CFD-DEM simulations of the effect of fines content on suffusion characteristics in gap-graded sandy gravels
Fines content(FC)is one of the geometric conditions determining whether suffusion occurs and has a complex influence on suffusion characteristics.Based on the computational fluid dynamics-discrete element method(CFD-DEM)coupling approach,numerical simulation tests for suffusion were conducted on gap-graded sandy gravels with two hydraulic gradients and seven FCs.The mechanism of fines content's effect on suffusion was investigated from both macroscopic and microscopic perspectives.The results show that the pore states of the soil can be classified into four types according to the FC:underfilled,filled,partially overfilled(where coarse particles are partially separated by fines),and completely overfilled(where coarse particles are completely separated by fines).In the underfilled state(i.e.,FC≤-25％),the erosion rate of fines increases with rising FC,but decreases during the transition from underfilled to filled states(i.e.,FC=30％).This is primarily because the void ratio of filled soil reaches its minimum,making it hard for fine particles to migrate.Subsequently,as the FC continues to increase,the erosion rate rises again.However,the erosion type gradually shifts from suffusion to backward erosion.The erosion mechanism can be determined through a comprehensive analysis of particle migration distribution and the composition of eroded particles.Specifically,in the case of partially overfilled soil(i.e.,FC=35％),it displays a transitional internal stability and exhibits suffusion.Conversely,for samples in a completely overfilled state(i.e.,FC=40％),fines cannot migrate through the pores,leading to backward erosion during testing.
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