Study On Local Scour Characteristics And Protective Measures Of Cylindrical Pier Under The Action Of Water Flow

With the proposal of “One Belt and One Road” initiative and “Ocean Power” strategy,China has made a series of brilliant achievements in the water transport engineering undertaking.More and more bridges across the rivers and seas have been built worldwide.But these bridges are different from the general highway bridges,they will suffer from the complex water environment attack at the same time of vehicle,wind,earthquake and other loads,which is more likely to cause damage to these bridges.Scholars at home and abroad have analyzed and counted the causes of bridge disasters,and found that most of the bridge accidents were caused by foundation scour or other hydraulic factors.The bridges play an important economic function and strategic significance in the inland river and sea,and its structural stability and durability are particularly important.Therefore,it is of great significance to study the local scour characteristics of bridge foundation and scour protection measures to reduce the scour disaster and ensure the safety of bridge structure.In this paper,the method of flume test and numerical simulation is used to study the local scour characteristics of cylindrical pier and the foundation scour protection measures.The main research contents are as follows:(1)The key parameters such as threshold velocity of sediment and equilibrium scour time are studied,and the scour test of cylindrical pier under the action of unidirectional flow is carried out.The influence of different flow conditions on the local scour characteristics around the single pier is revealed from two aspects of flow velocity and water depth.The comparison and analysis of unidirectional and tidal flow are also carried out.(2)The numerical simulation framework of unidirectional flow with boundary layer effect is established.The RANS equation is used as the control equation.Under the condition that the numerical velocity profile is consistent with the actual flume profile,the numerical model is verified from the flow field around the pier,the pressure coefficient and the maximum scour depth to ensure the accuracy and feasibility of the CFD software.(3)The numerical simulation of different flow conditions,sediment parameters and structural dimensions is carried out to explore the influence of various scour parameters on the local scour characteristics of cylindrical pier.The maximum scour depth calculation formula with high goodness of fit is used to predict the balanced scour depth of various numerical conditions.(4)Through the flume test,the influence of collar installation height,outer diameter and protection range on the local scour around the cylindrical pier under the action of the unidirectional flow is studied.The protection laws of unidirectional and tidal flow are compared.A calculation formula for the protection efficiency of collar is proposed.Finally,the protection mechanism of collar against scour is studied by numerical simulation.