Suffusion in gap-graded granular soils subjected to strain-controlled cyclic loading with coupled CFD-DEM method

The suffusion mechanism of gap-graded soils subjected to cyclic loading, which is common in foundations of transportation engineering and marine structures, has not been fully understood. This paper employs the coupled computational fluid dynamics and discrete element method (CFD-DEM) to investigate the effect of cyclic loading on suffusion. The cyclic loading is simulated in a strain-controlled way, by which, samples with different frequencies (i.e., 0.5 Hz, 1 Hz, and 2 Hz) and strain amplitudes (i.e., 0.5 %, 1 %, 2 %) undergo erosion of 20 s duration with a constant hydraulic gradient and confining pressure. The influence of cyclic loading on suffusion is examined from both the macroscopic and microscopic perspective through the capture of erosion mass, void ratio variation, particle velocity field, fines trajectory, and force chain. Results indicate that the higher the cyclic frequency and strain magnitude, the more severe the loss of the fines. The vibratory compaction of dynamic loading could lead to the clogging of the sample, decreasing the hydraulic conductivity. In addition, the different micromechanisms of fines erosion during loading and unloading is presented.