Indian Standard Soil Classification system (ISSCS)
The three major groups in the Indian Standard Soil classification system(ISSCS) are coarse grained, fine grained, peat/organic.
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How is soil classified?
• Coarse grained soil classification by Grain Size Distribution
• Fine grained soil classification by Consistency and Plasticity Index
What are the different methods?
• Unified soil classification system(USC)
• American Association of State Highways and Transport office system(AASHTO)
• Indian Standard Soil classification system(ISSCS).
The three major groups in ISSCS are coarse grained, fine grained, peat/organic.
Sieve Analysis for grain size distribution
Sieve analysis is used for grain size distribution. Different sizes of sieves are used to classify the soil.
Sieve analysis by mechanical shaking (10-15min).
• % retained on a sieve = (Weight of soil retain ×100)/(Total weight taken)
• Cumulative % retained = sum of % retained on all the sieves of larger size and that of a particular size.
• % finer than the sieve under consideration=100-cumulative %retained
Coarse Grained (ISSCS)
It is coarse-grained when % retained in 75-micron sieve is greater than 50%.
Gravel: If %retained on 4.75mm is greater than 50%.
• If %fines passing 75microns <5% and Cu greater than 4 and Cc between 1-3 then GW(Well graded Gravel).
• If any of this condition fails then GP(Poorly graded Gravel)
Sand: If %retained on 4.75mm is greater than 50%.
• If %fines passing 75microns <5% and Cu greater than 6 and Cc between 1-3 then SW(Well graded Sand)
• If any of this condition fails then SP(Poorly graded Sand).
It is fine-grained when % retained in 75-micron sieve is less than 50%. Further classification (See the image above) depends on the liquid limit, plasticity index and A-line.