Growth through Research, development & demonstration in Offshore Wind

Project:

Tubular Pile Pull-out Testing Program II (TPPT-II)

Analysis of static and dynamic tensile test data from four tubular mooring piles for floating offshore wind

WHY

Open-ended steel pipe piles are commonly used to support jacket and floating structures in the offshore oil & gas sector. This solution is also attractive for the renewable energy sector, in particular for offshore wind. A floating offshore wind farm may include several hundred anchor points, which may be driven piles. The wind turbine and environment cause both static and dynamic loads on the anchor points. The current best practices for driven anchor piles were developed in the 1980s and applied to permanently moored offshore oil and gas systems such as CALM buoys and manned FPSOs. However, load cases that include predominantly cyclic loads in full tension are not considered by the existing anchor pile design guidelines. Anchor pile design parameters are currently based on conservative guidelines. The soil strength parameter is based on the interpretation of the strength of each soil layer.

In 2023, a pile testing programme was conducted on four tubular piles at the Maasvlakte in the Netherlands, with piles loaded in compression and tension including monotonic and cyclic loading (Tubular Pile Pull-out Test Program – TPPT). To fully utilise the value of the tests, it is required to carefully analyse the test data obtained from the previous TPPT project.

This TPPT-II project will provide a better understanding of the load transfer between pile and soil as well as the degradation of the soil-pile interface friction under cyclic tensile loads and the correlation of this degradation with the results of the Unified Cone Penetration Tests (CPT) results. This will enable the application of existing industry design methodology to the offshore renewable foundation concepts with an understanding of what factors need to be applied on static and cyclic capacity. The results will allow for optimised designs and reduced floating offshore wind energy turbine costs.

WHAT

The main objectives of this project are to interpret the pile load tests and compare them with the predictions made before the tests. In addition, the project will make use of steel plate-soil interface tests in the laboratory to back-calculate the tensile response observed in the field tests. This results in more knowledge about the load transfer from the pile surface to the surrounding soil.

In this project, we carry out the following main activities:

EXPECTED RESULTS

The main result will be the interpretation of the compression and tensile tests performed in the TPPT project. An estimate of the maximum load-bearing capacities for tubular piles that are loaded under compression and under tension will be given. We also discuss the holding capacity evolution as a result of cyclic loading for both soil softening or soil hardening.

Particular attention will be paid to the stress regime around the pile and its evolution during the compression and tensile test campaigns. We will translate the interpretation into load transfer (t-z) curves, taking into account any ageing, degradation or strength recovery during the loading history of the pile and – as far as possible – correlated with the pile geometry, the pile installation method and the soil conditions. The results include a comparison with calculations using existing recommended methods.

In addition, we outline the impact of the gained insights on the industrial method for installing piles for offshore floating wind turbines. This will be done in close consultation with all project partners.

Contact Details

Deltares

Anderson Peccin da Silva
+31 6 1160 1969

Technology Readiness Level

Maturity level:

Project duration

Theme

Floating Foundation
Test set-up TPPT magnify Test set-up TPPT

Test set-up TPPT

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Test set-up TPPT

Test set-up TPPT magnify Test set-up TPPT

Test set-up TPPT

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Test set-up TPPT

Other information

This project is supported with a subsidy by the Dutch Ministry of Economic Affairs and Climate Policy and TKI Offshore Energy.

GROW-to-GO podcast logopodcast & article | 29 Jul 2023 Solid as a rock

Partners

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