Scour is considered as one of the most important issues in river engineering. Each year, a large number of bridges are destroyed in the world mostly due to non-construction reasons. Rather, it is because of ignoring a hydraulic role in their design. Determining the depth of the scour is of utmost importance as it is an indicator of the degree of the destruction of the flow around the piers. Hence, the prediction of the pattern of the scour is essential for the safety of the constructions which are prone to the water flow. The bulk of the studies conducted about the control and reduction of the scour has been focused on single-pier bridges while the majority of the bridges currently built around the world are of the multiple-pier type. Various techniques have been employed for reducing the scour. These include techniques such as using the roughness, the collars, submerged plates, and sacrificial piles. In the present study, the effect of transverse protection piles in controlling and reducing scour around the circular pier has been investigated. In this study, a circular pier with a diameter of 5 cm and three sacrificial piles transversely with a ratio of pile diameter to pier diameter of 0.2 and the distance between the pier axis and the bottom of the pile X = 1D were used. In tests in order to registration of 3D and momentary speed in different sections, the ADV speedometer device was used to determin velocity, turbulent intensities and Reynolds stress. Experiments was done in a channel in length of 15, width of 0.9 and depth of 0.6m with particles of sand in 0.77mm diameter. Experiments showed that the rate of reduction of scouring of the circular pier with sacrificial piles compared to the control circular pier was 58.28%. The studies performed on the velocity and stress profiles around the spark plugs indicate the presence of downstream currents upstream. In addition, the existence of wake vortex in the downstream caused serious fluctuations in flow structure. The eva‎luation of the features of the downward flow when the design includes sacrificial piles showed a tangible decrease in the upward flow and, consequently, a reduction in the power of the horseshoe flow. Longitudinal turbulence intensity and velocity profiles at the back of pier showed that wake vortex creates velocity fluctuations at the back of the pier and reduces velocity in this area. Quadrant analysis further revealed that Sweep and Ejection are the dominant phenomena in the process of scour.

منوچهر حيدرپور

الهام فاضل، سعيد سلطاني