Investigation Experimentally the Effect of Roughness of Pile Group on Local Scouring at Presence of Harvesting of River Material Pit

Scouring around the bridge piers due to harvesting of river materials is one of the causes of bridge damage. Therefore, this study has investigated the scouring around the bridge pile group in the presence of material harvesting in several hydraulic conditions. For the first in this study, the surface of the piers was reinforced using gravel to reduce scouring. Comparing the results of scour depth of the reinforced model with simple model showed that the using of roughness caused maximum reduction of the scour depth in the flow of 45 L s-1 and Froude number of 0.1. After that, the maximum reduction of scour depth in other experiments was 64.29% and related to the flow of 15 L s-1 and the Froude number of 0.1. Also, the results of this section showed that the using of gravel on the surface of the piers reduced the rate of scouring and increased the equilibrium time. The results of time development of scour depth showed that in simple model the scour depth increased due to the increase in both Froude number and flow discharge, but in the reinforced model the scour depth increased with increasing Froude number but did not increase with increasing flow discharge. Evaluating of the scour area around the piers showed that the scour area increased with increasing Froude number and decreased with increasing flow discharge. The results of this study and its comparison with other studies showed the appropriateness of gravel roughness at the surface of piers to reduce scour.