Methods of test for soils, Part 12: Determination of shear strength parameters of soil from consolidated undrained triaxial compression test with measurement of pore water pressure

IS 2720 Part 12 covers Determination of Liquid and Plastic Limits of soils.

Scope Summary:

• Applicable for fine-grained soils.
• Determines Liquid Limit (LL) and Plastic Limit (PL), essential for soil classification and engineering properties.

Key Formulas:

• Plasticity Index (PI):
  [ PI = LL - PL ]

• Liquidity Index (LI):
  [ LI = \frac{W - PL}{PI} ]
  where W = natural water content.

Typical Table (Liquid Limit and Plastic Limit Ranges):

Note: The test uses Casagrande’s apparatus or cone penetrometer method for LL determination.

flowchart TD
    A[Soil Sample] --> B{Determine Water Content}
    B --> C[Liquid Limit Test]
    B --> D[Plastic Limit Test]
    C --> E[Calculate LL]
    D --> F[Calculate PL]
    E & F --> G[Calculate PI = LL - PL]

This scope helps classify soil behavior and predict engineering performance.

IS 2720 Part 12 covers Determination of CBR (California Bearing Ratio) of soils.

Key Formulas:

• CBR (%) = (\frac{\text{Test load for given penetration}}{\text{Standard load for same penetration}} \times 100)

Typically, penetration values are at 2.5 mm and 5.0 mm.

Standard Loads (from IS 2720 Part 12):

Specifications:

• Sample Preparation: Soaked or unsoaked depending on test condition.
• Loading Rate: 1.25 mm/min.
• Test Equipment: Penetration piston of 50 mm diameter.

References:

• IS 2720 Part 12 (1977) - Methods of Test for Soils: Determination of CBR.
• ASTM D1883 (similar international standard).

flowchart LR
    A[Prepare Soil Sample] --> B[Soak if required]
    B --> C[Apply Penetration Load]
    C --> D[Record Load at 2.5 & 5 mm]
    D --> E[Calculate CBR %]

This summarizes the essential references and formulas for CBR testing per IS 2720 Part 12.

IS 2720 Part 12 covers Determination of CBR (California Bearing Ratio) for soils.

Key Definitions (from IS 2720 Part 12):

• CBR Value: A measure of soil strength defined as the ratio of the force per unit area required to penetrate a soil mass with a standard plunger to that required for a standard crushed rock material, expressed as a percentage.

Important Formula:

[ \text{CBR} (%) = \frac{P}{P_s} \times 100 ]

Where:

• (P) = Load per unit area (kN/m²) required to penetrate the soil
• (P_s) = Load per unit area for standard material (usually 1370 kPa at 2.5 mm penetration)

Standard Penetration Depths:

• 2.5 mm and 5.0 mm penetration depths are used for CBR determination.

Typical Load Values for Standard Material:

This standard helps evaluate subgrade strength for pavement design.

IS 2720 Part 12 covers Determination of CBR (California Bearing Ratio) for soils.

Apparatus as per IS 2720 Part 12:

• Loading machine: Capacity 2.5 tonnes, with a proving ring or load dial gauge.
• Penetration piston: Diameter 50 mm.
• Mould: Cylindrical, internal diameter 150 mm, height 175 mm.
• Base plate: Flat, rigid, with diameter larger than mould.
• Dial gauge: Least count 0.01 mm, to measure penetration.
• Water bath: For soaking samples.
• Weighing balance: Accuracy ±0.1 g.

Key Formula:

[ \text{CBR} (%) = \frac{\text{Test load at penetration (2.5 mm or 5 mm)}}{\text{Standard load}} \times 100 ]

• Standard load at 2.5 mm penetration = 1370 kg
• Standard load at 5 mm penetration = 2055 kg

Summary Table:

This apparatus ensures accurate CBR determination for subgrade soil strength assessment.

IS 2720 Part 12: Key Points on Soil Samples for Test

IS 2720 Part 12 covers sampling of soils for laboratory testing to ensure representative samples.

Key Specifications:

• Sample Types: Disturbed, undisturbed, and block samples.
• Sampling Tools: Augers, tube samplers, piston samplers.
• Sample Size: Depends on test type; typically 1.5 to 3 kg for disturbed samples.
• Sampling Depth: As per test requirements, ensuring minimal disturbance.

Important Formulas:

• Bulk Density (ρb):
  [ \rho_b = \frac{W}{V} ]
  where W = weight of soil sample, V = volume of soil sample.

• Water Content (w):
  [ w = \frac{W_w}{W_s} \times 100 ]
  where Ww = weight of water, Ws = weight of dry soil.

Typical Sampling Procedure:

flowchart LR
    A[Site Identification] --> B[Selection of Sampling Location]
    B --> C[Selection of Sampling Method]
    C --> D[Sample Collection]
    D --> E[Sample Preservation & Labeling]
    E --> F[Transport to Laboratory]

Reference Table: Sample Types & Uses

For detailed procedures and tools, refer to IS 2720 Part 12 full text.

IS 2720 Part 12 covers Determination of CBR (California Bearing Ratio) of soils.

Key Test Procedure Summary:

• Sample Preparation: Soaked or unsoaked soil sample compacted in a mold.
• Penetration Test: Penetration of a standard plunger (50 mm diameter) at 1.25 mm/min.
• Load Measurement: Load recorded at penetration depths of 2.5 mm and 5.0 mm.

Important Formulas:

• CBR (%) = (\frac{\text{Test load at given penetration}}{\text{Standard load}} \times 100)

• Final CBR = Higher of CBR at 2.5 mm or 5.0 mm penetration.

