Method for determination of the strength of rock materials in triaxial compression

IS 13047: Scope & Key Specifications

Scope Summary

• Applies to testing rock specimens for axial strength under various confining pressures.
• Specifies specimen shape, dimensions, test conditions, and reporting requirements.

Key Specifications

1. Specimen Shape & Dimension (Clause 4.3)

• Cylindrical specimens preferred.
• Dimensions must be accurately recorded (height, diameter).

2. Test Report Requirements (Clause 7.2)

Include:

• Lithologic description.
• Loading axis orientation relative to rock anisotropy.
• Sample source, location, depth, orientation, date.
• Storage history and environment.
• Moisture content & room temperature.
• Test duration & stress rate.
• Machine type and date.
• Number of specimens.
• Failure mode with sketches.
• Physical properties: specific gravity, absorption, permeability, porosity (refer to relevant IS codes).
• Specimen dimensions, confining pressure, axial strength (to 3 significant figures).
• Notes on non-cylindrical specimens.
• Any additional observations.

3. Strength Envelope (Fig. 3)

• Shows relationship between axial strength and confining pressure (both in MPa).
• Used to understand rock strength under triaxial conditions.

Typical Formula for Axial Stress (σₐ)

[ \sigma_a = \frac{P}{A} = \frac{P}{\pi (d/2)^2} ]

• (P) = axial load (N)
• (d) = specimen diameter (mm)
• (A) = cross-sectional area (mm²)

Reporting Table Format (Example)

graph TD
A[Rock Sample] --> B[Specimen Preparation]
B --> C{Specimen Shape}
C -->|Cylindrical| D[Dimension Measurement]
D --> E[Testing under axial load + confining pressure]
E --> F[Record axial strength & failure mode

IS 13047 Key References, Formulas, and Tables

1. Test Report Requirements (Clause 7.2)

Include in the test report:

• Lithologic description, sample source, orientation, storage, moisture content, test conditions.
• Number of specimens, failure mode (with sketches).
• Physical properties: specific gravity, absorption, permeability, porosity (refer to relevant IS codes).
• Tabulated data: specimen number, height, diameter, confining pressure, axial strength (3 significant figures).
• Mention if non-cylindrical specimens are tested.

2. Specimen & Platens (Clause 1.02)

• Platens hardness: Rockwell Hardness ≥ HRC 30 (IS 1586:1968).
• Platens diameter: between D and 1.02D (D = specimen diameter).
• Platens thickness: ≥ 15 mm or D/3.
• Surface flatness tolerance: ±0.005 mm.

3. Strength Envelope Plot (Clause 6.2 & Fig. 3)

• Plot confining pressure (x-axis) vs axial strength (y-axis).
• Used to determine rock strength under triaxial loading.

4. Typical Test Setup (Fig. 1 & 2)

• Components: Loading piston, platens, triaxial cell, confining pressure equipment.
• Ensure proper sealing and alignment for accurate results.

Useful Formula (Axial Strength)

[ \sigma_1 = \frac{P}{A} ]

• ( \sigma_1 ) = axial strength (MPa)
• ( P ) = axial load (N)
• ( A ) = cross-sectional area of specimen (mm²)

Summary Table: Platens Dimensions

flowchart LR
    P(Loading Piston) -->|Axial Load| Specimen
    Specimen -->|Confined by| C(Triaxial Cell)
    C -->|Pressure Controlled by| HP(Confining Pressure

IS 13047: Apparatus for Triaxial Compressive Strength Test

Key Components & Specifications

• Device for Generating & Measuring Confining Pressure (Clause 3.4):

  • Hydraulic pump/pressure intensifier with capacity to maintain confining pressure within ±2% of target.
  • Pressure gauge/transducer accurate to ±2%.

• Test Specimen Platens (Clause 1.02b):

  • Rockwell Hardness ≥ HRC 30 (per IS 1586:1968).
  • Diameter: between D and 1.02D (D = specimen diameter).
  • Thickness: minimum 15 mm or D/3.
  • Surfaces ground flat within ±0.005 mm deviation.

Apparatus Components (Clause 3.1 & Figures)

• Triaxial Cell (C): Contains specimen, flexible membrane, O-ring clamps.
• Loading Device (P): Applies axial load.
• Confining Pressure Equipment (HP): Controls lateral pressure.
• Control Unit (MC): Manages axial load application.

Typical Design Features (Fig. 2)

• Loading piston with seals.
• Bleeder hole for pressure relief.
• Platens with spherical seating to ensure uniform load distribution.
• Hydraulic connections and clamps for sealing.

flowchart LR
    P[Loading Device] --> MC[Control Unit]
    MC --> P
    HP[Confining Pressure Equipment] --> C[Triaxial Cell]
    P --> C
    C --> Specimen

This setup ensures precise loading and pressure control for accurate triaxial strength measurement.

