Monopile Lateral Response Calibration from in-situ Monitoring Data-Paper

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The study uses in-situ monitoring data to calibrate models of the lateral response of offshore wind turbine monopiles. Three monopiles at a Belgian offshore wind farm were instrumented with strain sensors above and below the seabed. The measurements were converted into bending-moment profiles and compared with predictions from one-dimensional beam-column analyses.<br /><br />The analyses tested API RP2 GEO and PISA response models, accounting for different seabed levels, scour protection, and soil stiffness. Because site-specific small-strain shear modulus data were limited, the researchers adjusted literature correlations between cone resistance and small-strain shear modulus using available site measurements.<br /><br />Including the surveyed seabed level and scour protection substantially improved the match between predicted and measured bending moments. PISA predictions generally matched the observations well, particularly when using the adjusted, site-specific soil stiffness values. The results support the use of PISA guidance for monopile design in the site’s overconsolidated sand and clay soils.<br /><br />Measurements after two years of operation remained broadly consistent with the initial calibrated model, indicating no significant change in pile-soil stiffness during that period. A sensitivity study found that uncertainty in soil stiffness had little effect in shallow layers, where soil resistance was highly mobilized, but mattered more at depth.<br /><br />The calibrated models provide a baseline for monitoring long-term foundation performance. Future changes in seabed conditions or soil properties, including possible effects of severe storms, could be detected by comparing new monitoring data with this baseline.

Keywords

offshore wind turbine

monopile

in-situ monitoring

bending-moment profiles

beam-column analysis

PISA model

API RP2 GEO

soil stiffness

scour protection

seabed level