Methods of test for soils, Part 14: Determination of density index (relative density) of cohesionless soils

IS 2720 Part 14 - Scope & Key Specifications

This part covers the determination of minimum density (relative density) of cohesionless soils using specified moulds, accessories, and procedures.

Key Specifications:

• Calibration Bar: Metal bar of 75 x 300 x 3 mm (Clause 3.1.7).
• Dial Gauges: As per standard specifications for precise measurement.
• Soil Sample Mass & Mould Size: (Clause 3.3.1, Table 1)

Calculation Clauses:

• Clause 3.6 & 4.3: Provide guidelines for calculations related to density index and relative density determination.

Summary:

• Use appropriate soil sample mass based on max particle size.
• Use correct pouring device for uniform sample placement.
• Use specified mould sizes for consistency.
• Follow calibration and measurement standards for accuracy.

flowchart LR
    A[Select Soil Sample] --> B{Max Particle Size}
    B -->|>75 mm| C[Use 45 kg sample, Shovel, 15000 cm³ mould]
    B -->|37.5-75 mm| D[Use 12 kg sample, Scoop, 3000 cm³ mould]
    B -->|19 mm| D
    B -->|9.5 mm| E[Use 12 kg sample, 25 mm spout pouring device, 3000 cm³ mould]
    B -->|4.75 mm| F[Use 12 kg sample, 12 mm spout pouring device, 3000 cm³

IS 2720 Part 14 (1983) – Key Definitions & Specifications

1. Definitions (Clause 2.0)

• Density Index (Relative Density), Dr:
  [ D_r = \frac{e_{max} - e}{e_{max} - e_{min}} \times 100% ] where:

  • ( e ) = void ratio of the soil sample
  • ( e_{max} ) = maximum void ratio
  • ( e_{min} ) = minimum void ratio

• Calibration Bar (Clause 3.1.7):
  A metal bar of 75 mm x 300 mm x 3 mm used for calibrating dial gauges.

2. Specifications for Moulds and Accessories

• Moulds must be of standard size and shape to ensure consistent volume for density index tests.
• Dial gauges should have a least count of 0.01 mm for precise measurement of soil sample deformation.

3. Calculations (Clauses 3.6 & 4.3)

• Calculations primarily involve determining void ratios and relative density using soil sample weights and volumes.
• Use calibrated dial gauges for displacement measurement to calculate volume changes.

Summary Table: Density Index Calculation

flowchart LR
    A[Soil Sample] --> B[Measure Volume & Weight]
    B --> C[Calculate Void Ratio (e)]
    C --> D[Use e_max & e_min]
    D --> E[Calculate Density Index (Dr)]

This concise framework ensures uniformity in determining relative density of cohesionless soils as per IS 2720 Part 14.

IS 2720 Part 14 (1983) - Apparatus and Equipment Summary

Key Apparatus Specifications

• Calibration Bar (Clause 3.1.7)

  • Material: Metal
  • Dimensions: 75 mm x 300 mm x 3 mm

• Pouring Devices (Clause 3.1.8)

  • Funnels with diameters: 12 mm and 25 mm
  • Length: 15 cm
  • Features: Cylindrical spouts, lipped brims for attachment to cans (15 cm diameter, 30 cm height)

• Moulds and Accessories

  • Selected based on maximum particle size (see Table 1, Clause 3.4.1)
  • Mould is weighed before use; oven-dry soil is used for testing

Table 1: Mould Selection Based on Maximum Particle Size

Calculations (Clause 4.3)

• Relative Density (Dr) is calculated as:

[ D_r = \frac{e_{max} - e}{e_{max} - e_{min}} \times 100% ]

Where:

• ( e ) = void ratio of the soil sample
• ( e_{max} ) = maximum void ratio (loosest state)
• ( e_{min} ) = minimum void ratio (densest state)

This setup ensures accuracy in determining the relative density of cohesionless soils by standardizing apparatus dimensions and procedures.

IS 2720 Part 14: Sampling and Sample Preparation

Key Specifications from Clause 3.3.1 and Table 1

Sample Preparation (Clauses 4.2.1.1 & 4.2.2.2)

• Mix soil sample thoroughly with water as per soil type before testing.
• For Kach samples, treat as per Clauses 4.2.1.2 to 4.2.1.5; discard remainder after sampling.

