The document describes the Indian Standard (IS) Classification System for soils. It divides soils into 3 main categories - coarse grained, fine grained, and highly organic soils - based on grain size. Coarse grained soils are further divided into gravel and sand, each with subcategories based on fines content and plasticity. Fine grained soils are subdivided into low, intermediate, and high compressibility categories based on liquid limit and plasticity index. The document provides detailed explanations of each soil group and examples of classifying soils according to their properties.

1. VIJAI KRISHNAN V
M. Tech Student
RIT Kottayam

2. IS Classification System (ISCS)
 Similar to USC system
 Fine grained soil – subdivided into 3 categories
 Low compressibility
 Medium Compressibility
 High compressibility

3. Divisions
1. Coarse Grained Soils
 More than 50% of total material by weight > 75μ
2. Fine Grained Soils
 More than 50% of total material by weight < 75μ
3. Highly Organic & other miscellaneous soils
 Contain large % of fibrous organic matter
 Peat, decomposed vegetation particles, shells,
cinders & other non-soil materials

4. Sub-divisions
 Coarse Grained Soils
1. Gravels – more than 50% of coarse fraction > 4.75mm
2. Sands – more than 50% of coarse fraction < 4.75mm
 Fine Grained Soils
 Silt & clays of :-
1. Low compressibility (L) – Liquid limit < 35
2. Medium compressibility(I) – LL b/w 35 & 50
3. High compressibility(H) – LL > 50

5. Groups
 Coarse grained soil – 8 groups
 Fine grained soil – 9 groups
 Highly organic and other miscellaneous soils
as separate group
TOTAL = 18 Groups
 Groups are designated by symbols

6. Basic Soil Components

7. Contd...

8. Classification of Coarse Grained Soils
 Gravel (G)
I. Clean Gravel – fines < 5%
1. Well Graded Gravel (GW) – all particle sizes (Cu > 4)
2. Poorly Graded Gravel (GP) – excess or absence of
intermediate particle sizes
II. Dirty Gravel – fines > 12%
3. Silty Gravel (GM) – little fine/no plasticity (Ip < 4)
4. Clayey Gravel (GC) – fines are of low to medium/high
plasticity (Ip > 7)
Boundary classification – GM-GC (Ip b/w 4 & 7) &
GW-GM, GW-GC, GP-GM (fines 5-12%)

9. Contd...
 Sand (S)
I. Clean Sand – fines < 5%
5. Well graded sand (SW) – Cu > 6 & Cc b/w 1 & 3
6. Poorly graded sand (SP)
II. Dirty Sand – fines > 12%
7. Silty sand (SM) - Ip < 4
8. Clayey sand (SC) - Ip > 7
 Boundary classification  SM-SC (Ip b/w 4 & 7)
& SW-SM, SW-SC, SP-SM (fines 5-12%)
 Boundary classification b/w gravel & sand group
 GW-SW, GP-SP, GM-SM, GC-SC

11. Classification of Fine Grained Soils
 Low Compressibility (L)
1. ML – Inorganic silts of none to low plasticity
– Ip < 4 & Atterberg limits are below A-line
2. CL – Inorganic clay of low plasticity
– Ip > 7 & Atterberg limits are above A-line
3. OL – Organic silt of low plasticity
– Atterberg limits are below A-line
o Ip b/w 4 & 7  ML-CL

12. Contd...
 Intermediate Compressibility (I)
4. MI – Inorganic silts of medium plasticity
– Atterberg limits are below A-line
5. CI – Inorganic clay of medium plasticity
– Atterberg limits are above A-line
6. OI – Organic silt of medium plasticity
– Atterberg limits are below A-line

13. Contd...
 High Compressibility (H)
7. MH – Inorganic silts of high plasticity
– Atterberg limits are below A-line
8. CH – Inorganic clay of high plasticity
– Atterberg limits are above A-line
9. OH – Organic silt of high plasticity
– Atterberg limits are below A-line

14. High Organic Soil
 Peat & other highly organic soils
 Denoted as Pt
 Identified by
 Colour
 Odour
 Spongy feel
 Fibrous texture

16. Plasticity Chart
 For classifying fine grained soil
 A – line Ip = 0.73 (LL – 20)
 Boundary classification on plasticity chart

17.  Also included in IS 1498-1970
 Characteristics of each soil groups pertinent to:-
o Roads & airfields - Suitability as subgrade, sub-base
& base
- Potential to frost action
- Drainage characteristics
- Unit weight, CBR-value
- Modulus of subgrade reaction (k)
- Compaction equipment
o Embankments & Foundations – Permeability...

18.  Ex. 1:-
 Classify the soil according to IS Classification based
on following plasticity characteristics
o Liquid limit = 40%
o Plasticity Index = 10%
o %age of soil passing 0.075mm = 55%
o %age of soil passing 4.75mm = 99%
 Soil is MI or OI

19.  Ex. 2:-
 Classify the soil according to IS Classification based
on following plasticity characteristics
o Liquid limit = 28%
o Plasticity Index = 12%
o %age of soil passing 0.075mm = 13%
o %age of soil passing 4.75mm = 62%
 Soil is SC

20.  Ex. 3:-
 Classify the soil according to IS Classification based
on following plasticity characteristics
o %age of soil passing 0.075mm = 8%
o %age of soil retained 4.75mm = 35%
o Coefficient of curvature = 2.5
o Uniformity coefficient = 7
o Plasticity Index = 3
 Soil is SW-SM