Auto-Calibrated Kinematic Hardening Clay Model with Application to Monopile Foundations for Offshore Wind Turbines-Paper

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The paper presents a simplified kinematic-hardening framework for modelling soil behaviour, designed to retain the history-dependent stiffness and hysteresis of multi-surface plasticity while being easier to implement numerically. Instead of using multiple yield surfaces directly in the governing equations, it introduces evolving “memory surfaces” to determine the soil’s effective stiffness. This produces a simple rate-form stress–strain model and allows calibration directly to laboratory measurements, without relying on conventional parameters such as Young’s modulus and friction angle.<br /><br />The authors develop a model for undrained, total-stress analysis of clay. Its memory surfaces use a generalized Tresca strength criterion, allowing undrained shear strengths in compression and extension to differ. Model parameters are obtained by fitting piecewise-linear stress–strain curves to triaxial test data.<br /><br />The framework is applied to a laterally loaded monopile using data from the PISA field-testing project. The model is calibrated to clay tests from different depths and used in a finite-element analysis of the pile. The predicted load–displacement response agrees well with the available test results, including the initially stiff response and subsequent stiffness reduction as yielding spreads around the pile.<br /><br />The authors note that the field tests included pauses during which creep and pore-pressure dissipation occurred, affecting the measured response. They also caution that success for the slender pile studied does not establish performance for other pile geometries. The analysis reaches nominal failure only at very large displacements, beyond the reliable range of a standard small-deformation analysis.

Keywords

kinematic hardening

soil behavior

memory surfaces

multi-surface plasticity

undrained clay

Tresca criterion

triaxial test calibration

PISA field testing

monopile analysis

finite element modeling