Grain Size Analysis of Soil – Sieve Analysis Procedure, Calculation & Interpretation
1. Introduction
The Grain Size Analysis of Soil, commonly known as the Sieve Analysis, is a fundamental laboratory test to determine the particle size distribution of soil. Understanding soil gradation is essential for designing pavements, embankments, subgrades, and other civil engineering structures. This test provides critical data for evaluating soil compaction, permeability, and stability.
Soil in natural deposits contains a mixture of gravel, sand, silt, and clay. Proper gradation ensures good drainage, uniform compaction, and strong load-bearing characteristics. Coarse-grained soils are better for pavement sub-base, whereas fine-grained soils may need stabilization.
2. Purpose of Grain Size Analysis
- Determine particle size distribution and gradation
- Assist in soil classification (Gravel, Sand, Silt, Clay)
- Design highway subgrades, embankments, and pavement layers
- Assess permeability and drainage characteristics
- Guide soil stabilization or replacement decisions
3. Applicable Standards
- IS 2720 (Part 4) – Grain Size Analysis / Sieve Analysis
- IS 2720 (Part 1) – Preparation of dry sample
- MoRTH Specifications – Subgrade, GSB & WMM layer quality
- ASTM D6913 / D422 – International reference for particle size distribution
4. Apparatus Required
- Set of standard sieves (4.75 mm to 75 μm) with pan and lid
- Mechanical or hand shaker
- Weighing balance (accurate to 0.1 g)
- Oven for drying soil samples
- Glass or plastic containers for sample handling
- Hydrometer (for fine soils & particle <0.075 mm)
- Spatula, brush, and sieve brush
5. Sample Preparation
Proper sample preparation is crucial for accurate results. The soil sample should be air-dried or oven-dried at 105°C to 110°C. Remove organic matter, stones, and debris before testing. If lumps are present, break them gently without crushing the particles.
Example: For a 500 g test sample:
- Weigh 500 g of dry soil
- Ensure moisture content < 2%
- Remove stones > 20 mm and organic debris
- Mix well to homogenize
- Split sample if needed for multiple tests
6. Test Procedure – Sieve Analysis
Step 1: Dry Sieving
- Stack sieves in decreasing order of aperture size, largest on top, smallest at bottom.
- Place a pan at the bottom to collect soil passing the smallest sieve.
- Pour the soil sample on top sieve evenly.
- Use mechanical shaker or hand shake for 10–15 minutes.
- Weigh soil retained on each sieve and record the values.
Step 2: Wet Sieving (Optional for cohesive soils)
- Soak sample in water to disintegrate clay lumps.
- Use dispersion solution (e.g., 0.1 N NaOH) for high plasticity soils.
- Wash soil over the sieve stack and allow to dry before weighing retained soil.
Step 3: Hydrometer Analysis (Fines <0.075 mm)
- Prepare a dispersed soil suspension in distilled water using dispersing agent.
- Pour into cylinder and insert hydrometer.
- Record hydrometer readings at standard intervals (e.g., 1, 2, 4 hours).
- Calculate % finer using Stokes’ law and temperature corrections.
7. Calculations
Determine cumulative percentage retained and passing:
| Sieve Size (mm) | Weight Retained (g) | % Retained | Cumulative % Retained | % Passing |
|---|---|---|---|---|
| 20 | 50 | 10 | 10 | 90 |
| 10 | 100 | 20 | 30 | 70 |
| 4.75 | 150 | 30 | 60 | 40 |
| 2.36 | 80 | 16 | 76 | 24 |
| 0.425 | 70 | 14 | 90 | 10 |
| 0.075 | 50 | 10 | 100 | 0 |
Plot particle size distribution curve with sieve size (log scale) vs % passing.
Uniformity and Coefficient of Gradation
Uniformity Coefficient: Cu = D60 / D10
Coefficient of Gradation: Cc = (D30)^2 / (D10 × D60)
Where D10, D30, D60 = particle sizes corresponding to 10%, 30%, 60% passing.
8. Soil Classification
Based on particle size distribution, classify soil as:
- Gravel: >4.75 mm
- Sand: 0.075 – 4.75 mm
- Silt: 0.002 – 0.075 mm
- Clay: <0.002 mm
Soil gradation impacts compaction, permeability, and pavement design. Well-graded soil (GW/GP) is preferred for embankments and subgrade layers.
9. Engineering Significance
- Well-graded soils have higher density, strength, and lower permeability.
- Uniformly graded soils may lead to higher voids and lower stability.
- Critical for subgrade, embankment, and base layer design in highways.
- Determines suitability for GSB/WMM layer and drainage planning.
10. Common Mistakes
- Using wet lumps without proper dispersion
- Inadequate shaking duration or intensity
- Improper oven drying of sample
- Neglecting hydrometer method for fines
- Incorrect weighing of retained soil
11. FAQs
What is the purpose of grain size analysis?
To determine soil gradation, particle size distribution, and suitability for subgrade or embankment design.
Which IS code covers sieve analysis?
IS 2720 Part 4 – Grain Size Analysis.
How often should this test be performed on site?
One test per 500–1000 m² of embankment or subgrade, depending on project QA/QC plan.
Can both sieve and hydrometer methods be used together?
Yes, sieve for particles >0.075 mm and hydrometer for fine particles <0.075 mm for complete distribution.
Why is well-graded soil preferred?
Well-graded soil has lower voids, higher stability, and better load-bearing capacity.
12. Conclusion
Grain Size Analysis of Soil is a critical test in highway and civil engineering projects. Accurate sieve and hydrometer analysis provides particle size distribution, guides subgrade, embankment, and base layer design, ensures MoRTH compliance, and prevents structural failures. Always conduct this test for durable and stable pavement structures.