Method for the quantitative description of discontinuities in rock masses, Part 11: Core recovery and rock quality

IS 11315 Part 11 relates to Structural Steel Sections – Hot Rolled.

Introduction Key Points:

• Covers hot rolled steel sections for structural use.
• Specifies dimensions, tolerances, and sectional properties.
• Applies to I, H, T, and other rolled sections.

Commonly Referenced Formulas & Tables:

Typical Tables Include:

• Section dimensions (depth, flange width, thickness)
• Weight per meter
• Moment of inertia and section modulus values

Summary:

IS 11315 Part 11 standardizes hot rolled steel section properties essential for structural design, ensuring uniformity in dimensions and mechanical properties.

flowchart LR
    A[Hot Rolled Steel Sections] --> B[Dimensions & Tolerances]
    A --> C[Sectional Properties]
    C --> D[Moment of Inertia (I)]
    C --> E[Section Modulus (Z)]
    C --> F[Radius of Gyration (r)]

For detailed tables and exact dimensions, refer to the full IS 11315 Part 11 document.

IS 11315 Part 11 - Scope Summary

• Purpose:
  This part of IS 11315 guides field data collection for applying geomechanics classification in civil engineering projects.

• Definitions:
  Terms are as per IS 11358-1986.

• Reporting:
  Final test or analysis values must be rounded according to IS 2-1960.

Key Points for Scope:

Notes:

• No direct formulas or tables are provided in the scope clause.
• The scope sets the framework for data collection, not calculations.
• For formulas and classification criteria, refer to later clauses or IS 11358.

flowchart LR
    A[Field Data Collection] --> B[Geomechanics Classification]
    B --> C[Civil Engineering Applications]
    A --> D[Use IS 11358 Terms]
    C --> E[Reporting as per IS 2-1960]

This diagram illustrates the scope flow from data collection to application and reporting standards.

IS 11315 Part 11 refers to definitions as per IS 11358-1986. Since IS 11315 defers to IS 11358 for definitions, here are key points:

Key Definitions (from IS 11358-1986)

• Structural Steel: Steel used in construction with specified mechanical properties.
• Yield Strength (fy): Stress at which steel begins to deform plastically.
• Ultimate Strength (fu): Maximum stress steel can withstand.
• Modulus of Elasticity (E): Steel's stiffness, typically 2 × 10^5 MPa.
• Section Modulus (Z): Geometric property used in bending calculations.

Typical Relevant Formulas:

• Bending Stress, σ = M / Z
• Axial Stress, σ = P / A
• Slenderness Ratio, λ = L / r (L = effective length, r = radius of gyration)

Tables to Refer:

• Mechanical properties of steel grades (fy, fu)
• Section properties (area, moment of inertia, radius of gyration) for standard steel sections

flowchart TD
    A[IS 11315 Part 11] --> B[Definitions as per IS 11358-1986]
    B --> C[Structural Steel]
    B --> D[Yield Strength (fy)]
    B --> E[Ultimate Strength (fu)]
    B --> F[Modulus of Elasticity (E)]
    B --> G[Section Properties]

For detailed definitions and values, consult IS 11358-1986 directly.

IS 11315 Part 11: Symbols and Terminology

• RQD (Rock Quality Designation):
  Percentage of core pieces > 10 cm length in a drill run, indicating rock mass quality.
  [ RQD = \left(\frac{\sum \text{length of core pieces} > 10 \text{ cm}}{\text{total length of core run}}\right) \times 100% ]

• Vp (P-wave velocity):
  Velocity of primary seismic waves measured by seismic refraction surveys, indicating rock stiffness.

• Vi (Ultrasonic wave velocity):
  Velocity of waves in rock cores from ultrasonic tests, used to assess rock integrity.

• Fv (Volumetric Joint Count):
  Number of joints per cubic meter, representing joint density in rock mass.

Note: Definitions follow IS 11358-1986.

Summary Table of Symbols

flowchart LR
    A[RQD] -->|Core pieces >10cm| B[Rock Quality]
    C[Vp] -->|Seismic waves| D[Rock Stiffness]
    E[Vi] -->|Ultrasonic test| F[Rock Integrity]
    G[Fv] -->|Joint count| H[Rock Mass Discontinuity]

This concise terminology is essential for interpreting rock mass properties in IS 11315 Part 11.

