Code of practice for field control of moisture and compaction of soils for embankment and subgrade
1982 Edition

Introduction to Field Control of Soil Moisture and Compaction

Scope Overview:

• Procedures for controlling moisture content and compaction in embankment and subgrade soils.
• Ensures soil properties satisfy design quality with recommended testing every 1000 m².

Highlights:

• Applicable to diverse soil types including gravely and non-gravely soils (refer to Clause 3.4).
• Shear strength sensitivity to density in gravely and rockfill materials is minimal, reducing water content control precision requirements.
• Employs various IS 2720 test methods for water content and density assessments.

Result Handling:

• Test outcomes are rounded following IS 2-1960 standards.

Core IS 2720 Test Methods Referenced:

Recommended Testing Frequency Summary

flowchart TD
    A[Soil in Embankment/Subgrade] --> B[Field Control Operations]
    B --> C{Soil Classification}
    C -->|Gravely or Rockfill| D[Lower sensitivity to moisture variations]
    C -->|Non-Gravely| E[Strict moisture regulation required]
    B --> F[Tests as per IS 2720]
    F --> G[Water Content Measurement]
    F --> H[Dry Density Assessment]
    F --> I[In-situ Density Evaluation]

This standard ensures consistent control over soil compaction and moisture in field conditions.

Summary of Scope for IS 10379

• Coverage: Defines field control techniques for moisture content and compaction in soils used in embankments and subgrades.
• Applies across different soil categories, ensuring soil characteristics conform to engineering requirements.
• Suggests conducting tests at intervals close to 1000 m² of compacted soil surface.
• Addresses specific methods for non-gravelly soils and mentions lesser precision needed for gravely or rockfill soils.
• Emphasizes the importance of rounding test results according to IS 2-1960.

Essential Parameters:

Key IS References:

• Water Content Determination: IS 2720 Part II
• Moisture-Density Tests: IS 2720 Part VII (light), Part VIII (heavy)
• In-situ Density Tests: IS 2720 Part XXXIII (ring & water), Part XXVIII (sand replacement)

flowchart LR
    A[Soil for Embankment/Subgrade] --> B{Soil Type}
    B -->|Non-Gravelly| C[Strict Moisture & Density Control]
    B -->|Gravel/Rockfill| D[Relaxed Moisture Control]
    C --> E[Routine Testing every 1000 m²]
    D --> F[Shear Strength Less Sensitive to Density Changes]

In essence, this code guides effective soil moisture and compaction management to ensure embankment and subgrade stability.

Guidelines for Non-Gravelly Soils (Clause 2.3 - Method 3)

• Objective: Address soils where actual field moisture and dry density values differ from laboratory results.
• Test Embankment Setup:
  • Construct a test strip measuring 3 m by 10 m.
  • Evenly place soil and adjust moisture within ±6% of lab optimum.
  • Allow a waiting period of 5 to 30 minutes before compaction.
  • Compact soil using rollers, measuring dry density after every two roller passes using core cutter or sand replacement methods (IS 2720 Part XXVIII, XXIX).
• Data Analysis:
  • Plot roller passes against dry density for each moisture content.
  • Plot maximum dry density versus moisture content to identify field optimum moisture and maximum attainable dry density.
• Outcome:
  • Establishes minimum roller passes needed to achieve maximum field compaction at optimum moisture.

Relevant IS Test Standards:

flowchart TD
    A[Prepare 3m x 10m Test Strip] --> B[Adjust Moisture ±6% of Lab Optimum]
    B --> C[Wait 5-30 Minutes]
    C --> D[Roll Soil; Measure Dry Density Every 2 Passes]
    D --> E[Plot Passes vs Dry Density]
    E --> F[Plot Max Dry Density vs Moisture Content]
    F --> G[Determine Field Optimum Moisture & Dry Density]
    G --> H[Set Required Roller Passes for Compaction Control]

This approach facilitates tailored field compaction control for non-gravelly soils, reflecting actual site conditions.

Method 1 Overview: Laboratory and Field Tests for Gravely and Rockfill Soils

Main Procedures:

• Determination of Optimum Moisture Content (OMC) and Maximum Dry Density (MDD):
  • Conducted via laboratory compaction tests as per IS 2720 Part VII (light compaction) and Part VIII (heavy compaction).
• Field Moisture Content Measurement:
  • Carried out according to IS 2720 Part II.
• Field Dry Density Measurement:
  • Using one or more of the following methods: sand replacement (IS 2720 Part XXVIII), core cutter (IS 2720 Part XXIX), or rubber balloon (IS 2720 Part XXXIV).
• Testing Protocol:
  • Remove the upper 5 cm soil layer before sampling.
  • Measure field moisture and dry density to calculate compaction efficiency.

