Experimental Study On Local Scour Evolution Process Of Bridge Foundation Considering Pier Type

Due to the water blocking of the pier,the flow structure around the pier is changed,resulting in the erosion and damage of the river bed sediment around the pier,and finally the local scouring of the bridge foundation.Local scour is considered to be one of the important factors causing bridge damage and failure.The types of bridge foundation piers are different in engineering,and the existing research results lack of systematic research on the law of local scour.Through model test,numerical simulation and theoretical analysis,this paper deeply studies the evolution process of local scour of bridge foundation considering pier type,and reveals the evolution mechanism and internal law of local scour of bridge foundation.The experimental research results mainly include:(1)At the same survey line and horizontal position,the flow velocity along each pier type has the same variation law,but due to the different pier size and the shape side of the upstream surface,the flow velocity around the pier changes sharply,resulting in obvious differences in the variation range of flow velocity along each pier type.(2)After in-depth analysis,it is found that the main dynamic mechanism of local scouring is the downflow in front of the pier and the horseshoe vortex on the side of the pier.However,under the same conditions,compared with the rectangular pier,the downflow in front of the cylindrical,round end and triangular pointed pier and the horseshoe vortex around the pier are relatively small,which makes the balanced scouring depth of the rectangular pier the largest and the triangular pointed pier the smallest.(3)The evolution process of local scour of each pier type has experienced initial,main and equilibrium stages,but the local scour of three kinds of piers with "L: b > 1" starts from the corner in front of the pier,while the local scour of cylindrical pier starts from the side of the pier;In the scouring balance stage,the balanced scouring depth of triangular pointed pier appears on the pier side,and the other pier types appear in front of the pier.(4)Under clear water scouring,the change of scouring depth around each pier also has obvious difference with the increase of.The scouring depth on the side of rectangular pier is obviously less than that of other pier types,and the sediment behind the pier is always in the state of accumulation,showing the form of high and low staggered;With the increase of other pier types,the accumulated sediment behind the pier is slowly eroded,and finally a closed scouring pit is formed around the pier,and the sediment is accumulated at a certain distance behind the pier.It can be seen that the causes of local scouring dynamics of each pier type are different.Combined with different test velocities,the scouring evolution laws of each pier in the equilibrium stage are different.At the same time,with the help of numerical simulation software,the local scouring evolution process of each pier and the distribution characteristics of flow field around the pier under different velocity are calculated and analyzed.Compared with the indoor test,the simulated value is in good agreement with the experimental value.The high coincidence not only reflects the rationality of the model test,but also further verifies the conclusions of the model test,and deeply reveals and analyzes the internal mechanism and evolution law of local scour of piers.