Method for the quantitative description of discontinuities in the rock mass, Part 12: Drillcore study

IS 11315 Part 12: Scope - Key Specifications & Data Presentation

Scope:
This part deals with the presentation of rock core logging results, emphasizing parameters critical for design.

Key Parameters to Present (Clause 16.4)

• Strength Index Tests:

  • Point load test or Schmidt hammer test results.

• Block Size Index:

  • Quantitative measure of block sizes within rock mass.

• Roughness Number:

  • Compared against standard roughness charts (see IS 11315 Part 4).

• Degree of Weathering / Slake Durability:

  • Important for soft rocks like shale or mudstone.

• Filling Material:

  • Identification of clay minerals or gouge in discontinuities.

Important Core Measurements (Fig. 4)

Typical Data Table Format (Clause 16.4)

References for Detailed Methods (Clause 2.1)

Summary Diagram: Core Logging Data Flow

flowchart TD
    A[Drill Hole Info] --> B[Core Recovery]
    B --> C[Measurement of RQD]
    C --> D[Discontinuity Description]
    D --> E[Strength Tests]
    E --> F[Data Presentation & Reporting]

Note: Use IS

IS 11315 Part 12: References & Key Specifications

Key Indian Standards Referenced (Clause 2.1)

Important Parameters for Rock Mass Characterization (Clause 16.3 & 16.4)

• Rock Type with foliation/bedding dip symbols
• Depth of drill runs
• Core Recovery (%)
• Rock Quality Designation (RQD)
• Fracture Frequency (F)
• Water Injection Test Results (Lugeon values)
• Strength Indices: Point Load, Schmidt Hammer
• Block Size Index
• Roughness Number (from standard charts)
• Degree of Weathering / Slake Durability (for soft rocks)
• Filling Material (clay minerals, gouge)

Typical Data Presentation Table (Example)

Notes:

• RQD is calculated as the sum of lengths of core pieces >100 mm divided by total core

IS 11315 Part 12 - Definitions: Key Points

• Definitions Reference:
  Clause 3.1 states that definitions follow IS 11358:1987 (Glossary of terms and symbols applicable to rock mechanics). For precise terms, refer to IS 11358.

• Related Standards for Quantitative Description:
  These IS parts define parameters relevant to rock mass characterization:

  • Part 4: Roughness
  • Part 5: Wall strength
  • Part 10: Block size
  • Part 11: Core recovery and rock quality

• Key Rock Mass Parameters (Clause 16.4):

  • Strength index: via Point load or Schmidt hammer tests
  • Block size index
  • Roughness number (compare with standard charts)
  • Degree of weathering / Slake durability (for soft rocks)
  • Filling material (e.g., clay minerals)

• Core Measurement (Fig. 4):

  • ( X ) = Tip to tip length of discontinuity
  • ( Z ) = Full surface core length
  • ( Y ) = Total length of full surface + half of split parts

• Rock Quality Data Presentation (Example Table):

Summary Diagram: Rock Mass Parameters

graph LR
A[Rock Mass] --> B[Discontinuities]
B --> C[Roughness Number]
B --> D[Wall Strength]
B --> E[Block Size Index]
A --> F[Core Recovery & RQD]
A --> G[Strength Index Tests]
A --> H[Weathering Degree]
A --> I[Filling Material]

For detailed definitions and symbols, consult IS 11358:1987.
For measurement methods and indices, refer to IS 11315 Parts 4,5,10,11.

IS 11315 Part 12: General Requirements for Drill Core Study

Key Parameters & Specifications

• Core Recovery (R): Percentage of drill core length recovered.
• Rock Quality Designation (RQD): Sum of lengths of core pieces >10 cm / total core run length × 100.
• Discontinuity Frequency (F): Number of fractures per meter of core.
• Water Loss (Lugeon Test): Measures permeability; expressed in Lugeon units (1 Lugeon = 1 L/min/m).
• Strength Indices: Point load test or Schmidt hammer values.
• Block Size Index: Quantifies block sizes between discontinuities.
• Roughness Number: Compared against standard charts.
• Degree of Weathering / Slake Durability: Especially for soft rocks like shale.
• Filling Material: Identification of clay minerals or gouge in discontinuities.

