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 used to determine the particle size distribution of soil. It plays a crucial role in highway and civil engineering projects.
Proper soil gradation ensures good drainage, uniform compaction, and strong load-bearing capacity. Coarse-grained soils are generally suitable for sub-base layers, while fine-grained soils may require stabilization.
2. Purpose of Grain Size Analysis
- Determine particle size distribution and gradation
- Assist in soil classification (Gravel, Sand, Silt, Clay)
- Design subgrade, embankment, and pavement layers
- Assess permeability and drainage characteristics
- Guide soil stabilization decisions
3. Applicable Standards
- IS 2720 (Part 4) – Grain Size Analysis
- IS 2720 (Part 1) – Sample Preparation
- MoRTH Specifications – Subgrade, GSB & WMM
- ASTM D6913 / D422 – International standards
4. Apparatus Required
- Standard sieve set (4.75 mm to 75 μm)
- Mechanical sieve shaker
- Weighing balance (0.1 g accuracy)
- Oven (105°C to 110°C)
- Hydrometer (for fine soils)
- Brush, spatula, containers
5. Sample Preparation
The soil sample should be oven-dried at 105°C–110°C and cleaned of organic matter. Lumps should be broken gently without crushing particles.
- Take ~500 g dry soil sample
- Ensure moisture content is minimal
- Remove oversized particles and debris
- Mix thoroughly for uniformity
6. Test Procedure – Sieve Analysis
Step 1: Dry Sieving
- Arrange sieves in descending order
- Place sample on top sieve
- Shake for 10–15 minutes
- Weigh retained soil on each sieve
Step 2: Wet Sieving (Optional)
- Soak soil to break clay lumps
- Use dispersing agent if required
- Wash and dry before weighing
Step 3: Hydrometer Analysis
- Prepare soil suspension
- Take readings at intervals
- Calculate % finer using Stokes’ law
7. Calculations
| 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 |
Uniformity Coefficient: Cu = D60 / D10
Coefficient of Gradation: Cc = (D30²) / (D10 × D60)
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8. Soil Classification
- Gravel: > 4.75 mm
- Sand: 0.075 – 4.75 mm
- Silt: 0.002 – 0.075 mm
- Clay: < 0.002 mm
9. Engineering Significance
- Well-graded soil provides better strength and compaction
- Uniform soil has higher voids and lower stability
- Critical for subgrade and embankment design
- Helps in drainage and pavement design
10. Common Mistakes
- Improper drying of soil sample
- Insufficient shaking time
- Incorrect weighing
- Ignoring fine particle analysis
11. FAQs
What is the purpose of grain size analysis?
To determine soil gradation and suitability for construction.
Which IS code is used?
IS 2720 Part 4.
Can sieve and hydrometer be used together?
Yes, for complete particle size distribution.
12. Conclusion
Grain Size Analysis is essential for highway engineering. It ensures proper soil selection, improves design accuracy, and helps achieve durable pavement structures.