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Suction caisson jackets are promising foundation solutions for offshore wind turbines (OWTs) in deep water. The resistance of such a foundation against overturning actions depends on the uplift response of individual caisson. Winkler models (i.e., foundation displacement versus soil reaction relationships) have been shown powerful and efficient in modeling general soil–foundation interactions, whereas those targeting suction caisson subjected to tensile loading are relatively underdeveloped. The goal of this study was to construct a soil reaction model capable of accounting for site-specific soil stress–strain relations and project-specific foundation geometries. This objective is pursued via the concept of "inferred Winkler model" and by constructing soil reaction curves based on the outcomes of rigorous numerical modeling. First, finite element analyses (FEAs), in combination with a well-established hyperbolic soil model, are utilized to evaluate the soil reaction responses associated with vertically loaded caisson in undrained clays. The FEA then establishes the interrelationships between the key characteristics of soil reaction behavior, soil stress–strain relations, and foundation geometries, leading to an inferred Winkler model capable of directly utilizing soil model parameters. Lastly, the proposed soil reaction model is assessed against centrifuge test results and shown capable of reasonably representing test observations and delivering solutions comparable to FEA but at a much lower computational cost. [ABSTRACT FROM AUTHOR]

Pile foundations supporting long-span bridges, offshore platforms and offshore wind turbines often suffer from repeated lateral loads due to wind, waves and currents. To predict the degradation of the pile's lateral resistance and cumulative lateral deformation through cyclic loading, a theoretical cyclic p-y model is derived for a laterally loaded pile in undrained clay, formulated within the framework of the bounding-surface elastoplastic theory. Unlike the conventional p-y curves which models the degradation of the pile's lateral resistance based on the cycle number and amplitude, bounding surface contraction is employed in this study to model the softening of the soil resistance during laterally cyclic loading. To ensure practicability, the softening model parameter can be easily calibrated by the in-situ T-bar testing technique. A series of verifications with centrifuge tests having various pile-head conditions, pile-soil relative stiffness and load amplitudes are performed. The good agreement demonstrates its ability to predict the degradation of pile lateral resistance. • A cyclic p-y model based on the bounding-surface elastoplastic theory is formulated for a laterally loaded pile in clay. • The lateral stiffness degradation is modeled by the contraction of bounding surface due to the accumulated plastic strain. • The soil softening model based on in-situ T-bar testing technique is introduced to describe the contraction process. • Verifications with centrifuge tests are performed. [ABSTRACT FROM AUTHOR]

Rigid foundations supporting offshore wind turbines (OWT) like short piles and caissons can sustain multi-directional lateral loading. Moreover, the monotonic and cyclic response of these foundations can be affected by recent loading history aligned along directions different from the present one. To represent such recent loading history effects, a multi-directional p-y model is proposed for rigid foundations in undrained clays. The model is constructed by extending the uni-directional p - y model previously proposed by the authors based on Total-displacement-loading Extended Mobilisable Strength Design (T-EMSD) approach, and thus considering site-specific soil stress-strain relations and foundation geometries. The crux of the extension is to combine bounding surface plasticity and radial mapping with a moving projection center. The former effectively couples p - y response along orthogonal directions, while the latter is crucial for representing the influences of loading direction reversal and recent loading history effects. The proposed p - y model is evaluated against existing centrifuge tests and finite element analysis (FEA) of this work. Lastly, the proposed p - y model and FEA are used in parallel to highlight the effects of loading path rotation on monotonic and cyclic accumulative foundation response. These comparative analyses indicate that the proposed p-y model can reasonably represent recent loading history effects. • Multi-directional p-y model is proposed for recent loading history effect. • Loading path rotation on monotonic and cyclic response of OWT foundation is studied. • p - y model captures recent loading history effect from centrifuge tests and FEA. [ABSTRACT FROM AUTHOR]

The small-strain performance of offshore wind turbine (OWT) pile foundations under lateral loading is critical for the foundation safety and the fatigue analysis of superstructure but is less explored in recent studies. This work presents p-y curve analyses of monopiles in marine clay that account for complete nonlinear soil stress–strain relationship. Based on a small-strain stress–strain relation, Total-displacement-loading Extended Mobilisable Strength Design (T-EMSD) analyses are performed to interpret the pile-soil interaction. On the basis, an analytical p-y curve model is proposed. An elastoplastic constitutive model with small-strain non-linearity is developed, and then p-y curve validation against finite element simulations is carried out. Furthermore, by comparing to centrifugal test observations and existing p-y models, good agreement and noticeable improvement are shown. This paper provides industry engineers with a timely and effective approach for OWT foundation design, allowing for inputting soil characteristics measured at in-situ site and laboratory. [ABSTRACT FROM AUTHOR]