Glossary of terms and symbols relating to rock mechanics

IS 11358: Scope Summary

IS 11358 covers definitions, terms, and symbols related to rock mechanics. It standardizes the vocabulary used in rock mechanics engineering, ensuring uniform communication.

Key Points from Scope:

• Applies to rock mechanics terminology.
• Covers definitions related to rock properties, testing, and behavior.
• Includes symbols used in rock engineering calculations.

Important Specifications:

• No direct formulas or tables in the scope clause.
• Serves as a reference glossary for other IS codes involving rock mechanics.

Typical Symbols & Terms (examples):

Usage:

• Refer IS 11358 for standardized terms when designing or analyzing rock structures.
• Use alongside IS codes on rock testing and design (e.g., IS 6928).

flowchart LR
    A[IS 11358] --> B[Glossary of Terms]
    A --> C[Symbols for Rock Mechanics]
    B --> D[Rock Properties]
    C --> D
    D --> E[Design & Analysis]

For detailed formulas and tables, consult related IS codes on rock testing and design.

IS 11358: Definitions of Terms and Symbols in Rock Mechanics

IS 11358 primarily provides a glossary of standardized terms and symbols used in rock mechanics, ensuring uniformity in communication rather than formulas or tables.

Key Highlights:

• Scope: Defines terminology related to rock properties, behavior, and testing.
• Symbols: Standard symbols for parameters like:
  • σ = Stress
  • ε = Strain
  • E = Modulus of Elasticity
  • c = Cohesion
  • φ = Angle of internal friction
  • γ = Unit weight
• Terms: Includes definitions of rock mass, discontinuities, joint sets, rock strength, deformability, and failure criteria.

Typical Parameters Defined:

Usage:

• Use these terms and symbols consistently in rock mechanics analysis, reporting, and design.
• Refer to IS 11358 for exact definitions to avoid ambiguity.

flowchart LR
    A[Rock Mechanics] --> B[Terminology]
    A --> C[Symbols]
    B --> D[Rock Mass]
    B --> E[Discontinuities]
    C --> F[Stress (σ)]
    C --> G[Strain (ε)]
    C --> H[Modulus of Elasticity (E)]

Note: For detailed formulas and testing procedures, refer to complementary IS codes like IS 11282 (rock testing) or IS 14687 (rock slopes).

IS 11358: Key Rock Properties & Parameters

The standard emphasizes a Basic Geotechnical Description (BGD) of rock mass using five key parameters (Clause 2.22):

Hydraulic Conductivity (K) (Clause 2.148) defines permeability of rock mass to water, crucial for seepage and drainage analysis.

Typical UCS Classification (for reference):

Summary Diagram of BGD Parameters:

graph LR
A[Rock Mass] --> B[Rock Name (Geology)]
A --> C[Layer Thickness (L)]
A --> D[Fracture Intercept (F)]
A --> E[UCS (S)]
A --> F[Angle of Friction (A)]
A --> G[Hydraulic Conductivity (K)]

Use these parameters for consistent rock mass characterization per IS 11358.

IS 11358 focuses on terminology and basic parameters for rock mechanics but lacks detailed formulas on rock mass behavior and deformation. Based on standard rock mechanics principles, here are key points:

Key Parameters (from Clause 2.22)

• Rock Name (Geological description)
• Layer Thickness (L)
• Fracture Intercept (F)
• Uniaxial Compressive Strength (σ_c)
• Angle of Friction of Fractures (φ)

Typical Formulas for Rock Mass Behavior

1. Deformation Modulus (E_rm) of Rock Mass
   Empirical relation (Hoek & Brown): [ E_{rm} = 5000 \times \text{GSI} \times \left(\frac{\sigma_c}{100}\right) ] where GSI = Geological Strength Index.

2. Hoek-Brown Failure Criterion
   [ \sigma_1 = \sigma_3 + \sigma_c \left(m_b \frac{\sigma_3}{\sigma_c} + s \right)^a ]

   • ( \sigma_1, \sigma_3 ) = major and minor principal stresses
   • ( m_b, s, a ) = constants based on rock mass quality

3. Hydraulic Conductivity (K)
   From Clause 2.148, permeability is key for fluid flow analysis.

Typical Table: Rock Mass Quality (GSI)

flowchart LR
    A[Rock Mass Parameters] --> B[Geological Description]
    A --> C[Layer Thickness (L)]
    A --> D[Fracture Intercept (F)]
    A --> E[Uniaxial Compressive Strength (σ_c)]
    A --> F[Angle of Friction (φ)]
    B & C & D & E & F --> G[Rock Mass Behavior & Deformation]

Summary: Use rock mass parameters to estimate deformation modulus and strength via Ho

IS 11358 Key Parameters for Rock Discontinuities & Structural Features

The code defines 10 essential parameters describing discontinuities in rock masses:

Important Notes:

• Shear Strength of Discontinuity depends on roughness, wall strength, filling, and aperture.
• Block Size influences stability and excavation design.
• Orientation and spacing govern rock mass anisotropy and strength.

