Experimental study of local scour around bucket foundation in sand

Laboratory flume experiments were conducted to study scour characteristics around bucket foundation under current only condition and current-wave condition. Scour topography from the experiments shows that the evolution of scour can be divided into three stages, rapid scouring stage, slow scouring stage, and scouring equilibrium stage. Semicircular scour pit occurs in front of the bucket and herringbone siltation appears behind the bucket. Scour depth of the mono-bucket was compared with that of the unsubmerged monopile and submerged monopile. Slope of the scour pit is found to be smaller than the predicted value of the monopile. Maximum scour depth of the tripod-bucket foundation is shown to be affected by the factors including the ratio of exposed height to diameter H/D, the relative bucket spacing G/D, and the incoming flow angle α. The maximum scour depth increases with the increase of H/D. Scour depth of the inner side of the tripod-bucket foundation is shown to be significantly affected by G/D due to the jet effect. The rear bucket may be influenced by shielding effect or vortex shedding. And the incoming angle has influence on the scour development around tripod-bucket foundation.