Numerical investigation of local scour characteristics around a single pile subjected to turbidity currents

Pile foundations are widely used in marine engineering, and local scour is a key factor leading to structural instability and failure. Most existing studies have focused on scour characteristics under clear-water conditions, whereas the regulatory mechanisms of fine particles in turbidity current environments remain to be further clarified. This study employs numerical simulations to compare the local scour characteristics around a single pile foundation under clear-water and turbidity current conditions, with particular emphasis on the regulatory effects and synergistic mechanisms of suspended particle size and mass concentration. The results indicate that particle size is the core controlling factor in turbidity-current scour. For turbidity currents carrying fine particles (0.005 mm), the scour pattern is highly consistent with that of clear-water flow; increasing particle concentration reduces the equilibrium scour depth by less than 12%, and the inhibitory effect on scour rate is relatively weak. In contrast, turbidity currents carrying coarse particles (0.075 mm) alter the evolution pattern of the scour pit, and increasing particle concentration can reduce the equilibrium scour depth by more than 30%. Under high-concentration conditions, overall deposition and complete scour cessation may even occur. These findings provide a theoretical basis for scour-resistant design and safety protection of pile foundations in sea areas affected by sediment-laden turbidity currents.