Part 4 determines the particle-size distribution: dry/wet sieving for the coarse fraction and hydrometer (sedimentation) analysis for silt/clay-size fines. The grading curve (with the Atterberg limits) drives soil classification (IS classification system), filter/drainage design, and liquefaction-susceptibility screening of sands. It is the most-run soil index test.
Key Requirements
•Sieve analysis for the fraction retained on 75 µm; hydrometer/sedimentation for the finer fraction
•Representative, properly prepared sample (IS 2720 Part 1 — preparation of dry soil sample)
•Grading curve → percentage gravel/sand/silt-clay, Cu/Cc; combined with Atterberg limits for classification
•Use the right method for the fraction — sieving alone misses the silt/clay behaviour that governs fine soils
•Feeds filter design, frost/liquefaction screening and the geotechnical report
Reference Tables
IS 2720 — key parts (the soil-test-method family)
Part
Test
Part 4
Grain-size analysis (sieve + hydrometer)
Part 5
Liquid & plastic limit (Atterberg)
Part 7 / 8
Compaction (Proctor) — water content–dry density
Part 16
Laboratory CBR
Part 13
Direct shear test
Part 10
Unconfined compressive strength
Cite the exact part/section; this clause set links the family from the most-used grain-size page.
Practical Notes
✓Grain size + Atterberg limits together classify the soil — neither alone is sufficient for fine-grained soils.
✓Sample preparation (Part 1) decides everything downstream — a non-representative or wrongly-prepared sample invalidates the grading and classification.
Common Mistakes
⚠Sieving only and ignoring the hydrometer fines analysis for silty/clayey soils.
⚠Non-representative / poorly prepared sample (IS 2720 Part 1 not followed).
⚠Classifying soil on grading alone without the Atterberg limits.