Experimental Study of Local Scour Around Two Compound Piles in Tandem, Side-by-Side and Staggered Arrangements Under Steady Current

Scour around two compound piles (CPs) in tandem, side-by-side (SBS), and staggered arrangements is investigated through experiments. Each CP has a larger diameter foundation, which is partially buried, and a smaller diameter top part with a diameter ratio of 0.5. The exposed height of the foundation is equal to its diameter. Experiments are conducted for gap ratios from 1 to 3. Due to the shadowing effect from the upstream CP, the downstream CP in the tandem arrangement has shallower scour depth and its most downstream point has deposition at an early stage. In the SBS arrangement, the scour does not have much difference from that of a single CP, but the inner side of each CP has a slightly deeper scour hole than the outer side of each CP and scour hole became independent at gap ratio of 3. In the staggered arrangement, the shadowing effect from the upstream CP was experienced by the downstream CP when G/D = 1, but not 1.5 and 3.