INVESTIGATION OF EFFECT OF ROUGHNESS ON RIPRAP STABILITY AROUND THE BRIDGE PIER IN 180 DEGREE RIVERAlireza Masjedi, Amir Taeedi, Bita Jafari and Mohsen Mojtahed
The bridges are the main construction of river, so that it is important for road buildings. Occurrence of scour around bridge pier on curved paths is one of the main reasons for destruction of bridges. Riprap is one of the methods to control of scouring around the bridge piers. In order to study of stability of riprap around the bridge piers, experiments were done in a laboratory flume made of Plexiglass in 180 degree bend. In this research, by placing the two cylindrical piers with separately with a smooth body and roughness with riprap around its, they proceeded to a series of tests. Experiments were done by two different types of riprap with diferent density, four different diameters and one rate of discharge under pure water condition. In each experiment, flow depth measured in terms of failure threshold then stability number calculated by using data obtained. The results of the research showed that the sustainability of riprap around the cylindrical pier to two the Froude number in failure threshold and the relative diameter of the riprap is dependent. There are also the same, in terms of roughness in cylindrical pier of the bend enhances the sustainability of riprap around the cylindrical pier.
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