Core Recovery (IS 11315 Part 11)

Key Definitions & Formulas

• Core Recovery (CR):
  [ \text{CR} (%) = \frac{\text{Sum of lengths of all recovered core pieces}}{\text{Length drilled}} \times 100 ]

  • Measured to nearest ±2%.
  • Fragmented core lengths estimated by assembling fragments.

• Rock Quality Designation (RQD):
  [ \text{RQD} (%) = \frac{\text{Sum of lengths of sound core pieces ≥ 10 cm}}{\text{Length drilled}} \times 100 ]

  • Only sound pieces ≥ 10 cm counted.
  • Smaller fragments excluded (due to joints/faults/weathering).

Notes

• Core recovery evaluates drilling effectiveness and rock mass quality.
• RQD refines core recovery by filtering out broken fragments, indicating rock quality.
• Both metrics apply to individual runs or entire boreholes, not specific rock units.
• Results depend on drilling equipment and crew skill.

Illustration (Fig.1 Conceptual)

flowchart LR
    A[Length Drilled] --> B[Recovered Core Pieces]
    B --> C[Sum Lengths of All Pieces]
    B --> D[Sum Lengths of Pieces ≥ 10 cm (Sound Core)]
    C --> E[Calculate Core Recovery %]
    D --> F[Calculate RQD %]

This concise approach helps assess rock mass quality for design and construction.

Rock Quality Designation (RQD) - IS 11315 Part 11

Definition (Clause 5.1)

• RQD = (Sum of lengths of sound core pieces ≥ 10 cm) / (Total length drilled) × 100%
• Excludes smaller pieces caused by joints, faults, or weathering.

Calculation Example (Fig. 1)

• Modified Core Recovery = 85 cm / 150 cm = 57%
• Core Recovery = 125 cm / 150 cm = 83%

Relation with P-wave Velocity (Clause 5.3.1)

[ RQD \approx \left(\frac{V}{V_r}\right)^2 \times 100 ]

• (V) = P-wave velocity from seismic refraction (field)
• (V_r) = Ultrasonic velocity of intact rock core

Core Quality Classification (Clause 5.3.3, Table 5.2)

Summary

• RQD is a simple index to assess rock mass quality from core samples.
• It helps in design decisions for foundations, tunnels, slopes, etc.
• Always report both core recovery and RQD for clarity.

flowchart LR
    A[Total Core Length Drilled] --> B{Measure Core Pieces}
    B -->|≥10 cm| C[Sum Lengths of Sound Core]
    B -->|<10 cm| D[Exclude]
    C --> E[Calculate RQD = (C/A)*100]
    E --> F[Classify Core Quality]

This diagram shows the RQD calculation process.

General Principles of RQD (IS 11315 Part 11 - 1985)

• Definition (Clause 5.1):
  RQD = (Sum of lengths of sound core pieces ≥ 10 cm) / (Total length drilled) × 100%
  Smaller pieces (<10 cm) due to joints, faults, or weathering are excluded.

• Velocity Ratio Relation (Clause 5.3.1):
  [ \text{RQD} \approx (\text{Velocity Ratio})^2 \times 100 ] where,
  [ \text{Velocity Ratio} = \frac{V}{V_r} ]

  • (V) = P-wave velocity from seismic refraction (field)
  • (V_r) = Ultrasonic velocity from rock cores (lab)

• Core Quality Classification (Clause 5.3.3, Table 5.2):

• Example (Modified Core Recovery):
  For core length 150 cm, sound core 85 cm →
  [ RQD = \frac{85}{150} \times 100 = 57% ]

flowchart TD
    A[Drilling Core] --> B{Measure Core Pieces}
    B -->|≥10 cm| C[Sum Length of Sound Core]
    B -->|<10 cm| D[Discarded]
    C --> E[Calculate RQD %]
    E --> F[Classify Core Quality]

Summary: RQD is a practical index indicating rock mass quality, closely related to seismic velocities, and classified into five quality levels for engineering assessment.

