Multiscale Morphological Effects on Stress-Dilation Behaviors of Natural Sands: A 3D Printing Simulation Method

Abstract

Particle morphology is a basic inherent feature of granular materials that plays an important role on their macroscopic behaviors. A multiscale description of particle morphology is generally developed from three levels: large (general form), medium (local roundness), and small (surface roughness). The morphological features of two typical natural sands (Fujian sand and calcareous sand) were investigated in the present study based on spherical harmonic (SH) analysis. Three-dimensional (3D) printing was employed to develop the mass manufacture of grains with independent control of morphology and material properties. Full-scale morphologies of the sphere, Fujian sand (FS) as well as calcareous sand (CS), and single-scale morphologies of calcareous sand at large-(CS24), medium-(CS58), and small-(CS915) levels were printed. A series of triaxial tests were performed on these printed grains to explore their strength-dilation behaviors. The results suggested obvious strain-softening and volume-dilation behaviors were observed at a confining pressure varying from 20 to 100 kPa. A significant enhancement of both shear strength and bulk dilation was indicated from irregularly shaped particles compared with the volume-equivalent spheres. Also, the morphologically derived enhancement of shear strength is weakened from the general form to surface roughness while the enhancement of dilation is the strongest at the medium-scale level of local roundness, indicating different morphological origins between strength and dilatancy. In addition, Bolton’s dilatancy coefficient is a fixed value of 0.452 in this paper, independent of particle shape.