IS 2720:1983 Part 8 is the Indian Standard (BIS) for methods of test for soils - determination of water content-dry density relation using heavy compaction. This standard outlines the procedure for determining the relationship between the moisture content and dry density of soils using heavy compaction, often referred to as the Modified Proctor Test. It is crucial for determining the maximum dry density (MDD) and optimum moisture content (OMC) required for heavy-duty earthworks like highways and dams.
Describes the procedure for determining the optimum moisture content and maximum dry density of soil using the heavy compaction (Modified Proctor) test.
Modified (heavy) compaction parameters — rammer 4.9 kg / drop 450 mm / 5 layers × 25 blows for highway and heavy-load earthwork.
| Reference | Value | Clause |
|---|---|---|
| Test | Modified Proctor compaction (heavy compaction) | Cl. 1 |
| Mould volume — small | 1000 cm³ (100 mm dia × 127.3 mm) | Cl. 4.1 |
| Mould volume — large | 2250 cm³ (150 mm dia × 127.3 mm) | Cl. 4.1 |
| Rammer mass | 4.9 kg | Cl. 4.2 |
| Rammer drop | 450 mm | Cl. 4.2 |
| Rammer face diameter | 50 mm | Cl. 4.2 |
| Layers | 5 | Cl. 5.3 |
| Blows per layer — small mould | 25 | Cl. 5.3 |
| Blows per layer — large mould | 56 | Cl. 5.3 |
| Compactive energy | ≈ 2700 kJ/m³ (heavy, ~4.5 × standard) | Cl. 5.3 |
| Result | Higher MDD, lower OMC vs Part 7 | Cl. 6 |
| Typical OMC reduction vs standard | 1 – 4 % drop | Cl. 6 (general) |
| Typical MDD increase vs standard | 0.05 – 0.15 g/cc | Cl. 6 (general) |
| Application | Pavement subgrade, embankments under heavy loading | Cl. 1 (foreword) |
| Number of points | ≥ 4 across OMC ± 4 % | Cl. 5.4 |
| Water-content increment between trials | ≈ 1 – 2 % | Cl. 5.4 |
| Reporting precision — MDD / OMC | 0.01 g/cc / 0.1 % | Cl. 7 |
IS 2720 (Part 8) specifies the method for determining water content-dry density relation of soils using heavy compaction (Modified Proctor) — the laboratory test that establishes the optimum moisture content (OMC) and maximum dry density (MDD) for a soil under heavy compaction effort. Heavy Proctor (Modified) is more rigorous than the standard Proctor (IS 2720 Part 7:1980), reflecting modern construction equipment (vibratory rollers, sheepsfoot rollers).
Use IS 2720 Part 8 for: - Embankment fill compaction control (especially under high-traffic / heavy-load applications) - Pavement subgrade compaction (IRC:36:2010) - Granular sub-base + base courses - Dam fill compaction - Industrial / heavy-vehicle yard subgrade - Modern highway construction (per MoRTH specs which often require heavy compaction)
Standard vs Heavy Proctor:
| Property | Standard (Part 7:1980) | Heavy (Part 8:1983 — this code) | |---|---|---| | Hammer mass | 2.5 kg | 4.9 kg | | Drop height | 305 mm | 457 mm | | Energy per blow | 7.45 J | 22.2 J | | Layers | 3 | 5 | | Blows per layer | 25 | 25 (or 56) | | Total energy | 596 kJ/m³ | 2693 kJ/m³ (4.5× more) |
Higher compaction energy → higher MDD + lower OMC for same soil. Modern road construction (NHAI, MoRTH 5th Revision Section 300) often requires Heavy Proctor density compliance.
Equipment: - 1000 mL cylindrical mould (2200 mL alternative) - Hammer: 4.9 kg with 457 mm drop height - Standard sand for adjustments - Balance + drying oven
Procedure: 1. Sample preparation: dry soil; sieve through 19 mm (or 4.75 mm for fine soil); ~5-6 kg total. 2. Mix soil with measured water (start ~5 % less than expected OMC). 3. Compact in mould in 5 layers; 25 blows per layer with 4.9 kg hammer dropping 457 mm. 4. Strike off top surface flush with mould rim. 5. Weigh full mould; subtract empty mould mass; divide by mould volume = bulk density. 6. Take subsample for moisture content (oven-dry 24 hr at 105-110 °C). 7. Compute dry density: γ_d = γ_bulk / (1 + w), where w = moisture content fraction. 8. Repeat at increasing water content (typically 5-6 points) bracketing OMC. 9. Plot dry density vs moisture content; identify peak = MDD; corresponding moisture = OMC.