Typical Data Presentation (Clause 16.3 & 16.4)

RQD Calculation Formula

[ \text{RQD} = \frac{\sum \text{length of core pieces} > 10 \text{cm}}{\text{total core run length}} \times 100 ]

Visual Representation of Core Measurement (Fig. 4)

flowchart LR
    A[a] --> B[Discontinuity]
    B --> C[b]
    subgraph Core Length Measurement
        direction LR
        A -- X --> B -- Z --> C
    end

• X: Tip-to-tip core length between discontinuities.
• Z: Full surface core length.
• Y: Total length including full surface + half of split core parts.

This comprehensive approach ensures reliable rock mass characterization for design purposes per IS 11315 Part 12.

Core Recovery (R) and Rock Quality Designation (RQD) per IS 11315 Part 12

1. Core Recovery (R)

• Definition: Total length of core pieces recovered (including all pieces) expressed as a percentage of the drilled interval.
• Formula:

[ R = \frac{\text{Total length of core recovered}}{\text{Length of drill run}} \times 100% ]

2. Rock Quality Designation (RQD)

• Definition: Modified core recovery considering only sound core pieces ≥ 10 cm in length.
• Formula:

[ RQD = \frac{\sum \text{Length of core pieces} \geq 10 \text{ cm}}{\text{Length of drill run}} \times 100% ]

• Used to assess rock mass quality; smaller pieces from joints or weathering are excluded.

3. Discontinuity Frequency (F)

• Number of fractures per meter of core length.
• Helps identify rock fracturing intensity.

4. Key Table (Clause 16.4) for Design Parameters

5. Measurement Sketch (Fig. 4)

• X: Tip-to-tip length of core pieces.
• Y: Total length of full surface + half length of split cores.
• Z: Full surface core length.

Summary

flowchart TD
    A[Drilled Interval] --> B[Core

Orientation of Discontinuities (IS 11315 Part 12:1992)

Key Points & Formulas

• Apparent Orientation Measurement (Clause 6.1):
  Measure acute angle ( \theta ) between discontinuity and core axis using a protractor (accuracy ±5°).

  • For vertical holes:
    [ \text{True dip} = 90^\circ - \theta ]
  • Without core orientation, dip direction remains unknown.

• Correction for Inclined Holes (Clause 4.7):
  When drill hole is inclined at angle ( i ), correct measured angle ( \theta ) to get true dip ( \delta ) using trigonometric relations (requires inclination and azimuth data).

• Core Orientation Methods (Clause 6.4):

  1. Craclius method: Match adjacent core pieces to orient runs.
  2. Steel groove & compass-photo device: Mark and photograph core for azimuth.
  3. Integral sampling: Use grouted bar with known azimuth inside core.

Summary Table: Orientation Data

Roughness & Shear Strength (Clause 9.1)

• Roughness classified as planar, curved, irregular (see IS 11315 Part 4:1987).
• Direct shear strength estimation requires additional tests; core alone insufficient.

flowchart TD
    A[Drill Core] --> B[Measure angle θ with protractor]
    B --> C{Is hole vertical?}
    C -- Yes --> D[True dip δ = 90° - θ]
    C -- No --> E[Apply correction for inclination i]
    E --> F[Calculate true dip δ]
    D & F --> G[Determine dip direction if core oriented]

This approach ensures accurate discontinuity orientation essential for rock mass characterization and stability analysis.

IS 11315 Part 12: Measurement of Spacing and Frequency of Discontinuities

Key Formulas:

• Spacing (S) for oblique joints:

[ S = \frac{L}{\cos \theta} ]

Where:

• (L) = length measured along core axis between adjacent discontinuities

• (\theta) = acute angle between discontinuity and core axis

• Frequency (F):

[ F = \frac{\text{Number of natural discontinuities}}{\text{Length of core (m)}} ]

Count discontinuities per meter of recovered core, excluding artificial breaks.

Important Specifications:

• Direct Measurement: When drill hole intersects joint set perpendicularly, spacing (S = L).
• Frequency Counting: Only natural discontinuities are counted; differentiate using procedure in Clause 5.4.1.1.
• Presentation Data (Clause 16.4): Include strength index, block size index, roughness number, weathering degree, and filling material.

