Grain size analysis (hydrometer, 200 sieves) is any test that seeks to quantify the statistical distribution of different sizes of soil grains within a sample. Soil behavior can be accurately predicted by knowing information such as clay content, fines content (percent of silt and clay), rock content, the uniformity of particles, etc. The most commonly performed grain size analysis test on soils is the “200 wash”, which is a test designed to determine the fines content of a soil, by washing it through a fine mesh steel sieve (No. 200 sieves). Other methods involve shaking a dry sample through a nest of sieves with progressively smaller openings, and hydrometer testing. Hydrometer testing mathematically computes the diameter of silt and clay particles in a soil based on the rate of decline in specific gravity of a soil/water slurry as larger particles settle out of suspension over set time intervals.
