile properties, ascertain performance at predicting frequencies from experiments. Results suggest that predicted highly sensitive choice model degradation method used.