Scour Around Vertical Pile in Waves

TLDR

The Keulegan‑Carpenter number governs the development of flow structures that control equilibrium scour depth on a live bed. The study experimentally investigates scour around piles in waves and derives a design equation linking scour depth to the Keulegan‑Carpenter number. Scour tests were complemented by bed shear‑stress measurements, flow visualization, and data used to formulate a design equation for scour depth versus Keulegan‑Carpenter number. Lee wake and horseshoe vortex drive scour; scour disappears for KC < 6, while normalized scour depth rises with KC and levels off near KC ≈ 100.

Abstract

This paper presents the results of an experimental investigation on scour around piles exposed to waves. In addition to the actual scour tests, bed shear‐stress measurements and a flow visualization study are carried out. The effects of lee wake and horseshoe vortex are demonstrated to be the two key elements in the scour process. The development of these flow structures mainly depends on the Keulegan‐Carpenter (KC) number that hereby becomes the main parameter that governs the equilibrium scour depth on a live bed. Based on the present data, a design equation is established, relating the scour depth to the Keulegan‐Carpenter number. For the values of the Keulegan‐Carpenter number below six, the scour around the pile practically ceases to exist. The scour depth normalized by the pile diameter is found to increase with increasing Keulegan‐Carpenter number and approaches its steady‐current value for Keulegan‐Carpenter numbers above approximately 100.