rock joints-direct shear strength-laboratory method of determination

IS 12608 – Scope & Key Specifications for Shore Scleroscope Method

Scope (Summary from Clause 4.3 & 5.2.1)

• Purpose: To determine hardness of rock using the Shore scleroscope.
• Instrument Models: Model C (recommended Model C-2 for rock) and Model D.
• Model C Hammer Specifications:

• Measurement: Hammer drops inside a glass tube; rebound height (0 to 140 mm scale) indicates hardness.

Calculation & Reporting (Clause 4.3 & 4.4)

• Calculation: Use rebound height as hardness number.
• Rounding: Follow IS 2:1960 rounding rules matching significant figures.
• Report Includes:
  • Rock lithology, sample source/location.
  • Specimen type, size, shape.
  • Sampling/testing dates, storage conditions.
  • Hammer axis orientation, clamping method.
  • Schmidt hardness value.

flowchart TD
    A[Sample Preparation] --> B[Clamping Specimen]
    B --> C[Hammer Drop]
    C --> D[Measure Rebound Height]
    D --> E[Calculate Hardness Number]
    E --> F[Report Results with Details]

This concise scope ensures standardized hardness testing using the Shore scleroscope per IS 12608.

IS 12608 - Key References, Formulas, and Tables Summary

1. Rounding Off (Clause 4.3)

• Final test or calculated values must be rounded as per IS 2:1960.
• Retain the same number of significant figures as specified in the standard.

2. Reporting of Test Results (Clause 5.2.4)

Include in test reports:

• Lithologic description, sample source, depth, orientation.
• Mineral composition and grain size.
• Sampling/testing dates, storage, specimen prep.
• Orientation relative to bedding/foliation.
• Number of tests and average shore hardness.

3. Scleroscope Hardness Apparatus (Clause 5.2.1)

• Recommended: Model C-2 for rock.
• Hammer specs:

4. Standard Mark & BIS

• Products with Standard Mark comply with BIS inspection, testing, and quality control.
• BIS copyrights publications; permission needed for reproduction.

flowchart LR
    A[Test Specimen] --> B[Prepare & Store]
    B --> C[Conduct Scleroscope Test]
    C --> D[Record Data: Hardness, Orientation, Composition]
    D --> E[Round off results per IS 2:1960]
    E --> F[Report Results with all details]

For detailed formulas or tables, refer directly to IS 12608 and IS 2:1960.

IS 12608: Definitions - Key Formulas & Specifications

1. Rounding Off (Clause 4.3):

• Final test or analysis values must be rounded as per IS 2:1960.
• Number of significant digits retained should match the specified value in the standard.

2. Reporting of Test Results (Clause 5.2.4):
Reports must include:

• Lithologic description, sample source, depth, and orientation.
• Mineral composition and grain sizes.
• Sampling/testing dates, storage, and preparation details.
• Orientation of test surface relative to bedding/foliation.
• Number of tests and average shore hardness.

3. Correction Factor (Clause 4.3.1):
[ \text{Correction Factor} = \frac{\text{Specified standard value of anvil}}{\text{Average of 10 readings on calibration anvil}} ]

Summary Table for Reporting (Clause 5.2.4)

This ensures consistent, traceable, and reliable test data reporting and evaluation per IS 12608.

IS 12608: Schmidt Impact Hammer Method Key Points

Apparatus (Clause 4.1)

• Type L Schmidt Hammer with impact energy = 0.74 Nm.
• Steel base ≥ 20 kg for specimen clamping.
• Core specimen holders: steel cradle with semi-cylindrical slot or V-block (Fig. 1).

Testing Procedure (Clause 4.3.2)

1. Take multiple rebound readings.
2. Arrange values in descending order.
3. Discard the lower 50% of values.
4. Average the upper 50%.
5. Multiply by correction factor → Schmidt Rebound Hardness.

Principle (Clauses 3.1.1 & 3.1.2)

• Impact hammer piston rebounds off rock surface.
• Rebound height ∝ hardness.
• Limited accuracy for very soft/hard rocks.
• Shore scleroscope (lab device) uses diamond indenter; needs many tests due to rock heterogeneity.

