Macro- and micro-scopic suffusion behavior of gap-graded soils under cyclic hydraulic gradient reversal

Abstract

Wave surging, fracking operations, and tides can cause seepage flow with hydraulic gradient reversals, resulting in complex hydraulic conditions. These complex hydraulic conditions can lead to more intricate suffusion processes, affecting the movement and loss of fine particles, and thereby weakening the internal stability of hydraulic structures. In this study, the coupled computational fluid dynamics and discrete element method (CFD-DEM) was employed to investigate the suffusion behavior of gap-graded soils under cyclic hydraulic gradient reversal. The suffusion behavior of gap-graded soil under constant hydraulic gradient and cyclic hydraulic gradient reversal conditions were first compared. Then, the influences of cyclic frequencies and reversal ratios on the suffusion behavior of gap-graded soils were analyzed. The simulation results show that the fine particle loss of gap-graded soils under cyclic hydraulic gradient reversal is greater than that under constant hydraulic gradient conditions. A higher reversal ratio or lower frequency can lead to a more significant fines loss. During suffusion, the evolution of micro-scale quantities such as fines migration, coordination number, and particle force characteristics is tracked, offering a more insightful explanation for the observed macroscopic behavior of gap-graded soils under cyclic hydraulic gradient reversal.