Predictions of Multi-Amplitude Simple Shear Tests Using Hyperplasticity Models-Paper

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The study evaluates whether a total-stress hyperplasticity model can predict the response of overconsolidated clay to irregular, multi-amplitude cyclic loading relevant to offshore wind turbine monopiles. Such real-world loading is often simplified into constant-amplitude cycles by conventional design methods, potentially losing important effects of load magnitude, reversal, and sequence.<br /><br />Researchers used the model to make “Class C” predictions of direct simple shear tests conducted within the WAS-XL project. The model was calibrated using separate monotonic and fixed-amplitude cyclic tests on the same clay, without access to the multi-amplitude test results. It represents nonlinear stress–strain behaviour, rate effects, cyclic softening, and strain accumulation (ratcheting).<br /><br />The predictions broadly reproduced measured strain development, hysteresis-loop shapes, and ultimate strains. The model also captured abrupt strain increases when loading exceeded previous maximum stresses. However, accuracy generally declined at higher stress levels: ultimate strains were often underpredicted, and some strain accumulation and stiffness changes were not represented well.<br /><br />A revised “Class C.1” version, adjusted using evidence from the multi-amplitude tests, improved predictions by softening the backbone response at high stresses, adding global softening, and reducing the stress-level dependence of ratcheting. These adjustments highlighted the sensitivity of predictions to model assumptions and calibration data.<br /><br />Overall, the results suggest that hyperplasticity models can efficiently predict complex cyclic loading histories using calibration from simpler tests. Reliable application depends on calibration tests covering stress conditions similar to those expected in practice. Further work is needed, particularly to improve predictions of stiffness reduction and softening at high stress levels.

Keywords

hyperplasticity

overconsolidated clay

cyclic loading

offshore wind turbine monopiles

direct simple shear

WAS-XL project

ratcheting

cyclic softening

stress-strain behavior

Class C prediction