الفهرس 
Problem DefinitionOnly 14 pages are availabe for public view
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Abstract
Worldwide, Scour around bridge piers is the common cause to bridge failure. Being confident in any countermeasure depends on the prior experience of its performance; cost and ability to protect bridge piers from scour. In this research, two kinds of countermeasures were combined 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 function 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 nose). 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), Ministry of Water Resources and Irrigation (MWRI). The used types of piers were a cylindrical pier (10cm) and rectangular pier with rounded edge (30cm long and 8cm wide). 224 runs were executed on three types of deflectors varying their position above the bed level to determine, the position that produces a minimum scour 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 10cm 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 rectangular pier with rounded edge than in case of using circular piers. The use of the described system vanish the scour for all considered flow conditions.