Grain Size Distribution Using Sieve Analysis and Hydrometer Method

If the mass percentage of the grains with a diameter smaller than 0.0025 in (0.063 mm) in a given soil sample is small (≤ 3%), the grain size distribution curve can be determined by dry screening only.

If the mass percentages of these small grains are too high, a combined screening- and sedimentation analysis or hydrometer method has to be carried out.

“In the sedimentation process the grain size distribution of the particle percentages that are smaller than 0.005 in (0.125 mm) is determined. Particles with sizes smaller than 0.000039 in (0.001 mm) cannot be classified any further using this method“ [DIN18123].

Accordingly, [ASTM D422] says that "the distribution of particle sizes smaller than 75 μm (0.003 in / 0.075 mm) retained on the No. 200 sieve is determined by a sedimentation process, using a hydrometer to secure the necessary data.