Are Sieving and Sedimentation Still Fit-for-Purpose? A Comparison with Dynamic Image Analysis for Soil PSD

Abstract

Particle size distribution (PSD) is a fundamental parameter in soil characterization because it strongly influences macroscopic properties such as packing, pore structure, permeability, and mechanical behaviour. In routine geotechnical practice, PSD is still mainly determined by dry sieving for coarse fractions and sedimentation for fines. Although these methods are standardized and widely used, they provide method-defined size measures and do not capture particle morphology. Dynamic image analysis (DIA) offers an alternative by measuring both particle size and shape with lower operator burden and potentially lower cost.

This study evaluates whether conventional PSD methods remain fit for purpose by comparing dry sieving and sedimentation with DIA across shape-controlled reference materials and representative engineering soils and powders. For coarse particles, the DIA minimum-dimension metric showed the closest agreement with sieving, confirming that sieve-based sizing is primarily controlled by the smallest particle dimension. For fine materials, sedimentation generally agreed best with minimum-type DIA metrics, but agreement decreased toward the finest sizes and deteriorated markedly for clay-rich materials. Overall, conventional methods remain useful reference procedures, whereas DIA provides a faster and more informative route to PSD determination, supporting more reliable method selection in laboratory practice.