An Analysis of Scouring Effects on Various Shaped Bridge Piers

A series of bridge failures due to pier scour, as reported during floods, has rekindled interest in our understanding of the scouring process and for developing improved ways of protecting bridges against scour. As such, attention is being given to the scour design of new bridges and to the inspection, maintenance and management of existing bridge structures. The two major countermeasure techniques employed for preventing or minimizing local scour at bridge piers are increased scour resistance and flow alteration. In the former case, the objective is to combat the erosive action of the scour-inducing mechanisms using hard engineering materials or physical barriers such as rock riprap. In the latter case, the objective is to either inhibit the formation of the scour-inducing mechanisms or to cause the scour to be shifted away from the immediate vicinity of the pier. Other than these, there is another measure that could result in relatively less scouring depth around a pier due to difference in pier shapes. All pier shapes do not exhibit the same amount of scouring for the same flow velocity. In this study, the effect of local scour at a bridge pier is presented for different flow parameters. The adoption of a countermeasure is based on the concept that its existence will sufficiently inhibit and/or deflect the local scour mechanisms so as to reduce the local scour immediately adjacent to the pier. The overall objective of the research is to study the temporal development of scour around a bridge pier in an alluvial channel. More specifically, the objectives are to i) to identify pier shape that responses best in order to minimize scouring effect; ii) to find out the relationship of scouring depth with flow velocity, discharge, depth of flow; iii) to find out parameters on which scouring depth depends and develop a relationship with scour depth for changes in the parameters. The selection of the pier width and shape can help in the reduction of the local scour depth in an appreciable manner. A reduction of about 15% in local scour depth can be obtained by using an elliptical shaped pier instead of using a diamond shaped pier and about 10% in local scour depth can be obtained by using an elliptical shaped pier instead of a circular shaped pier.