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.
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
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
10.
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
15.
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