Study On Local Scour Of Staggered Twin Circular Pile

Local scour of foundation is one of the important factors that affect the safety and stability of bridge engineering.Twin pile or multiple pile foundation are widely used in the foundation of bridge.Compared with the single pile,local scour around twin pile foundation is more complex because of the interaction between each pile.The current research on local scour of twin pile foundation focuses on serialized or juxtaposed layout and rarely on staggered layout.The central axis of the twin pile with staggered arrangement will form an angle with the flow,so that the twin pile foundation will cross diagonally with the flow,the structure of flow will be more complicated,the effect on sediment in the riverbed will be stronger,and the influence on bridge safety will be worse.This thesis focuses on the engineering phenomenon of local scour around staggered twin column pile,the process of local scour around twin pile under different flow angles,flow velocity and pile arrangement were explored through flume experiment and numerical simulation.Based on the flume experiment and numerical simulation,the thesis studies the flow filed and the velocity of 3D flow around the pile,summarizes the relevant connection between the process of local scour and the variables.It has important theoretical guidance and engineering significance to preserve the safety and stability of bridge.The main conclusions are as follows:(1)Based on the flume experiment,the function of scour depth around pile with time was obtained,and the local scour evolution law around the staggered twin column pile was explored.By comparing the results of maximum scour depth and equilibrium scour depth around the upstream or downstream pile in different test groups,the influence of flow angle,Froude number and relative pile spacing on scour depth around the staggered twin column pile was obtained.(2)By measuring the flow velocity in three dimensions by ADV,the structural change of the flow velocity in three dimensions around the pile at different flow angles was obtained.The flow velocity distribution along different longitudinal sections in the test area were studied.The results show that,with the increase of flow angle,the relative position of single pile in staggered twin pile arrangement changes from downstream pile shelter from upstream pile to the appearance of narrow gap between upstream pile and downstream pile.The flow velocity between piles has an increase because of the gap,and the local scour around downstream pile will be stronger.(3)Based on the numerical simulation,a few test groups in the flume experiment were selected as the simulated conditions.The characteristics of flow structure and local scour pit around the staggered twin pile were obtained and compared with the results of flume experiment.