Effect of fines loss on the microstructure and shear behaviors of gap-graded soils: A multiscale perspective

Natural sand is typically composed of both coarse and fine particles and are susceptible to suffusion erosion under seepage effect. Fines loss caused by suffusion is a critical factor affecting the mechanical and hydraulic properties of soils. This paper investigates the effect of fines loss on the microstructure and shear behaviors of gap-graded soils using a three-dimensional finite element and discrete element coupling method. A modified particle removal scheme based on the internal moment tensor is first presented, which is utilized to generate several specimens with varying degrees of fines loss. The macroscopic shear responses of both eroded and noneroded specimens are benchmarked using the responses of representative volume elements (RVEs) in pure discrete element method (DEM). The results reveal that the eroded specimen exhibits a reduced peak stress ratio yet almost unchanged critical state values compared to the non-eroded specimen. Fines loss restrains the formation of shear band and results in more uniform stress and strain distribution inside the specimens. In addition, fine particles in gap-graded soils only sustain a small proportion of external loads, particularly for the specimens with more fines loss. The RVEs at different locations of the specimens are found to exhibit distinct packing assemblies and force networks at the end of shearing.