Code of practice for reinforcement of rock slopes with plane wedge failure

IS 14448 Scope Summary & Key Specifications

• Scope: IS 14448 covers methods and criteria for slope stability analysis, including parameters affecting slope stability and testing procedures.

• Referenced Standards:

  IS No.	Title
  456:1978	Code of Practice for Plain and Reinforced Concrete
  4031 (Part 5):1988	Methods for Determining Initial & Final Setting Times of Hydraulic Cement
  11309:1985	Pull-out Test Method for Anchor Bars and Rock Bolts

• Partial Safety Factors (Clause 9.1.2): Use prescribed partial factors of safety for design, typically:

  • Material strength factors (γ_m)
  • Load factors (γ_f)

  (Exact values depend on the design scenario and should be taken from the relevant clause.)

• Rounding Off (IS 2:1960): Numerical results must be rounded maintaining the same significant figures as specified in IS 14448.

Typical Parameters Affecting Slope Stability:

• Soil/rock shear strength
• Slope geometry (height, angle)
• Water table position
• Load conditions

Example: Factor of Safety (FoS) for Slope Stability

[ FoS = \frac{\text{Resisting Forces or Moments}}{\text{Driving Forces or Moments}} ]

flowchart LR
    A[Slope Parameters] --> B{Stability Analysis}
    B --> C[Shear Strength]
    B --> D[Geometry]
    B --> E[Water Conditions]
    B --> F[Loads]
    C & D & E & F --> G[Factor of Safety Calculation]

For detailed formulas and partial factors, refer to Clause 9.1.2 and related sections in IS 14448.

IS 14448: Terminology and Definitions (Clause 3.1)

• This clause establishes the standard definitions used throughout the code for clarity and uniformity.
• Definitions align with related Indian Standards such as:
  • IS 456:1978 – Concrete practice
  • IS 4031 (Part 5):1988 – Cement setting times
  • IS 11309:1985 – Pull-out test methods

Key Specifications & Notes:

• Partial Safety Factors (Clause 9.1.2):
  Use specified partial factors of safety for design and testing (refer to Clause 9.1.2 for exact values).

• Rounding Off (per IS 2:1960):
  Final reported values must be rounded maintaining the same number of significant digits as the specified values.

Summary Table of Referenced Standards

This ensures consistency in terminology, testing, and reporting across structural engineering practices.

Key Formulas and Tables for Components of Rock Anchors (IS 14448)

1. Effective Fixed Anchor Length (F.A.L.)

From Clause 6.4.1:

[ L = \frac{P \times F}{n \times D \times T} ]

• L = Fixed anchor length (mm)
• P = Pull-out force per anchor (N)
• F = Factor of safety (3 to 5 recommended)
• n = Number of anchors (usually 1)
• D = Diameter of borehole (bar diameter + 30 mm) (mm)
• T = Bond stress at failure (N/mm²)

2. Safe Bond Strength (T/F) for Rock Conditions (Table 2)

3. Fixed Anchor Length (F.A.L.) Based on Rock Quality (Table 1)

• Minimum F.A.L. = 60d for deformed bars, 100d for plain bars (d = bar diameter)

4. Length of Rock Bolts on Slope (Clause 9.2.1.4)

[ L = \frac{N \times S \times \sin(VI - W_p)}{\cos \theta} + F.A.L. ]

• (N), (S), (VI), (

IS 14448: Modes of Failure and Stability Requirements

Modes of Failure (Clause 4.2)

• Three main types:
  • Planar Slide
  • 3D Wedge Failure
  • Toppling Failure
• Code focuses on: Plane wedge failure (refer Fig. 1 in the code).

Stability Requirements & Partial Safety Factors (Clause 9.1.2)

• Use prescribed partial factors of safety for design (values in the code, typically ≥ 1.5 for sliding).

Fixed Anchor Length (Clause 3.7 & Table 1)

• Anchor length (F.A.L.) depends on rock quality (RMR):

• Minimum F.A.L. based on bar diameter (d_s):
  • Deformed bars: ≥ 60 d_s
  • Plain bars: ≥ 100 d_s

Summary Formula for Fixed Anchor Length:

[ F.A.L. = \max(\text{Length from Table 1}, \quad \text{60} d_s \text{ or } 100 d_s) ]

flowchart TD
  A[Rock Slope] --> B{Failure Modes}
  B --> C[Planar Slide]
  B --> D[3D Wedge Failure]
  B --> E[Toppling Failure]

  F[Anchor Design] --> G[Determine RMR]
  G --> H{Select F.A.L.}
  H --> I[2 m for RMR 81-100]
  H --> J[3 m for RMR 61-80]
  H --> K[4 m for RMR 21-60]
  H --> L[6 m for RMR 0-20]
  H --> M[Check min length: 60d_s or 100d_s]

This ensures stability against wedge failure with adequate anchorage length and safety factors

IS 14448: Principles of Rock Reinforcement - Key Points

1. When is Rock Reinforcement Needed? (Clause 10.4)

• Static Factor of Safety (FOS) < 1.2
• Dynamic Factor of Safety < 1.0
• Even after ensuring complete drainage, reinforcement is necessary if these limits are not met.

