Methods of Test for Soils, Part XV: Determination of Consolidation Properties

IS 2720 Part 15: Scope & Key Specifications for Consolidation Test

The scope covers determination of consolidation properties of soils by measuring volume change under load.

Key Formulas & Parameters (from Appendix A & Clauses 5.1, 5.2.1)

Data to Record (Clause 5.1 & 5.2.1)

• Soil identification, specific gravity, specimen measurements
• Water content & type of water used
• Weights: can + wet soil, can + dry soil, ring + specimen (wet & dry)
• Final dial readings and compression values during loading

Typical Data Table Columns (Clause 6.2.1.4)

Additional Notes

• Use Square Root of Time Fitting Method for consolidation curve analysis.
• Follow specimen preparation and measurement strictly as per Appendix A.

flowchart TD
    A[Specimen Preparation] --> B[Initial Measurements: Area, Thickness, Weight]
    B --> C[Apply Load]
    C --> D[Record Dial Readings & Compression]
    D --> E[Calculate Void Ratio & Consolidation Parameters]
    E --> F[Plot & Analyze Consolidation Curve]

This summarizes the scope and key data/formulas for consolidation testing per IS 2720 Part 15.

IS 2720 Part 15 (1986) - Key References for Consolidation Test

1. Specimen Measurements & Calculations (Appendix A)

• Area, A = πD²/4
• Thickness, Hc = measured specimen height
• Dry weight of specimen (W_dry) = (Wt of can + dry soil) - (Wt of can)
• Void ratio, e calculated from volume and weight data
• Equivalent height of solids = H × (1 - e)/(1 + e)

2. Consolidation Test Data Recording (Appendix A & B)

• Record Applied Pressure (kgf/cm²) vs. Dial Gauge Readings
• Track Compression (ΔH), Specimen Height (H), and Void Ratio (e)
• Use Square Root of Time Fitting Method for consolidation curve interpretation

3. Important Parameters

4. Calculation Highlights

• Void ratio at each pressure increment:
  [ e = \frac{V_v}{V_s} = \frac{H \times A - W_s / (\rho_s)}{W_s / (\rho_s)} ] where (W_s) = dry weight, (\rho_s) = soil particle density
• Compression:
  [ \Delta H = H_{initial} - H_{final} ]
• Coefficient of consolidation, (C_v), from time-settlement curve fitting.

5. Presentation of Results

• Tabulate pressure, dial readings, compression, void ratio, and time data as per Tables in Appendix A & B.
• Use graphical plots of pressure vs. void ratio and time vs. settlement for interpretation.

flowchart TD
    A[Specimen Preparation] --> B[Measure Initial Dimensions]
    B --> C[Apply Incremental Pressure]
    C --> D[

IS 2720 Part 15: Apparatus Key Formulas & Specifications

1. Specimen Measurements

• Area, A = (\frac{\pi D^2}{4})
  where (D) = diameter of specimen
• Thickness, (H_c) = measured specimen height
• Equivalent height of solids, (H_e) = (H_c - \Delta H) (compression)

2. Weights

• Weight of ring, (W_1)
• Weight of specimen + ring, (W_2)
• Weight of dry soil = (W_2 - W_1)
• Weight of wet soil (final), (W_w)

3. Consolidation Test Data Table (Appendix A format)

4. Key Calculation Steps (Clause 6.2.1.1)

• Transfer dial gauge readings per pressure increment.
• Calculate compression (\Delta H) = initial height - final height.
• Calculate void ratio changes using volume and weight data.

5. Notes on Apparatus Assembly (Clause 4.2)

• Proper assembly ensures accurate pressure application and dial gauge reading.
• Use water type as specified for saturation.

flowchart TD
    A[Start] --> B[Assemble apparatus]
    B --> C[Prepare specimen]
    C --> D[Apply pressure increment]
    D --> E[Record dial reading]
    E --> F[Calculate compression & void ratio]
    F --> G[Plot pressure vs void ratio]
    G --> H[Interpret consolidation behavior]

This summarizes essential apparatus data and calculations per IS 2720 Part 15 for consolidation tests.

IS 2720 Part 15: Sample Preparation Key Points

1. Specimen Preparation (Clause 4.1 & 4.1.2)

• From tube samples:
  • Extrude a representative soil sample.
  • Cut a disc with parallel faces.
  • Thickness > height of consolidation ring.
• From block samples:
  • Cut a disc with parallel faces, diameter ≥ consolidation ring inside diameter + 10 mm.
  • Orient soil stratum to simulate field loading direction.

