METHODS OF REDUCTION OF SCOUR AROUND PIERS OF BRIDGE

Abstract

Worldwide, Scour around bridge piers is the common cause tc bridge failure. Being confident in any countermeasure depends on the prior experience of its performance; cost and ability to protect bridge piers from cour.

In this research, two kinds of countermeasures were combmcd together. These are the deflectors (attached to the pier at different heights above the bed level) and riprap to reduce erosion of the bed at the pier. The deflector's fu1.ction is to reduce the intensity of the flow at the pier in case of high velocity flow. The reason behind using both the deflectors and riprap combination is to safeguard the failure of riprap caused by shear, winnowing, and edge failure under clear-water conditions or instability of bed-form progression under live bed- conditions.

An experimental study was thus conducted to investigate the local scour depth for two types of piers (circular and rectangular with rounded no"e). Three different shapes of deflectors were used.

This was achieved using a flume (23.00 m long, 0.74m wide and 1.00 m deep) that was constructed in the Hydraulics Research Institute (HRI), 1V1inistry of Water Resources and Irrigation (MWRI). The used types of piers were a cylindrical pier (lOcm) and rectangular pier with rounded edge (30cm long and Scm wide).

224 runs were exel:uted on three types of deflectors varying their position above the bed level to determine, the position that produces a minimum scgur depth. A riprap was used in combination with the deflector.Also, based on the experimental results, empirical formulae were developed and design charts were plotted.

The experimental results showed that the use of a 1Ocm long deflector at a distance of 0.2 of the water depth with riprap is more effective than using other types of deflectors. This combination proved to be more effective in the case of using a n.:l...angular pier with rounded edge than in case of using circular piers. The ust: of the described system vanish the scour for all considered flow conditions.