Executive Summary : | Scour is a natural phenomenon in alluvial streams caused by the erosive action of flowing water. Bridge piers, constructed on stream beds, are often undermined due to river-bed erosion and scouring, which are the main causes of pier failure. This results in local scour around the pier, which is three-dimensional and forms a vortical flow-field. Twin piers play a significant role in preventing loss of lives and economic resources in India due to transportation demand and population growth. The construction of another bridge in the upstream or downstream direction changes the flow properties and local scour around the piers. Studies have shown that the scour depth around an upstream pier in tandem, side-by-side, and staggered positions is the same as that of around a single pier in the same condition. Pier scour is a challenging problem for engineers involved in civil, bridge, and hydraulic work, and many researchers have developed formulas or design equations for pier scour prediction. Local scour around the downstream pier is less than that around the upstream pier in tandem arrangement, and wake vortices from the upstream pier affect the local scour around the downstream pier. The sediments and flow conditions are not uniform in real field conditions, and armouring effects can reduce scour depth in single, side-by-side, staggered, and tandem bridge piers due to non-uniformity of sediments for clear water flow under a given discharge condition. Therefore, it is important to study local scouring around parallel bridge piers (tandem, side-by-side, and staggered) for different flow conditions on uniform and non-uniform bed and varied flow. |