2. Specimen Data Recording (Clauses 5.1 & 5.2.1)

• Record on Appendix A data sheet:
  • Soil identification, specific gravity (G), specimen dimensions, water content (w).
  • Preparation procedure and type of water used.
  • Final wet weight (W_w) and dry weight (W_d) after disassembly.

3. Key Calculations

• Water Content, w:
  [ w = \frac{W_w - W_d}{W_d} \times 100% ]

• Bulk Density, ρ and Dry Density, ρ_d can be calculated if volume (V) is known:
  [ \rho = \frac{W_w}{V}, \quad \rho_d = \frac{W_d}{V} ]

Summary Diagram of Specimen Preparation

flowchart TD
    A[Sample Source] -->|Tube Sample| B[Extrude & Cut Disc]
    A -->|Block Sample| C[Cut Disc with +10mm Diameter]
    B --> D[Ensure Parallel Faces]
    C --> D
    D --> E[Thickness > Consolidation Ring Height]
    E --> F[Orient Soil Stratum Properly]
    F --> G[Record Data on Appendix A]

This ensures representative, standardized specimens for consolidation testing per IS 2720 Part 15.

IS 2720 Part 15: Record of Observations - Key Formulas & Table Summary

Specimen Data to Record (Clause 5.1 & 5.2.1)

• Soil Identification details
• Specific Gravity (G)
• Specimen dimensions: Diameter (D), Thickness (Hc)
• Weights:
  • W₁ = Weight of ring
  • W₂ = Weight of ring + wet soil
  • W₃ = Weight of ring + dry soil
  • Final wet weight (W_w)
  • Dry weight of specimen (W_d) = W₃ - W₁
• Type of water used

Key Formulas

• Area, A = πD²/4

• Dry weight of soil, W_d = W_dry specimen + ring - W_ring = W₃ - W₁

• Void ratio, e (Clause 6.2.1.6):
  [ e = \frac{G \times w}{S} \quad \text{or calculated from volume and weight data} ] (Where w = water content, S = degree of saturation)

• Equivalent height of solids, H_e = H_c - ΔH (compression)

Appendix A Table Columns Summary (Consolidation Test Data)

IS 2720 Part 15 — Key Formulas and Test Procedure Summary

1. Specimen Preparation (Clause 4.1 & 5.1)

• Record soil identification, specific gravity (G), specimen dimensions (diameter D, thickness Hc).
• Calculate cross-sectional area, A: [ A = \frac{\pi D^2}{4} ]
• Weigh specimen and container at various stages:
  • ( W_1 ) = weight of ring
  • ( W_2 ) = weight of specimen + ring (wet)
  • ( W_d ) = weight of specimen + ring (dry)
• Calculate dry weight of soil: [ W_{\text{dry soil}} = W_d - W_1 ]

2. Consolidation Test Data (Appendix A & Clause 6.2.1.4)

3. Key Calculations (Clause 6)

• Void ratio at any stage: [ e = \frac{V_v}{V_s} = \frac{(V - V_s)}{V_s} ]
• Compression ((\Delta H)): [ \Delta H = H_{\text{initial}} - H_{\text{final}} ]
• Coefficient of Consolidation (C_v) using square root of time fitting method: [ C_v = \frac{T_v H_d^2}{t_{50}} ] where
  • (T_v) = theoretical time factor (from charts, typically 0.197 for 50% consolidation)
  • (H_d) = drainage path length (half specimen thickness for double

IS 2720 Part 15: Key Formulas and Tables for Consolidation Test Calculations

1. Specimen Measurements

• Area, A = ( \frac{D^2}{4} \pi ) (cross-sectional area of specimen)
• Thickness, ( H_c ) = specimen height (cm)
• Dry weight of soil, ( W_d ) = (Weight of specimen + ring) - (Weight of ring)
• Specific gravity, ( G ) = given or measured

2. Consolidation Test Data Table (Appendix A)

3. Key Formula for Coefficient of Consolidation ( C_v ) (Clause 6.1.2.4)

[ C_v = \frac{T_v \cdot H_d^2}{t_{90}} ]

Where:

• ( T_v ) = time factor (from standard charts or square root of time fitting method)
• ( H_d ) = drainage path length (half or full specimen thickness depending on drainage condition)
• ( t_{90} ) = time for 90% consolidation (min)

4. Square Root of Time Fitting Method

• Plot compression vs. square root of time.
• Determine ( t_{90} ) from the curve where 90% of total compression occurs.