Table: Presentation of Results (Summary)

Visual Concept (Mermaid.js):

flowchart LR
    A[Drill Core] --> B{Discontinuity Angle θ}
    B -->|θ = 90°| C[Spacing S = L]
    B -->|θ < 90°| D[Spacing S = L / cos θ]
    A --> E[Count Natural Discontinuities]
    E --> F[Frequency F = Number / Length]

This concise approach ensures accurate measurement and reporting of discontinuities for rock mass characterization per IS 11315 Part 12.

Persistence of Discontinuities (IS 11315 Part 12:1992) key points:

1. Persistence Assessment (Clause 8.1)

• Persistence generally cannot be directly measured from drill cores unless holes are very closely spaced.
• For major discontinuities (faults, shear zones, rock unit contacts), persistence can be inferred by correlating multiple drill holes.
• Requires careful correlation of discontinuities between holes.

2. Attitude Measurement (Clause 4.7)

• Discontinuity attitudes are measured relative to the drill core axis.
• For inclined drill holes, corrections must be applied based on hole inclination and outcrop data.

3. Roughness & Shear Strength (Clause 9.1)

• Drill cores allow only qualitative roughness assessment: planar, curved, irregular.
• Roughness classification aligns with IS 11315 Part 4:1987.

4. Key Parameters for Presentation (Clause 16.4)

5. Core Length Measurements (Fig. 4)

• X: Tip-to-tip discontinuity length
• Y: Total length of full surface + half split core parts
• Z: Full surface core length

Summary Table: Core Data Example

flowchart LR
    A[Drill Holes] --> B{Spacing}
    B -->|Closely spaced| C[Correlate discontinuities]
    B -->|Widely spaced| D[Persistence unknown]
    C --> E[Estimate persistence of faults/shear zones]
    E --> F[Design

IS 11315 Part 12: Roughness Assessment Key Points

1. Roughness Evaluation (Clause 9.2):

   • Visual observation of natural fracture surfaces on core pieces.
   • Comparison with standard charts, e.g., Barton's Roughness Chart, to assign a fixed roughness number.
   • Roughness number quantifies the surface irregularity affecting shear strength.

2. Surface Planarity (Clause 9.1):

   • Assign planarity type: planar, curved, irregular.
   • Procedure consistent with IS 11315 Part 4 (1987) on roughness description.

3. Presentation of Roughness Data (Clause 16.4):

   • Roughness number from chart comparison.
   • Combined with other parameters like strength index, block size, weathering, filling material.

Barton's Roughness Number (Typical Reference)

Procedure Summary

flowchart TD
    A[Visual Inspection of Core Fracture Surface] --> B[Compare with Barton's Chart]
    B --> C[Assign Roughness Number (JRC)]
    C --> D[Classify Surface Planarity (Planar/Curved/Irregular)]
    D --> E[Report Roughness Number with Other Rock Mass Parameters]

References for Detailed Methodology

• IS 11315 Part 4 (1987) — Roughness Quantification
• IS 11315 Part 5 (1987) — Wall Strength
• IS 11315 Part 10 (1987) — Block Size
• IS 11315 Part 11 (1985) — Core Recovery & Quality

Summary: Roughness is visually assessed on core surfaces and quantified using Barton's roughness number by comparison to standard charts, combined with planarity classification for design inputs.

Wall Strength Evaluation as per IS 11315 Part 12

Key Points:

• Wall Strength Assessment (Clause 10.1 & 10.3):

  • Use weathering grade of rock mass/material.
  • Conduct manual index tests and Schmidt hammer tests (refer IS 11315 Part 5:1987).
  • Check core piece fit; poor fit may indicate lost filling, shear displacement, or grinding of weathered walls.

• Important Parameters to Present (Clause 16.4):

  • Point Load or Schmidt Hammer Strength Index.
  • Block Size Index.
  • Roughness Number (compare with standard charts).
  • Degree of Weathering or Slake Durability (for soft rocks like shale, mudstone).
  • Filling Material (e.g., clay minerals).

Typical Data Table Format (Clause 16.4)

Notes on Core Measurement (Fig. 4)

• X: Tip-to-tip length of core.
• Z: Full surface core length.
• Y: Total length of full surface + half of split core parts.

