The document discusses various soil classification systems, particularly focusing on the Unified Soil Classification System (USCS) and the Indian Standard Soil Classification System (ISSC). It categorizes soils into coarse-grained and fine-grained based on grain size distribution and plasticity characteristics, with further subdivisions for different types of soils. Key features such as group symbols and the plasticity chart are also highlighted to differentiate soil properties.

1. Classifications of Soils
Dr. Dipjyoti Baglari
JIST, Jorhat

2. General Introduction
• Soil may be classified as:
– Cohesionless or coarse grained
– Cohesive or Fine grained
• But these are too general term and requires
further classification
• Thus objective of soil classification system is to
sort or group soils in different category, each
group showing similar properties
• The most commonly used properties are grain
size distribution and plasticity

3. Various soil classification system
• Unified soil classification system (USCS)
• American Assocation of state highway and
Transport Officials (AASHTO)
• Indian Standard Soil classification System
(ISSCS)

4. USCS System (Overview)
• The coarse grained soils are classified on the basis of their
grain size distribution and the fine grained soils on the basis of
their plasticity characteristics
• Here all the soils are classified in four major groups
– Coarse grained
– Fine grained
– Organic soils and peat
• Group symbols consisting of a prefix
and suffix are used for various groups

5. USCS System (Overview)
• Coarse grained soils are those having 50% or
more retained on 0.075mm sieve
• Coarse grained soil
• Gravel (G)
• Sand (S)
The coarse soil is termed as Gravel (G) if 50% or more is
retained on 4.75mm sieve otherwise termed S
• Both gravel and sand are further divided into
– GW and SW
– GP and SP
– GM and SM
– GC and SC

6. USCS System (Overview)
• Fine grained soils are those which has 50% or
more passes through 0.074mm sieve
• Fine grained soil
– Silt
– Clay
Based on its liquid limit and plasticity index

7. Plasticity Chart
• The A-line on the plasticity chart separates
clay and silt (also organic soils)
• Silt, clay and
organic soils are
further classified
into Low (L) and
High (H) plasticity
depending upon
liquid limit

8. Indian Standard Soil classification System (ISSCS)