A coupled CFD-DEM investigation into hydro-mechanical behaviour of gap-graded soil experiencing seepage erosion considering cyclic hydraulic loading

Abstract

The internal erosion of soils is a critical factor that can cause infiltration damage in slope and embankment works. Under conditions of heavy rainfall, storm surge, and waves, the soil is subjected to the cyclic changing hydraulic loads that are different from constant or monotonically changing hydraulic gradient loads, resulting in significant differences in the internal erosion response. The internal erosion response of gap-graded soil under cyclic hydraulic gradient is investigated in microscopic view based on the three-dimensional coupled computational fluid dynamics and discrete element (CFD-DEM) method. Three average hydraulic gradients (i.e., i¯= 7, 9, 11) and different cyclic hydraulic gradient amplitudes (i.e., Δi = 2 ∼ 10) are considered. It is found that the erosion mass me is significantly increased under cyclic hydraulic loading, as the amplitude of the cyclic hydraulic gradient increases, the erosion ratio gradually increases. The particle migration in the upstream layer is more susceptible to the influence of cyclic hydraulic gradients, and the distribution of fine particles is more uniform after erosion with the increase of Δi. The mechanism of the effect of cyclic hydraulic gradient is revealed from a micro perspective, including coordination number, connectivity distribution, particle force characteristics, local packing profile and the force chain evolution, it is found that the cyclic hydraulic loading affects the erosion process mainly by disturb or destroy the local clogging. The work provides insights into the effect of more complex hydraulic loading on internal erosion from a micromechanical perspective.