Summary

• Record wet and dry weights, dial readings, and compression at each load increment.
• Use Appendix A table for systematic data entry.
• Calculate ( C_v ) using the formula above for consolidation

IS 2720 Part 15 (1986) — Key Formulas & Tables for Consolidation Test Report

Specimen Data (Clause 5.1 & 5.2.1)

• Specimen Area, A:
  [ A = \frac{D^2}{4} ] where (D) = diameter of specimen

• Thickness, (H_c): Measured specimen height

• Weights:

  • Ring weight, (W_1)
  • Wet specimen + ring, (W_2)
  • Dry specimen + ring, (W_3)
  • Dry specimen weight, (W = W_3 - W_1)

• Specific Gravity, (G) and Type of Water Used to be recorded.

Key Calculations (Clause 6.2.1.6)

• Void ratio, (e):
  Calculated and recorded in column 5 of Appendix A (formula depends on volume and dry weight).

• Compression, (\Delta H): Measured dial reading change (column 3).

• Specimen height at each stage, (H_e):
  [ H_e = H_0 - \Delta H ]

• Coefficient of volume compressibility, (m_v), and coefficient of consolidation, (C_v): Calculated using standard methods (e.g., square root of time fitting).

Appendix A Table Structure (Summary)

Notes:

• Record soil identification, specific gravity, weights, and water content accurately.

• Use square root of time fitting method for consolidation curve analysis.

flowchart TD
    A[Specimen Preparation] --> B[Measure Initial Dimensions & Weight]
    B --> C[Apply Load & Record Dial Readings]
    C --> D[Calculate Compression \(\Delta H\)]

Precision and Accuracy in IS 2720 Part 15 (Soil Consolidation Test)

Key Specifications:

• Dial Gauge Accuracy (Clause 3.4):

  • Accuracy: ≥ 0.01% of specimen height
  • Travel: ≥ 50% of specimen height
  • Reference: IS 2092-1983

• Initial Height Measurement (Clause 3.9):

  • Accuracy: ±0.1 mm
  • Instruments: Vernier calipers, micrometer screw gauge, or 25 mm travel dial gauge mounted in comparator

• Rounding Off Results:

  • Follow IS 2-1960 for rounding final test values to ensure uniformity.

Important Formulas:

• Specimen Area: [ A = \frac{D^2}{4} ] where (D) = diameter of specimen

• Compression: [ \Delta H = H_{\text{initial}} - H_{\text{final}} ]

• Void Ratio Change: [ \Delta e = \frac{\Delta H}{H_e} ] where (H_e) = equivalent height of solids

Table Reference (Clause 6.2.1.4):

flowchart LR
    A[Specimen Height Measurement] --> B[Dial Gauge Measurement]
    B --> C[Calculate Compression ΔH]
    C --> D[Calculate Void Ratio Change Δe]
    D --> E[Record & Round Off Results (IS 2-1960)]

Summary:
Use dial gauges with 0.01% height accuracy and 50% travel, measure initial height to ±0.1 mm accuracy, apply formulas for area and compression, and round results per IS 2-1960 for precision and accuracy compliance in consolidation tests.

IS 2720 Part 15: Appendix A — Consolidation Test Data & Key Formulas

Appendix A provides a detailed tabular format and formulas for recording consolidation test data, focusing on pressure-void ratio relationships.

Key Formulas:

• Area of specimen, A:
  [ A = \frac{\pi D^2}{4} ]

• Void Ratio, e:
  [ e = \frac{V_v}{V_s} = \frac{(W_s / G)}{V_s} \quad \text{or from measurements as per clause 6.2.1.6} ]

• Compression, ΔH:
  Obtained from dial gauge readings (col 2), recorded in col 3.

• Differences in void ratio and pressure:
  [ \Delta e = e_{i} - e_{i+1} \quad \text{(col 6)}, \quad \Delta p = p_{i+1} - p_i \quad \text{(col 7)} ]

• Coefficient of volume compressibility, ( m_v ):
  [ m_v = \frac{\Delta e}{(1+e_0) \Delta p} ]

• Coefficient of consolidation, ( C_v ): (from col 11 and 12)
  [ C_v = \frac{T_v H^2}{t_{50}} ]

Table Columns Summary (Appendix A):