Soil Compaction Test as per Indian Standards

Soil Compaction Test as per Indian Standards 

1. Introduction

Soil compaction is a fundamental geotechnical test used in civil engineering to determine how soil behaves when compacted at different moisture contents.
As per Indian Standards (IS), compaction testing helps us decide:

• How much water (moisture) is required

• How much density can be achieved

• Whether soil is suitable for foundation, road, embankment, and backfilling works

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2. Purpose of Soil Compaction Test

The compaction test is carried out to:

• Determine Maximum Dry Density (MDD)

• Determine Optimum Moisture Content (OMC)

• Control field compaction quality

• Prevent settlement and failure

• Improve shear strength and bearing capacity

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3. Indian Standards for Compaction Test

Soil compaction tests in India are conducted as per:

IS Code	Description
IS 2720 (Part 7)	Light Compaction Test
IS 2720 (Part 8)	Heavy Compaction Test
IS 2720 (Part 28)	Dry Density by Sand Replacement
IS 2720 (Part 29)	Core Cutter Method

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4. Types of Soil Compaction Tests

A. Light Compaction Test (Standard Proctor Test)

IS 2720 (Part 7)

• Rammer weight: 2.6 kg

• Height of fall: 310 mm

• Number of layers: 3

• Blows per layer: 25

Used for:

• Light structures

• Residential buildings

• General earthwork

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B. Heavy Compaction Test (Modified Proctor Test)

IS 2720 (Part 8)

• Rammer weight: 4.9 kg

• Height of fall: 450 mm

• Number of layers: 5

• Blows per layer: 25

Used for:

• Highways

• Runways

• Heavy foundations

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C. Field Compaction Tests

Used to check actual field density.

1. Sand Replacement Test – IS 2720 (Part 28)

• Suitable for coarse-grained soil

• Determines in-situ dry density

2. Core Cutter Method – IS 2720 (Part 29)

• Suitable for soft to medium cohesive soils

• Simple and quick field test

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5. What is Maximum Dry Density (MDD)?

MDD is the maximum dry unit weight of soil obtained at a specific moisture content during compaction.

👉 In simple words:
It is the highest density soil can achieve when compacted properly.

Why MDD is important:

• Used as reference value for field compaction

• Helps in calculating % compaction

• Ensures structural stability

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6. What is Optimum Moisture Content (OMC)?

OMC is the percentage of water content at which soil achieves MDD.

• Too little water → soil particles don’t rearrange

• Too much water → water occupies voids

• Correct water → best compaction

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7. Why Moisture Content Test is Required

Moisture directly affects compaction.
As per IS 2720 (Part 2), moisture content is measured by oven drying method.

Importance:

• Helps identify OMC

• Prevents over-watering or under-watering

• Ensures uniform compaction

• Reduces settlement and cracks

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8. Percentage of Moisture Content

Moisture content (%) is calculated by:

$$\text{Moisture Content (\%)} = \frac{\text{Weight of water}}{\text{Weight of dry soil}} \times 100$$

Moisture Content (%)=Weight of dry soilWeight of water​×100

Typical Moisture Content Ranges:

Soil Type	Moisture %
Sandy Soil	6 – 12 %
Silty Soil	10 – 20 %
Clayey Soil	15 – 30 %

(Values vary based on soil type and site condition)

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9. Compaction Test Procedure (Brief)

1. Air-dry the soil sample

2. Add water in increments

3. Compact soil in mould using rammer

4. Measure wet density

5. Calculate dry density

6. Plot Dry Density vs Moisture Content curve

7. Determine MDD and OMC

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10. Compaction Curve Explanation

• Curve rises as moisture increases

• Peak point = MDD

• Corresponding moisture = OMC

• After OMC, density reduces due to excess water

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11. Field Compaction Acceptance Criteria

As per specifications:

• Earthwork: ≥ 95% of MDD

• Road subgrade: ≥ 97% of MDD

• Embankment: As specified in drawings/contract

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12. Conclusion

Soil compaction testing as per Indian Standards ensures:

• Safe and durable construction

• Proper load transfer

• Reduced maintenance

• Compliance with quality standards

MDD, OMC, and moisture control are the backbone of successful earthwork and foundation engineering.

1. What is Percentage of Compaction?

Percentage of compaction indicates how well the soil is compacted in the field compared to the maximum dry density (MDD) obtained in the laboratory.

It is a key quality control parameter in earthwork, road works, and foundation construction.

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2. Formula for Percentage of Compaction

$$\textbf{Percentage of Compaction (\%)} = \frac{\text{Field Dry Density}}{\text{Maximum Dry Density (MDD)}} \times 100$$

Where:

• Field Dry Density = Dry density obtained from field tests

• MDD = Maximum Dry Density from lab compaction test (IS 2720 Part 7 / 8)

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3. Indian Standard Reference

• IS 2720 (Part 7) – Light Compaction (Lab MDD)

• IS 2720 (Part 8) – Heavy Compaction (Lab MDD)

• IS 2720 (Part 28) – Sand Replacement (Field Density)

• IS 2720 (Part 29) – Core Cutter Method

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4. Recommended Percentage of Compaction (Typical Practice in India)

Type of Work	Required % Compaction (of MDD)
General Earth Filling	90 – 95 %
Building Foundation Backfill	95 %
Road Subgrade	97 %
Pavement Layers / WMM	98 %
Embankments	95 – 97 %
Airport Runways	98 % or more

(Exact requirement depends on project specification and drawings)

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5. Importance of Achieving Required Compaction %

• Prevents excess settlement

• Increases bearing capacity

• Improves shear strength

• Reduces water ingress

• Ensures long-term stability

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6. Field Testing to Check Compaction %

To calculate percentage of compaction:

1. Conduct lab compaction test → get MDD & OMC

2. Perform field density test

   • Sand Replacement Test

   • Core Cutter Method

3. Determine field dry density

4. Apply formula and compare with specified %

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7. Common Reasons for Low Compaction Percentage

• Improper moisture content (not near OMC)

• Insufficient roller passes

• Wrong compaction equipment

• Thick soil layers (>200–250 mm)

• Poor soil gradation

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8. Practical Site Tip

✔ Compact soil within ±2% of OMC
✔ Control layer thickness
✔ Maintain proper rolling pattern
✔ Re-test if compaction % is not achieved

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9. Summary

Percentage of compaction ensures that soil in the field performs as designed in the laboratory.
Matching field density with MDD is essential for safe and durable construction.

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