I.S. classification of soil:
The soils are classified by Indian standard code i.e. IS 1498:1970 into three categories.
1.Coarse grained soil:
In these soils, more than half of total soil by weight is larger than 75 micron I S. sieve size.
The coarse grained soil is further classified as follows.
i. Boulders having particle size more than 300 mm.
ii. Cobble having particle size between 80mm to 300mm.
iii. Coarse gravel having size 20mm to 80 mm.
iv. Fine gravel having size 4.75mm to 20 mm.
v. Coarse sand having size 2mm to 4.7mm.
vi. Medium sand having size 425 micron to 2mm.
vii. Fine sand having size 75 to 425 micron.
2. Fine grained soil:
In these soils, more than half of total soil by weight is smaller than 75 micron I.S sieve size.
The fine grained soil is further classified as follows.
i. Silt having particle size 2 to 75 micron.
ii. Clay having particle size less than 2 micron.
3. Highly organic soil:
These soils contain large percentage of fibrous organic matter such as peat and particles of decomposed vegetation. In addition, certain soils containing shells, concretions, cinders and other non-soil materials in sufficient quantities are grouped under this category.