Experimental Study Of Local Scour Around Inclined Pile Under Combined Waves And Current

China has a long coastline and abundant marine resources.With the rise of large-scale development and utilization of marine resources,inclined pile foundation has been widely used in marine structures such as cross-sea bridge,offshore platform and piled wharf due to its good horizontal bearing capacity.However,under the strong nonlinear action of wave and current,serious local scour will occur near the inclined pile,which will reduce the buried depth,change the stress state of the inclined pile,reduce the safety of the structure and even lead to damage.Therefore,it is of great significance to study local scour near inclined piles.In this paper,an experimental study on local scour of inclined piles under the combined waves and current is carried out based on wave-current flume.First,tests are carried out on inclined piles with inclined angles α=-30°,-20°,-10°,10°,20° and 30°,the relationship between inclination angle a and scour duration,relative time scale,scour development process,scour pit shape and maximum scour depth are analyzed.Then,the influence of wave height,inclination angle and dimensionless parameters Fr,KC and Ucw on the maximum scour depth of inclined pile is analyzed.Through detailed comparison with vertical piles,the differences of scour characteristic between inclined and vertical piles are obtained.Finally,the empirical formulas for predicting scour depth of inclined pile under the combined action of current and wave-current are fitted by dimensionless treatment and combined with the analysis results of influencing factors.The results show that the inclination angle has an important effect on the scour characteristics of the inclined pile under the combined action of waves and current,when the pile is tilted upstream or downstream.Compared with vertical piles,with the increase of inclination angle,the scour depth development rate,scour pit size and depth of inclined pile decrease gradually,and the relative time scale increases gradually.The change rate of downstream inclined piles is greater than that of upstream inclined piles.The larger inclination angle is,the longer time for the maximum scour depth point transfers from lateral front to front,and the time required by downstream inclined pile is longer than that of downstream inclined pile under the same inclination angle.The shape of scour hole of positive inclined pile is obviously different from vertical pile.The dune is symmetrically distributed along the central axis and presents a bimodal structure.However,the dune behind upstream inclined pile is a common single peak shape.Under the condition of live bed,regular sand waves are formed on the bed surface,and the size of scour pit is further reduced.However,the angle corresponding to the maximum scour depth of inclined pile changes from 0° of clear water to-20° of live bed.The scour duration curve of live bed has a depth peak.When the scour depth reachs the peak value,the scour regime changes from clear water to live bed,and then the depth gradually decreases with periodic fluctuation.The relative scour depth of inclined pile is the function of dimensionless parameters KC and Ucw,the variation rules are consistent with the fitting curves of vertical pile.According to the test data,the prediction formulas of scour depth under the combined action of current and wave-current are obtained by using multivariate nonlinear fitting,which provide theoretical basis for engineering protection and design.