Highway QA/QC Mastery Series Part-8 – Grain Size Analysis (Sieve Analysis Test) Complete Guide
Grain Size Analysis soil mechanics और highway engineering का एक fundamental laboratory test है जिसका उपयोग soil particles के size distribution को determine करने के लिए किया जाता है। यह test soil classification, gradation assessment, compaction behavior prediction, drainage characteristics evaluation तथा pavement material suitability determination के लिए अत्यंत महत्वपूर्ण माना जाता है।
Highway projects में embankment, subgrade, Granular Sub Base (GSB), Wet Mix Macadam (WMM), drainage layers तथा filter materials की quality assessment के लिए grain size distribution का knowledge आवश्यक होता है।
IS 2720 (Part 4), IS 1498, MoRTH Specifications तथा IRC guidelines के अनुसार Grain Size Analysis geotechnical investigations तथा highway material quality control का mandatory component है।
📌 Highway QA/QC Mastery Series Navigation
- Main Highway QA/QC Hub
- Part-1 Soil Classification
- Part-2 Moisture Content Test
- Part-3 Modified Proctor Test
- Part-4 CBR Test
- Part-5 Field Density Test
- Part-6 Atterberg Limits Test
- Part-7 Soil Stabilization Methods
📌 Introduction to Grain Size Analysis
Every soil consists of particles having different sizes. Some soils contain large gravel particles while others contain sand, silt and clay fractions. The relative proportion of these particle sizes significantly influences engineering behavior.
Grain Size Analysis determines the percentage of particles present in different size ranges. Based on this information engineers can classify soil and predict its performance under field conditions.
Well-graded soils generally exhibit better compaction characteristics and higher stability compared to poorly graded soils.
📌 Why Grain Size Analysis is Important in Highway Engineering?
Particle size distribution affects almost every engineering property of soil. Therefore Grain Size Analysis is considered one of the first laboratory tests performed during geotechnical investigations.
- Soil Classification
- Compaction Behavior Prediction
- Permeability Assessment
- Drainage Evaluation
- Subgrade Suitability Assessment
- Filter Design
- GSB Material Approval
- WMM Quality Control
- Pavement Design Investigations
Without proper gradation analysis, long-term pavement performance cannot be accurately predicted.
📌 Particle Size Classification
According to Indian Standards, soil particles are classified into different size ranges.
| Soil Fraction | Particle Size |
|---|---|
| Boulder | > 300 mm |
| Cobble | 80 mm – 300 mm |
| Gravel | 4.75 mm – 80 mm |
| Sand | 75 Micron – 4.75 mm |
| Silt | 2 Micron – 75 Micron |
| Clay | < 2 Micron |
This classification forms the basis of engineering soil identification systems.
📌 Applicable IS Codes and Standards
| Standard | Description |
|---|---|
| IS 2720 Part 4 | Grain Size Analysis |
| IS 1498 | Soil Classification |
| IS 460 | Test Sieves Specification |
| MoRTH Specifications | Road Material Requirements |
| IRC Guidelines | Pavement Engineering Standards |
📌 Principle of Sieve Analysis
Sieve Analysis is based on the principle of mechanical separation of particles according to size.
A stack of standard sieves arranged in decreasing opening size is used. When soil sample is shaken through the sieve stack, larger particles remain on upper sieves while smaller particles pass through to lower sieves.
The weight retained on each sieve is measured and percentage distribution is calculated.
📌 Equipment Required
- IS Standard Sieves
- Sieve Shaker
- Electronic Balance
- Drying Oven
- Brush
- Sample Trays
- Mechanical Splitter
- Mixing Pan
- Moisture Containers
📌 Standard Sieve Sizes Used in Highway Laboratories
| Sieve Size |
|---|
| 80 mm |
| 40 mm |
| 20 mm |
| 10 mm |
| 4.75 mm |
| 2.36 mm |
| 1.18 mm |
| 600 Micron |
| 425 Micron |
| 300 Micron |
| 150 Micron |
| 75 Micron |
📌 Sample Preparation
Representative sampling is essential for obtaining accurate results.
