On the Modelling of Pore Pressure Developments Below Cyclically Loaded Offshore Gravity Foundations-Article

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The paper presents a method for modelling excess pore pressure (EPP) beneath offshore gravity foundations subjected to irregular cyclic loading. In saturated sand, cyclic loading can generate pore pressure, while drainage and resulting densification alter the soil’s response over time. These processes make pore pressure strongly dependent on the sequence and variability of loads, so simplified regular or equivalent load histories may not capture peak pressures reliably.<br /><br />The method is applied to a 30 m diameter gravity foundation supporting an 8 MW offshore wind turbine on medium-dense sand. Wind, wave and turbine loads are derived in the frequency domain using appropriate spectra, then converted into time histories with random phases to represent realistic load irregularity. The resulting cyclic loads are combined with soil stress ratios and input to the DCycle model, which represents pore-pressure generation, dissipation and densification using a one-dimensional consolidation model with three-dimensional dissipation. The approach is explicit and does not account for stress redistribution, so its EPP estimates may be conservative.<br /><br />Simulations show that pore pressures fluctuate with individual load cycles and that dissipation and densification can reduce further pressure generation during a storm. Crucially, different random realizations of the same storm produce substantially different maximum EPPs. A single load simulation therefore cannot provide a reliable estimate. The authors recommend generating many realizations for each storm and using the resulting distribution—such as its 90th-percentile value—to inform foundation stability assessments.<br /><br />The method incorporates real storm histories and irregular loading, but requires further validation against laboratory or field measurements. The authors also recommend developing a probabilistic design approach and coupling empirical pore-pressure modelling with constitutive soil models to account for changing stress distributions.

Keywords

excess pore pressure

offshore gravity foundations

irregular cyclic loading

saturated sand

pore pressure generation

dissipation

densification

DCycle model

offshore wind turbine

probabilistic design