|
The soil particles vary in shape from spherical to angular. They differ in
size from gravel and sand to fine clay. The effective size limits adopted
are given in Table 2.
Table 2. Particle sizes--USDA and International Classification
Systems.
|
International or Atterberb system |
USDA system |
|
(Diameter in mm) |
|
| Gravel |
2 and more |
2 and more |
| Very coarse sand |
2-1 |
- |
| Coarse sand |
1.0-0.5 |
2.0-0.2 |
| Medium sand |
0.5-0.25 |
- |
| Fine sand |
0.25-1 |
0.2-0.02 |
| Very fine sand |
0.10-0.05 |
- |
| Silt |
0.05-0.02 |
0.02-0.002 |
| Clay |
less than 0.002 |
less than 0.002 |
While the International
System is commonly used to designate textures, the US system is necessary
for classifying soils according to Soil Taxonomy which is being adapted in
the soil-survey organizations all over the country. |