Centrifuge modelling for seismic response of single pile for wind turbine subjected to lateral load

Abstract

The soil around the pile foundations of offshore wind turbines (OWTs) would suffer from earthquakes which are widely believed to undermine the bearing capacity and serviceability of foundations. The non-intermittent lateral environmental loads in the ocean (e.g., wave, wind, and current) continuously act on OWTs. However, the seismic response of pile foundations and the soil around is less clear when considering the OWTs are subjected to lateral environmental loads. This paper presents two sets of centrifuge modelling tests on single piles, with a prototype diameter (D) of 1.5 m and a first-order natural frequency highly comparable to that of a prototype wind turbine. Two model piles with the same dimension and stiffness, but one with a lateral load on the pile head, were both installed in a dry sand ground and a saturated sand ground. Owing to the fact that the lateral load increased the initial static shear stresses of the soil in front of the pile, the development of excess pore pressure was inhibited and the permanent ground lateral displacement was accumulated during shaking. The existence of the lateral load led to a pile head displacement as much as 34 cm and increased the bending moment along the pile up to 6 MN·m. Moreover, the seismic response of piles and soils were compared between the dry sand ground and saturated sand ground to clarify the influence of excess pore pressure. It was also found that the residual bending moment after unloading the pile was still very large up to 17 MN·m because of the rebalanced soil-pile interaction. These findings highlight the necessity to consider the lateral load effect in the seismic design of pile foundations for OWTs.