Typical Formula for Shear Strength (Coulomb Criterion):

[ \tau = c + \sigma_n \tan \phi ]

Where:

• (\tau) = shear strength of discontinuity
• (c) = cohesion (depends on filling and wall strength)
• (\sigma_n) = normal stress on discontinuity
• (\phi) = friction angle (affected by roughness and filling)

graph TD
A[Rock Mass] --> B[Discontinuities]
B --> C[Orientation]
B --> D[Spacing]
B --> E[Persistence]
B --> F[Roughness]
B --> G[Wall Strength]
B --> H[Aperture]
B --> I[Filling]
B --> J[Seepage]
B --> K[Number of Sets]
B --> L[Block Size]

This framework aids in rock mass classification, stability analysis, and design of rock structures per IS 11358.

IS 11358: Blasting and Excavation Key Terms & Concepts

• Blastability (Clause 2.31):

  • Definition: Index representing rock resistance to blasting.
  • Use: Helps select explosive type and charge.

• Bench Blasting (Clause 2.28):

  • Definition: Excavation in steps (benches) with blast holes drilled parallel to the free face.
  • Application: Common in quarries/open pits for controlled rock breakage.

Typical Parameters & Formulas (General Rock Mechanics Context)

Basic formula for explosive charge per hole:
[ Q = B \times S \times H \times \rho_r \times PF ]
Where:

• ( Q ) = Explosive charge per hole (kg)
• ( \rho_r ) = Rock density (kg/m³)

Conceptual Diagram: Bench Blasting Layout

graph TD
    A[Free Face] --> B[Bench 1]
    B --> C[Bench 2]
    C --> D[Bench 3]
    subgraph Blast Holes
        B --> E[Row 1 Holes]
        B --> F[Row 2 Holes]
    end

Note: IS 11358 primarily defines terms; detailed blasting design parameters are found in IS 6922 and IS 8168.

IS 11358: Rock Pressure and Ground Conditions

Key Definitions (Clauses)

• Long-Term Rock Pressure (2.181): Ultimate rock pressure acting on underground supports over time.
• Horizontal Rock Pressure (2.146): Pressure exerted horizontally on tunnel supports.
• Vertical Rock Pressure (2.254): Pressure exerted vertically on tunnel supports.

Important Formulas

1. Vertical Rock Pressure, ( P_v ):
   [ P_v = \gamma \times H ]
   Where:

   • ( \gamma ) = Unit weight of rock (kN/m³)
   • ( H ) = Depth of tunnel (m)

2. Horizontal Rock Pressure, ( P_h ):
   [ P_h = K \times P_v ]
   Where:

   • ( K ) = Lateral earth pressure coefficient (depends on rock mass properties, typically 0.3 to 1.0)

Typical Values for ( K ) (Lateral Pressure Coefficient)

Notes:

• Long-term rock pressure accounts for creep and time-dependent deformation.
• Rock pressure values guide tunnel lining and support design.

flowchart LR
    A[Depth H] --> B[Calculate Vertical Pressure \(P_v = \gamma H\)]
    B --> C[Apply Lateral Coefficient K]
    C --> D[Calculate Horizontal Pressure \(P_h = K P_v\)]
    D --> E[Design Tunnel Supports]

Use these values and formulas as a baseline; adjust based on site-specific investigations and IS 11358 guidelines.

IS 11358 mainly provides glossary and definitions in rock mechanics, not detailed design formulas or tables for failure modes and rock stability.

Key Concepts on Failure Modes (from IS 11358 & general rock mechanics):

• Shear Failure (Clause 2.276): Movement caused by shear stresses exceeding rock shear strength.
• Other common failure modes (general knowledge):
  • Tensile failure
  • Compressive failure
  • Sliding failure along discontinuities
  • Toppling failure

Common Rock Stability Checks (beyond IS 11358):

Typical Parameters:

• c = Cohesion of rock
• φ = Angle of internal friction
• σ = Normal stress on failure plane

Summary:

• IS 11358 defines terms like shear failure but does not provide design tables or formulas.
• For rock stability, use Mohr-Coulomb criterion and factor of safety calculations.
• Refer to IS 6922 or IS 9456 for detailed rock slope stability design.

flowchart TD
    A[Rock Mass] --> B{Stress Applied}
    B -->|Shear Stress > Shear Strength| C[Shear Failure]
    B -->|Normal Stress + Shear Stress| D[Sliding Failure]
    B -->|Overturning Moment > Resisting Moment| E[Toppling Failure]

For detailed design, consult specific codes like IS 6922 or rock mechanics manuals.

IS 11358 primarily provides definitions and symbols related to rock mechanics, including hydraulic and mechanical testing terms, but does not include detailed formulas or tables.