Formula Summary

Diagram: Core Specimen Holder Setup

graph LR
A[Core Specimen] --> B[Steel cradle with semi-cylindrical slot]
A --> C[Steel V-block]
B --> D[Clamped on Steel Base ≥ 20kg]
C --> D

Note: Always calibrate the hammer before use and ensure specimen surface is smooth and clean for reliable results.

IS 12608: Apparatus Specifications for Hardness Testing

1. Scleroscope Hardness Tester (Clause 5.2.1)

• Models: Model C (recommended: C-2 for rock), Model D
• Hammer Dimensions (Model C):

• Operation: Hammer drops inside a glass tube; rebound height on a 0–140 mm scale indicates hardness.

2. Schmidt Hammer (Clause 4.1)

• Type: Type L with impact energy of 0.74 Nm
• Operation: Spring-loaded mass impacts plunger; rebound height on scale measures hardness.
• Specimen Support: Steel base ≥ 20 kg; use steel cradle or V-block for cores (see Fig. 1).

3. Rounding Off (General)

• Follow IS 2:1960 rules for rounding numerical results.
• Retain significant figures consistent with the specified values.

4. Specimen Holding (Fig. 1 Conceptual)

graph LR
A[Steel Base ≥ 20 kg] --> B[Steel Cradle with Semi-cylindrical Slot]
A --> C[Steel V-block]
B & C --> D[Secure Specimen for Testing]

This apparatus setup ensures consistent and reliable hardness measurements per IS 12608.

IS 12608: Test Procedure Key Points

Apparatus (Clause 4.1)

• Schmidt Hammer Type L: Impact energy = 0.74 Nm
• Measures rebound height of mass → indicates hardness.
• Portable for lab/field use.
• Specimen held on a steel base (min 20 kg) or in a steel cradle/V-block for cores (Fig.1).

Calculations (Clause 4.3.2)

1. Arrange measured values in descending order.
2. Discard the lower 50% values.
3. Calculate the average of the upper 50% values.
4. Multiply this average by a correction factor to get the Schmidt rebound hardness.

Rounding Off (General Clause)

• Follow IS 2:1960 rules.
• Retain the same significant figures as specified in the standard.

Summary Table: Schmidt Hammer Test

flowchart TD
    A[Take multiple rebound readings] --> B[Arrange values in descending order]
    B --> C[Discard lower 50% values]
    C --> D[Calculate average of upper 50%]
    D --> E[Multiply by correction factor]
    E --> F[Obtain Schmidt rebound hardness]

This procedure ensures reliable and standardized hardness measurement of concrete using the Schmidt hammer.

IS 12608 – Key Calculation Guidelines

1. Rounding Off (Clause 4.3)

• Final values (test or analysis results) must be rounded as per IS 2:1960.
• Retain the same number of significant digits as the specified value in the standard.

2. Correction Factor (Clause 4.3.1)

[ \text{Correction Factor} = \frac{\text{Specified standard value of the anvil}}{\text{Average of 10 readings on calibration anvil}} ]

• Use this factor to adjust test results for calibration accuracy.

3. Shore Scleroscope Hardness (Clause 5.2.3)

• Calculate hardness as the average of at least 25 measurements on the same specimen.

Summary Table:

flowchart LR
    A[Test/Analysis Result] --> B[Rounding off per IS 2:1960]
    B --> C[Apply Correction Factor]
    C --> D[Calculate Average of ≥ 25 Readings (Shore Hardness)]
    D --> E[Final Compliant Value]

This ensures accuracy, repeatability, and compliance with IS 12608.

IS 12608: Reporting of Results - Key Points

Required Information in Test Report (Clauses 4.4 & 5.2.4)

• Rock Description & Source:

  • Lithology, mineral composition, grain size
  • Geographic location, depth, orientation of sample

• Specimen Details:

  • Type (core, blasted, broken, in situ)
  • Size and shape of specimen
  • Orientation of test surface relative to bedding/foliation planes

• Testing Details:

  • Date of sampling and testing
  • Storage and preparation conditions (temperature, moisture)
  • Orientation of hammer axis during test
  • Method of clamping (V-block/clamps)
  • Number of tests and average hardness value (e.g., Shore or Schmidt hardness)

Rounding Off Results (Clause None)

• Follow IS 2:1960 rules for rounding numerical values.
• Retain the same number of significant figures as specified in the standard.

