IS 2720:1980 Part 7 is the Indian Standard (BIS) for methods of test for soils - determination of water content-dry density relation using light compaction. This standard specifies the laboratory methods for determining the specific gravity of soil solids. It covers procedures for both fine-grained soils (using a pycnometer or density bottle) and coarse-grained soils (using a gas jar). This fundamental soil property is essential for calculating phase relationships like void ratio and degree of saturation.
Describes the procedure for determining the optimum moisture content and maximum dry density of soil using the light compaction (Standard Proctor) test.
Quick Reference — IS 2720 Part 7:1980 Standard Proctor
Standard (light) compaction — mould, rammer, drop, blows, layers and energy used to obtain OMC / MDD.
| Reference | Value | Clause |
|---|
| Test | Standard Proctor compaction (light compaction) | Cl. 1 |
| Mould volume — small (≤ 4.75 mm) | 1000 cm³ (100 mm dia × 127.3 mm) | Cl. 4.1 |
| Mould volume — large (≤ 19 mm material) | 2250 cm³ (150 mm dia × 127.3 mm) | Cl. 4.1 |
| Rammer mass | 2.6 kg | Cl. 4.2 |
| Rammer drop | 310 mm | Cl. 4.2 |
| Rammer face diameter | 50 mm | Cl. 4.2 |
| Layers | 3 | Cl. 5.3 |
| Blows per layer — small mould | 25 | Cl. 5.3 |
| Blows per layer — large mould | 56 | Cl. 5.3 |
| Compactive energy | ≈ 595 kJ/m³ (light) | Cl. 5.3 |
| Number of points (compaction curve) | ≥ 4 (varying water content) | Cl. 5.4 |
| Water content increment (between trials) | ≈ 2 % between points | Cl. 5.4 |
| Result — OMC and MDD | Peak of dry density vs water content curve | Cl. 6 |
| Zero air voids line | γd = γw·G / (1 + w·G); G = specific gravity | Cl. 6 |
| Specimen retained for next layer — protocol | Material reused or fresh per IS guidance | Cl. 5 |
| Reporting precision — γd | 0.01 g/cc | Cl. 7 |
| Reporting precision — w | 0.1 % | Cl. 7 |
⚠ Standard Proctor is the reference for many earthwork specs (≥ 95 % MDD). Modified Proctor (Part 8) is used for pavement subgrade/road work.
Overview
- Status
- Current
- Usage level
- Essential
- Domain
- Geotechnical — Soil and Foundation
- Type
- Testing Method
- Amendments
- Amendment 1 (1983); Amendment 2 (1987)
Also on InfraLens for IS 2720
Practical Notes
! Complete removal of entrapped air by vacuum is the most critical step; insufficient de-airing leads to erroneously low specific gravity values.
! Applying the temperature correction factor (Kt from Table 1) to normalize the result to the standard 27°C is mandatory for reporting.
! The code is split into two sections within Part 3: Section 1 for fine-grained soils and Section 2 for coarse-grained soils, which require different apparatus sizes and sample quantities.
Frequently referenced clauses
Updates & Amendments2 amendments
1983Amendment 1 (1983)
1987Amendment 2 (1987)
Consolidated list per BIS. For the text of each amendment, refer to the BIS portal link above.
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International Equivalents
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We're adding equivalent international standards for this code.
Key Values6
Quick Reference Values
Standard reporting temperature27 °C
Accuracy of weighing balance0.001 g for fine-grained soils
Pycnometer/Density Bottle capacity50 ml for fine-grained soils
Typical G for sand (inorganic)2.65 - 2.68
Typical G for clay (inorganic)2.70 - 2.80
Minimum mass of soil for fine-grained soil test25 to 50 g
Key Formulas
G = (M2 - M1) / [ (M4 - M1) - (M3 - M2) ] — Specific Gravity at test temperature T°C
G_27°C = Kt * G_T°C — Specific Gravity corrected to standard temperature 27°C
Tables & Referenced Sections
Key Tables
Table 1 - Temperature Correction Factor Kt
Key Clauses
Clause 3 - Apparatus (Lists pycnometer, density bottle, vacuum source etc.)
Clause 4 - Procedure (General steps for the test)
Clause 8 - Calculations (Formula for determining specific gravity)
Section 1 - Determination of specific gravity of fine-grained soils
Section 2 - Determination of specific gravity of coarse-grained soils
Frequently Asked Questions4
What is the standard temperature for reporting specific gravity?+
The specific gravity is reported at a standard temperature of 27°C, after applying a temperature correction factor (Clause 8.2).
Why is a vacuum source needed for the specific gravity test?+
A vacuum is used to remove all entrapped air bubbles from the soil and water slurry. Air bubbles occupy volume and would cause the calculated specific gravity to be inaccurately low.
What is the difference between Part 3 / Section 1 and Section 2?+
Section 1 covers the test for fine-grained soils using a small pycnometer or density bottle. Section 2 is for coarse-grained soils (particles larger than 4.75 mm) and requires a larger gas jar and sample size.
What does an unusually low specific gravity value indicate?+
A value significantly below 2.60 may indicate the presence of organic matter in the soil or testing errors, such as incomplete de-airing.