Summary

• Select representative soil sample based on max particle size.
• Use specified mass and pouring device for minimum density tests.
• Prepare sample by thorough mixing with water before testing.

flowchart TD
    A[Select Soil Sample] --> B{Max Particle Size?}
    B -->|>75 mm| C[Take 45 kg sample]
    B -->|≤75 mm and >4.75 mm| D[Take 12 kg sample]
    C --> E[Use Shovel / Large Scoop]
    D --> F[Use Scoop or Pouring Device]
    E --> G[Use 15,000 cm³ mould]
    F --> H[Use 3,000 cm³ mould]
    G & H --> I[Mix sample with water thoroughly]
    I --> J[Proceed to testing]

This ensures representative sampling and proper preparation for accurate soil density and compaction tests.

IS 2720 Part 14 — Procedure for Determination of Maximum Density

Key Formulas:

• Maximum Dry Density, (\rho_{max}) (g/cm³):

[ \rho_{max} = \frac{M}{V - (D_i - D_f) \times A} ]

Where:

• (M) = Mass of dry soil in test (g)
• (V) = Volume of soil mould (cm³)
• (D_i) = Initial dial gauge reading (cm)
• (D_f) = Final dial gauge reading after vibration (cm)
• (A) = Cross-sectional area of mould (cm²)

Procedure Highlights:

• Conduct vibration compaction, record dial gauge readings before and after.
• Calculate volume correction using ((D_i - D_f) \times A).
• Determine dry density at various moisture contents.
• Plot moisture content vs dry density curve.
• Maximum dry density = dry density at peak of curve (to nearest 0.01 g/cm³) (Clause 5.2).

Summary:

flowchart TD
    A[Prepare Soil Sample] --> B[Fill Mould & Record \(D_i\)]
    B --> C[Vibrate Soil Sample]
    C --> D[Record \(D_f\)]
    D --> E[Calculate Volume Correction \((D_i - D_f) \times A\)]
    E --> F[Calculate \(\rho_{max} = \frac{M}{V - (D_i - D_f) \times A}\)]
    F --> G[Plot Moisture Content vs Dry Density]
    G --> H[Identify Maximum Dry Density at Peak]

This procedure ensures accurate

IS 2720 Part 14: Procedure for Determination of Minimum Density

Key Formula (Clause 3.6.1)

[ Y_{\min} = \frac{W_{sm}}{V_c} ]

• (Y_{\min}) = Minimum density (g/cm³)
• (W_{sm}) = Mass of dry soil in minimum density test (g)
• (V_c) = Calibrated volume of the mould (cm³)

Sample & Equipment Specifications (Clause 3.3.1, Table 1)

Summary:

• Select representative soil sample based on max particle size.
• Use appropriate pouring device and mould size per Table 1.
• Calculate minimum density by dividing dry soil mass by mould volume.

flowchart TD
    A[Select Soil Sample] --> B{Max Particle Size}
    B -->|>75 mm| C[Use 45 kg soil, Shovel, 15,000 cm³ mould]
    B -->|37.5-75 mm| D[Use 12 kg soil, Scoop, 3,000 cm³ mould]
    B -->|19-37.5 mm| D
    B -->|9.5-19 mm| E[Use 12 kg soil, 25 mm spout pouring device, 3,000 cm³ mould]
    B -->|<9.5 mm| F[Use 12 kg soil, 12 mm spout pouring device, 3,000 cm³ mould]
    C & D & E & F --> G[Fill mould, measure dry soil mass

Density Index (Relative Density), (I_a) or (D_r), quantifies the compactness of cohesionless soils, crucial for correlating soil properties like strength and permeability.

Key Formulas (IS 2720 Part 14)

1. Using Densities:

[ I_a \text{ or } D_r = \frac{Y_{\max} - Y_a}{Y_{\max} - Y_{\min}} \times 100 ]

• (Y_a) = Bulk density of soil in field
• (Y_{\max}) = Maximum dry density (densest state)
• (Y_{\min}) = Minimum dry density (loosest state)

2. Using Void Ratios:

[ I_a \text{ or } D_r = \frac{e_{\max} - e}{e_{\max} - e_{\min}} \times 100 ]

• (e) = Void ratio of soil in field
• (e_{\max}) = Void ratio in loosest state
• (e_{\min}) = Void ratio in densest state

Notes:

• (D_r) is expressed as a percentage.
• (D_r = 0%) means loosest state; (D_r = 100%) means densest state.
• Determined by laboratory tests: vibratory table (principal) or vibratory hammer (alternate).

Summary Table:

flowchart LR
    A[Soil Sample] --> B{Measure}
    B --> C[Bulk Density \(Y_a\)]
    B --> D[Void Ratio \(e\)]
    E[Lab Tests] --> F[Max Density \(Y_{\max}\),

IS 2720 Part 14: Reporting of Results – Key Points

1. Rounding Off Results (Clause 0.4)

• Final test values (observed or calculated) must be rounded off as per IS 2-1960.
• The number of significant digits retained should match the specified value in the standard.

