Investigation of the effect of discharge and pier diameter size in depth and volume of local scour around bridge pier

Scouring around the bridge piers is one of the most important issues in bridge piers hydraulic. This phenomenon has led to a discharge under the bridge piers and the results caused their reversal. The local scour mechanism around the piers is very complicated issue and many researchers were conducted to discuss the investigation of this important matter. Many bridges are destroyed due to their often piers scouring and causing human and financial losses. Generally, two fundamental factors of flow contact with the bridge pier and water flow separation from the pier, led to the formation of vortices around the pier at the bridge piers site and cause the local scour. The present research has investigated the effect of flow discharge and pier diameter in depth and scour volume around the bridge piers using a physical model. For analyzing the effect of flow discharge and also the size of the pier diameter on local scour around the bridge piers, three piers were used with 21, 30 and 40 mm diameter with five different discharges in each pier. Experiments were carried out in a sandy bed (with a median size of 0.88 mm) flume of 8.0, 0.255 and 0.3 m in length, width and height a, respectively. The results showed that by increasing the discharge and Froude number in each pier, the volume and scour depth were increased. In a constant Froude number, the volume and scour depth increased by increasing the pier diameter. In 21, 30 and 40 mm piers, the scour depth also increased by 128.5, 94.7 and 135.1 percent by increasing of 40, 68.7 and 23.9 percent of flow discharge.