Calculation of Compaction Efficiency (CE):

[ CE = \frac{\text{Field Dry Density}}{\text{Maximum Dry Density from Lab}} \times 100% ]

• Note: In gravely and rockfill soils, strict water content control is less critical due to the minimal impact of density variations on shear strength.

Applicable IS Codes Summary:

flowchart TD
    A[Soil Sample] --> B[Laboratory Compaction Tests]
    B --> C[Determine OMC & MDD]
    C --> D[Field Sampling (Remove Top 5 cm)]
    D --> E[Measure Field Moisture & Dry Density]
    E --> F[Calculate Compaction Efficiency]

This method forms the foundation for controlling compaction in gravely and rockfill soils.

Method 2 Overview: HILF Method for Quick Field Compaction Control

• Purpose: Enable swift field assessment of soil compaction and moisture conditions without direct moisture measurement.
• Applicability: Suitable primarily for non-gravelly soils.
• Standard Reference: IS 2720 Part XXXVIII (1976).

Key Steps:

• Construct a test embankment.
• Rapidly compact soil while monitoring dry density with specialized HILF devices.
• Establish indirect relationships between moisture content, dry density, and lab optimum values within about one hour.
• Use results for moisture and/or density control during construction.

Compaction Efficiency Formula:

[ \eta = \frac{\rho_{field}}{\rho_{max}} \times 100% ]

Where:

• (\rho_{field}) = Dry density from HILF measurement
• (\rho_{max}) = Maximum dry density from laboratory compaction tests

Control Limits:

• Moisture content within ±6% of lab optimum
• Dry density within ±3% of lab maximum

Workflow Diagram:

flowchart TD
    A[Build Test Embankment] --> B[Rapid Compaction with Controlled Passes]
    B --> C[Measure Dry Density Using HILF Device]
    C --> D[Compare with Lab Maximum Dry Density]
    D --> E{Within Acceptable Range?}
    E -- Yes --> F[Proceed with Construction]
    E -- No --> G[Adjust Moisture or Compaction and Re-test]

This technique facilitates prompt decision-making in field compaction control without moisture content tests.

Method 3 Summary: Test Embankment Approach for Weathered Soil Conditions

• Construct a test strip of dimensions 3 m by 10 m.
• Spread soil and adjust moisture content within ±6% of laboratory optimum.
• Allow a waiting period of 5 to 30 minutes before compaction, depending on soil characteristics.
• Compact soil using rollers, measuring dry density after every two passes using IS 2720 methods like sand replacement, core cutter, or rubber balloon.
• Plot roller passes versus dry density for each moisture level.
• Plot maximum dry density versus moisture content to determine field optimum moisture and maximum achievable dry density.
• Identify the minimum number of roller passes required to achieve maximum compaction at field optimum moisture.

Relevant IS Test Methods:

• Moisture content: IS 2720 Part II
• Dry density: IS 2720 Parts XXVIII (sand replacement), XXIX (core cutter), XXXIV (rubber balloon)
• Compaction control: IS 2720 Part XXXVIII

graph TD
    A[Spread Soil Layer on Test Strip] --> B[Adjust Moisture ±6% Around Lab Optimum]
    B --> C[Wait 5-30 Minutes]
    C --> D[Roll Soil; Measure Dry Density Every 2 Passes]
    D --> E[Plot Passes vs Dry Density for Each Moisture]
    E --> F[Plot Max Dry Density vs Moisture Content]
    F --> G[Identify Field Optimum Moisture and Dry Density]
    G --> H[Determine Minimum Roller Passes for Field Compaction]

This method ensures realistic compaction parameters tailored for weathered soils under field conditions.

Procedures for Managing Soils with Gravels and Rockfills

• Gravel Content Limit: Up to 30% gravel (particles exceeding 40 mm in size).
• Laboratory Testing: Conduct moisture-density relationship tests on soil fraction passing through 40 mm IS sieve (IS 2720 Part VII and Part VIII).
• Field Testing: Measure field moisture and dry density preferably by core cutter method (IS 2720 Part XXXIII) or alternatively via sand replacement method (IS 2720 Part XXVIII).

Stepwise Procedure (Clause 3.3):

Additional Notes from Clause 2.3 (Method 3):

• Use test embankment (3 m × 10 m) with water variation ±6% around lab optimum moisture content.
• Measure dry density after every two roller passes.
• Plot density against passes and moisture to find optimum parameters.

Relevant IS Tests:

flowchart TD
  A[Soil Sample Passing 40mm] --> B[Laboratory Compaction Tests (IS 2720 Part VII/VIII)]
  B --> C[Moisture-Density Curve]
  C --> D[Determine Optimum Moisture & Maximum Dry Density]
  E[Field Embankment] --> F[Controlled Compaction with Water Content]
  F --> G[Field Moisture & Dry Density Measurement]
  G --> H[Quality Control Assessment]

This approach integrates lab and field tests to ensure effective compaction control of gravely soils and rockfills.

