Soil Mechanics Lab: Sieve Analysis

Experiment: Sieve Analysis of Soil

Objective

To determine the grain size distribution of a soil sample using sieve analysis.

Apparatus Required

• Set of standard IS sieves (e.g., 4.75 mm to 75 µm)
• Weighing balance (accuracy 0.01 g)
• Mechanical sieve shaker
• Brush
• Sample of dry soil (coarse or fine)
• Tray and containers

Theory

Sieve analysis is a laboratory method used to determine the grain size distribution of soil particles. It helps classify soil based on the particle size and is part of mechanical analysis — a process for separating soil particles into different size fractions.

This analysis is conducted by passing soil through a series of standard sieves with progressively smaller openings. The particles get separated based on size, allowing classification into sand, gravel, and finer materials.

Procedure

A. Coarse Sieve Analysis (for soil retained on 4.75 mm IS sieve)

1. Approximately 100 g of oven-dried soil was taken (for soils with majority particles > 4.75 mm)
2. The IS sieves were arranged in descending order of aperture size (4.75 mm, 2.36 mm, 1.18 mm, 600 µm, 425 µm, 300 µm, 212 µm, 150 µm, and 75 µm) with a pan placed at the bottom
3. The sample was placed on the topmost sieve (4.75 mm) and covered with a lid
4. The sieve stack was secured in a mechanical sieve shaker and shaken for about 10 minutes
5. After shaking, the soil retained on each sieve was carefully weighed using a balance within 2% accuracy
6. The weights were recorded and cumulative percentages retained as well as percentage passing (percent finer) were calculated

B. Fine Sieve Analysis (for soil passing 4.75 mm IS sieve)

1. A representative sample of about 500 g of oven-dried soil passing 4.75 mm IS sieve was taken
2. The finer IS sieves (2.36 mm to 75 µm) were arranged in order with a pan at the bottom
3. The sample was placed on the top sieve (2.36 mm) and the sieves were shaken manually or mechanically for 10 minutes
4. The material retained on each sieve was weighed accurately to 2% error
5. All weights were recorded and percentage passing for each sieve was calculated

Observations and Calculations

From Grain Size Distribution Curve (Plotted on Semi-Log Graph):

• \( D_{10} = 0.28 \text{ mm} \)
• \( D_{30} = 0.86 \text{ mm} \)
• \( D_{60} = 1.80 \text{ mm} \)

Result and Conclusion

Based on the sieve analysis and grain size distribution curve, the effective particle size (\( D_{10} \)) of the soil sample was found to be 0.28 mm, which represents the size below which 10% of the particles by weight are finer. The particle size corresponding to 30% finer (\( D_{30} \)) was 0.86 mm, and that corresponding to 60% finer (\( D_{60} \)) was 1.80 mm.

Using these values, the Uniformity Coefficient (\( C_u \)) was calculated as 6.42, indicating that the soil has a wide range of particle sizes and is therefore well-graded. The Coefficient of Curvature (\( C_c \)) was found to be 1.467, which falls within the acceptable range of 1 to 3, suggesting that the soil does not have any major gaps in its gradation.

Conclusion:

The soil sample analyzed is well-graded, meaning it contains a good distribution of different particle sizes. Such soil is generally suitable for use in engineering applications like road construction, embankments, and filter materials, as it offers good compaction characteristics, strength, and drainage performance.