Methods of test for soils, Part 7: Determination of water content-dry density relation using light compaction

IS 2720 Part 7: Scope Summary & Key Points

Scope:

• Determines the water content-dry density relation of soils using light compaction.
• Applicable primarily to cohesive soils; less reliable for clean sands and gravels.
• Helps establish optimum moisture content and maximum dry density for field compaction control.

Key Specifications:

• Compaction Method: Light compaction using a 2.6-kg rammer (standard drop height).
• Mould Size: Typically 1000 cm³ or as specified; report size used.
• Sample Type: Single or separate samples; specify in reporting.

Important Notes:

• For highly permeable soils (clean gravels, coarse sands), this test may underestimate achievable field density and overestimate optimum moisture.
• Heavy compaction method covered separately in IS 2720 Part 8.

Typical Formula (Moisture Content Calculation):

[ w = \frac{W_w}{W_s} \times 100 ]

Where:

• (w) = water content (%)
• (W_w) = weight of water
• (W_s) = weight of dry soil

Reporting Table (Clause 7.5):

flowchart TD
    A[Soil Sample] --> B[Prepare Sample at Various Moisture Contents]
    B --> C[Compact in Mould with 2.6-kg Rammer]
    C --> D[Measure Wet Weight & Calculate Dry Density]
    D --> E[Plot Dry Density vs Moisture Content]
    E --> F[Determine Optimum Moisture Content & Max Dry Density]

Summary: IS 2720 Part 7 standardizes light compaction testing for soil water content-dry density relations, mainly for cohesive soils, enabling field compaction control by identifying optimum moisture and maximum dry density.

IS 2720 Part 7 (1980) — Key References & Specifications Summary

• Test Method: Determination of water content–dry density relation using light compaction with a 2.6-kg rammer.
• Reporting (Clause 7.5):
  • State method used (e.g., 2.6-kg rammer method).
  • Specify procedure: single or separate samples.
  • Mention mould size used in compaction.
• Important Note:
  • For highly permeable soils (clean gravels, coarse sands), lab compaction results may not reflect field compaction accurately.
  • Optimum moisture content from lab tests may be higher than field desirable; max dry density in lab may be lower than field achievable.
• Related IS Codes:
  • IS 2720 Part 8 (Heavy compaction method) for heavy compaction tests.
  • IS 2809-1972 for soil testing definitions.
• Corrections:
  • Replace “40 mm” by 37.5 mm (clause 5.3).
  • Replace “20 mm” by 19 mm (Note 2).
  • Formula correction:
    [ Y = \frac{100}{100 + 1} ]
• Equipment: Steel straightedge ~30 cm with one beveled edge (Clause 3.6).

Summary Table: Reporting Requirements (Clause 7.5)

Practical Tip:

For field compaction control, use lab optimum moisture content and dry density as a guideline but verify with field tests especially for clean sands and gravels.

flowchart LR
    A[Soil Sample] --> B[Light Compaction Test]
    B --> C{Report}
    C --> D[Method Used (2.6-kg Rammer)]
    C --> E[Sample Procedure]
    C --> F[Mould Size]
    B --> G[Determine Optimum Moisture Content]
    B --> H[Determine Max Dry Density]
    G & H --> I[Field Comp

IS 2720 Part 7 — Apparatus Key Specifications & Notes

1. Metal Rammer (Clause 3.9):

• Must conform to IS: 9198-1979.
• Used for light compaction with a 2.6-kg rammer.

2. Container (Clause 3.5):

• Non-corrodible, airtight container for water content determination.

3. Mould Size (Clause 7.5):

• Specify mould size used for compaction (commonly 1000 cm³ or as per test requirement).

4. Reporting (Clause 7.5):

• State method of compaction (e.g., 2.6-kg rammer method).
• State sample procedure (single or separate sample).
• Mention mould size.

Important Notes:

• For cohesive soils, this light compaction test is reliable for optimum moisture content and dry density.
• For clean gravels and coarse sands, results may not reflect field compaction accurately; optimum moisture content may be overestimated and dry density underestimated.
• Laboratory compaction results guide field compaction control but must be interpreted cautiously for non-cohesive soils.

