effect of combination wrapping cable and collar on depth of scour around cylindrical bridge pier groups on rivers meander

a large number of authors have studied to find out how to control scouring around a pier along direct stream. the objective of this research is then to study a scour pattern around such piers on curves rivers due to the fact that there may be a difference between a flow pattern on a direct line and the meander. thus, this study tries to check whether the use of cable and collar alone and in a combination of cable and collar affects scouring around bridge pier group constructed on rivers meander. in this study two thickness of cable 0.2d and 0.4d and three steps 0.2d, 0.5d and d are used. the results showed that more scouring depth is decrease as a cable diameter increases and the pitch of helix decrease. about pier groups that are in the direction of water flow, scour depth for first pier is more than single pier, that represents increase of reinforcing phenomenon, also scouring depth for middle and back piers due to sheltering phenomenon, is less than single pier. about piers perpendicular to the flow direction, the maximum scour depth is observed in middle pier, also at this case scour depth is reduced by increasing distance between piers. using collar is more effective than cable for small distances between piers.  also it is found that using a combination of cable and collar results the most reduction in scoring depth.