Exploring the effect of 3D grain shape on the packing and mechanical behaviour of sands

This paper investigated the dependence of three-dimensional grain shape characteristics on particle size by applying X-ray micro-computerized tomography. A series of packing and triaxial shearing experiments are performed, which suggest that the macroscale behaviour of sands at different scales of stress states progressively correspond to the characteristic scales of the microscale morphological descriptors of particles. That is, the packing behaviour are more reliant on grain aspect ratio (AR), whereas the critical state mechanical behaviour are more reliant on grain sphericity. As the AR of particulates increases, the extreme void ratios and packing index decrease. The shearing friction angles at the critical state decrease as the sphericity of grains increases and the intercept void ratios become smaller. The drained peak friction angles and maximum friction angles of undrained stable and strain-hardening specimens of angular sands are larger than those of rounded sands at the same state parameter level because the interlocking of angular sands with many projecting corners is stronger than that of rounded sands during shearing. At the same initial state level, rounded sands are more susceptible to softening and liquefaction than angular sands under undrained conditions, because smooth corners permit easier grain rotations in undrained unstable specimens.