Method for the determination of unconfined compressive strength of rock materials

IS 9143: Scope & Key Specifications Summary

Scope (from context & standard practice):
IS 9143 covers the testing of rock specimens under axial compression to determine strength and related properties, harmonizing international practices with Indian field conditions.

Key Specifications:

• Test Specimens (Clause 3):
  Cylindrical rock samples, typically with diameter-to-height ratio as per standard practice (e.g., 1:2).

• Loading Machine (Clause 2.1):

  • Must apply axial load with sufficient capacity.
  • Load application rate per Clause 4.3 (usually constant strain or stress rate).
  • Must be calibrated regularly.

• Test Report Requirements (Clause 6.2):
  Include:

  • Number & dimensions of specimens
  • Mode of failure
  • Rock lithology & anisotropy orientation
  • Sampling details (location, depth, date)
  • Storage & environmental conditions
  • Testing date & machine type
  • Moisture content, temperature
  • Stress rate & test duration
  • Other physical properties (specific gravity, porosity, etc.)

Typical Formula for Axial Compressive Strength (σc):

[ \sigma_c = \frac{P}{A} = \frac{4P}{\pi d^2} ]

• (P) = Maximum axial load (N)
• (A) = Cross-sectional area (mm²)
• (d) = Diameter of specimen (mm)

Summary Table: Specimen Dimensions & Loading Rate

flowchart TD
    A[Rock Sample Preparation] --> B[Dimension Check]
    B --> C[Load Application]
    C --> D[Measure Load & Deformation]
    D --> E[Record Failure Mode]
    E --> F[Prepare Test Report]

Note: For detailed test procedures,

IS 9143 - Apparatus Specifications Summary

Test Specimen (Clause 3.1)

• Preferably right circular cylinder.
• Tolerances as per Clause 3.3.
• Other regular shapes allowed with mention in report.
• Preparation per IS 9179-1979.

Loading Machine (Clause 2.1)

• Must apply and measure axial load.
• Sufficient capacity for specimen size.
• Load application rate per Clause 4.3.
• Periodic verification & calibration required.

Test Report Requirements (Clause 6.2)

Include:

• Number & shape of specimens.
• Mode of failure.
• Rock lithology.
• Loading axis orientation relative to anisotropy.
• Sample source, location, depth, orientation, date.
• Storage & environment history.
• Test date & machine type.
• Specimen dimensions (diameter, height).
• Moisture content & room temperature.
• Test duration & stress rate.
• Other physical properties (specific gravity, absorption, permeability, porosity).
• Any other observations.

Key Formula for Compressive Strength:

[ \sigma_c = \frac{P}{A} = \frac{4P}{\pi d^2} ]

• ( \sigma_c ) = Compressive strength (N/mm²)
• ( P ) = Maximum load at failure (N)
• ( d ) = Diameter of cylindrical specimen (mm)
• ( A ) = Cross-sectional area (mm²)

Diagram: Apparatus Setup

flowchart LR
    A[Loading Machine] -->|Axial Load| B[Test Specimen]
    B --> C[Load Measurement]
    B --> D[Failure Observation]

For detailed specimen preparation, refer to IS 9179-1979. Calibration and loading rate details are critical for test validity.

IS 9143: Specimen Preparation and Dimensions Summary

1. Specimen Shape & Size (Clauses 3.1, 3.3)

• Shape: Preferably a right circular cylinder.
• Length to Diameter Ratio (L/D): Preferably 2 to 3.
  • If L/D < 2, apply correction assuming standard L/D = 2.
• Diameter (D):

  • 10 × largest mineral grain size.

  • Preferably 45 mm, but not less than 35 mm.

2. Dimensional Tolerances

• Ends flatness: Within 0.05 mm.
• Ends parallelism: Within 0.002 D (where D = diameter).
• Ends perpendicularity: Within 0.001 radians (≈ 0.05 mm for 45 mm diameter).
• Cylindrical surface:
  • Smooth, free from irregularities.
  • Straightness within 0.3 mm over length.
• Diameter variation: Not more than 0.2 mm along length.
• Diameter measurement: Average of two diameters at upper, mid, and lower heights, measured at right angles; accuracy to 0.1 mm.

3. Measurement Method

• Measure diameter at 3 heights (top, middle, bottom).
• Take two diameters at right angles at each height.
• Average these six measurements for specimen diameter.

Key Formula for Length Correction (if L/D < 2):

[ \text{Corrected Strength} = \text{Measured Strength} \times \frac{L/D}{2} ]

flowchart LR
    A[Specimen Preparation] --> B[Shape: Right Circular Cylinder]
    B --> C[Diameter: ≥ 35 mm, Preferably 45 mm]
    B --> D[Length/Diameter Ratio: 2 to 3]
    D --> E{If L/D < 2}
    E -->|Yes| F[Apply correction]
    E -->|No| G[No correction]
    A --> H[Ends flatness ≤ 0.05 mm]
    A --> I[Ends parallel ≤ 0.002 D]
    A --> J[Ends perpendicular ≤ 0.001 radians]
    A --> K[Cylindrical surface smooth & straight]

IS 9143: Test Procedure Key Points

• Test Specimen (Clause 3.1 & 2.3):

  • Preferably a right circular cylinder with tolerances per Clause 3.3.
  • Other regular geometric shapes allowed.
  • Preparation as per IS 9179-1979.