Summary Diagram of Wall Strength Evaluation Process

flowchart TD
    A[Drill Core Extraction] --> B[Visual Inspection]
    B --> C{Core Piece Fit?}
    C -- Yes --> D[Strength Tests]
    C -- No --> E[Check for Filling Loss/Shear]
    D --> F[Calculate Strength Indices]
    E --> F
    F --> G[Present Data: RQD, Fracture Frequency, Water Loss]
    G --> H[Design Input]

Use IS 11315 Part 5 for Schmidt hammer test details and Part 12 for core handling and wall strength evaluation.

IS 11315 Part 12: Aperture and Seepage Characteristics

Key Points & Specifications:

• Aperture Nature (Clause 11.3 & 11.2):

  • Aperture openness is critical for design.
  • Use water injection tests, combined with RQD and fracture frequency (Clause 5.7, Fig. 5), to assess if apertures are open or tight.
  • Real aperture > theoretical smooth wall aperture due to roughness/tortuosity.
  • TV camera inspections help distinguish open vs. tight apertures but may not measure finest joints accurately.

• Seepage Estimation (Clause 13.3):

  • Use falling head tests (IS 5529 Part 1), Lugeon packer tests (IS 5529 Part 2), tracer tests, and piezometer measurements.
  • Lugeon values indicate hydraulic conductivity of discontinuities.
  • Present Lugeon values alongside core recovery and RQD logs for comprehensive seepage assessment.

• Relation of Seepage to Aperture (Clause 5.7):

  • Low RQD → high fracture frequency → higher seepage.
  • High seepage in water injection tests + low RQD = open fracture apertures.

Typical Formula for Hydraulic Conductivity from Lugeon Test:

[ K = \frac{L \times Q}{A \times h} ]

Where:

• (K) = hydraulic conductivity (m/s)
• (L) = length of test section (m)
• (Q) = flow rate (m³/s)
• (A) = cross-sectional area of the test section (m²)
• (h) = hydraulic head (m)

Summary Table: Aperture-Seepage Indicators

flowchart LR
    A[Drill Hole Data] --> B{RQD & Fracture Frequency}
    B -->|Low RQD

IS 11315 Part 12: Filling Material Description - Key Points

1. Description of Filling Material (Clause 12.1)

• Softer filling materials often not recovered by conventional drilling; use integral sampling or best quality drilling (double/triple tube barrels, split tubes).
• Describe recovered filling by:
  • Width
  • Mineralogy (e.g., clay minerals like montmorillonite, calcite)
  • Strength
• Clearly state the interpretative nature of these descriptions.

2. Parameters to Present (Clause 16.4)

3. Measurement Notes (Clause 5.6)

• Filling examined if recovered or core recovery is 100%.
• Other parameters (orientation, persistence, aperture, seepage) best studied in outcrop or tunnels.
• Borehole cameras and water injection tests assist in situ measurement.

Typical Filling Material Description Table (Example)

Visual Concept: Filling Material in Discontinuity

graph LR
A[Discontinuity] --> B[Crushed Zone]
B --> C[Clay Filling]
B --> D[Calcite Vein]
C --> E[Weak Strength]
D --> F[Moder

IS 11315 Part 12: Groundwater and Seepage Observations - Key Points

1. Testing Methods (Clause 13.3)

• Falling Head Test (IS 5529 Part 1:1985): Measures permeability by observing water level drop in drill holes.
• Lugeon Packer Test (IS 5529 Part 2:1985): Estimates rock mass permeability; results expressed in Lugeon units (1 Lugeon = 1 L/min/m/MPa).
• Tracer Tests & Piezometer Measurements: For hydraulic conductivity and seepage estimation along discontinuities.

2. Data Collection (Clause 13.2)

• Groundwater levels checked by electrical contact devices.
• Seepage horizons identified via borehole walls inspection (periscopes, TV cameras).
• Drillers’ logs provide additional standing water level data.

