Research On Scour Mechanism And Calculation Method Of Skewing Bridge In The Complex Boundary Conditions

With the rapid development of railway and highway, a lot more bridges are built acrossthe river. Bridges over natural rivers often have a complex boundary system. These boundaryconditions should be including skew bridge, river bend, river longitudinal slope and rapids orsubcritical flow conditions, pebble bed or sand bed. The formula about scour depth is basedon certain theoretical basis, and used a lot of measured data to confirm it, but due to a lot oftheory is established on the basis of straight channel, and the bridge pier scour in the naturalriver is often accompanied by complex boundary conditions, which threaten the safety ofbridge, and there is seldom theory to solve it. So we should pay more attention to it and domore intensive study.This paper provides a relatively novel method for calculating the scour depth when theskew bridge across the river bends. Combined with Yan river movable bed model test,observation data is fit well with the theoretical calculation. There are some innovative resultsas follows: pointed out that the bridge scour engineering problems should be solved. Skewbridge crossing the bend. It couldn’t provide a fixed reference for defining oblique angle, sothe skew angle will change at the different positions of the bend. This paper uses the similardefining method as in the straight channel. The skew angle of these boundary conditions canbe defined as the angle between flow direction and the perpendicular direction angle of skewbridge. Moreover, it presented the scour depth Influence coefficient based on the longitudinalvelocity distribution formula and the theory of sine derivative curve. In the end, established acalculation model about the scour depth in this complex boundary conditions, and also get thecalculating method about related parameters.In order to verify the correctness of the calculate method, according to a certain modelsimilar conditions, design and production on the basis of comprehensive consideration of themodel the metamorphosis rate as well as a reasonable modeling sand choice about the YanRiver experimental model. The model test observe the flow velocity, mainstream line, waterlevel and depth of scour of the piers under the dominant discharge and10years,20years,30years,50years flow.Through the observation, get the scour pit pattern under the complex boundary conditions. The scour pit patterns become as an inverted triangle shape which with the skewbridge as the baseline of it. And the scour pit extends downward with the increase of flow, andso does the scour depth; when the corner on the left bank, basically the triangle vertices wouldat the right bank pier, and the left piers would be the middle point of bottom, and the bridgeaxis would be the triangle median line. As the change of flow, triangle scour pit present aconsistent regularity, the triangle bottom would develop downstream and upstream with thepiers at left bank as the center, meanwhile, the peak would change along the axis with theincrease of the flow, and the regularity with the time development is as the same like the flowincrease.