IS 13047: Preparation of Test Specimen - Key Points

1. Specimen Preparation (Clause 4.1)

   • Follow IS 9179:1979 for specimen preparation methods.
   • Specimen shape and dimensions per Clause 4.3 (typically cylindrical).

2. Platens Specifications (Clause 1.02 b)

   • Platens hardness: Rockwell Hardness ≥ HRC 30 (per IS 1586:1968).
   • Diameter: Between D and 1.02 D, where D = specimen diameter.
   • Thickness: Minimum of 15 mm or D/3.
   • Surfaces must be ground flat with deviation ≤ ±0.005 mm.

3. Test Setup (from Fig.1 & Fig.2)

   • Use platens with spherical seating to ensure uniform load distribution.
   • Specimen enclosed in a flexible membrane inside a triaxial cell.
   • Confining pressure applied via hydraulic system with ±2% accuracy.

Summary Table: Platens Dimensions

flowchart LR
    P[Loading Piston] --> L[Load Applied]
    L --> Specimen[Specimen in Membrane]
    Specimen --> Platens[Platens with Spherical Seating]
    Specimen --> C[Triaxial Cell]
    C --> HP[Hydraulic Pressure System]
    HP --> MC[Control Unit]

This ensures accurate and repeatable triaxial compressive strength tests.

IS 13047: Test Procedure Key Points

1. Device for Generating & Measuring Confining Pressure (Clause 3.4)

• Use a hydraulic pump/pressure intensifier maintaining confining pressure within ±2% of target.
• Pressure gauge/transducer accuracy: ±2%.

2. Test Specimen Preparation (Clause 4)

• Platens hardness: Rockwell HRC ≥ 30 (IS 1586:1968).
• Platens diameter: between D and 1.02D (D = specimen diameter).
• Platens thickness: minimum 15 mm or D/3.
• Platens surfaces flatness tolerance: ±0.005 mm.

3. Test Setup (Fig.1 & Fig.2)

• Components: Loading piston, seals, bleeder hole, flexible membrane, O-ring clamps.
• Load applied axially; confining pressure controlled hydraulically.

4. Test Reporting (Clause 7.2)

Include:

• Lithology, sample orientation, source, moisture, temperature.
• Test duration, stress rate, machine type.
• Specimen dimensions, confining pressure & axial strength (3 significant figures).
• Failure mode sketch.
• Other physical properties (specific gravity, porosity, etc.).

5. Specimen Marking (Clause 4.3.7)

• Assign specimen number with in-situ orientation.

Typical Strength Envelope Representation

graph LR
A[Confining Pressure (MPa)] --> B[Axial Stress (MPa)]
B --> C[Strength Envelope Curve]

Summary: Maintain precise confining pressure, prepare specimen with specified platen hardness and dimensions, record detailed test data, and report all relevant parameters for reproducibility and standard compliance.

IS 13047: Calculation and Interpretation of Results - Key Points

• Rounding off results: Follow IS 2:1960 for rounding numerical values.

• Axial Strength: Use axial strength (not axial stress) in calculations.

• Test Report Requirements (Clause 7.2): Include

  • Lithology, sample source, orientation, storage, moisture, test duration, machine type, number of specimens.
  • Failure mode with sketches.
  • Physical properties: specific gravity, absorption, permeability, porosity.
  • Specimen dimensions, confining pressure, axial strength (3 significant figures).
  • Any other observations.

• Plotting Strength Envelope (Clause 6.2):
  Plot confining pressure (x-axis) vs axial strength (y-axis) to visualize strength envelope (see Fig. 3 in IS 13047).

Typical Calculation Steps:

1. Calculate axial strength for each specimen under given confining pressure.
2. Tabulate specimen number, height, diameter, confining pressure, axial strength.
3. Plot strength envelope:
   [ \text{X-axis} = \text{Confining Pressure (MPa)}, \quad \text{Y-axis} = \text{Axial Strength (MPa)} ]

Example Table Format for Results:

graph LR
A[Confining Pressure] --> B[Axial Strength Calculation]
B --> C[Tabulate Results]
C --> D[Plot Strength Envelope]
D --> E[Interpret Rock Strength]

This approach ensures standardized reporting and clear interpretation of rock strength under varying confining pressures.

IS 13047 - Key Specifications for Test Report (Clause 7.2 & 7.1)

The test report must include:

• Lithologic description of rock.
• Orientation of loading axis relative to anisotropy (bedding, foliation).
• Sample details: source, location, depth, orientation, date.
• Storage history and environment.
• Moisture content and room temperature at testing.
• Test duration and stress rate.
• Date of test and machine type.
• Number of specimens tested.
• Failure mode with sketches.
• Other physical properties like specific gravity, absorption, permeability, porosity (refer IS standards).
• If non-cylindrical specimens used, mention shape.
• Table of results with specimen number, height, diameter, confining pressure, axial strength (3 significant figures).
• Any other observations.

Plot & Parameters (Clause 7.1):

• Plot Axial Strength (σ₁) vs Confining Pressure (σ₃) (Fig. 3).
• Determine apparent cohesion (c) and angle of internal friction (φ) valid over confining pressure range.

