COLLAR-SLEEVE COMIBINATION AS A SCOUR PROTECTION DEVICE AROUND A CIRCULAR PIER

摘要

The primary cause of local scour around bridge piers is horse-shoe vortex system. The growth of vortex can be arrested by retaining the vortex on rigid surface as a collar plate or by confining it within an enclosure like a sleeve skirting around the pier. A collar plate equal to twice the diameter of the pier when placed at the bed is able to reduce scour by 68% while a sleeve equal to 1.5 times the diameter of the pier reduces scour by 38% in comparison to that of an unprotected pier. The two devices in a suitable combination are able to do away with scour altogether for uniform as well as unsteady hydrographic-like flow. The two devices being axisymmetric, are efficient even for large change in the angle of attack of flow. However, in the eventuality of lowering of the general bed level its efficiency decreases.