The collected sample is first dried in air or oven depending upon project requirements. Large lumps are broken carefully without crushing individual particles.
The sample is thoroughly mixed and reduced to testing quantity using quartering or sample splitter methods.
Organic matter, roots and foreign materials are removed before testing.
📌 Dry Sieve Analysis Procedure
- Take representative dry soil sample.
- Record total sample weight.
- Arrange sieves in descending order.
- Place sample on top sieve.
- Fix sieves in sieve shaker.
- Shake for 10–15 minutes.
- Measure weight retained on each sieve.
- Record all observations carefully.
- Check mass balance.
The sum of retained weights should approximately equal the original sample weight.
📌 Wet Sieve Analysis
When soil contains significant fine particles, wet sieving may be necessary.
In this procedure soil is washed through 75 micron sieve to separate fine fractions. The retained material is dried and then subjected to normal sieve analysis.
Wet sieving improves accuracy when cohesive fines are present.
📌 Observation Table Format
| Sieve Size | Weight Retained (g) |
|---|---|
| 20 mm | 120 |
| 10 mm | 220 |
| 4.75 mm | 180 |
| 2.36 mm | 140 |
| 1.18 mm | 110 |
Part-8 Section-1 Complete.
Next Section: Percentage Retained Calculation, Percentage Passing, Gradation Curve, D10-D30-D60, Uniformity Coefficient, Coefficient of Curvature, Well-Graded vs Poorly Graded Soil, Highway Applications, QA/QC Checklist, Interview Questions, FAQs and Conclusion.
📌 Calculation of Percentage Retained
After completing sieve analysis, the next step is calculating the percentage of material retained on each sieve. These calculations form the basis for preparing the particle size distribution curve.
The percentage retained on each sieve is calculated using the following formula:
Percentage Retained = (Weight Retained on Sieve / Total Sample Weight) × 100
This calculation is performed for every sieve used in the test.
📌 Calculation of Cumulative Percentage Retained
Cumulative percentage retained is obtained by progressively adding the percentage retained values from the top sieve downward.
This parameter is important because percentage passing values are derived from cumulative retained values.
Cumulative % Retained = Sum of Percentage Retained Values
📌 Calculation of Percentage Passing
Percentage passing represents the percentage of particles smaller than a particular sieve size.
Formula:
Percentage Passing = 100 − Cumulative Percentage Retained
Percentage passing values are used to plot the grain size distribution curve.
📌 Sample Calculation Table
| Sieve Size | Wt. Retained (g) | % Retained | Cumulative % Retained | % Passing |
|---|---|---|---|---|
| 20 mm | 120 | 12 | 12 | 88 |
| 10 mm | 220 | 22 | 34 | 66 |
| 4.75 mm | 180 | 18 | 52 | 48 |
| 2.36 mm | 140 | 14 | 66 | 34 |
| 1.18 mm | 110 | 11 | 77 | 23 |
📌 Grain Size Distribution Curve
After obtaining percentage passing values, a grain size distribution curve is plotted.
The particle size is plotted on the logarithmic scale of the X-axis, while percentage passing is plotted on the arithmetic scale of the Y-axis.
This graph is commonly known as the Gradation Curve.
The shape of the gradation curve provides valuable information regarding soil grading characteristics.
📌 Effective Size (D10)
D10 is the particle size corresponding to 10% passing on the gradation curve.
It is called the Effective Size because it significantly influences permeability characteristics.
Coarser D10 values generally indicate higher permeability.
📌 D30 and D60 Values
D30 is the particle size corresponding to 30% passing.
D60 is the particle size corresponding to 60% passing.
These values are obtained directly from the gradation curve and are used for calculating grading coefficients.
📌 Uniformity Coefficient (Cu)
Uniformity Coefficient indicates the range of particle sizes present in the soil.
Cu = D60 / D10
A higher Cu value generally indicates a wider range of particle sizes and better grading characteristics.
For sands:
- Cu > 6 → Well Graded Sand
- Cu < 6 → Poorly Graded Sand
📌 Coefficient of Curvature (Cc)
Coefficient of Curvature helps evaluate the shape of the gradation curve.