Output: - MDD (Maximum Dry Density) — γ_d at peak (kN/m³) - OMC (Optimum Moisture Content) — w at peak (%) - Compaction curve (plot)
Test cadence: - Source qualification: every borrow material - Periodic re-test: per source change OR per 10,000 m³ - Quality control: as backup when field density drifts
Acceptance for field compaction: - Field dry density / MDD ≥ specified % (typically 95-98 %) - Field moisture: OMC ± 2 % (Heavy Proctor based) - Tested by: sand-replacement method, nuclear density gauge, core method
Typical MDD + OMC for Indian soils (Heavy Proctor):
| Soil type | OMC (%) | MDD (kN/m³) | |---|---|---| | Sandy / silty sand | 8-15 | 17-21 | | Lateritic gravel | 9-14 | 19-22 | | Murrum / weathered rock | 7-12 | 19-23 | | Cohesive (sandy clay) | 14-20 | 16-19 | | High-plastic clay (PI > 30) | 18-30 | 13-16 | | Black cotton soil | 22-32 | 13-15 |
Field compaction acceptance (per IRC:36:2010 for highway):
| Layer | Density (% of MDD) per Heavy Proctor | |---|---| | Embankment body | 95 % MDD | | Top 500 mm subgrade | 98 % MDD | | Granular sub-base (GSB) | 98 % MDD | | Wet-mix macadam (WMM) | 98 % MDD | | Bituminous | per BC density (theoretical maximum) |
Comparison with Standard Proctor: - Heavy Proctor MDD typically 5-15 % higher than Standard Proctor - Heavy Proctor OMC typically 1-3 % lower than Standard Proctor - For a given soil: same compaction at site can pass Standard but fail Heavy - Modern MoRTH spec increasingly requires Heavy Proctor
Field test methods (for compaction verification): - Sand replacement (IS 2720 Part 28): traditional; cheap; ±2-3 % accuracy - Nuclear density gauge (IS 2720 Part 33): fast; ±1-2 % accuracy; needs trained operator + safety regulations - Core method: most accurate; destructive; for thin pavement layers
Test sample size: - Per layer per 1000 m² (typical highway QC) - More frequent at start of new layer; less as practice settles - Random + systematic sampling per project QC plan
Common deviation from MDD: - 95 % MDD: typical for general embankment fill - 98 % MDD: standard for subgrade + sub-base - 100 % MDD: not achievable; field compaction always slightly less than lab - < 92 % MDD: re-compact OR replace; not acceptable
Heavy Proctor vs vibratory compaction: - Heavy Proctor simulates impact compaction (sheepsfoot, padfoot rollers) - Granular soils respond better to vibratory roller (different compaction physics) - For clean granular materials, relative density (per IS 2720 Part 14) more relevant than Proctor
1. Standard Proctor used when Heavy Proctor required. MoRTH NHAI projects typically require Heavy; Standard reads 5-15 % lower MDD; field compaction passes Standard but fails Heavy spec. Verify which is required. 2. Single test on heterogeneous borrow. Soil from different parts of borrow has different MDD; one test misleading. Multiple samples per source. 3. OMC drift not monitored at site. Soil moisture varies with weather + storage; field compaction at wrong moisture. Daily moisture check. 4. Compaction at moisture > OMC. 'Pumping' under roller; layer instability. Aerate or re-compact when dryer. 5. Compaction at moisture < OMC. Density never reaches target. Add water + re-compact. 6. Hammer mass / drop wrong. Test result invalid. Verify equipment per IS 2720 Part 8. 7. Dry sample not properly representative. Coarse particles excluded; result over-states soil quality. Use proper sieving + sample preparation. 8. Field test ignored or mis-conducted. Sand-replacement accuracy depends on careful execution. Train field staff. 9. Nuclear gauge not calibrated. Drift over time; readings biased. Calibrate per manufacturer schedule. 10. Acceptance based on single test point. Random sampling needs multiple points per layer. Per QC plan. 11. Compaction with wrong roller for soil. Cohesive needs sheepsfoot; granular needs vibratory. Match equipment to soil. 12. Compaction in monsoon without drainage. Saturated soil cannot be compacted; layer fails. Suspend work or drain.
Earthwork compaction QC cascade:
1. Design (IRC:36:2010, IS 1080:1985) — compaction targets per layer. 2. Borrow source qualification: - Material classification + tests - Heavy Proctor (this code, IS 2720 Part 8) — establish MDD + OMC - CBR (IS 2720 Part 17) 3. Field compaction: - Layer thickness 200-300 mm loose; 150-225 mm compacted - Pre-compaction moisture: OMC ± 2 % - Compaction equipment: sheepsfoot for cohesive, vibratory for granular - Number of passes: typically 6-10 4. Field density tests: - Per 1000 m² per layer (or as per QC plan) - Sand-replacement, nuclear gauge, or core method - Spot-test moisture for context 5. Acceptance: - Field dry density ≥ % MDD per spec - Continue if pass; re-compact if fail 6. Documentation: - Per-layer test register - Trend monitoring - Investigation of failures
IS 2720 Part 8 Heavy Proctor is the industry-standard reference for modern Indian highway + heavy-compaction work. Standard Proctor remains relevant for low-volume / rural / building applications where lower compaction effort is acceptable.