Seabed scour beneath an unburied pipeline under regular waves

The scouring of seabed beneath an unburied pipeline under regular waves was investigated in a large wave flume. Sands and silts were employed for the contrast experiment and the results obtained were compared with data from literature. It was found that the standard formula of Sumer and Freds?e was best at predicting scour depth of sands while underestimating that of sandy silts; time evolution of sand-scour depth better followed traditional exponential curves than did those of sandy silts; an empirical formula in the form of is suggested for predicting the non-dimensional time scale of the scour process beneath pipeline in the Yellow River delta. The underestimated scour depth of silts was related to the wave-induced pore pressure responses not found in sands. It was wave-forced seepage flows that promoted the normal scour process during the initial period by exerting an uplifting seepage force on the surface particles.