Field trials on monotonic behaviour of a driven pile at an offshore wind farm in China

Abstract

The existing database of the loading response of offshore pile foundations needs to be enriched, so that safety and economic considerations can be optimally balanced in design. This paper details a programme of field tests on an open-ended steel pile. The pile with a diameter of 2 m was driven to a depth of 72.8 m in a stratified soil site and then subjected to monotonic compressive, tensile and lateral loadings. Resting periods were allowed before each test to enable strength recovery, and a period of about one month was found to be sufficient (i.e., the axial bearing capacity increases from about 10 MN to 25 MN). The test results were interpreted in terms of the internal forces and displacements/deformations of the pile, and the more detailed pile-soil interactions (i.e., q_s-s and p-y curves). It is found that, for cohesive soils, the unit shaft resistance q_s remains constant through each soil layer regardless of the almost linearly varying undrained shear strength s_u obtained from CPTu tests, and the soil layer with overall higher s_u does not guarantee greater q_s owing to different proportions of silty and clayey components. Upon reaching the ultimate uplift load, the shaft resistance within the cohesive soils shows a clear softening response. Extensive comparisons were made between these results and the predictions from existing design methods wherever applicable to discuss the accuracy of each.

Keywords:

• Pile(s)
• field test
• offshore engineering
• q-s curves
• p-y curves

Acknowledgments

The authors are thankful for the work done in connection with the load test by Huadong Engineering Corporation Ltd. and Shanghai Harbour Engineering Quality Control & Testing Co., Ltd.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors gratefully acknowledge the funds provided by National Natural Science Foundation of China (Grant 51679211, 51579227 and 51809232) and the Fundamental Research Funds for the Central Universities (2019QNA4036).