Accumulated rotations of bucket foundations under long-term cyclic loads in sandy ground-Paper

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The study investigated the accumulated rotation of suction bucket foundations in sand under long-term cyclic horizontal loading, relevant to offshore wind turbines. Researchers conducted 16 one-gravity model tests: four static tests and 12 cyclic tests. Aluminum bucket models had embedment ratios (L/D) of 0.5 or 1.0 and were installed in dry sand at two relative densities, 18% and 25%. Cyclic loading was applied at 0.25 Hz for up to 10,000 cycles, with load amplitude varied relative to the static failure load.<br /><br />Foundation displacement and rotation accumulated as cycles increased. Rotation also increased with cyclic load amplitude. Displacement rose rapidly during the initial cycles, then its rate of increase diminished. Static failure loads were higher in denser sand and for the bucket with the larger embedment ratio.<br /><br />Based on the test results, the authors proposed an empirical equation for estimating accumulated rotation as a function of cycle count, embedment ratio, and cyclic load ratio. Regression-derived parameters differed between the two sand densities and embedment ratios. The equation was reported to represent the model-test results adequately.<br /><br />The findings indicate that both the magnitude and duration of cyclic loading should be considered when assessing bucket-foundation rotation. However, the proposed relationship was developed from small-scale tests in dry sand, so its broader application requires appropriate consideration of field conditions and scale effects.

Keywords

suction bucket foundations

accumulated rotation

cyclic horizontal loading

offshore wind turbines

sand

model tests

embedment ratio

relative density

static failure load

empirical equation