The quantitative classification system of rock mass-Guidelines, Part 3: Determination of slope mass rating

IS 13365 Part 3: Scope Summary

• Scope: Part 3 focuses on the Determination of Slope Mass Rating (SMR), a quantitative classification system for rock masses related to slope stability assessment.

• Purpose: To provide guidelines for evaluating rock mass conditions influencing slope design and stability.

• Key Concept: SMR modifies the Rock Mass Rating (RMR) based on slope orientation and discontinuity characteristics.

Key Formula: Slope Mass Rating (SMR)

[ \text{SMR} = RMR_b + F_1 + F_2 + F_3 ]

• RMR_b: Basic Rock Mass Rating (from IS 13365 Part 1)
• F1, F2, F3: Adjustment factors based on:
  • F1: Orientation of discontinuities relative to slope face
  • F2: Parallelism between discontinuities and slope face
  • F3: Excavation method and slope geometry

Typical Adjustment Factors (Example):

Notes:

• Use IS 2:1960 for rounding final numerical values.
• SMR helps in designing stable rock slopes by quantifying rock mass quality and structural orientation.

flowchart LR
    RMR_b --> SMR
    F1 --> SMR
    F2 --> SMR
    F3 --> SMR
    SMR --> Slope_Stability_Design

For detailed tables and factor values, refer to IS 13365 Part 3 text.

Estimation of Rock Mass Rating (RMR basic) - IS 13365 Part 3

RMR basic is the sum of ratings from five key parameters (Clause 3.1, Table 1):

Slope Mass Rating (SMR) Calculation (Clause 3.4):

[ \boxed{ \text{SMR} = \text{RMR}_{basic} + (F_1 \times F_2 \times F_3) + F_4 } ]

• F1, F2, F3: Adjustment factors based on discontinuity orientation relative to slope (Table 2).
• F4: Adjustment for excavation method (Table 3).

Adjustment Factors for Joints (Table 2 Summary):

Excavation Method Adjustment (F4) - Table 3:

Stability Classification Based on SMR (Clause 3.4):

Determination of Failure Modes in Rock Slopes (IS 13365 Part 3)

Key Points:

• Failure modes depend on geological discontinuities; main types are Plane Failure, Wedge Failure, and Toppling Failure.
• Field Data Collection: 100-500 discontinuity readings plotted on an equal area stereonet to identify pole concentration maximas indicating failure mode (Fig. 1).

Failure Mode Identification

Rating System for Rock Mass (RMRbasic) [Table 1]

Adjustment Ratings for Joints (F1, F2, F3) [Table 2]

Adjustment for Excavation Method (F4) [Table 3]

| Method

Estimation of Slope Mass Rating (SMR) as per IS 13365 Part 3

Key Formula:

[ \boxed{ \text{SMR} = \text{RMR}_{basic} + (F_1 \times F_2 \times F_3) + F_4 } ]

• RMR_basic: Basic Rock Mass Rating (from IS 13365 Part 1)
• F1, F2, F3, F4: Adjustment factors based on slope geometry and discontinuity characteristics

Stability Classification (Table 4):

Notes:

• F1, F2, F3 are multiplicative factors modifying RMR_basic based on orientation of discontinuities relative to slope face.
• F4 is an additive correction factor for special conditions (e.g., groundwater, weathering).
• SMR is widely used for landslide hazard zonation and slope stability assessment in rock masses.

If you need detailed values or charts for F1, F2, F3, and F4, please specify.

Key Formulas & Tables from IS 13365 Part 3: Adjustment Ratings for Joints & Excavation Methods

1. Slope Mass Rating (SMR) Formula:

[ \boxed{ \text{SMR} = \text{RMR}_{basic} + (F_1 \times F_2 \times F_3) + F_4 } ]

• RMRbasic: Rock Mass Rating from 5 parameters (strength, RQD, spacing, condition, groundwater).
• (F_1, F_2, F_3): Adjustment factors based on joint-slope geometry.
• (F_4): Adjustment for excavation method.

