WAVE SCOUR AROUND PILES AND PIERS

Abstract

As coastal structures are often located on erodible bottoms, the scouring action of waves and currents may lead to exposure of their foundations. In order to avoid these risks, the knowledge of the processes involved in the phenomenon of scour around such structures due to waves is an essential factor, both for designing coastal structures and for considering preventive measures. A methodology is required for estimation of scour depth that utelises information regarding characteristics of waves, currents etc. and soil characteristics. When a structure (pile/pier) is placed in the coastal flow, the presence of the structure will change the flow pattern in its immediate neighborhood, resulting in one or more of the following phenomenon: the contraction of flow, the formation of horseshoe vortex in front of the structure, the formation of lee-wake vortices behind the structure, the generation of turbulence, and the occurrence of reflection and diffraction of waves. Whereas the topic of scour around piers due to uni-directional flow i.e. currents has been studied extensively, relatively less number of investigations are available on the topic of scour around piers due to waves. The review of literature has revealed that the relationship of Sumer and Fredsoe for scour depth estimation for small and large piles is not consistent while the Keulegan-Carpenter number 6.0. A unified relation was therefore, proposed by Ishottama (2003) for estimation of scour around small as well as large piles. Additional data collected from literature on wave scour around small and large piles and piers revealed that method of Ishottama (2003) to have larger error of estimation. Therefore all the data is reanalyzed herein with a point of view of developing a unified relationship having significantly better accuracy than that of existing relationships.