Summary Table for Reporting

This ensures traceability, reproducibility, and clarity in rock hardness testing reports as per IS 12608.

Shore Scleroscope Method (IS 12608)

Key Specifications (Clause 5.2.1)

• Instrument Models: Model C (recommended Model C-2 for rock), Model D
• Hammer Dimensions (Model C):

  Parameter	Value
  Diameter	5.94 mm
  Mass	2.300 ± 0.500 g
  Overall length	20.7 to 21.3 mm
  Drop height	251.2 +0.13 / -0.38 mm

Test Procedure (Clause 5.2.3)

• Perform at least 25 rebound tests on the same specimen.
• Compute the average rebound height as the Shore scleroscope hardness number.

Important Notes

• Due to rock heterogeneity and small indenter size, multiple tests ensure representativeness.
• The rebound height (in mm) is read from a scale visible through the glass tube.
• The hardness value correlates with material resistance to indentation.

Summary Formula

[ \text{Shore Hardness} = \frac{1}{n} \sum_{i=1}^{n} h_i \quad \text{where } n \geq 25, \quad h_i = \text{rebound height (mm)} ]

flowchart LR
    A[Start Test] --> B[Place Specimen]
    B --> C[Drop Hammer from 251.2 mm]
    C --> D[Measure Rebound Height]
    D --> E{Completed 25+ tests?}
    E -- No --> C
    E -- Yes --> F[Calculate Average Rebound]
    F --> G[Report Shore Hardness Number]

This method provides a quantitative, repeatable measure of rock hardness using rebound height.

IS 12608 - Apparatus for Hardness Testing

1. Scleroscope Hardness Tester (Clause 5.2.1)

• Models: Model C (recommended C-2 for rock) and Model D.
• Hammer Dimensions (Model C):

• Operation: Hammer drops from fixed height inside a glass tube; rebound height on scale 0–140 mm indicates hardness.

2. Schmidt Hammer (Clause 4.1)

• Type: Type L hammer with impact energy 0.74 Nm.
• Function: Measures rebound height of mass after impact on specimen.
• Specimen Holding: Steel base ≥ 20 kg; use steel cradle or V-block for cores (see Fig. 1).

3. Rounding Off (General)

• Follow IS 2:1960 for rounding final hardness values to match significant figures of specified values.

flowchart LR
    A[Push Schmidt Hammer Plunger] --> B[Spring Compression]
    B --> C[Spring Releases Mass]
    C --> D[Mass Impacts Specimen]
    D --> E[Mass Rebounds]
    E --> F[Measure Rebound Height on Scale]
    F --> G[Calculate Hardness Number]

This summarizes key apparatus specs and operation principles from IS 12608.

IS 12608: Test Procedure Key Points

Apparatus (Clause 4.1)

• Schmidt Hammer Type L with impact energy 0.74 Nm.
• Steel base: Minimum weight 20 kg for clamping specimens.
• Core specimens tested in a steel cradle (semi-cylindrical slot matching core radius) or steel V-block (see Fig. 1).

Test Data Handling (Clause 4.3.2)

1. Measure test values and tabulate in descending order.
2. Discard the lower 50% of values.
3. Calculate the average of the upper 50%.
4. Multiply this average by a correction factor to get the Schmidt rebound hardness.

Rounding Off (General Clause)

• Round final test values as per IS 2:1960.
• Retain the same number of significant figures as specified in the standard.

Summary Table: Test Value Processing

flowchart TD
    A[Measure test values] --> B[Sort in descending order]
    B --> C[Discard lower 50%]
    C --> D[Average upper 50%]
    D --> E[Multiply by correction factor]
    E --> F[Round off as per IS 2:1960]
    F --> G[Schmidt rebound hardness]

This ensures consistent, accurate hardness values per IS 12608.

IS 12608 - Key Formulas & Specifications for Calculations

• Rounding Off (Clause 4.3):
  Follow IS 2:1960 rules for rounding.

  • Final values (test or analysis) must be rounded to the same number of significant figures as the specified value in the standard.

• Correction Factor (Clause 4.3.1):
  [ \text{Correction Factor} = \frac{\text{Specified standard value of the anvil}}{\text{Average of 10 readings on calibration anvil}} ]

• Shore Scleroscope Hardness (Clause 5.2.3):

  • Calculate the hardness as the average of at least 25 measurements on the same specimen.

