Effect of vibration on the scour process around cylindrical structures under unidirectional flow in a sandy bed

Abstract

The structures that support wind turbines in offshore wind farms are dynamically sensitive and can vibrate as a consequence of their slenderness and their location in severe environments subject to strong wind and wave load. The granular soils in which such structures are often located are highly responsive to vibrations; depending on their initial state, these soils might experience processes such as compaction, dilation, and liquefaction. Their behaviour in response to structural movement and the effect on the rate of scour is the subject of the present work. Laboratory experiments have been conducted to investigate the effects of vibration on the scour process in granular soil. A series of storms were simulated by a continuous sequence of periods with and without vibration applied to a model pile. The results show that although scour depths are initially reduced by vibration (backfilling), the lateral extent of the scour hole grows and the final scour depth and extent can be significantly greater than for an equivalent test without vibration.