2. Adjustment Factors for Joints (Table 2):

• (a_s): slope dip direction
• (a_j): joint dip direction
• (B_j): joint dip
• (B_s): slope dip

3. Adjustment Rating for Excavation Methods (Table 3):

| Method | (

IS 13365 Part 3: Collection of Field Data & Stereonet Analysis

1. Collection of Field Data (Clause 3.2.4)

• Take 100 to 500 readings of geological discontinuities on rock slopes.
• Plot poles on an equal area stereonet.
• Contour pole concentrations to identify maxima indicating failure modes.
• Failure modes identified by pole concentration patterns:
  • Plane failure (Fig.1a)
  • Wedge failure (Fig.1b)
  • Toppling failure (Fig.1c)

2. Key Failure Mode: Wedge Failure (Clause 3.2.2)

• Occurs along two intersecting discontinuities.
• Line of intersection dips towards slope but plunge < slope inclination.
• More frequent than planar slides.

3. Rock Mass Rating (RMR) Basic Parameters (Table 1)

4. Adjustment Ratings for Rock Slopes (Table 2 & 3)

• Adjustment factor = F1 × F2 × F3 + F4
• F1, F2, F3 depend on slope and discontinuity orientation.
• F4 depends on excavation method.

5. SMR Calculation Formula:

[ \boxed{ SMR = RMR_{basic} + (F_1 \times F_2 \times F_3) + F_4 } ]

Stereonet Concept (Mermaid Diagram):

graph LR
A[Field Data: Geological Discontinuities] --> B[Plot Poles on Equal Area Stereonet

Slope Mass Rating (SMR) - IS 13365 Part 3

Key Formula:

[ \boxed{ \text{SMR} = \text{RMR}_{basic} + (F_1 \times F_2 \times F_3) + F_4 } ]

• RMR_basic: Basic Rock Mass Rating from IS 13361 (Part 1).
• F1, F2, F3: Adjustment factors related to discontinuity orientation, mode of failure, and excavation method.
• F4: Adjustment for seepage and weathering effects.

Classification of Slope Stability (Table 4):

Notes:

• SMR incorporates joint orientation, fracture spacing, seepage, weathering, and excavation method.
• Used for preliminary slope stability assessment and landslide hazard zonation.
• Failure modes considered: Planar slide, wedge slide, toppling failure.

Conceptual flow of SMR calculation:

flowchart TD
    A[RMR_basic] --> B[Calculate F1 (Orientation)]
    A --> C[Calculate F2 (Failure Mode)]
    A --> D[Calculate F3 (Excavation Method)]
    A --> E[Calculate F4 (Seepage & Weathering)]
    B & C & D --> F[Multiply F1 × F2 × F3]
    F & E & A --> G[Calculate SMR]
    G --> H[Classify Slope Stability]

For detailed factor values (F1, F2, F3, F4), refer to IS 13365 Part 3 tables specifying adjustment factors based on joint-slope angle, excavation method, and failure mode.

Determination of Safe Cut Slope Angle (IS 13365 Part 3)

IS 13365 (Part 3) provides a systematic approach to evaluate rock slope stability using the Slope Mass Rating (SMR) method, which helps determine safe slope angles.

Key Formulas:

1. Slope Mass Rating (SMR):

[ \boxed{ \text{SMR} = \text{RMR}_{basic} + (F_1 \times F_2 \times F_3) + F_4 } ]

• RMR_basic: Basic Rock Mass Rating (Table 1)
• F1, F2, F3: Adjustment factors based on discontinuity orientation (Table 2)
• F4: Adjustment for excavation method (Table 3)

Important Tables:

(Refer Table 1 for full RMR_basic ratings)

(See Table 2 for detailed angle ranges)

Stability Classification Based on SMR:

Remedial Measures for Unstable Slopes (IS 13365 Part 3)

1. Slope Stability Classification (Clause 3.4 & Table 4)

Slope Mass Rating (SMR) is calculated as:

[ \text{SMR} = \text{RMR}_{basic} + (F_1 \times F_2 \times F_3) + F_4 ]

• SMR Stability Classes:
  • Fully stable: 81–100
  • Stable: 61–80
  • Partially stable: 41–60
  • Unstable: 21–40
  • Very unstable: <20

2. Remedial Measures (Clause 3.5)

• Very unstable slopes (<20 SMR): Require re-excavation or major corrective works.
• Unstable slopes (21–40 SMR): Need extensive corrective measures.
• Partially stable slopes (41–60 SMR): Use systematic supports such as:
  • Rock bolts
  • Rock anchors
• Stable to fully stable slopes (>60 SMR): Occasional or no support required.

