Suction Bucket Foundations under Cyclic Tensile Loading—Physical and Numerical Modeling

Abstract

Although suction buckets are believed to be a promising alternative for multipod foundations of offshore wind turbines, the economic and ecological advantages are still limited because of a lack of knowledge regarding the tensile bearing behavior. Major uncertainties exist in terms of the response under cyclic loading and the assessment of the partially drained loading condition, where negative differential pressure beneath the suction bucket’s lid contributes to the total tensile resistance. This article presents findings from 1-g model tests of suction buckets in sand subjected to various cyclic tensile loads. The suction bucket was installed via negative differential pressure (suction). The results show a strong effect of the applied load magnitude on the evolution of displacement, plug heave, and suction induced. Greater displacement accumulation is observed for the smaller considered frequency. Monotonic tests with varying displacement rates supplement the cyclic tests and serve for the verification of a hydraulic-mechanic coupled finite element model, which is afterward utilized for the back-calculation of cyclic model tests. Although a rather simple elasto-plastic material law was used for the sand, good agreement was found, indicating that the bearing behavior is mainly governed by the hydraulic conditions and only subordinately by the soil mechanics.

Vertical Monotonic and Cyclic Responses of a Bucket in Over-Consolidated Clay

“…In contrast, upwards w a occurred under zero and tensile average loading, independent of the V c value [24]. The decrease in stiffness with N was more severe under zero average loading (ζ c = −1) than that under one-way tensile loading [6,28], indicating loading with ζ c = −1 may be more dangerous. For the bucket in sand over clay, the direction of w a was also governed by V a [25].…”