الفهرس 
ABSTRACT
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Abstract
Local scour around piers is the main cause of destruction of many bridges constructed on the open streams. The formation of scour around bridge piers is one of the main causes of bridge foundation collapse. An estimate of maximum possible scour around a bridge pier is necessary for its safe design. The aim of this study is to evaluate the effectiveness of rectangular slots through an oblong pier with different arrangements and replacing the solid pier by two pier groups on the reduction of scour dimensions at bridge pier comparing to a solid oblong shaped pier. The experiments were carried out under clear-water conditions in a flume of a rectangular cross section located at the hydraulics laboratory of Civil Engineering department at Assiut University. The flume has 30 cm wide, 50 cm deep with 20.0 m long. The original flume bed is covered by a false bed to ensure a sand basin with 20 cm deep and has sand material of size 0.71 mm. Five wooden oblong piers with width 3.0 cm and 15 cm length without and with rectangular slots differ in shape were installed in the channel centreline at 5.5 m away from the entrance of the flume in the sand basin and two other models consist of six glass piers with 0.75 cm diameter with two arrangements, were used. A total of 112 experiments were conducted on seven different models of piers. Water flow rate was varied four times, while flow depths were changed to cover a range of Froude number from 0.089 to 0.25 which is compatible with that of Egyptian canals. The parameters affecting scour at bridge piers are normalized with the help of the method of dimensional analysis. Based on the analysis and discussions of the experimental data, it is found that:
1) Rectangular slot connecting with two openings along the pier’s sides (pier type 7) gives the highest reduction of scour dimensions 92%, 53%, 69% and 85% for depth, width, length and volume respectively in comparison with solid oblong pier.
2) Pier type (7) - pier groups of staggered arrangement - gives the highest scour reduction in comparison with all tested models; 93%, 73%, 79% and 89%, for depth, width, length and volume respectively.
3) from economical point of view, rectangular slots and pier groups were considered good tools for reducing the dimensions of scour hole.
4) The dimensions of scour hole increasing with the increase of Froude number, water flow rates and the decrease of flow depth.
5) Applying multiple linear regression analysis resulted in empirical formulas for estimating the relative dimensions of scour hole for the examined pier models.