A Study on Scouring Around Bridge Piers of Different Shapes

Abstract

A series of recent bridge failures due to pier scour, as reported in literature, has rekindled interest in furthering our understanding of the scour process and for developing improved ways of protecting bridges against scour. Moreover, increased attention is being given to the state of Bangladeshi infrastructure, a major aspect of which is the transportation network. In part, there is concern about both the impact of a failure on the handling of traffic flow while the failure is being remedied and on the cost of replacing the failed system component. 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 might be another measure that could result in relatively less scouring depth around a pier due to difference in pier shapes. That is not all pier shapes 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: (i) to study the causes of scouring around bridge piers, types of scouring and threats it imposes on bridges and overall structures; ii) to identify pier shape that responses best in order to minimize scouring effect; iii) to find out the relationship of scouring depth with flow velocity, discharge, depth of flow; iv) to find out parameters on which scouring depth depends and develop a relationship with scour depth for changes in the parameters.