Experimental Investigation Of Local Scour Around Porous Piles

The local scour around the foundation of the marine engineering structure is the key factor causing structural damage.Previous research has focused on solid piles,but in practical engineering,permeable structures are also widely used in marine engineering structures.Therefore,to understand the local scour characteristics of the permeable structure,this article simplifies the permeable structure into a porous pile,and then discusses the following three parts using the method of physical model test.First,the local scour characteristics of the permeable column under unidirectional flow was studied in this paper.The experiment drilled holes in the square pile model,and changed the model porosity by changing the diameter of the hole.The experiment used UDV to monitor the scour depth changes,and used a three-dimensional terrain scanner to scan the terrain after scour,and analyzed the effect of porosity on the scour development process.The test results show that as the front porosity increases,the equilibrium scours depth S0 decreases significantly,the time scale T~*increases,and the local scour range and dune distance decrease almost linearly.However,side porosity will not significantly affect the development process of erosion.Secondly,the interaction between tandem piles is further studied.The test results show that when the model interval is G/D<4,the scour of the tandem piles is dominated by global scour,and the tandem piles form an overall scour hole.As the interval increases,the scour process evolves from global scour to local scour of a single column.Local scour;the development process of the front pile and the scour depth are almost not affected by the rear pile;when scouring ability of the rear pile is weak,as the interval increases,the rear model is most affected at the highest part of the dune formed by the front pile,the scour depth is the smallest;when the rear column has strong scouring ability,as the interval increases,the influence of the front column gradually decreases.Finally,the scour protection of a single column under steady current is studied.The experiment adopts the method of arranging a rock dump around the column to achieve the scour protection effect.The principle is to use the rock dump to weaken the migration effect of the horseshoe vortex on the sand bed around the column to reduce the depth and range of the local scour and thereby maintain the stability of the pile.Two types of stones were selected for the experiment.By changing the number of stone-throwing layers and the scope of stone-throwing,the influence of these variables on the effect of erosion protection was observed.The test results show that when the throwing range is relatively small,the protective effect of the stones with a smaller diameter is more obvious;increasing the throwing range,the stone dump is more stable,and the protective effect is significantly enhanced;increasing the throwing layer n,the protection effect is obvious enhanced.The scouring depth can be reduced by a maximum of 96.4%.In this case,except for the corners of the model,there is no scouring around the model.