Modified Proctor Test – OMC and MDD of Soil (IS 2720 Part 8)

For 1000 cc Mould (Standard Proctor Compaction)

1. Prepare a representative soil sample passing through the 37.5 mm IS sieve and mix it thoroughly with the required amount of water to obtain uniform moisture content.
2. Place the soil in the mould in three equal layers.
3. Compact each layer with 25 blows using a 4.89 kg rammer falling freely from a height of 450 mm.
4. After compaction of the top layer, remove the collar carefully and trim the excess soil so that the surface is flush with the top of the mould.
5. Clean the outside of the mould and weigh the mould with compacted soil to determine bulk density.
6. Take a representative soil sample for moisture content determination.
7. Repeat the procedure for at least 5–6 different moisture contents to obtain the complete compaction curve.

Modified Proctor Test (2250 cc Mould)

1. Take a soil sample and allow it to air dry. Break the lumps gently.
2. Pass the soil through 19 mm IS sieve (or 4.75 mm sieve for fine-grained soils).
3. Add the required amount of water and mix the soil thoroughly to get uniform moisture.
4. Weigh the empty mould along with base plate.
5. Fix the collar properly on the mould.
6. Fill the mould with soil in 5 equal layers.
7. Compact each layer using a rammer by giving 55 blows (as per IS standard).
8. After compaction, remove the collar carefully.
9. Trim the extra soil so that the surface is level with the top of the mould.
10. Clean the outside of the mould and weigh it with the compacted soil.
11. Take a small soil sample to determine moisture content.
12. Repeat the test by adding more water each time to cover different moisture contents.
13. Calculate the bulk density and dry density for each trial.
14. Plot a graph between moisture content and dry density.
15. From the graph, determine OMC (Optimum Moisture Content) and MDD (Maximum Dry Density).

Oversize Correction Method (IS 2720 Part 8)

When the soil contains particles larger than the specified sieve size (typically 19 mm for Modified Proctor Test), these are called oversize particles. Since such particles affect compaction results, a correction is applied to obtain accurate dry density.

Procedure:

1. Sieve the soil sample through 19 mm sieve and separate the oversize fraction (>19 mm).
2. Determine the percentage of oversize material (by weight).
3. Conduct the Modified Proctor Test on the fraction passing 19 mm sieve.
4. Determine the Maximum Dry Density (MDD) and Optimum Moisture Content (OMC) for the passing fraction.
5. Apply correction to account for oversize particles using IS recommended approach.

Correction Formula:

Corrected Dry Density (γ_d) = (100 × γ_d1) / [100 − P × (1 − (G_m / G_o))]

• γ_d1 = Dry density of soil passing sieve
• P = Percentage of oversize material (%)
• G_m = Specific gravity of oversize fraction
• G_o = Specific gravity of soil passing fraction

Important Notes:

• If oversize material is more than 30%, the test result may not be reliable.
• Always report the percentage of oversize fraction in the test result.
• Correction is essential for coarse-grained soils used in embankments.

Applications

• Design of embankment and subgrade layers
• Field compaction control
• Quality control as per MoRTH
• Evaluation of soil improvement

Summary and Precautions

• Uniform soil-water mixing
• Correct compaction energy
• Accurate moisture measurement
• Clean equipment
• Maintain oven temperature 105–110°C