2. Calculation Methods (Clauses 3.6 & 4.3)

• Calculations for test results should follow prescribed formulas or procedures in the relevant clauses.
• Ensure clarity on whether results are from a single sample or multiple samples.

3. Reporting Format (Clause 5.5)

• Report must clearly state:
  • The method used to obtain results.
  • The procedure followed (e.g., single sample or separate samples).
• Include all relevant test conditions and observations.

Example Table Extract: Reporting Details (Clause 5.5)

Summary Flow for Reporting:

flowchart TD
    A[Test Conducted] --> B[Calculate Results]
    B --> C{Round off as per IS 2-1960}
    C --> D[Prepare Report]
    D --> E[State Method & Procedure]
    E --> F[Include Observations & Final Values]

In brief: Always round off test results per IS 2, clearly mention calculation and sampling methods, and maintain precision consistent with the standard. This ensures uniformity and reliability in reporting soil test results.

IS 2720 Part 14: Accuracy and Precision Key Points

• Clause 4.3 & 3.6 (Calculations):
  Calculations must adhere to standard rounding rules per IS 2-1960.

  • Final test results should be rounded to the same number of significant digits as the specified value in the standard.
  • Ensures consistent accuracy and comparability of results.

• Measurement Device Accuracy (Clause 3.1.16):

  • Micrometer range: 0 to 25 mm
  • Accuracy: ±0.025 mm

Important Notes on Accuracy and Precision:

Rounding Off Rule (IS 2-1960 Summary):

• If the digit after the last significant figure is >5, round up.
• If <5, round down.
• If exactly 5, round to the nearest even digit.

flowchart LR
  A[Measurement] --> B[Calculate Result]
  B --> C[Round off as per IS 2-1960]
  C --> D[Final Value with Correct Precision]

This ensures accuracy (closeness to true value) and precision (repeatability) in soil testing measurements.

IS 2720 Part 14 (1983) - Safety and Calibration Key Points

Calibration

• Calibration Bar (Clause 3.1.7):

  • Material: Metal
  • Size: 75 mm x 300 mm x 3 mm
  • Used for calibrating moulds and accessories for relative density tests of cohesionless soils.

• Dial Gauges:

  • Must conform to specifications ensuring accuracy and reliability for deformation measurements.

Calculations (Clauses 3.6 & 4.3)

• Follow prescribed formulas for relative density and density index determination.
• Use IS 2-1960 rounding rules:
  • Round off final test values to the same number of significant figures as specified in the standard.

Important Specification Summary:

Example: Rounding off rule (IS 2-1960)

• If specified value = 0.123 (3 significant figures), round test result to 3 significant figures.

flowchart LR
    A[Calibration Bar] --> B[Check Dimensions: 75x300x3 mm]
    B --> C[Calibrate Moulds & Accessories]
    C --> D[Perform Test]
    D --> E[Calculate Relative Density]
    E --> F[Round off per IS 2-1960]
    F --> G[Report Final Value]

This ensures precision and consistency in soil density testing.

IS 2720 Part 14 (1983) – Key References and Specifications

This part covers determination of density index (relative density) of cohesionless soils.

Key Specifications:

• Calibration Bar (Clause 3.1.7):

  • Material: Metal
  • Size: 75 mm x 300 mm x 3 mm

• Moulds and Accessories:

  • Designed specifically for density index tests on cohesionless soils.
  • Must conform to dimensions and material requirements ensuring accuracy.

• Dial Gauges:

  • Used for precise measurement of volume changes during testing.
  • Should meet standard specifications for sensitivity and accuracy.

Important Calculation Clauses:

• Clause 3.6 and 4.3:
  • Provide formulas for calculating relative density (Dr) from measured densities:

[ D_r = \frac{e_{max} - e}{e_{max} - e_{min}} \times 100% ]

Where:

• (e = ) void ratio of soil sample
• (e_{max} = ) maximum void ratio (loosest state)
• (e_{min} = ) minimum void ratio (densest state)

Summary Table: Calibration Bar Dimensions

flowchart LR
    A[Soil Sample] --> B[Measure Bulk Density]
    B --> C[Calculate Void Ratio (e)]
    C --> D[Use e_max and e_min from standard tests]
    D --> E[Calculate Relative Density (Dr)]

This concise framework ensures reliable determination of relative density per IS 2720 Part 14.