Investigation of Suffusion in Soil with Arching Based on CFD-DEM Simulation

The nonuniform stress distribution caused by soil arching can affect suffusion in soil under seepage. To investigate the development of suffusion in soil with arching and the evolution of soil arching during suffusion, coupled computational fluid dynamics (CFD) and discrete-element method (DEM) simulation of trapdoor tests under horizontal seepage flow was performed. A soil sample susceptible to suffusion was prepared by mixing particles in two sizes with a size ratio of 5.0. Soil arching consisting of stress reduction and concentration areas was formed by lowering the trapdoor at the bottom of the model and then a horizontal seepage flow was introduced to trigger soil suffusion. It was discovered that, due to the existence of soil arching, the fine particles within the stress reduction area were more prone to migrate, while the fine particles within the stress concentration areas were hindered by strong force chains. Soil arching degrading with the suffusion process was characterized as the decrease of critical soil arching height and soil arching ratio, the breakage of horizontal force chains, and the reconnection of vertical force chains. The degradation of soil arching during suffusion led to additional surface settlement during the postsuffusion stage.