Supplementary Provisions for Gravelly Soil Management

• Applicable for soils containing up to 30% gravel.
• Laboratory tests focus on the soil fraction passing 40 mm sieve, following IS 2720 Part VII (light compaction) and Part VIII (heavy compaction).
• Field moisture and density measurements can be conducted using sand replacement (IS 2720 Part XXVIII), core cutter (IS 2720 Part XXIX), or rubber balloon (IS 2720 Part XXXIII) methods.
• Test embankment construction (3 m × 10 m) involves varying moisture content ±6% around lab optimum, rolling soil, and measuring density after every two roller passes.
• Plotting dry density against roller passes and moisture content helps determine optimum field compaction parameters.

Summary Table for Gravelly Soil Compaction:

flowchart TD
    A[Soil with ≤30% Gravel] --> B[Pass Through 40 mm Sieve]
    B --> C[Lab Moisture-Density Testing]
    C --> D[Test Embankment Construction (3x10 m)]
    D --> E[Roll Soil & Measure Density After Every 2 Passes]
    E --> F[Plot Dry Density vs Passes & Moisture]
    F --> G[Determine Field Optimum Moisture & Density]

These additional details ensure appropriate compaction control for gravelly soils in field conditions.

Impact of Gravel Proportion on Soil Compaction Characteristics

• Soil density tends to increase and moisture content decreases as gravel content rises up to approximately 60–75%.
• Beyond gravel contents of 75%, the overall soil density may decrease.

Testing Recommendations:

• For gravel content up to 30%, conduct laboratory moisture-density tests on soil passing 40 mm sieve per IS 2720 Part VII & VIII.
• For weathered soils, employ test embankment methods to determine moisture and density parameters.
• Rapid control methods like the HILF technique (IS 2720 Part XXXVIII) can expedite moisture-density assessments.

Gravel Content Effects Summary:

flowchart TD
    A[Soil Sample] --> B{Gravel Content}
    B -- ≤30% --> C[Lab Tests on <40mm Fraction]
    B -- >30% --> D[Test Embankment Method]
    C --> E[Compare Field & Lab Density]
    D --> F[Determine Field Moisture & Density via Rolling & Water Adjustment]
    E & F --> G[Manage Field Compaction]

IS 2720 References for Testing:

• Part II: Water Content Measurement
• Part VII: Moisture-Density Relation (Light Compaction)
• Part VIII: Moisture-Density Relation (Heavy Compaction)
• Part XXVIII: Field Dry Density by Sand Replacement
• Part XXXIII: Field Dry Density by Core Cutter

Understanding how gravel content affects soil properties aids in optimizing compaction strategies.

Establishing Moisture-Density Curves for Gravelly Soils (Up to 30%)

• Laboratory tests should be performed on soil fractions passing through the 40 mm IS sieve.
• Follow IS 2720 Part VII (light compaction) or Part VIII (heavy compaction) to derive moisture-density relationships.
• Field moisture and dry density measurements are to be conducted using IS 2720 Part XXVIII (sand replacement) or Part XXIX (core cutter).
• Field dry density values are compared against laboratory maximum dry density to evaluate compaction quality.

Procedure Outline:

1. Sieve soil to obtain fraction <40 mm.
2. Conduct laboratory compaction tests to obtain moisture-density curve.
3. Measure in-situ moisture and dry density using standard field methods.
4. Compare field results with laboratory benchmarks to verify compaction.

Additional Considerations:

• Gravel presence up to 30% generally increases total soil density.
• For gravel contents exceeding 30%, refer to Clause 3.2 for density behavior.
• Test embankment procedures (Clause 2.3) are recommended for field verification.

Conceptual Moisture-Density Curve:

graph LR
A[Moisture Content] --> B[Dry Density]
B --> C[Peak Dry Density at Optimum Moisture]

Relevant IS Standards:

These procedures ensure appropriate compaction assessment for soils with moderate gravel content.

Compaction Control Measures for Gravely and Rockfill Soils

• Employ the test embankment method (Clause 2.3) by constructing a 3 m × 10 m test strip.

• Adjust moisture within ±6% of laboratory optimum during test construction.

• Measure dry density after every two roller passes.

• Plot roller passes against dry density for each moisture level and maximum dry density against moisture content.

• Determine field optimum moisture content and maximum achievable dry density.

• Identify the minimum number of roller passes needed to achieve maximum compaction.

• For soils containing up to 30% gravels:

  • Use soil fraction passing 40 mm sieve for laboratory moisture-density testing (IS 2720 Part VII & VIII).
  • Field moisture and density measurements preferably via core cutter method (IS 2720 Part XXXIII) or sand replacement (IS 2720 Part XXVIII).