Typical Formula for Water Content Correction (Clause 6.2):

[ Y = \frac{100}{100 + W} ] Where:

• (Y) = correction factor
• (W) = water content (%)

Summary Table for Apparatus:

flowchart TD
    A[Start] --> B[Select Soil Sample]
    B --> C[Determine Water Content]
    C --> D[Compact Soil in Mould with 2.6-kg Rammer]
    D --> E[Measure Dry Density]
    E --> F[Plot Water Content vs Dry Density]
    F --> G[Determine Optimum Moisture Content &

IS 2720 Part 7: Sampling and Preparation of Soil - Key Points

Sampling Quantity & Sieving

• Representative sample size:
  • Soils not susceptible to crushing: ~6 kg passing 20 mm IS sieve.
  • Soils susceptible to crushing: ~15 kg passing 20 mm IS sieve.
• Sieving on 20 mm IS sieve to remove coarse fraction (record proportion).

Sample Preparation

• Take a 5 kg air-dried soil sample passing 20 mm sieve.
• Mix thoroughly with water depending on soil type (see Notes 3 & 4 in IS 2720-7).

Reporting of Results (Clause 7.5)

• Specify:
  • Method used (e.g., 2.6-kg rammer method).
  • Procedure (single or separate samples).
  • Mould size used.

Important Notes

• For highly permeable soils (clean gravels, coarse sands), lab compaction tests may not reflect field compaction well.
• Optimum moisture content in lab may be higher than field; max dry density lower than field compaction state.

Summary Table: Sampling Size

Conceptual Flow for Sampling & Preparation

flowchart TD
    A[Collect Bulk Soil Sample] --> B{Soil Type}
    B -->|Not crushing| C[Take ~6 kg passing 20 mm sieve]
    B -->|Crushing| D[Take ~15 kg passing 20 mm sieve]
    C --> E[Sieve on 20 mm IS sieve]
    D --> E
    E --> F[Reject coarse fraction & record proportion]
    F --> G[Air dry sample]
    G --> H[Take 5 kg passing 20 mm sieve]
    H --> I[Mix with water as per soil type]
    I --> J[Ready for lab compaction test]

This concise guide follows IS 2720-7 for representative sampling and preparation ensuring reliable compaction test results.

IS 2720 Part 7 - Test Procedure Key Points

• Compaction Method: Use the 2.6-kg rammer dropped from 31 cm height, 25 blows per layer, typically 3 layers in a standard mould (usually 1000 cc or 500 cc).

• Sample Preparation: Either a single sample or separate samples for each moisture content; size of mould must be stated.

• Reporting (Clause 7.5):

  • State the method (2.6-kg rammer).
  • Specify if single or separate samples used.
  • Mention mould size.

• Optimum Moisture Content (OMC) and Maximum Dry Density (MDD):

  • Plot dry density vs. moisture content curve.
  • OMC corresponds to peak dry density.

• Limitations:

  • For clean gravels, coarse sands: lab test may overestimate OMC and underestimate MDD compared to field compaction.

Key Formula for Dry Density (ρd):

[ \rho_d = \frac{W_s}{V \times (1 + w)} ]

Where:

• ( W_s ) = weight of dry soil (g)
• ( V ) = volume of mould (cm³)
• ( w ) = moisture content (decimal)

Typical Test Setup Summary:

flowchart TD
    A[Prepare soil sample at given moisture content]
    B[Fill mould in 3 layers]
    C[Compact each layer with 25 blows of 2.6-kg rammer dropped from 31 cm]
    D[Weigh compacted sample]
    E[Calculate dry density]
    F[Repeat for various moisture contents]
    G[Plot dry density vs moisture content curve]
    
    A --> B --> C --> D --> E --> F --> G

Note: For heavy compaction, refer to IS 2720 Part 8.

IS 2720 Part 7 (1980) - Key Formulas and Specifications for Calculations

This part covers determination of water content-dry density relation using light compaction (2.6-kg rammer method).

Key Specifications:

• Compaction Method: 2.6-kg rammer, 31 cm drop height.
• Mould Size: Typically 1000 cm³ or as specified.
• Sample Type: Single or separate samples must be stated.
• Reporting: State compaction method, sample type, and mould size used.

