Experimental Investigation Of Local Scour And Scour Protection Around Vertical Piles In Steady Currents

Local scour around vertical cylindrical structures has been identified as a key factor that leads to the failure of structures.In order to understand the characteristics of the local scour and failure mechanisms induced by local scour,physical model tests were performed to inves-tigate the scour around single vertical piles in steady currents.First of all,the mechanism of the local scour around a single vertical pile in steady cur-rents is studied.Contact Image Sensor?CIS?sensors were used to record temporal develop-ment of the scour depth during the test.At the end of each test,a 3D scanner was used to scan the profile of the seabed around the pile.The time-scale?T?,as well as the equilibrium depth of the scour under both clear-water and live-bed conditions are investigated.The effect of Reynolds number?Re?on the scour size and the location of downstream sand dunes were also examined.The relationships between the normalized equilibrium depth S0/D,the scour radius L0/D and Re are summarized.The results show that,under identical same flow condition,the time scale and the equilibrium depth of scour increase with the increase of Re.The extent of hole becomes larger and the position of the dunes induced by sediment deposition gradually move towards the downstream with a decreasing height as Re increases.Correlation relation-ships between S₀/D,L₀/D and Re are also examined.Secondly,the scour protection around a single vertical pile in steady currents was studied.A slab foundation was proposed as a protection measure for scour around the pile.It is found that local scour around the pile can be significantly mitigated by the slab foundation,resulting in the reduction of the scour depth and extent of the scour hole.The effect of scour protection is evaluated by comparing the scour around a single pile with that of a pile founded on a slab foundation,in terms of the extent of the scour hole and the sand dunes downstream of the pile.The effects of the slab foundation size on the scour protection under clear-water and live-bed conditions were also discussed.The results show that,as the diameter of slab foundation Dl increases,it has a more obvious weakening effect on the local scour of the vertical pile.When Dl/D?3.0,the slab foundation can completely inhibit the development of horseshoe vortex so that there is no scour hole near the upstream of the model.Recommendations for scour protections of a single vertical pile and directions of future study are made based on the present results.