• Loading Machine (Clause 2.1):

  • Must apply and measure axial load accurately.
  • Capacity must suit specimen size and strength.
  • Load application rate per Clause 4.3 (typically controlled to avoid shock).
  • Machine must be regularly calibrated.

• Rounding Off Results (Clause 0.4):

  • Follow IS 2-1960 for rounding numerical values in reporting.

Typical Load Application Rate (from Clause 4.3, general practice):

Summary Flow of Test Procedure:

flowchart TD
    A[Specimen Preparation] --> B[Load Machine Setup]
    B --> C[Apply Axial Load at Specified Rate]
    C --> D[Measure Load & Deformation]
    D --> E[Calculate Test Results]
    E --> F[Round Off Results (IS 2-1960)]
    F --> G[Report Test Data]

For exact specimen dimensions, tolerances, and detailed load rates, refer to IS 9143 Clauses 3.3 and 4.3, and IS 9179 for specimen preparation.

IS 9143: Unconfined Compressive Strength (UCS) of Rock

Key Formula (Clause 5.1)

[ \text{UCS} = \frac{P_{\max}}{A} ]

• Pₘₐₓ = Maximum load carried by the specimen (N)
• A = Average original cross-sectional area of specimen (mm²)
  (Refer IS 9143 Clause 3(g) for area measurement)

Specifications

• Test applies to rock specimens of regular geometry (Clause 1.1)
• Test is an index test for strength classification (Clause 0.2)
• Apparatus is portable, suitable for field and lab use

Notes

• Cross-sectional area is usually measured at mid-height of the specimen.
• Specimens are typically cylindrical with diameter (d) and height (h).
• UCS is expressed in MPa (N/mm²).

Typical specimen dimensions

• Diameter: 38 mm to 54 mm
• Height: 2 to 2.5 times diameter

flowchart TD
    A[Rock Specimen] --> B[Measure Diameter & Height]
    B --> C[Calculate Cross-sectional Area A = πd²/4]
    C --> D[Apply axial load till failure]
    D --> E[Record Maximum Load Pₘₐₓ]
    E --> F[Calculate UCS = Pₘₐₓ / A]

This concise method allows quick strength classification of rock materials in the field or lab.

IS 9143 - Reporting of Results: Key Points

1. Rounding Off

   • Follow IS 2-1960 for rounding final observed/calculated values.

2. Uniaxial Compressive Strength Reporting

   • Report strength for each specimen to 3 significant figures.
   • Provide the average strength of the sample.

3. Mandatory Report Contents (Clause 6.2):

Summary Formula for Average Strength:

[ f_{avg} = \frac{\sum_{i=1}^n f_i}{n} ]

• (f_i) = Strength of individual specimen
• (n) = Number of specimens tested

Reporting Checklist Diagram:

graph TD
  A[Start Reporting] --> B[Record Individual Strengths]
  B --> C[Calculate Average Strength]
  C --> D[Include Specimen Details]
  D --> E[Include Test Conditions]
  E --> F[Include Physical Properties]
  F --> G[Round Off as per IS 2-1960]
  G --> H[Finalize Report]

Note: This ensures clarity, traceability, and international coordination in rock strength testing reports.

IS 9143: Key Precautions and Specifications for Test Specimens

Specimen Dimensions (Clause 3.3)

• Length to diameter ratio: Preferably 2 to 3.
  • If < 2, apply correction using slenderness ratio = 2.
• Diameter: > 10 × largest mineral grain size; preferably 45 mm, minimum 35 mm.
• End flatness: Within 0.05 mm.
• End parallelism: Within 0.002 × D (D = specimen diameter).

Loading Machine (Clause 2.1)

• Must have sufficient capacity.
• Apply axial load at rate per Clause 4.3.
• Calibrated and verified regularly based on workload.

Notes:

• For specimens < 45 mm diameter, reduce tolerances accordingly.
• Numerical rounding follows revised rules (details in code).

Summary Table:

flowchart TD
    A[Test Specimen] --> B{Dimensions}
    B --> C[Length/Diameter: 2-3]
    B --> D[Diameter > 10× grain size]
    B --> E[Ends flat ≤ 0.05 mm]
    B --> F[Ends parallel ≤ 0.002×D]
    A --> G[Loading Machine]
    G --> H[Capacity as per 2.1]
    G --> I[Load rate per 4.3]
    G --> J[Calibrated regularly]

This ensures reliable, repeatable testing per IS 9143 standards.