Key Points on Hydraulic and Mechanical Testing Terms in Rock Mechanics (IS 11358):

• Hydraulic Testing Terms: Include permeability, porosity, pore pressure, hydraulic conductivity.
• Mechanical Testing Terms: Include uniaxial compressive strength, tensile strength, modulus of elasticity, Poisson’s ratio.

Commonly Used Formulas (from general rock mechanics knowledge):

Typical Symbols:

• ( \sigma ): Stress (MPa)
• ( \epsilon ): Strain (dimensionless)
• ( k ): Permeability (m/s)
• ( P ): Load (N)
• ( A ): Area (m²)

For detailed testing procedures and numerical values, refer to IS 2809 (under revision) or other rock mechanics standards.

flowchart TD
    A[Rock Sample] --> B[Mechanical Testing]
    A --> C[Hydraulic Testing]
    B --> D[UCS, Tensile Strength, Modulus]
    C --> E[Permeability, Porosity, Pore Pressure]

IS 11358: Support and Protection Methods - Key Points

1. Support Types (Clause 2.334)

• Stiff Supports:

  • Minimal deflection under rock pressure
  • Examples: Concrete linings, heavy steel sections
  • Function: Provide rigid confinement

• Flexible Supports:

  • Significant deflection with rock pressure
  • Examples: Thin steel sections with gravel packing, shotcrete
  • Function: Dissipate strain energy via controlled deformation

2. Yielding Supports (Clause 2.351)

• Designed to undergo substantial deformation
• Modify stress distribution around supports
• Useful in squeezing ground conditions

3. Support Definition (Clause 2.316)

• Structural elements maintaining underground opening stability

4. Unsupported Span (Clause 2.340)

• Distance between excavation face and first support or opening width (whichever is less)
• Critical for stand-up time (time before collapse without support)

Typical Design Considerations:

flowchart LR
    ExcavationFace -->|Unsupported Span| FirstSupport
    FirstSupport -->|Support Type| StiffSupport & FlexibleSupport
    FlexibleSupport -->|Deforms| EnergyDissipation
    StiffSupport -->|Rigid| RockConfinement
    YieldingSupport -->|Deforms| StressRedistribution

Summary: Select support type based on rock behavior; stiff supports for stable rock, flexible/yielding supports for squeezing or deforming rock. Control unsupported span to ensure stability.

IS 11358: Stress and Strain Representations

Key Concepts

• Strain Ellipsoid (Clause 2.305):
  Represents strain by deforming a unit sphere into an ellipsoid.

  • Axes = Principal strains (\varepsilon_1, \varepsilon_2, \varepsilon_3)
  • Shows directional strain magnitudes.

• Stress Ellipsoid (Clause 2.312):
  Represents stress state as an ellipsoid with semi-axes proportional to principal stresses (\sigma_1, \sigma_2, \sigma_3).

  • Axes align with principal stress directions.
  • Coordinates on ellipsoid relate to stress components on planes normal to direction vectors.

• Young's Modulus (E) (Clauses 2.193 & 2.352):
  Axial modulus relating axial stress (\sigma) and axial strain (\varepsilon):
  [ E = \frac{\sigma}{\varepsilon} ]

Principal Stresses and Strains

• Stress tensor (\sigma) diagonalized to principal stresses: [ \sigma = \begin{bmatrix} \sigma_1 & 0 & 0 \ 0 & \sigma_2 & 0 \ 0 & 0 & \sigma_3 \end{bmatrix} ]

• Strain tensor (\varepsilon) diagonalized to principal strains: [ \varepsilon = \begin{bmatrix} \varepsilon_1 & 0 & 0 \ 0 & \varepsilon_2 & 0 \ 0 & 0 & \varepsilon_3 \end{bmatrix} ]

Visualization (Mermaid.js)

graph LR
    O[Origin: Unit Sphere] --> SE[Strain Ellipsoid]
    O --> ST[Stress Ellipsoid]
    SE -->|Axes = Principal Strains| ε1[ε1], ε2[ε2], ε3[ε3]
    ST -->|Axes = Principal Stresses| σ1[σ1], σ2[σ2], σ3[σ3]

Summary

• Use **strain ell

IS 11358 (1987) is primarily a glossary of terms and symbols related to rock mechanics, not a design or calculation code. It defines and standardizes terminology used across rock mechanics.

Key Points:

• No formulas or tables are directly provided in IS 11358.
• It serves as a reference for consistent use of terms in related IS codes.
• Terms cover rock properties, stresses, discontinuities, and mechanical behavior.

Common Miscellaneous Terms in Rock Mechanics (examples):

Usage:

Refer to IS 11358 for standard terminology when reading or preparing documentation and design based on other rock mechanics standards like IS 6925, IS 11282, etc.

flowchart LR
A[Rock Mass] --> B[Properties]
B --> C[Strength]
B --> D[Elasticity]
B --> E[Discontinuities]

For detailed formulas or tables, consult design codes or specialized rock mechanics standards.