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Armored Layer Bed Effect on Local Scouring Around Bridge Abutment

In this study the effects of armored-bed layer on local scouring around semi-circular and semi-elliptical abutments have been studied based on model experimentation. The main objective of this research includes the effect of armor layer on mechanism of clear-water scouring around bridge abutments. Experiments were performed under different conditions such as bed shear velocities, flow depths, dimension and shape of abutments, as well as grain size of the bed and armor layer materials in a glass-wall channel of 6.5 m length, 0.3 m width and 0.3 m height. Two types of abutments, semicircular and semi-elliptical with b/l=3 arid 2 respectively were used. Results show that by increasing the bed material diameter for a constant armor layer, maximum scouring depth (dsa) increases and by increasing the grain size of the armor layer for a constant bed layer, dsa decreases. For a given armor layer thickness, by increasing the grain size of the bed layer, dsa increases. While small bed particles are under the protective effect of armor layer, increasing the water velocity increases the secondary armor layer depth provided that the armor layer itself is not influenced by the flow. The maximum scour depth for semi-elliptical abutment is less than that of semi-circular abutment.