Precautions in Core Handling (IS 11315 Part 11)

Key Precautions (Clauses 5.2 & 4.3)

• Broken Core Pieces:

  • Fit fresh broken pieces together and count as one if length > 10 cm.
  • Exclude obviously weaker materials (e.g., over-consolidated gauge), even if intact and >10 cm.

• Core Barrel & Supervision:

  • Use double tube core barrel NX size (54 mm dia inside) for better recovery.
  • Ensure proper supervision to minimize human error.

• Core Length Measurement:

  • Measure core length along the center line to avoid underestimating RQD due to parallel discontinuities.

• Core Grinding & Loss:

  • Record any core loss due to grinding.
  • Diamond core boring preferred for smooth, regular cores.

• Core Loss Zones:

  • Mark start/end depths of lost core zones; use wooden blocks with markings to represent lost lengths.

• Solution Cavities in Limestone:

  • Estimate cavity thickness by noting sudden drilling rate increases.

Rock Quality Designation (RQD) Table (Clause 5.3.3)

Summary Diagram: Core Handling Flow

flowchart TD
    A[Drilling Core] --> B{Core Broken?}
    B -- Yes --> C[Fit pieces >10cm together]
    B -- No --> D[Measure core length along center line]
    C --> D
    D --> E{Core Quality?}
    E -->|Weak Material| F[Exclude from RQD]
    E -->|Good Material| G[Calculate RQD]
    G --> H[Record Core Loss Zones]
    F --> H
    H --> I[Report Results]

Use these guidelines to ensure accurate core recovery and reliable RQD evaluation as per IS 11315 Part 11.

IS 11315 (Part 11) - Indirect Methods for Estimating RQD

Key Formulas:

1. Using Velocity Ratio (Clause 5.3.1):
   [ \boxed{ RQD \approx ( \frac{V}{V_r} )^2 \times 100 } ]

• (V) = P-wave velocity from seismic refraction (field)
• (V_r) = Ultrasonic velocity from rock cores

2. Using Joint Frequency (J_v) (Clause 3.3):
   [ \boxed{ RQD = 115 - 3.3 J_v \quad \text{for } J_v \geq 4.5 } ]

• For (J_v < 4.5), (RQD = 100)
• Note: Actual RQD may be less than this estimate.

Specifications & Notes:

• RQD is a more sensitive and consistent indicator of rock quality than core recovery percentage (Clause 5.1.1).
• Modified Core Recovery example:
  • RQD = 57% (85/150)
  • Core Recovery = 83% (125/150)
• RQD is practical for describing core quality; geomechanics classification is more comprehensive for rock mass rating.

Summary Table:

flowchart LR
    A[Seismic Refraction Survey] -->|Measure V| B[Calculate Velocity Ratio \(V/V_r\)]
    C[Ultrasonic Test on Core] -->|Measure \(V_r\)| B
    B --> D[Estimate RQD using \( (V

IS 11315 Part 11: Reporting of Results - Key Points

1. Core Quality Classification (Clause 5.3.3, Table 5.2)

• RQD (Rock Quality Designation) is the percentage of core pieces longer than 10 cm in a drill run.

2. Symbols Used (Clause 3.1)

3. Reporting Guidelines (Clause 6.1)

• Report shall include:
  • Geological description of site
  • Core recovery data
  • Test results rounded as per IS 2-1960 (rounding rules)

4. Rounding Off (IS 2-1960)

• Values should be rounded to the nearest unit based on the digit following the last retained digit.
• For example, 12.56 rounded to one decimal place is 12.6.

Summary Diagram of Reporting Flow

flowchart TD
    A[Start Geological Investigation] --> B[Core Recovery Measurement]
    B --> C[Calculate RQD & Other Parameters]
    C --> D[Classify Core Quality (Table 5.2)]
    D --> E[Prepare Report]
    E --> F[Include Geological Description]
    E --> G[Include Core Recovery & Quality]
    E --> H[Round off results as per IS 2-1960]
    F & G & H --> I[Final Report Submission]

This ensures standardized, clear, and consistent reporting of rock core test results per IS 11315 Part 11.