Important Notes:

• For clean gravels and coarse sands, light compaction test results may poorly represent field compaction.
• Optimum moisture content (OMC) from lab may be higher than field OMC.
• Maximum dry density (MDD) from lab may be lower than field achievable density.

Basic Formula for Dry Density (ρd):

[ \rho_d = \frac{W}{V \times (1 + w)} ] Where:

• ( W ) = weight of wet soil (g)
• ( V ) = volume of mould (cm³)
• ( w ) = water content (decimal)

Moisture Content Calculation:

[ w = \frac{W_{wet} - W_{dry}}{W_{dry}} \times 100% ]

Typical Procedure Summary:

1. Compact soil in mould using 2.6-kg rammer.
2. Measure wet weight, dry weight after oven drying.
3. Calculate moisture content and dry density.
4. Plot dry density vs moisture content to find OMC and MDD.

flowchart TD
    A[Prepare Soil Sample] --> B[Compact in Mould with 2.6-kg Rammer]
    B --> C[Measure Wet Weight]
    C --> D[Oven Dry Sample]
    D --> E[Measure Dry Weight]
    E --> F[Calculate Moisture Content & Dry Density]
    F --> G[Plot Dry Density vs Moisture Content]
    G --> H[Determine OMC and MDD]

For more detailed procedures, refer to IS 2720 Part 7 and IS 2720 Part 8 (heavy compaction).

IS 2720 Part 7 - Reporting of Results (Clause 7.5 & related)

• Method Description: Clearly state the compaction method used, e.g., 2.6-kg rammer method.
• Sample Details: Specify if results are from a single sample or multiple samples.
• Mould Size: Report the size of the mould used for compaction.

Additional Reporting Requirements:

• Dry Density vs Moisture Content Curve (Clause 6.3 & 7.1):

  • Plot dry densities (γ_d) against moisture contents (w).
  • Draw a smooth curve to identify the Maximum Dry Density (MDD) and Optimum Moisture Content (OMC).

• Stone Content (Clause 7.4):

  • Report the percentage of stone retained on 20-mm IS sieve to the nearest 1%.

Notes:

• For highly permeable soils (clean gravels, coarse sands), lab compaction results may not represent field compaction accurately.
• Laboratory OMC may be higher and MDD lower than field achievable compaction.

Summary Table for Reporting:

graph LR
A[Soil Sample] --> B[Compaction using 2.6-kg Rammer]
B --> C[Measure Dry Density (γ_d) & Moisture Content (w)]
C --> D[Plot γ_d vs w Curve]
D --> E[Determine MDD & OMC]
E --> F[Report Results with Method, Sample, Mould Size, Stone Content]

This ensures clarity and uniformity in reporting soil compaction test results as per IS 2720 Part 7.

IS 2720 Part 7 (1980) - Notes and Limitations Summary

Key Points from Clause 7.5 and Notes:

• Reporting Requirements:

  • State the compaction method (e.g., 2.6-kg rammer).
  • Specify sample procedure (single/separate) and mould size.

• Limitations:

  • For highly permeable soils (clean gravels, coarse sands):
    • Lab compaction test may poorly represent field conditions.
    • Optimum moisture content from lab is often higher than field optimum.
    • Maximum dry density in lab is often lower than achievable in field.
  • The test is more reliable for cohesive soils.
  • For cohesionless soils, water-density curves may be not well defined.

Practical Implications:

• Use lab compaction results as a guide, not absolute values for field compaction.
• Field control tests are essential to verify compaction quality.
• Heavy compaction methods (IS 2720 Part 8) may be more suitable for some soils.

Formula Highlight (Clause 6.2 correction):

[ Y = \frac{100}{100 + 1} ] (Exact context/formula usage to be checked in full clause)

Summary Table for Reporting:

flowchart TD
    A[Start: Soil Sample] --> B{Soil Type?}
    B -->|Cohesive| C[Lab Compaction Test (2.6-kg rammer)]
    B -->|Clean Sand/Gravel| D[Lab Test less reliable]
    C --> E[Determine Optimum Moisture & Max Dry Density]
    D --> F[Use Lab Data as Guide + Field Tests]
    E --> G[Field Compaction Control]
    F --> G

Reference: IS 2720 Part 7 (1980), Clause 7.5 and Notes.