Experimental Study on the Influence of Seepage on Sediment Initiation Under Steady and Oscillatory Flows

Sediment incipient motion is a crucial stage in the erosion process, making it imperative to study its mechanism. Seepage can significantly alter hydrodynamic forces around soil particles near seabed surfaces and affect erosion processes. Most previous studies ignored the effect of seepage by assuming the seabed surface as impermeable. Some studies attempted to clarify the effect of seepage force on sediment initiation theoretically, but quantitative analysis through laboratory tests is necessary. In this study, an in-house designed Erosion-Seepage System (ESS) is used to simulate the erosion process with seepage under either steady or oscillatory flow. Through the designed ESS, the erosion rate and seepage can be directly determined and their relationship can be established. The experimental results show that the upward seepage reduces the initial shear stress of the sandy bed under a steady flow. Furthermore, the upward seepage under an oscillatory flow also results in a reduction of the shear stress amplitude required for the motion of the sediment as well as an increase in the erosion rate. In addition, the erosion rate becomes more pronounced for large seepage.