3. Key Parameters for RMR_basic (Table 1 Summary)

4. Typical Supports for Partially Stable Slopes

• Rock bolts/anchors: Increase slope stability by reinforcing rock mass.
• Drainage measures: Reduce pore water pressure.
• Shotcrete or mesh: Surface protection against weathering.

flowchart TD
    A[Assess Slope] --> B[Calculate RMR_basic]
    B --> C[Calculate SMR = RMR_basic + (F1*F

IS 13365 Part 3 (1997) primarily deals with rock mechanics testing procedures and references related Indian Standards for consistency and accuracy.

Key References to Related Indian Standards:

• IS 2:1960 — Rules for rounding off numerical values: Specifies how to round off test results or calculated values.
• Other related IS codes commonly referenced in rock mechanics and testing include:
  • IS 1121 series — Methods of test for soils (for geotechnical context)
  • IS 456:2000 — Plain and reinforced concrete code (for structural context)
  • IS 13827:1993 — Code of practice for rock excavation
  • IS 1893 — Criteria for earthquake resistant design (relevant for rock stability)

Rounding Off Rule (IS 2:1960):

• Round off to the nearest value based on the digit following the last significant figure.
• If the digit is ≥5, increase the last retained digit by 1; if <5, leave it unchanged.

Example:
Value = 12.3456, round to 3 decimals → 12.346
Value = 12.3444, round to 3 decimals → 12.344

Summary:

• Use IS 2:1960 for rounding.
• Refer to related IS codes for complementary tests and design criteria.
• Always cite these standards when reporting test results per IS 13365 Part 3.

flowchart LR
    A[IS 13365 Part 3] --> B[Testing Procedures]
    B --> C[Use IS 2:1960 for Rounding]
    B --> D[Refer to IS 1121, IS 456, IS 13827]
    D --> E[Geotechnical & Structural Design]

IS 13365 Part 3: Annex A - Technical Committee Composition

Annex A lists the detailed composition of the Rock Mechanics Sectional Committee, CED 48, responsible for formulating this standard.

Key Points:

• Chairman: Prof. Bhawani Singh, University of Roorkee
• Member Secretary: Shri W. R. Paul, Joint Director (Civil Engg), BIS
• Members: Experts from diverse organizations including:
  • Irrigation Departments (Roorkee, Haryana, Gujarat, Maharashtra)
  • Central Mining Research Institute (CSIR)
  • Geological Survey of India
  • Central Water and Power Research Station
  • Indian Institutes of Technology (Roorkee, Delhi, Kanpur)
  • National Thermal Power Corporation
  • Central Building Research Institute (CSIR)
  • Various private sector engineering firms and research institutes

Purpose of Annex A:

• Ensures multidisciplinary expertise in rock mechanics and slope stability.
• Includes academia, government bodies, research institutes, and industry professionals.
• Supports development of robust, practical standards for rock engineering.

Summary Table (Excerpt)

This committee composition ensures the standard reflects state-of-the-art knowledge and practical experience in rock mechanics and slope stability.

graph TD
    A[Technical Committee CED 48] --> B(Chairman: Prof Bhawani Singh)
    A --> C(Member Secretary: Shri W. R. Paul)
    A --> D[Members]
    D --> E(Irrigation Departments)
    D --> F(CSIR Institutes)
    D --> G(Indian Institutes of Technology)
    D --> H(Geological Survey of India)
    D --> I(Power Corporations)
    D --> J(Private Engineering Firms)

For detailed member names and affiliations, refer to Annex A in IS 13365 (Part 3):1997.