Accumulation of lateral pile displacements under general one- and two-way cyclic loading - Part 2
Final Report Abstract
Large diameter piles are often employed to transfer horizontal or lateral loads. Such loads are typically variable and must therefore be considered cyclic. This applies in particular to offshore piles, primarily subjected to intensive cyclic loading, i.e. high number of load cycles, mainly due to wind and wave action. A result of pronounced cyclic loading is the accumulation of permanent deformations, which can ultimately lead to tilting. The prediction of such permanent tilting is of great practical relevance, especially in the design of monopile foundations for offshore wind turbines. For one-way loads (swell loads) with complete unloading, the expected tilting can yet be predicted relatively well, e.g. by means of numerical models. However, for general swell and alternating loads, which must usually be taken into account in the design of offshore foundations, there were still considerable uncertainties. These were mainly related to the qualitative and quantitative influence of the load type, i.e. the ratio of cyclic minimum to maximum load, for different load magnitudes and variable system boundary conditions. In the context of this project, comprehensive and systematic 1g model tests were conducted to clarify the system and load variables on which the accumulation rate of a cyclically laterally loaded pile in non-cohesive soil significantly depends. In a first step, a simple empirical approach was determined to estimate the accumulation rate for the reference case of one-way loading with complete unloading. Afterwards, this was extended by a load type function, which allows arbitrary (one-dimensional) loading conditions as well as other relevant load and system boundary conditions to be taken into account. In addition, small-scale "illustrative experiments" were conducted, analysing and visualising the processes in the sandy soil around laterally loaded piles using Particle Image Velocimetry (PIV). The results of these investigations provide initial explanation of the phenomenological causes of different accumulation rates under variable load conditions.
Publications
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Model tests on the behaviour of monopiles under general cyclic lateral loading. Proceedings of the 2nd International Conference on Natural Hazards & Infrastructure (ICONHIC). National Technical University of Athens, Athens, Greece.
Frick, D. & Achmus, M.
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Model tests on the displacement accumulation of monopiles subjected to general cyclic loading. In: Goseberg, N.; Schlurmann, T. (Hg.): Coastal Structures 2019. Karlsruhe: Bundesanstalt für Wasserbau. 913-922
Frick, D. & Achmus, M.
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On the design of monopile foundations for monotonic and cyclic loading. 7th Int. Conf. on Structural Engineering, Mechanics and Computational Engineering (SEMC), Cape Town, South Africa, 2-4 September.
Achmus, M.
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An experimental study on the parameters affecting the cyclic lateral response of monopiles for offshore wind turbines in sand. Soils and Foundations, 60(6), 1570-1587.
Frick, Dennis & Achmus, Martin
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A model test study on the parameters affecting the cyclic lateral response of monopile foundation for offshore wind turbines embedded in non-cohesive soils. Presentation at the Wind Energy Science Conference 2022, Hannover, Germany, 25. – 28. May.
Frick, D.
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A model test study on the parameters affecting the cyclic lateral response of monopile foundations for offshore wind turbines embedded in non-cohesive soils. Wind Energy Science, 7(4), 1399-1419.
Frick, Dennis & Achmus, Martin
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„On the displacement accumulation of monopiles under cyclic lateral loading“ (Arbeitstitel), Einreichung bei der Fakultät für Bauingenieurwesen und Geodäsie der Leibniz Universität Hannover geplant für Frühjahr 2024.
Frick, D.
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Application of Particle Image Velocimetry for the Visualization of Soil Deformation Processes due to Cyclic Lateral Loading of Rigid Piles. Geotechnical Testing Journal, 48(3), 325-345.
Frick, Dennis; Hansmann, Dennis & Achmus, Martin
