| The existence of bridge piers in the river channel impedes the flow of water,and the water goes down to scour the bottom riverbed,leading to the reduction of the foundation buried depth around the bridge piers,which has an impact on the stability of the bridge piers.The formation of ice sheet increases the wet circumference of the channel,changes the hydraulic characteristics of the channel section,makes the maximum velocity point move down,and leads to the intensification of local scour near the bridge pier.Excessive local scour will lead to the water damage of the bridge.Therefore,it is of great significance to study the local scour,water flow characteristics and the protection of the bridge pier under the ice sheet.In this thesis,the local scour of composite piers under the ice sheet and the protective effect of a new anti-scour measure,the ridged collar,are studied by experiments.Based on the moving bed scour test,the influence of different flow conditions and pier size on local scour of composite pier was tested under different covering conditions.The flow field around pier was measured by ADV.Based on the clean water scour test,the indoor physical model test with different shapes of ridged collar was carried out to study the scour characteristics and hydraulic characteristics around the pier.A geometric model with the same size as the test model was established by flow-3D software for simulation calculation.The simulation results were compared with the measured results of the pit and Flow field.The results show that the numerical simulation results are in good agreement with the measured results of the test.Combined with the test results,the following conclusions are drawn:(1)The local scour pattern of composite pier is similar to that of tandem pier.The maximum scour depth always occurs in the upstream front of composite pier where the undercurrent and horseshoe vortex coexist,and the minimum scour depth always occurs directly behind composite pier.Under the same flow condition,the maximum scour depth of composite pier is found under rough ice cover.(2)The vertical velocity in front of the composite pier presents a parabolic distribution,and the flow velocity presents an inverted C-shape distribution.The presence of ice sheet makes the maximum velocity point closer to the riverbed.The maximum turbulent intensity and turbulent kinetic energy in front of pier always appear just above the riverbed and gradually decrease towards the upper part of the section.Under the same flow condition,the turbulence intensity and turbulence energy at the riverbed under rough ice cover are larger,and the turbulence intensity and turbulence energy before pier gradually increase with the increase of the size of composite pier.(3)Compared with the horizontal collar,the ridged collar has better protection effect.The 135° ridged collar with a height of 1 cm has the best protection effect when it is installed on the bed surface.Compared with no protection condition,the maximum crater depth under the open flow can be reduced by about 62.2%,and the maximum crater depth under the ice sheet can be reduced by about 59.1%.(4)Compared with the horizontal collar,the vertical velocity and turbulence intensity at the bottom of pier equipped with ridged collar are smaller,the vertical turbulence intensity at the side of pier decreases,and the flow turbulence around pier is smaller,and the maximum value always appears in the middle and lower section. |
PDF Full Text Request