labora01

labora01 - HONG KONG UNIVERSITY OF SCIENCE AND TECHNOLOGY...

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HONG KONG UNIVERSITY OF SCIENCE AND TECHNOLOGY Department of Civil & Structural Engineering CIVL 252-Hydraulics TA: Wong Minghoi Laboratory A-Flow and Scour around a Bridge Pier Spring of 2002 Laboratory A: Flow and Scour around a Bridge Pier 1. Introduction Local scour is a site specific phenomenon that a loose bed channel drops in bed level in the region where hydraulic structures exist. The aim of this experiment is to study erosion of bed material around a circular bridge pier. Formation of turbulence and high bed shear stresses around the bridge pier is illustrated in the experiment. The pattern and extent of bed erosion, i.e. maximum depth of scour around the pier, can be investigated. These details are of great importance for the safety of the structure supported by the pier. 2. Background The term “scour” implies enlargement of a flow section by removal of material comprising the boundary through the action of the fluid in motion (Laursen 1952). Scour occurs when the rate of sediment supply is less than the rate of sediment transport. For a given sediment, increase in shear stress results in increase of the rate of sediment transport. The presence of a bridge pier in a flowing fluid generates secondary circulation which is associated with the bending of streamlines. Flow pressure on the upstream side of the pier is high causes a horse-shoe vortex surrounding the pier. The horse-shoe vortex generates a strong shear stress
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labora01 - HONG KONG UNIVERSITY OF SCIENCE AND TECHNOLOGY...

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