Strength Envelope Equation

[ \sigma_1 = \sigma_3 \tan^2 \left(45^\circ + \frac{\phi}{2}\right) + 2c \tan \left(45^\circ + \frac{\phi}{2}\right) ]

Where:

• (\sigma_1) = axial strength (MPa)
• (\sigma_3) = confining pressure (MPa)
• (c) = apparent cohesion (MPa)
• (\phi) = angle of internal friction (degrees)

Report Table Format Example

graph LR
A[Sample Collection] --> B[Storage & Conditioning

IS 13047: Accuracy and Calibration Requirements Summary

• Axial Displacement Accuracy (Clause 5.8):
  Measurement accuracy must be ±0.5% or better of the axial displacement.

• Confining Pressure Control (Clause 3.4):

  • Pressure system must maintain confining pressure within ±2% of target.
  • Pressure gauges/transducers must have an accuracy of ±2%.

• Rounding Off Results:
  Follow IS 2:1960 for rounding numerical values to ensure consistency.

Key Specifications Table

Notes:

• Calibration of measuring devices should be traceable to national standards.
• Ensure specimen dimensions conform to Clause 4.3 for valid test results.

flowchart LR
    A[Hydraulic Pump] --> B[Pressure Control System]
    B --> C[Pressure Gauge / Transducer (±2% accuracy)]
    C --> D[Confining Pressure maintained within ±2%]
    E[Axial Displacement Measurement] --> F[Accuracy ±0.5%]
    G[Test Results] --> H[Rounded as per IS 2:1960]

This ensures test reliability and repeatability as per IS 13047.

IS 13047 (1991) primarily covers Test Methods for Axial Compression Strength of Concrete Specimens. Although it lacks a dedicated clause on Safety and Handling Precautions, here are key general guidelines based on good engineering practice and relevant IS codes:

Safety and Handling Precautions (General Guidelines)

• Specimen Handling:

  • Use appropriate lifting tools to avoid dropping or damaging specimens.
  • Handle specimens carefully to prevent cracks or surface damage.

• Testing Machine Operation:

  • Ensure the compression testing machine is calibrated and in good condition.
  • Operators must be trained and wear PPE (gloves, goggles).
  • Keep hands clear of moving parts during testing.

• Specimen Preparation:

  • Specimens should be free from loose particles and moisture before testing.
  • Dimensions must comply with Clause 4.3 (Shape and Dimension of Specimen).

• Data Reporting:

  • Round off results as per IS 2:1960 for numerical consistency.

Key Formula (Axial Strength substitution per Clause 6.3 & 6.4)

[ \text{Axial Strength} = \frac{P}{A} ]

Where:

• (P) = Maximum load at failure (N)
• (A) = Cross-sectional area of the specimen (mm²)

Specimen Dimensions (Clause 4.3)

• Typically, cylindrical specimens: Diameter = 150 mm, Height = 300 mm (Length-to-Diameter ratio = 2:1)
• Cubical specimens: 150 mm × 150 mm × 150 mm

flowchart TD
    A[Specimen Preparation] --> B[Handling & Transport]
    B --> C[Testing Machine Setup]
    C --> D[Load Application]
    D --> E[Record Max Load]
    E --> F[Calculate Axial Strength]
    F --> G[Report Results (IS 2:1960 rounding)]

For detailed safety, consult IS 456 and manufacturer guidelines of testing equipment.

IS 13047 Key Specifications: Annexes & Figures

1. Test Report Requirements (Clause 7.2)

The test report must include:

• Lithologic description of rock.
• Orientation of loading axis relative to anisotropy, bedding, foliations.
• Sample details: source, location, depth, orientation, date.
• Storage history and environmental conditions.
• Moisture content and room temperature during test.
• Test duration and stress rate.
• Test date and machine type.
• Number of specimens tested.
• Failure mode with sketches.
• Other physical properties (specific gravity, absorption, permeability, porosity) citing relevant IS codes.
• Mention if specimen shape differs from cylindrical.
• Tabulated data: specimen number, height, diameter, confining pressure, axial strength (to 3 significant figures).
• Any other observations.

2. Strength Envelope (Fig 3)

• Depicts relationship between axial strength (MPa) and confining pressure (MPa).
• Used to evaluate rock strength under triaxial stress.

3. Corrections in Clause 6.3 & 6.4

• Replace axial stress with axial strength.
• Updated formulae as per amendments (refer to latest edition).

Typical Table Format for Test Report (Clause 7.2n)

graph LR
A[Sample Collection] --> B[Test Preparation]
B --> C[Loading Orientation]
C --> D[Triaxial Test]
D --> E[Measure Axial Strength & Confining Pressure]
E --> F[Plot Strength Envelope (Fig 3)]
F --> G[Report Compilation (Clause 7.2)]

Note: Always refer to the latest IS 13047 edition for updates on formulae and figures.