Comparison of scour around two eccentric piers in clear water condition

Abstract

Scouring is a natural phenomenon generated by the passage of water in a river or stream. It is most noticeable in alluvial materials, but the severely worn rock can also be vulnerable under specific conditions. Every year, numerous bridges fail, resulting in the loss of lives and property as well as some uncomfortable circumstances for transportation systems. Because of this, bridge designers are increasingly considering the flow-soil-structure interaction. The urban setting around the world is getting densely populated and facing heavy traffic with the increased number of vehicles. This opens the scope for the construction of new bridges beside already existing old ones. On the other hand, in recent years tomaximize scour, several laboratory-based researches have been conducted using two or more in line, eccentric pier combinations keeping the aspect of the green dredging concept. The ultimate purpose is to shift the sediments to the bank of the channels without using any mechanical dredger. Thus arises the need to study the interference of inline and eccentric piers. Therefore, a thorough investigation of scour depth around inline and eccentric piers in such conditions is highly desirable. In this present study, the hydrodynamic consequences of different eccentric arrangements on scouring were investigated. Erosion and deposition patterns were studied around the front and eccentric piers at different time intervals along the flume. Inthis series of experiments, two identical circular piers are used to conduct twelve experiments. For the first six experiments,the inflow depth was kept constant at 12.7cm and for the remaining six experiments,the inflow depth was set fixed at 13.7cm. The eccentricity between the two piers was varied from 2-3.5 times the pier diameter. The longitudinal spacing between the upstream pier and the eccentric pier was also kept fixed. A fixed discharge of 27l/sand clear water condition was also maintained throughout the experiments. Six different eccentricities were used to run the experiments for 12 hours to observethe variation of scour with time. Several parameters like scour depth, width, length, area and volume were computed from the experimental outcomes. The results obtained from the series of experiments were carefully analysed to obtain the best arrangement for eccentricity which would be a beneficial aspect for bridge designers and dredging experts.