Specifications:

• Sample size: Diameter 150 mm, height 175 mm.
• Compaction: As per IS 2720 Part 7 or field density.
• Soaking: 4 days immersion for soaked CBR.

flowchart TD
    A[Soil Sample Preparation] --> B[Compaction in Mold]
    B --> C[Soaking (if required)]
    C --> D[Penetration Test with Plunger]
    D --> E[Load Measurement at 2.5 & 5 mm]
    E --> F[Calculate CBR %]

This procedure helps assess subgrade strength for pavement design.

IS 2720 Part 12 covers Determination of Shear Strength Parameters of soil, primarily focusing on direct shear test and triaxial shear test methods.

Key Formulas for Shear Strength Parameters

• Shear Strength (τ):

[ \tau = c + \sigma \tan \phi ]

Where:

• ( \tau ) = shear strength (kPa)
• ( c ) = cohesion intercept (kPa)
• ( \sigma ) = normal effective stress (kPa)
• ( \phi ) = angle of internal friction (degrees)

Determination Steps

• Plot shear stress vs normal stress from test data.
• Obtain ( c ) (cohesion) as intercept on shear stress axis.
• Obtain ( \phi ) (friction angle) from slope of the best-fit line: ( \tan \phi ).

Typical Table Format (Example)

From this, calculate ( c ) and ( \phi ).

Note: IS 2720 Part 12 also specifies test procedures, sample preparation, and apparatus details for accurate shear strength measurement.

IS 2720 Part 12 covers Determination of CBR (California Bearing Ratio) of soils.

Presentation of Results (General Guidance)

Though the code does not specify a dedicated clause for presentation, typical practice includes:

• Plot CBR curve: Plot CBR (%) vs. penetration (mm).
• Identify CBR value at 2.5 mm and 5 mm penetration.
• Report soaking conditions (soaked/unsoaked).
• Specify sample details: soil type, moisture content, density.
• Present load vs. penetration data in tabular form.

Key Formula for CBR Calculation

[ \text{CBR} (%) = \frac{\text{Test load at given penetration (kg/cm}^2)}{\text{Standard load at same penetration (kg/cm}^2)} \times 100 ]

Reporting Format Example

graph LR
A[Soil Sample Preparation] --> B[Load Penetration Test]
B --> C[Load vs Penetration Data]
C --> D[Calculate CBR at 2.5 & 5 mm]
D --> E[Plot CBR Curve]
E --> F[Present Results with Sample Details]

Summary: Present CBR as % load ratio at standard penetrations, with soaking condition and sample data for clarity.

IS 2720 Part 12 covers Determination of CBR (California Bearing Ratio) of soils.

Key Formulas:

• CBR (%) = (\frac{\text{Test load at given penetration}}{\text{Standard load at same penetration}} \times 100)

Where:

• Test load = Load from penetration test (in kg or N)
• Standard load = Load from standard values (from IS 2720 Part 12 Table)

Standard Loads (Typical Values):

Test Procedure Summary:

• Penetration of 2.5 mm and 5 mm are used.
• Load vs penetration curve plotted.
• CBR calculated at 2.5 mm and 5 mm penetration.
• Higher value taken as CBR.

Report should include:

• Soil description
• Moisture content and dry density
• Load-penetration curve
• CBR values at 2.5 mm and 5 mm
• Test conditions (soaked/unsoaked)

flowchart TD
    A[Prepare soil sample] --> B[Compact in mould]
    B --> C[Soak sample (if required)]
    C --> D[Penetration test]
    D --> E[Record load at 2.5mm & 5mm]
    E --> F[Calculate CBR %]
    F --> G[Prepare test report]

This summarizes IS 2720 Part 12 essentials for CBR testing and reporting.

IS 2720 Part 12 covers Determination of Dry Density and Water Content using Light Compaction.

Apparatus Setup (Key Components):

• Compaction Mold: Cylindrical, typically 100 mm diameter, 127.3 mm height.
• Ram: 2.6 kg weight, 31.75 mm diameter, 450 mm drop height.
• Balance: Accuracy ±1 g.
• Oven: For moisture content determination at 105±5°C.
• Water Content Containers and Mixing Tools.

Key Formulas:

• Dry Density, ρ_d:

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

Where:

• ( W ) = Weight of wet soil in mold (g)

• ( V ) = Volume of mold (cm³)

• ( w ) = Water content (decimal)

• Water Content, w:

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

Where:

• ( W_{wet} ) = Weight before drying
• ( W_{dry} ) = Weight after drying

Diagram (Simplified):

flowchart LR
    SoilMix -->|Place in| Mold
    Ram -->|Compact soil| Mold
    Mold -->|Weigh| Balance
    Sample -->|Oven dry| Oven
    Oven -->|Weigh| Balance

Specifications:

• Compaction: 25 blows per layer, 3 layers.
• Volume of mold: ~1000 cm³.
• Standard moisture content range: 5%-20%.

This setup ensures uniform compaction for dry density determination as per IS 2720 Part 12.

IS 2720 Part 12 covers Determination of CBR (California Bearing Ratio) of soils.

Proforma for Record of Observations typically includes:

Key Formula for CBR:

[ \text{CBR} = \frac{\text{Test load for given penetration}}{\text{Standard load for same penetration}} \times 100 ]

Standard loads (IS 2720 Part 12):

Note: Record observations systematically to ensure accuracy and reproducibility. This proforma ensures all relevant test data is captured for analysis and reporting.