Shape quantification of volcanic cinders and the influence of particle shape indexes on accumulation characteristics

Volcanic cinder is a low-cost subgrade fill material in East Africa. A reluctance to use volcanic cinders for subgrades in the past has stemmed from the compactness is substandard and variable. Considering the irregular shape of volcanic cinders, the compactness can be improved by controlling particle shapes. The shape feature can be described from the macro-meso-microscopic scales through the improved algorithms of shape indexes, namely elongation (EI), roundness (Rd), and roughness (Rg). The shape indexes were calculated based on 2D contours of 1000 volcanic cinder particles, and the influences of shape indexes on accumulation behaviors are explored from macro-mesoscales through the discrete element method (DEM). The shape indexes of volcanic cinders are normally distributed, and EI has the widest variation range. The mesoscale index Rd has an interval effect on compactness and coordination number, whereas are nearly unaffected by the microscale index Rg. The effect of elongation on particle accumulation behavior is stronger than roundness and roughness. Compactness is positively correlated with EI, and the force-fabric anisotropy degree weakens with increasing EI. Studies of shape quantification provide data reference for improving the utilization rate and accumulation compactness, which promotes the application of volcanic cinders in subgrade constructions.