Method for the quantitative description of discontinuities in rock masses, Part 6: Aperture

IS 11315 Part 6 - Introduction: Key Points, Terms & Units

Scope:

• Quantitative description of aperture in rock mass discontinuities.
• Aperture = perpendicular distance between adjacent rock walls (air or water filled).

Key Definitions (Clause 5.1, Table 1)

SI Units & Derived Units (Clause 5.4)

Important Notes

• Aperture measurement includes extremely wide (10–100 cm) and cavernous (>1 m) apertures, with photographic documentation recommended.
• Descriptions assist in rock mass behavior prediction and engineering design.
• Results rounding as per IS 2-1960.

flowchart LR
    A[Rock Mass Discontinuity] --> B[Aperture Measurement]
    B --> C{Aperture Size}
    C -->|<0.25 mm| D[Tight (Closed)]
    C -->|0.

IS 11315 Part 6: Scope & Key Specifications on Aperture

Scope:

• Defines aperture as the perpendicular distance between adjacent rock walls of a discontinuity, filled with air or water.
• Essential for describing rock mass discontinuities affecting mechanical behavior.
• Part of a unified system to quantify rock mass discontinuities (orientation, spacing, persistence, roughness, wall strength, aperture, filling, seepage, number of sets, block size).

Key Tables & Definitions

SI Units & Derived Units Relevant to Rock Mechanics

Notes on Presentation of Results (Clause 5.4)

• Photographs of extremely wide (10 - 100 cm) and cavernous (>1 m) apertures should be appended.
• Results must be rounded off as per IS 2-1960.

flowchart TD
    A[Rock Mass Discontinuity] --> B[Aperture Measurement]
    B --> C{Aperture Size}
    C -->|<0.25 mm| D[Tight (Closed)]
    C -->|0.25-0.5 mm| E[Partly Open]
   

IS 11315 Part 6 - Key References on Aperture

Definitions & Terms (Clause 5.1, Table 1)

Aperture describes the perpendicular distance between adjacent rock walls of a discontinuity.

Units & Symbols (SI Units)

Important Notes:

• Aperture measurement includes air or water-filled spaces.
• Photographs of extremely wide (10-100 cm) and cavernous (>1 m) apertures should be appended (Clause 5.4).
• Use IS:2-1960 for rounding off final values.

flowchart LR
    A[Rock Mass Discontinuity]
    A --> B[Aperture Measurement]
    B --> C{Aperture Size}
    C -->|<0.25 mm| D[Tight (Closed)]
    C -->|0.25-0.5 mm| E[Partly Open]
    C -->|0.5-2.5 mm| F[Open]
    C -->|2.5-10 mm| G[

IS 11315 Part 6: Terminology & Definitions for Aperture in Rock Discontinuities

Key Definitions:

• Aperture: Perpendicular distance between adjacent rock walls of a discontinuity, filled with air or water (Clause 0.5).
• Discontinuity: Any mechanical break with zero or low tensile strength (joints, faults, shear zones).

Aperture Classification (Table 1, Clause 5.1)

SI Units & Derived Units (Clause 5.4)

Notes:

• Use IS 2-1960 for rounding off values.
• Photographs of apertures >10 cm to 1 m should be appended (Clause 5.4).

flowchart LR
    A[Discontinuity] --> B[Aperture]
    B --> C{Size Classification}
    C -->|<0.25 mm| D[Tight (Closed)]
    C -->|0.25-0.5 mm| E[Partly

IS 11315 Part 6: Field Measurement Procedures for Apertures

Key Specifications & Procedures

• Measurement tools:

  • Fine apertures (<10 mm): Use feeler gauges.
  • Larger apertures (>10 mm): Use a steel rule graduated in mm.

• Recording:

  • Record apertures of all discontinuities intersecting the survey line.
  • For major discontinuities, measure variation along the trace.

• Special methods:

  • Borehole periscope (up to 30 m depth) with a calibrated scale for aperture reading.
  • Integral sampling method: reinforced core sampling for special cases.

• Notes:

  • Surface apertures often overestimate true rock mass apertures due to weathering or excavation.
  • Aperture measurements alone poorly predict water conductivity; in situ permeability tests are better.
  • Apertures vary widely in sheared/displaced discontinuities.

Aperture Classification (Table 1)

Units & Definitions (SI Units)

Summary Diagram

flowchart TD
    A[Measure Apertures] --> B{Aperture Size?}
    B -->|<10 mm| C[Use Fe

IS 11315 Part 6 - Presentation of Results (Clause 5)

Key Points:

• Aperture Classification (Table 1):

• Measurement Notes (Clause 4.2):

  • Fine apertures: use feeler gauges.
  • Larger apertures: use a rule graduated in mm.
  • Aperture measurements may be disturbed by surface weathering or excavation.
  • Borehole periscopes recommended for depths ≤ 30 m.
  • Correct aperture readings for borehole orientation if not perpendicular to discontinuities.

• Photographic Documentation (Clause 5.4):

  • Append photographs for extremely wide (10-100 cm) and cavernous (>1 m) apertures.

• Units (SI Units):

  • Length: metre (m)
  • Force: newton (N) = 1 kg·m/s²
  • Pressure: pascal (Pa) = 1 N/m²

Summary Diagram: Aperture Size Classification

graph LR
A[Tight < 0.25 mm] --> B[Partly open 0.25-0.5 mm]
B --> C[Open 0.5-2.5 mm]
C --> D[Moderately wide 2.5-10 mm]
D --> E[Wide > 10 mm]
E --> F[Very wide 1-10 cm]
F --> G[Extremely wide 10-100 cm]
G --> H[Cavernous > 1 m]

Additional Notes:

• Aperture measurements are approximate and

IS 11315 Part 6: Measurement Limitations and Accuracy for Aperture

Key Points on Measurement Limitations (Clause 4.2 & Notes):

• Measurement Methods:

  • Fine apertures: measured approximately with feeler gauges.
  • Larger apertures: measured with a rule graduated in mm.
  • Borehole apertures: use periscopes (up to 30 m depth), borehole cameras, TV equipment, or pressure sensitive packers.

• Limitations:

  • Surface apertures often disturbed by weathering or excavation.
  • Machine bored tunnels and borehole walls provide more reliable undisturbed aperture data.
  • Optical distortions occur in borehole periscopes beyond 30 m depth.
  • Apertures vary along discontinuities and may be unreliable due to asperity contact and debris.
  • Aperture size does not directly correlate with water conductivity due to wall roughness and flow characteristics.

Accuracy Notes:

• Apertures should be corrected for orientation if boreholes intersect discontinuities at non-right angles.
• Integral sampling method (core recovery with grouted bar) recommended for special cases.
• Aperture measurements are approximate and should be supplemented with in-situ permeability tests for flow assessment.

Aperture Classification (Table 1)

Units & Definitions (SI Units)