Cc = (D30²) / (D10 × D60)
For well-graded soils:
1 ≤ Cc ≤ 3
This criterion is widely used in IS Soil Classification System.
📌 Well-Graded Soil
A well-graded soil contains particles of different sizes in suitable proportions.
Because smaller particles fill the voids between larger particles, well-graded soils achieve higher density and better compaction.
Advantages include:
- Higher Stability
- Better Compaction
- Lower Void Ratio
- Improved Load Distribution
- Higher Strength
📌 Poorly Graded Soil
Poorly graded soil contains particles of nearly the same size.
Such soils usually exhibit higher void ratios and lower stability compared to well-graded materials.
Poorly graded soils may require blending or stabilization before highway use.
📌 Gap Graded Soil
Gap graded soils are characterized by the absence of one or more intermediate particle size groups.
Their gradation curve typically shows a flat portion indicating missing particle sizes.
Special engineering evaluation is often required before using gap graded materials in pavement layers.
📌 Importance in Highway Engineering
Grain Size Analysis plays a critical role in almost every highway construction activity.
- Borrow Area Evaluation
- Subgrade Assessment
- Embankment Material Approval
- Granular Sub Base (GSB)
- Wet Mix Macadam (WMM)
- Drainage Layer Design
- Filter Media Design
- Pavement Material Selection
Without proper gradation control, achieving desired field performance becomes difficult.
📌 Relationship with Other QA/QC Tests
Grain Size Analysis is directly related to several other soil tests:
📌 Common Sources of Error
- Improper Sampling
- Loss of Material During Sieving
- Dirty or Damaged Sieves
- Incorrect Weighing
- Insufficient Sieving Time
- Poor Record Keeping
- Improper Sample Drying
Proper laboratory practices help eliminate these errors.
📌 QA/QC Checklist
- ✔ Representative Sample Collected
- ✔ Sample Properly Dried
- ✔ Sieves Clean and Calibrated
- ✔ Correct Sample Weight Used
- ✔ Mass Balance Verified
- ✔ Calculations Checked
- ✔ Gradation Curve Prepared
- ✔ Results Properly Documented
📌 Interview Questions for Highway Engineers
- What is the purpose of Grain Size Analysis?
- What is D10 and why is it important?
- How is Uniformity Coefficient calculated?
- What is the difference between well-graded and poorly graded soil?
- Which IS code governs Grain Size Analysis?
- Why is gradation important for GSB and WMM?
- What is gap grading?
- How does particle size distribution affect compaction?
📌 Frequently Asked Questions (FAQs)
Q1. Which IS code is used for Grain Size Analysis?
IS 2720 (Part 4) is used for Grain Size Analysis of soils.
Q2. What is D10?
D10 is the particle size corresponding to 10% passing on the gradation curve.
Q3. What is the significance of Cu?
Uniformity Coefficient indicates the grading characteristics of soil.
Q4. Why is Grain Size Analysis important in highway construction?
It helps assess soil suitability, compaction behavior, drainage characteristics and pavement performance.
📌 Final Engineering Conclusion
Grain Size Analysis is one of the most fundamental soil laboratory tests used in highway engineering. It provides essential information regarding particle size distribution, soil classification, compaction characteristics and drainage behavior.
Accurate gradation analysis enables engineers to select suitable construction materials, improve pavement performance and ensure long-term highway durability.
Every Highway Engineer, QA/QC Engineer, Material Engineer and Geotechnical Engineer should have a strong understanding of Grain Size Analysis because it forms the foundation of soil evaluation and pavement material selection.
Next Article:
Highway QA/QC Mastery Series Part-9 – Specific Gravity Test Complete Guide
References:
- IS 2720 Part 4 – Grain Size Analysis
- IS 1498 – Classification and Identification of Soils
- IS 460 – Test Sieves Specification
- MoRTH Specifications for Road and Bridge Works
- IRC 37 – Guidelines for Flexible Pavement Design
- IRC SP 89 – Quality Assurance in Highway Construction