Experimental and DEM Study of Substitution Size Effect in the Direct Shear Behavior of Sand Mixtures

The deficiency of artificial sand in medium-sized particles leads to poor workability. A solution is the partial substitution of medium-sized artificial sand with natural sand particles of the same size range. Therefore, the effect of the particle size of replaced particles on the mechanical behavior of sand samples is an issue worth studying. This study investigates the substitution size effect (SSE) for the first time, defined as the influence of substituted particle size on the mechanical behavior of particles mixtures. Sand mixtures were prepared by substituting artificial sand particles of different size ranges with spherical glass beads of corresponding sizes, while keeping particle shape and grading parameters constant. Three pairs of mixtures with varying substitution sizes were subjected to direct shear tests, supported by macro- and microscale analyses. The findings confirm and quantitatively characterize the SSE and identify particle orientation anisotropy as a key factor in its underlying mechanisms. This mechanism, explored through the lens of interlocking mechanisms via visualization of discrete-element method (DEM) simulation, offers the potential to provide valuable insights into how alternative sand can be effectively used to substitute partial artificial sand particles as a new aggregate with better workability in the future construction industry.