3. Presentation of Results (Clause 16.4 & Table 16)

4. Important Formulas & Concepts

• Lugeon Value Calculation:

[ \text{Lugeon} = \frac{\text{Water loss (L/min)}}{\text{Test length (m)} \times \text{Pressure (MPa)}} ]

• RQD (Rock Quality Designation):

[ RQD = \frac{\text{Sum of lengths of core pieces > 10 cm}}{\text{Total core length}} \times 100% ]

• Fracture Frequency:

[ \text{Fracture frequency} = \frac{\text{Number of fractures}}{\text{Core length (m)}} ]

5. Logging Example (Fig. 5 style)

IS 11315 Part 12: Number of Discontinuity Sets - Key Formulas & Specifications

1. Frequency of Discontinuities (Clause 5.3)

• Frequency (F) = Number of natural discontinuities per meter of core length.
• Count all natural discontinuities intersecting a 1 m length of recovered core.
• Differentiate natural from artificial discontinuities as per procedure in Clause 5.4.1.1.

2. Spacing of Discontinuities (Clause 7.1 & 7.3)

• When the drill hole is perpendicular to joint set: [ S = L ] where:

  • ( S ) = true spacing between discontinuities
  • ( L ) = length measured along core axis between discontinuities

• For obliquely intersected discontinuities: [ S = \frac{L}{\cos \theta} ] where:

  • ( \theta ) = acute angle between discontinuity plane and core axis

3. Attitude Measurement (Clause 4.7)

• Measure discontinuity attitudes relative to the long axis of the drill core.
• Apply corrections for drill hole inclination or use known attitudes from outcrops.

Summary Table

flowchart LR
    A[Drill Core] --> B[Measure Length L between discontinuities]
    B --> C{Is drill hole perpendicular?}
    C -- Yes --> D[Spacing S = L]
    C -- No --> E[Measure angle θ]
    E --> F[Spacing S = L / cos θ]

This approach ensures accurate quantification of discontinuity sets from drill cores as per IS 11315 Part 12.

Block Size Estimation - IS 11315 Part 12

Key Concepts (Clause 15.1 & 7.1)

• Block Size depends on:
  • Spacing, number of joint sets, persistence, orientation.
• Typical block size is estimated by averaging core piece dimensions (±10%).
• For cubic joint systems, use diagonal drill holes intersecting all sets.
• Block Size Index (It) defined in IS 11315 Part 10 is used to quantify block size.

Spacing Calculation (Clause 7.1)

If joint spacing is measured along core axis:

[ S = \frac{L}{\cos \theta} ]

Where:

• ( S ) = true spacing between joints,
• ( L ) = measured distance between joints along core axis,
• ( \theta ) = acute angle between joint plane and core axis.

Presentation of Results (Clause 16.4)

• Include:
  • Strength index (Point load/Schmidt hammer),
  • Block size index (It),
  • Roughness number,
  • Weathering degree/slake durability,
  • Filling material type.

Typical Data Table Format (Clause 16)

flowchart TD
    A[Drill Core] --> B[Identify Joint Sets]
    B --> C[Measure Core Piece Lengths (L)]
    C --> D[Calculate Spacing S = L / cos(θ)]
    D --> E[Estimate Block Size Index (It)]
    E --> F[Compile Data Table]

This approach provides a practical method to estimate block size from core data consistent with IS 11315 Part 12.

IS 11315 Part 12: Presentation of Results (Clause 16.4 & 16.3)

Key parameters to present for rock mass characterization:

• Strength indices: Point load or Schmidt hammer test results.
• Block Size Index (It): Average core piece dimensions ±10%, representing block size (see IS 11315 Part 10).
• Roughness Number: Compared with standard charts.
• Degree of Weathering / Slake Durability: Especially for soft rocks like shale, mudstone.
• Filling Material: Presence of clay minerals or gouge in discontinuities.

Recommended Log Sheet Parameters (Clause 16.3):

Typical Table Format for Results:

Block Size Index (It) Estimation:

• Select typical core pieces.
• Measure average dimensions (length, width, height).
• Calculate average block volume or size index.
• Use orientation of drill hole to intersect all joint sets for accuracy.

Diagrammatic Representation (Fig. 5):

graph LR
A[Rock Type with Symbols] --> B[Core Recovery %]
B --> C[RQD %]
C --> D[Fracture Frequency]
D --> E[Water Transmissivity (Lugeon)]

Summary: Present rock mass data systematically with strength indices, block size, RQD