A theoretical hydrodynamic modification on the soil texture analyses obtained from the hydrometer test

The hydrometer test is one of the most reliable approaches to estimate the particle size distribution of fine-grained soil. The general approach neglects the particle hydrodynamic interactions which are known to hinder the settling rate of particles, and, as such, generally leads to an underestimation of the particle diameters. In this study, a theoretical hydrodynamic correction of the hydrometer test is proposed to account for the hindered velocity of particles settling through a suspension of monomodal spherical or non-spherical particles. The polydisperse nature of soil samples is then taken into consideration by introducing an effective volume fraction of particles for each partially sorted monomodal layer of particles. Using this approach, a model to correct for particle hydrodynamic interactions in conventional hydrometer tests is provided and tested successfully against results from laser diffraction measurements.