Proctor Compaction Test (IS 2720): Equipment & Procedure Guide
The Proctor Compaction Test determines the Optimum Moisture Content (OMC) and Maximum Dry Density (MDD) of soil — the control values used in every earthwork specification. Standardised under IS 2720 Parts 7 and 8, this guide covers both Standard and Modified Proctor variants, equipment requirements, and field density verification.
Soil compaction is critical in roads, embankments, earthen dams, and building foundations. Improperly compacted soil causes differential settlement, slope instability, and structural failure. The Proctor Compaction Test (IS 2720 Parts 7 and 8) determines the Optimum Moisture Content (OMC) and Maximum Dry Density (MDD) — the two values that control field compaction quality.
Standard Proctor vs Modified Proctor
| Parameter | Standard Proctor (Pt.7) | Modified Proctor (Pt.8) |
|---|---|---|
| Rammer weight | 2.6 kg | 4.9 kg |
| Drop height | 310 mm | 450 mm |
| Layers | 3 | 5 |
| Compaction energy | 595 kJ/m³ | 2700 kJ/m³ |
| Application | Earthworks, fills, low-traffic roads | Highways, airfields, runways |
Equipment Required
Proctor Compaction Moulds
- 100 mm diameter × 127.3 mm — soil passing 4.75 mm sieve
- 150 mm diameter × 127.3 mm — soil with particles up to 19 mm
Proctor Rammer
Manual or mechanised rammers with correct weight and drop height. Mechanised rammers ensure consistent compaction energy and eliminate operator fatigue errors.
Balance, Moisture Cans and Oven
Balance readable to 1 g; aluminium moisture cans; thermostatically controlled oven at 105°C ± 5°C for overnight drying.
Step-by-Step Procedure
- Air-dry and break clods. Sieve per mould size. Prepare 5 soil portions at moisture contents spanning ±4% of estimated OMC.
- Assemble mould with collar. Compact each layer with specified blows. Remove collar and trim flush.
- Weigh mould + compacted soil. Extract specimen for moisture content determination.
- Calculate dry density: γd = γb ÷ (1 + w)
- Plot dry density vs moisture for all 5 points. Peak = MDD at OMC.
Field Compaction Control
Lab MDD and OMC are the reference values. Field density is verified by:
- Core Cutter Method (IS 2720 Part 29) — cohesive soils
- Sand Replacement Method (IS 2720 Part 28) — all soil types
Road subgrade specification (IRC SP 72): 95% of MDD. Embankment: 90–95% of MDD.
Frequently Asked Questions
How many points are needed for a compaction curve?
Minimum 5 moisture-density pairs are needed to define the parabolic curve and identify the true peak. Fewer points risk missing the OMC.
Can the same soil be reused for multiple compaction points?
For cohesive soils — no. For granular soils (gravels, sands) — yes, after air-drying between test points.
What is the typical OMC for black cotton soil?
Black cotton (expansive) soils typically have OMC of 20–30% and MDD of 1.55–1.65 g/cc. These soils require careful compaction control due to high moisture sensitivity.
