An Investigation of Silty Sediment Erodibility Considering the Effects of Upward Seepage and Slope Gradient

The phenomenon of extensive erosion of silty submarine slopes in the Yellow River delta has been well documented in numerous studies. Due to poor drainage and high compressibility, silty sediments are particularly prone to pore pressure buildup and accumulated seepage under wave and current action, which can influence sediment erodibility (e.g., the critical bed shear stress and the erosion rate under various bed shear stresses). To date, there remains a lack of parametric formulation to quantitatively characterize the erodibility of silty sediments with the coupled effects of the hydraulic gradient of upward seepage and the slope gradient. In this study, a series of laboratory experiments were conducted to explore the erodibility of silt sediments from the Yellow River delta under varying hydraulic gradients of upward seepage and slope gradients. The results reveal that both upward seepage and increased slope gradients can enhance the erodibility of silty sediments. Specifically, as the seepage gradient increases from 0.1 to 0.8, the critical Shields parameter required for initiating silty particle motion decreases linearly, with a reduction rate of 0.01 per 0.1 increase in the seepage gradient, independently of changes in slope gradient. Additionally, the erosion coefficient of silty sediments grows exponentially with rising seepage gradients, with its average growth rate accelerating with increasing slope inclination. For flat sediment beds, the erosion coefficient influenced by upward seepage can be up to five times that in the absence of seepage. An empirical formula for calculating the critical Shields parameter and an erosion model incorporating upward seepage gradient and slope effects were developed through multiple regression analysis, providing an experimental basis for numerical simulations of scour in silty submarine slopes under combined waves and currents.