The Indian Standard Soil Classification System classifies soils into 18 groups based on particle size and composition. Soils are divided into three broad divisions: coarse-grained soils subdivided into 8 groups, fine-grained soils subdivided into 9 groups, and peat which is its own group. Coarse-grained soils are those where 50% or more of the material is retained on a 75 micrometer sieve. Fine-grained soils are those where more than 50% of the material passes a 75 micrometer sieve. The system further classifies soils based on gradation and the presence of silt or clay fines.

1. CE6405 SOIL MECHANICS
V.Nageshwaran, M.E.,
Assistant Professor,
Department of Civil Engineering,
UCET

2. SOIL CLASSIFICATION

3. INDIAN STANDARD SOIL CLASSIFICATION SYSTEM
 Published in 1959 and Revised in 1970.
 Revision is based on USCS – Fine Grained Soils – Subdivided
into 3 Sub-groups of Low, Medium & High Compressibility. (2 in
USCS)
 Lab Classification Criteria for Coarse Grained Soil – Same as in
the USCS.
 Soils are divided into three broad divisions:
 Coarse Grained Soil – Subdivided into 8 Basic Soil Groups –
when 50 % or more of the total material by weight retained on 75
µm IS sieve.
 Fine Grained Soils – Subdivided into 9 Basic Soil Groups – when
more than 50 % of the total material passes 75 µm IS sieve.
 If the soil is highly organic and contains a large percentage of
organic matter and particles of decomposed vegetation, it is kept
in a separate category marked as peat (Pt)
 Totally, 18 groups of soils: Coarse-grained soils – 8 groups Fine-
grained soils – 9 groups Peat – 1 group.

6. PARTICLE SIZE AND GROUP SYMBOLS (ISSCS)

7. INDIAN STANDARD SOIL CLASSIFICATION SYSTEM

8. INDIAN STANDARD SOIL CLASSIFICATION SYSTEM

9. CONT…
 According to gradation, they are further grouped as well-
graded (W) or poorly graded (P). If fine soils are present,
they are grouped as containing silt fines (M) or as
containing clay fines (C).
 'A' line in this chart is expressed as IP = 0.73 (WL - 20).
 Depending on the point in the chart, fine soils are divided
into clays (C), silts (M), or organic soils (O).
 The organic content is expressed as a percentage of the
mass of organic matter in a given mass of soil to the mass
of the dry soil solids.

10. GC