IS 2720:1975 Part 4 is the Indian Standard (BIS) for methods of test for soils - grain size analysis. This part of IS 2720 covers the method for determining the quantitative particle size distribution in soils. It specifies mechanical sieve analysis for coarse-grained fractions and sedimentation analysis (using either the hydrometer or pipette method based on Stokes' law) for fine-grained fractions passing the 75-micron sieve.
Prescribes methods for determining the grain size distribution of soil samples, crucial for track bed design and foundations.
Quick Reference — IS 2720 Part 4:1975 Soil Grain Size
Sieve and sedimentation analysis for soil particle-size distribution. Sieve sizes, hydrometer procedure, dispersing agents.
| Reference | Value | Clause |
|---|
| Method — coarse fraction (> 75 μm) | Sieve analysis | Cl. 3 |
| Method — fine fraction (≤ 75 μm) | Sedimentation (hydrometer / pipette) | Cl. 4 |
| Coarse-fine boundary (sieve cutoff) | 75 μm (No. 200 sieve) | Cl. 3.1 |
| IS sieve sizes — gravel | 80, 40, 20, 10, 4.75 mm | Table 1 |
| IS sieve sizes — sand | 2.0, 1.0, 0.6, 0.425, 0.3, 0.15, 0.075 mm | Table 1 |
| Sample size — wet sieving | 500 g (clean) to 2 kg (gravelly) | Cl. 3.2 |
| Dry sieving duration | 10 minutes mechanical shaker | Cl. 3.3.2 |
| Wet sieving — agitation | until water passes clear | Cl. 3.3.3 |
| Dispersing agent — sodium hexametaphosphate | 33 g/L (4% solution) | Cl. 4.2.1 |
| Soaking time before sedimentation | ≥ 16 hours | Cl. 4.3 |
| Hydrometer type | ASTM 152H or BS 1377 | Cl. 4.2.5 |
| Sedimentation cylinder volume | 1000 mL | Cl. 4.2.4 |
| Standard test temperature | 27 ± 2°C | Cl. 4.5 |
| Hydrometer reading times | 0.5, 1, 2, 4, 8, 15, 30, 60, 120, 240, 1440 min | Cl. 4.5.5 |
| Stokes' law — falling diameter— K depends on viscosity + density | D (mm) = K × √(L/t) | Annex B |
| Particle classification — boulder | > 300 mm | (Linked to IS 1498) |
| Particle classification — cobble | 80–300 mm | |
| Particle classification — gravel | 4.75–80 mm | |
| Particle classification — sand | 0.075–4.75 mm | |
| Particle classification — silt | 0.002–0.075 mm | |
| Particle classification — clay | < 0.002 mm | |
⚠ Methods of Test for Soils — Part 4: Grain Size Analysis. Forms the basis of IS 1498 soil classification.
Overview
- Status
- Current
- Usage level
- Essential
- Domain
- Geotechnical — Railway Engineering
- Type
- Testing Method
Also on InfraLens for IS 2720
Practical Notes
! Inadequate chemical dispersion or omitting the dispersing agent causes flocculation of clay particles, heavily underestimating the actual clay content.
! Always apply temperature, meniscus, and dispersing agent corrections to hydrometer readings for accurate grain-size calculations.
! Ensure the soil is washed gently over the 75-micron IS sieve during wet sieving to prevent the breakdown of individual fragile particles.
Frequently referenced clauses
soilclaysiltsandgravel
International Equivalents
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We're adding equivalent international standards for this code.
Key Values5
Quick Reference Values
boundary coarse and fine soil75 microns
boundary gravel and sand4.75 mm
sodium hexametaphosphate dose33 g/litre
sodium carbonate dose7 g/litre
standard test temperature27°C
Key Formulas
D = sqrt([30 * η * He] / [(G - 1) * γw * t]) — Stokes' Law for equivalent particle diameter
N = (W_D / W) * 100 — Percentage finer than a given diameter
Tables & Referenced Sections
Key Tables
Table 1 - Minimum Quantities of Soil for Sieve Analysis
Table 2 - Properties of Distilled Water (Viscosity and Density)
Key Clauses
Clause 3 - Preparation of Sample
Clause 4 - Sieve Analysis
Clause 5.1 - Sedimentation Analysis (Pipette Method)
Clause 5.2 - Sedimentation Analysis (Hydrometer Method)
Clause 6 - Calculations
Frequently Asked Questions4
When should sedimentation analysis be performed?+
When a significant proportion of the soil passes the 75-micron IS sieve, making it necessary to distinguish between the silt and clay fractions.
What dispersing agent is used for sedimentation?+
A standard mixture of 33g Sodium hexametaphosphate and 7g Sodium carbonate per litre of distilled water.
How is the meniscus correction applied in hydrometer testing?+
The meniscus correction is always added (positive) to the observed hydrometer reading.
What principle governs sedimentation analysis?+
Stokes' Law, which calculates the settling velocity of spherical particles in a viscous fluid.