Summary Table for Calculations

flowchart LR
    A[Start: Measurement] --> B[Take 10 readings on calibration anvil]
    B --> C[Calculate average of 10 readings]
    C --> D[Compute Correction Factor]
    D --> E[Take ≥ 25 hardness measurements on specimen]
    E --> F[Calculate average hardness]
    F --> G[Round off final values as per IS 2:1960]
    G --> H[Compliance check]

This ensures precision and standard compliance in hardness testing per IS 12608.

IS 12608: Reporting of Results – Key Points

Reporting Requirements (Clauses 4.4 & 5.2.4)

Each test report must include:

• Rock Description:

  • Lithology, mineral composition, grain size.
  • Source details: geographic location, depth, orientation.

• Specimen Details:

  • Type (core, blasted, broken, in situ).
  • Size and shape of specimen.
  • Sampling and testing dates.
  • Storage conditions (temperature, moisture, drying).

• Test Setup:

  • Orientation of test surface relative to bedding/foliation.
  • Orientation of hammer axis.
  • Clamping method (V-block, clamps).

• Results:

  • Number of tests conducted.
  • Average Shore hardness or Schmidt hardness values.

Rounding Off Results (Clause None)

• Follow IS 2:1960 for rounding numerical values.
• Retain the same number of significant figures as specified in the standard.

Summary Table for Reporting

flowchart TD
    A[Sample Collection] --> B[Specimen Preparation]
    B --> C[Testing]
    C --> D[Record Test Parameters]
    D --> E[Calculate Hardness]
    E --> F[Apply Rounding (IS 2:1960)]
    F --> G[Prepare Report]
    G --> H[Include Rock & Test Details]

This ensures consistency and traceability in test reporting as per IS 12608.

IS 12608 - Precautions and Notes Summary

Key Points from Clauses:

• Rounding Off (Clause 4.3):

  • Final test or calculation results must be rounded per IS 2:1960.
  • Retain the same number of significant figures as the specified values in IS 12608.

• Reporting of Results (Clause 5.2.4):
  Reports must include:

  • Lithologic description, source, depth, orientation.
  • Mineral composition and grain size.
  • Sampling/testing dates, storage, specimen preparation.
  • Orientation relative to bedding/foliation.
  • Number of tests and average shore hardness.

Important Specifications:

Practical Notes:

• Ensure accurate specimen orientation as it affects rock properties.
• Maintain traceability: sampling location, dates, and storage conditions.
• Use consistent rounding to avoid misinterpretation of results.

flowchart TD
    A[Specimen Sampling] --> B[Specimen Preparation]
    B --> C[Test Execution]
    C --> D[Data Recording]
    D --> E[Apply IS 2:1960 Rounding]
    E --> F[Report Compilation]
    F --> G[Include Geological & Procedural Info]

This ensures compliance and reliability in rock testing as per IS 12608.

IS 12608: References and Related Standards – Key Points

• Rounding Off (IS 2:1960)
  Final test or calculation results must be rounded per IS 2:1960 rules, retaining the same significant figures as specified in IS 12608.

• Reporting of Test Results (Clause 5.2.4)
  Include in the test report:

  • Lithologic description, source, location, depth, orientation
  • Mineral composition and grain sizes
  • Sampling/testing dates, storage, preparation details
  • Orientation of test surface relative to bedding/foliation
  • Number of tests and average shore hardness

• Standard Mark Usage
  Governed by BIS Act 1986; ensures compliance through inspection, testing, and quality control.

• Revision and Amendments
  Indian Standards are periodically reviewed; users must verify possession of latest versions.

Summary Table: Reporting Requirements (Clause 5.2.4)

Rounding Off Rule (IS 2:1960)

• Round to the same number of significant digits as the standard’s specified value.
• Example: If specified value is 3.56 (3 significant digits), round result to 3 significant digits.

flowchart TD
    A[Test/Analysis Result] --> B{Round off per IS 2:1960}
    B --> C[Retain same significant digits as specified]
    C --> D[Report rounded result]

For detailed formulas or test procedures, refer to respective clauses in IS 12608 and related BIS standards.