Testing and modelling of cyclic monopile behaviour in sand: highlights and insights from the MIDAS project

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4. Testing and modelling of cyclic monopile behaviour in sand: highlights and insights from the MIDAS project

This paper summarizes the main outcomes of the recent MIDAS project. MIDAS was executed between May 2020 and July 2024, led by TU Delft in collaboration with Deltares and NGI, with the support of several offshore industry partners. By combining advanced physical and numerical modelling, the ultimate goal of the project was to devise a new cyclic soil reaction model for the 1D analysis of cyclically loaded monopiles in sandy soil as well as suitable, practice-oriented recipes for model parameter calibration. The main activities of MIDAS included: (i) conducting scaled testing of cyclic monopile-soil interaction using the two centrifuge facilities available at TU Delft and Deltares; (ii) calibration of an advanced 3D FE model, which incorporates the SANISAND-MS model, against centrifuge test data, and its use to perform 3D numerical parametric studies and infer general features of cyclic behaviour; (iii) synthesizing experimental and numerical results to develop and calibrate the mentioned cyclic soil reaction model.

The MIDAS centrifuge datasets provide quantitative information regarding the sensitivity of cyclic monopile response to various geometrical, geotechnical, and loading factors. These factors include piles size and aspect ratio, sand density and its interaction with pore fluid, cyclic loading amplitude/asymmetry and sequence. The main features of observed monopile behaviour are captured through a new soil reaction model. This model combines the memory-enhanced bounding surface plasticity framework with previous insights on the necessity of multi-component soil reaction modelling. Mini-CPT test data obtained in the centrifuge before pile loading enabled the derivation of practical empirical relationships for CPT-based calibration of all model parameters.

While ongoing work focuses on further validation against additional experimental datasets, the paper concludes by linking MIDASs achievements to new research initiatives on cyclically loaded monopiles in clayey soil and under seismic loading.

5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG2025)

9 - Monopile design to cyclic loads: quasi-static, dynamic and seismic loads