Coupled CFD–DEM Investigation of Erosion Accompanied by Clogging Mechanism under Different Hydraulic Gradients

Soil internal erosion refers to any process that the finer grains are eroded from the matrix of coarser grains due to seepage. A coupled computational fluid dynamics and discrete element method (CFD–DEM) analysis of internal erosion is conducted on bimodal soils. The coupled influences of hydraulic gradient i and fine content Fc on different domination process of internal erosion is investigated. It is found that the erosion degree does not always increase as i increases for “underfilled” soil (e.g. Fc = 10 % and Fc = 20 %), there is a hydraulic gradient threshold ith above which local particle clogging plays a dominant role, resulting in a smaller erosion degree instead, the ith is larger for larger Fc, when Fc is equal to 10, the ith is 2 or less, while ith is 4 for the soil with a fine content of 20 %. For “transitional” soil (e.g. Fc = 30 %), no obvious clogging domination under larger i is observed. The mechanism is revealed through both macro- and microquantity perspectives. It is found that local clogging is formed by particle bridge formation under larger i values. These findings are highly significant for further understanding the influence of i on the erosion process and establishing the erosion law.