Degradation of soil arching caused by suffusion in gap-graded soils

To investigate evolution of soil arching during suffusion in gap-graded soils, a new suffusion apparatus was developed for trapdoor tests under a horizontal seepage flow. Glass beads with fine-grain contents ranging from 15% to 45% were adopted to represent coarse-grain controlled soils and fine-grain controlled soils. Coupled computational fluid dynamics (CFD) and discrete element method (DEM) models were developed to further investigate the evolution of soil arching from microscopic views. At the early stage of suffusion, soil arching degraded rapidly under seepage loads in both coarse-grain controlled and fine-grain controlled soils due to the compaction of soil skeleton and the clogging of voids, which increased in the number of fine particles connected to the stress-transfer matrix. At the later stage, soil arching was nearly maintained as the soil skeleton became stable in the coarse-grain controlled soils. In the fine-grain controlled soils, soil arching degraded continuously due to continuous loss of fine particles connected to the stress-transfer matrix. The decrease in the contact number of fine particles also made the soil skeleton more vulnerable to suffusion. The degradation of soil arching resulted in an increase of surface displacement and a decrease of soil arching height in fine-grain controlled soils.