IS Classification of Soils

Classification of soils based on Indian Standards IS 1498

1. VIJAI KRISHNAN V
M. Tech Student
RIT Kottayam

2. IS Classification System (ISCS)
Similar to USC system
Fine grained soil –subdivided into 3categories
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) –LLb/w 35 & 50
3.High compressibility(H) –LL > 50

5. Groups
Coarsegrained soil –8groups
Finegrained 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 (C
u> 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 (I
p< 4)
4.Clayey Gravel (GC) –fines are of low to medium/high
plasticity (I
p> 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) –C
u> 6 & C
cb/w 1 & 3
6.Poorly graded sand (SP)
II.Dirty Sand –fines > 12%
7.Silty sand (SM) -I
p< 4
8.Clayey sand (SC) -I
p> 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
oIp b/w 4 & 7 ML-CL

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

13. Contd...
High Compressibility (H)
7.MH –Inorganic silts of highplasticity
–Atterberg limits are below A-line
8.CH –Inorganic clay of highplasticity
–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:-
oRoads & airfields-Suitability as subgrade, sub-base
& base
-Potential to frost action
-Drainage characteristics
-Unit weight, CBR-value
-Modulus of subgrade reaction (k)
-Compaction equipment
oEmbankments & Foundations –Permeability...

18. Ex. 1:-
Classify the soil according to IS Classification based
on following plasticity characteristics
oLiquid limit = 40%
oPlasticity 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
oLiquid limit = 28%
oPlasticity 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%
oCoefficient of curvature = 2.5
oUniformity coefficient = 7
oPlasticity Index = 3
Soil is SW-SM