Summary Table:

Dry Density Calculation Formula:

[ \rho_d = \frac{\rho}{1 + w} ]

Where:

• (\rho_d) = dry density
• (\rho) = wet density
• (w) = moisture content (decimal fraction)

Workflow Diagram for Test Embankment Method:

flowchart TD
    A[Prepare 3 m × 10 m Test Strip] --> B[Apply Moisture ±6% of Lab Optimum]
    B --> C[Roll Soil; Measure Dry Density Every 2 Passes]
    C --> D[Plot Roller Passes vs Dry Density]
    D --> E[Plot Max Dry Density vs Moisture Content]
    E --> F[Determine Field Optimum Moisture & Dry Density]
    F --> G[Establish Minimum Roller Passes for Compaction]

This methodology ensures effective compaction control for gravel and rockfill soils.

Field Testing Frequency Guidelines

• For gravely and rockfill soils, due to minimal shear strength variation with density changes, testing frequency can be reduced compared to fine-grained soils (Clause 3.4).

• Method 1 (Clause 2.1) recommends:

  • Determination of OMC and MDD via IS 2720 Part VII and VIII.
  • Field moisture content by IS 2720 Part II.
  • Field dry density by IS 2720 Parts XXVIII, XXIX, or XXXIV.
  • Removal of top 5 cm soil before sampling.
  • Calculation of compaction efficiency.

• Method 3 (Clause 2.3) involves:

  • Test embankment construction (3 m × 10 m) with moisture variation ±6% of lab optimum.
  • Dry density measurement after every two roller passes.
  • Plotting passes vs dry density and moisture vs max dry density.
  • Determining minimum roller passes for maximum density at field moisture.

Testing Frequency Summary:

Key IS Testing References:

• IS 2720 Parts II, VII, VIII, XXVIII, XXIX, XXXIV

flowchart LR
    A[Test Embankment Setup] --> B[Moisture Varied ±6% of OMC]
    B --> C[Roller Passes Incremented by 2]
    C --> D[Dry Density Measurement]
    D --> E[Plot Passes vs Dry Density]
    E --> F[Determine Minimum Passes for Max Dry Density]

Adhering to these intervals ensures consistent field compaction quality in line with soil characteristics.

Guidelines for Computing and Reporting Compaction Efficiency

Compaction Efficiency Formula (Clause 2.1 - Method 1):

[ \text{Compaction Efficiency} = \frac{\text{Field Dry Density}}{\text{Lab Maximum Dry Density}} \times 100% ]

• Lab maximum dry density and optimum moisture content are obtained from IS 2720 Part VII or VIII.
• Field moisture content determined using IS 2720 Part II.
• Field dry density measured by IS 2720 Parts XXVIII, XXIX, or XXXIV.
• Top 5 cm soil layer must be removed before sampling.

Test Embankment Method (Clause 2.3 - Method 3):

• Construct a 3 m × 10 m test strip, vary moisture ±6% around lab optimum.
• Roll soil and measure dry density after every two passes.
• Plot number of passes against dry density and moisture content against maximum dry density.
• Determine field optimum moisture content and achievable dry density.
• Establish minimum roller passes for optimal compaction.

Special Considerations for Gravels up to 30% (Clause 3.3):

• Laboratory moisture-density relationships established on soil passing 40 mm sieve (IS 2720 Part VII/VIII).
• Field moisture and density measurements via IS 2720 Part XXXIII (preferred) or Part XXVIII.

Summary Table:

flowchart TD
    A[Laboratory Test Results] --> B[Max Dry Density & Optimum Moisture]
    C[Field Measurements] --> D[Field Moisture & Dry Density]
    B --> E[Calculate Compaction Efficiency]
    D --> E

Accurate calculation and documentation of compaction efficiency are vital for quality assurance.

Rounding Protocols for Test Results

• Final measurements, whether observed or computed, should be rounded in compliance with IS 2:1960.
• The number of significant figures retained must correspond to those specified for values in the standard.
• This practice ensures consistency and comparability in reporting soil moisture and compaction data.

Rounding Rules Summary (IS 2:1960):

Application Examples:

• Moisture content and dry density results should be rounded to the decimal places matching the specified values.
• For example, if moisture content is specified to one decimal place, report results accordingly.

Reference Standards for Soil Testing:

• IS 2720 Part II: Water Content Determination
• IS 2720 Parts VII & VIII: Moisture-Density Relations
• IS 2720 Parts XXVIII & XXIX: Field Dry Density Measurements

flowchart TD
    A[Raw Test Data] --> B[Apply IS 2:1960 Rounding Rules]
    B --> C[Match Significant Figures to Specification]
    C --> D[Final Reported Value]

Adhering to these rounding guidelines promotes uniformity and reliability in soil testing reports.