Local scour around varied-configuration pile groups in silty seabed under steady current: An experimental study

This experimental study investigates the effects of pile arrangement patterns on local scour characteristics around pile groups in silty seabed. A series of flume experiments were conducted with pile configurations ranging from 1 × 5 to 5 × 5, maintaining consistent hydraulic conditions and silt properties. The results reveal that scour depths downstream multi-row pile groups significantly exceed those upstream, contrasting with trends observed in sandy seabed. This phenomenon can be attributed to cyclic loading induced by wake vortices shedding by upstream piles, which can weaken the silty seabed. Meanwhile, equilibrium scour depths stabilize after approximately 10 h, with maximum depths plateauing at about 4.5D for configurations reaching four rows. A stable scour distribution pattern emerges when the row-number of pile groups reaches or exceeds three, characterized by increasing scour depths in the upstream three rows followed by stabilization. An estimation formula for pile groups was proposed by incorporating the row-number and spacing amplification factors based on the single-pile scour depth estimation formula used for silty seabed.