Laboratory investigation of basic geometry of the bridge on scour control around the river bend

Determination of the erosion depth at the base of the bridge requires knowledge of how to move the river bed sediments. The base of bridge disrupts the normal flow of the river، so turbulence and disturbance resulting in erosion of sediments surrounding the base. The hole created around the base depends on the shape and geometric properties. Moreover، ingredients of river bed and also flow hydraulic conditions such as flood conditions and dune cross can effect on depth of the hole. Since، development of erosion hole hazards the structural stability of the bridge. So predict for amount of hole and necessary measures to suppression are considered as common engineering practices in river engineering. For investigation of basic geometry of the bridge on control scouring around the river bend an experiment in a laboratory flume was done with a 180-degree bend، 2. 8 m for central radius، 0. 6 m wide and R/B= 4. 67 under the walls made of Plax glass. In this study، clear-water scour around the base were studied by putting a basic cylinder with 6 cm diameter، foursquare section، semicircle tip with 6 cm width and 18 cm length in flume at positions 30، 60 and 90 degrees، with rates of 24، 28، 30 and 32 liters per second and a constant depth of 12 cm. For flooring of flume a natural sand by uniform gradation with D50=2 mm and uniformity coefficient of 1. 3 were used. The results of this experiment showed that the maximum scour depth during placing the base with cylindrical section and foursquare section with the semicircle tip were alternative during the bend length and in the first half of the bend and at the position of 60 degrees had the maximum scour at the base. Also، scouring in all cases was lower for base with cylindrical section as compared to foursquare section with semicircle tip. In all conditions، increasing of flow have been increased the scour depth.