Correct Answer - Option 1 : 18
Concept:
It is adopted by IS code. It was given by A-line Casagrande. It uses particle size distribution for Coarse soils and plasticity for fine Soils.
Equation of A-line IP = 0.73 (WL- 20)
Soil classification as per Indian standards:
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Coarse-grained soils
(More than half of the material is larger than 75 μ sieve)
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Gravels
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Sands
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More than half of the coarse fraction is larger than the 4.75 mm sieve
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More than half of the coarse fraction is smaller than the 4.75 mm sieve
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Clean gravel
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Gravel with appreciable fines
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Clean sands
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Sand with appreciable fines
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GW
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GP
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GM
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GC
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SW
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SP
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SM
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SE
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Fine-grained soil
(More than half of the material is smaller than 75 μ sieve)
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Silts and clay
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Low compressibility
(wL < 35)
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Medium compressibility
(50 < wL > 35)
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Higher compressibility
(wL > 50)
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ML
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CL
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OL
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MI
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CI
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OI
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MH
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CH
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OH
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High organic peat soil → (Pt)
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∴ According to IS Classification, there are 18 groups of soils:
8 groups of coarse-grained, 9 group of fine-grained, and 1 of peat
