Experimental investigations of local scour around piles in a single-column and three-columns with multiple rows in steady current

Local scour around pile groups is a common phenomenon in fluvial and coastal engineering, leading to a reduction in the bearing capacity of pile foundations frequently. In this study, experimental tests were conducted in a flume to investigate local scour around piles arranged in tandems of single-column and three-columns, with rows ranging from 1 to 5. The objective was to examine the effects of upstream piles and lateral piles on local scour around downstream and central piles, respectively. Bed elevation profiles and temporal scour depths were measured and observed, respectively. The results revealed that sediment particles accumulated in the spaces between the third and the fifth rows in the 5 × 1 configuration, while local scour holes extended into these areas in the 5 × 3 configuration. Temporal scour depths were successfully fitted to an equation that divides the local scour process into three stages: initial, developing, and equilibrium scouring. Piles on either side of the central piles contributed to larger and deeper scour holes compared to those observed in a single-column arrangement. Furthermore, the equilibrium scour depth was found to decrease linearly with an increasing number of pile rows. Coefficients for both single-column and three-column configurations were proposed to estimate reductions in equilibrium scour depths, based on well-fitted curves derived from the experimental data.