Local Scour Experiment And Numerical Simulation Of Circular Pier

With the rapid development of China’s economy,the traffic network in western China has gradually improved,and there are more and more water-crossing bridges.Due to its unique geographical environment,those bridges are more vulnerable to scour.According to statistics from domestic and foreign data,bridge destruction is mostly caused by water damage,and pier scour takes the biggest proportion.Severe pier scour will reduce the side constraints of the river bed to the bridge pier,reduce the vertical bearing capacity of the bridge pier,and endanger the structural safety and stability of the bridge.Therefore,the research on the characteristics of bridge scour has important guiding significance and engineering practical value to ensure the safety and stability of the bridge structure.This thesis adopts the combination of flume experiment and CFD numerical simulation to study the local scouring characteristics of cylindrical pier under the condition of live-bed scour.The main research content is as follows:(1)Key parameters such as experiment flow fields,sediment characteristics,sediment incipient velocity,equilibrium scouring time and others were discussed,and conditions of flume experiment of circular pier scour were determined.Three scour experiment of circular pier with different diameter was carried out.The results showed that under the live-bed condition,the pier’s local scour depth is negatively related to the diameter of the bridge pier.(2)Based on the oblique photography technology,the photography measurement method for rapidly measurement scour pits was proposed,and the result of the photography measurement was compared to result that measured by vernier caliper or scale ruler around pier,showed that relative error of scour depth measured by photography measurement method is within 8%,and each measurement with this new method can save about 3 hours.It proved that the photography measurement method has good accuracy and applicability.(3)Flow 3D software was used to establish two-stage three-dimensional water-pier-sand coupling numerical model.The numerical results showed that velocity distribution of the simulation was basically the same as the experiment,the maximum scour depth was slightly smaller than the experiment’s value with the relative error was no more than 6.1%,so the feasibility and accuracy of the numerical simulation method was verified.(4)Based on numerical simulation and dimensionless analysis methods,a series of numerical simulation were carried out to study the influencing of factors of V/V_c and H/D on the local scour characteristics of circular pier.It was found that under the condition of live-bed scour,the local scour depth of pier is positively correlated with the inflow velocity and water depth.