Behavior of a Monopod Bucket Foundation Subjected to Combined Moment and Horizontal Loads in Silty Sand

Korea has started to build wind farms in the Yellow Sea, with the seabed consisting of a thick silty sand deposit. It is therefore important to understand the behavior of potential foundations of wind turbines. This paper reports results from a series of model tests undertaken to provide insight into the behavior of a bucket foundation subjected to monotonic horizontal and moment loading in silty sand. The tests were carried out at 70g in a beam centrifuge. The silty sand materials were cored directly from a wind farm site of Yellow Sea. The considered dimensions of the model bucket foundation and loading conditions represented those for a 3 MW wind turbine. The windward and leeward side, and inside and outside, of the model bucket was instrumented with 13 pressure transducers to obtain information in regards to soil-bucket interactions. The horizontal capacity or failure load increased with decreasing loading height due to decreasing induced moment at the load reference point (LRP). A horizontal-moment failure envelope was proposed calibrating against centrifuge test data. A loading rate 20 times faster augmented the horizontal failure load by 1.5 times. This was a consequence of dilation-induced excess pore water pressure. With the drainage valve on the lid shut, the soil inside the bucket was in tension and suction prevailed. The leeward outside of the skirt experienced significantly higher pressure, and that increased with the angle of rotation. Suction inside the skirt and resistance on the leeward outside dominate the capacity of the bucket foundation.