Soil Particle Size Distribution

Soil contains four primary components, for engineering purposes:

  1. gravel
  2. sand
  3. silt
  4. clay

Organic material can be present in surface samples as well but this has no relevance to engineering applications.

Gravel and sand are classified as coarse-grained, whereas silt and clay are classified as fine-grained.

Various classification schemes exist which attempt to define the grain size distribution of each of the four components. A summary table of these classifications is below:

System Date Sizes (mm)
gravel sand silt clay
Bureau of Soils 1890 1 – 100 0.05 – 1 0.005 – 0.05 < 0.005
Atterberg 1905 2 – 100 0.2 – 2 0.002 – 0.2 < 0.002
MIT 1931 2 – 100 0.06 – 2 0.002 – 0.06 < 0.002
USDA 1938 2 – 100 0.05 – 2 0.002 – 0.05 < 0.002
USCS 1953 4.75 – 75 0.075 – 4.75 < 0.075
ASTM 1967 4.75 – 75 0.075 – 4.75 < 0.075
AASHTO 1970 2 – 75 0.075 – 2 0.002 – 0.075 0.001 – 0.002
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