Experimental Study Of Riprap Stability Under The Action Of Flow Around The Pier

Most of the piers of the bridge project will inevitably have to be placed in the river, and the pier will impede water flow in the river, leading to the local effects of water on the pier and the river bed around the pier that cannot be ignored especially in the river in flood season, resulting in the instability and failure of a bridge pier caused by the scour. The throwing riprap is always difficult to stabilize around the pier, when we use the riprap protection the pier, part of which was taken to downstream by the turbulent flow, and part of which winnowing into the riverbed, unable to meet the protective effect on the pier. The study of riprap stability under the action of flow around the pier is of important significance in the actual pier protection engineering.The paper solve the stability of riprap under the action of flow around the pier through theoretical analysis and flume experiments to explore the instability conditions of the particles of different bed and the conditions of different regions around the pier and the modes of the riprap failure protecting the pier and protective stability. Contrast to the difference of riprap failure between fixed bed and live bed, to determine the stability region, scrolling region and winnow region in the uniform, raised the riprap failure in side back position of pier would experience four processes of buried, exposed, winnowing, and tipping. The development of scour hole size have a great impact to the effect of riprap protecting scour hole around pier for a hydraulic conditions. The actual project in the riprap range of0.7times of equilibrium scour hole size for the expected hydraulic conditions is the best protection. We should be consider the interaction of riprap and sand when protecting the pier, put the smaller particle size of riprap on the bottom of the pit near the bed sand, place the larger riprap on the middle pit, and filled the scour hole with mixed particles riprap to be flat. The enable of riprap around the pier would increase to1.4times of the flow using the suitable size and placement of riprap protection.