Prediction Of Equilibrium Scour Depth And Numerical Simulation Of Local Scour Around Piers In Sandy Riverbed

Accurate prediction of the local scour depth has an important influence on the design of the bridge across the river,which is the key factor to determine embedded depth of the pier foundation.With the development of bridge engineering,large-span bridges and large-diameter piers are more and more.A empirical depth prediction formula based on the laboratory data or measured data of small diameter piers has been unable to predict the local scour depth of wide piers accurately.Based on local scour mechanism and energy balance theory,the prediction equations of equilibrium scour depth with different flow fields were established.Based on the computational fluid dynamics,the flow field around piers and the dynamic development process of local scour were numerically simulated.The research works of this paper provide a theoretical basis for the design of bridge foundation in sandy riverbed.The main results are as follows:(1)Based on the theoretical analysis of fluid mechanics,considering the interaction between water flow,pier and sediment,the scour mechanism of uniform cylindrical pier was analyzed,and the interaction mechanism between flow,pier and sediment was revealed.According to the theory of energy balance and the analysis of scour mechanism,the prediction equations of equilibrium scour depth in the sandy riverbed for narrow piers in deep flow,transition piers and wide piers in shallow flow were established.The experimental data were selected to verify the applicability of the equations.By comparing with the existing prediction formulas,the equations in this paper effectively improve the prediction accuracy.(2)A method for solving non-uniform correction coefficient of sediment was proposed.The "effective pier width" was used to solve the local scour depth when presence of attack angle and accumulation of debris.For complex piers,the scour depth was calculated by "superposition of the scour components",and the applicability was verified by two examples.The unified calculation of complex piers and simple piers is realized.(3)The flow field characteristics around piers with different longitudinal section were analyzed by the three-dimensional numerical simulation.Longitudinal section form with strong anti-scouring ability was proposed.(4)Based on the computational fluid dynamics,Software developer programs werecompiled,considering the real-time changes of the critical shear stress of sediment with the slope of the river bed,the enhancement effect of turbulent vortex on sediment transport and the adjustment of sediment collapse,dynamic simulation of the scour process was realized.The simulation results are in good agreement with the experimental results.