2. Critical Plane Assessment (Clause 4.2.5)

• Use kinematic model analysis or stereographic plots to identify the most likely sliding plane relative to the slope face.

3. Parameters Affecting Rock Reinforcement (Clause 5.4)

• Density of reinforcement depends on:
  • Diameter (d) of anchors
  • Length (L) of anchors
  • Spacing (S) between anchors
• Can be combined with shotcreting and drainage for improved stability.

4. Bond Strength for Design (Clause 8.4)

• Use bond strength values from pull-out tests:
  • ( t_f ) = bond strength between grout and rock
  • ( T_a ) = bond strength between grout and steel anchor
• These values are critical for redesigning rock anchors.

Typical Formula for Pull-Out Capacity:

[ P = \pi \times d \times L \times t_f ]

Where:

• ( P ) = Pull-out capacity (force)
• ( d ) = Diameter of anchor
• ( L ) = Length of anchor embedded in rock
• ( t_f ) = Bond strength (from tests)

Summary Table: Rock Reinforcement Design Parameters

flowchart TD
    A[Assess Slope Stability] --> B{FOS < Limits?}
    B -- Yes --> C[Perform

Design Considerations for Rock Anchors (IS 14448)

1. Fixed Anchor Length (F.A.L.) (Clause 3.7)

• Minimum F.A.L. based on bar type:

  • Deformed bars: ≥ 60 × diameter (d)
  • Plain bars: ≥ 100 × diameter (d)

• Recommended F.A.L. based on Rock Mass Rating (RMR):

2. Length of Anchorage (L) Calculation (Clause 6.4.1)

[ L = \frac{P \times F}{n \times D \times r} ]

Where:

• L: Effective anchor length (mm)
• P: Pull-out force (N)
• F: Factor of safety (3 to 5 recommended)
• n: Bond stress at failure (N/mm²)
• D: Borehole diameter (d + 30 mm)

3. Safe Bond Strength (T) for Preliminary Design (Table 2)

4. Pull-out Test (Clause 5.5.2)

• Conducted as per IS 11309 to verify anchor load capacity and validate design assumptions.

flowchart TD
    A[Determine Rock Condition] --> B{RMR Value}
    B -->|81-100| C[Set F.A.L = 2

IS 14448: Installation Procedures for Rock Anchors

Key Specifications & Formulas

1. Fixed Anchor Length (F.A.L.) — Clause 3.7

• Definition: Length of rock-anchor transmitting tensile forces to rock.
• Minimum Length:
  • Deformed bars: ≥ 60 × diameter (d_s)
  • Plain bars: ≥ 100 × diameter (d_s)

2. Bearing Failure Prevention — Clause 6.4.4

• Use large bearing plates founded on thin grout layers over a large contact area to minimize bearing failure at anchorage face.

3. Partial Factors of Safety — Clause 9.1.2

• Apply appropriate partial safety factors as per design requirements (refer to IS 456 for concrete, IS 14448 for anchors).

Summary Diagram: Installation Concept

flowchart LR
    A[Anchor Bar] --> B[Fixed Anchor Length (F.A.L.)]
    B --> C{Rock Condition}
    C -->|Very Good| D[2 m]
    C -->|Good| E[3 m]
    C -->|Fair/Poor| F[4 m]
    C -->|Very Poor| G[6 m]
    H[Grouting] --> I[Thin grout layer]
    I --> J[Large bearing plate]
    J --> K[Rock Face]

References:

• IS 456: Concrete design
• IS 4031 (Part 5): Cement setting times
• IS 11309: Pull-out tests for anchors

This ensures rock anchors are installed with adequate length and bearing capacity for safety and durability.

IS 14448: Testing and Quality Control - Key Points

• Referenced Standards for Testing:

  • IS 456:1978 – Concrete mix design and testing.
  • IS 4031 (Part 5):1988 – Cement setting times.
  • IS 11309:1985 – Pull-out test for anchor bars and rock bolts.

• Tests to be Conducted (Clause 5.5):

  • Physical tests on cement and concrete as per referenced IS codes.
  • Pull-out tests for anchorage strength.
  • Setting time tests for cement.

• Rounding Off Results:

  • Follow IS 2:1960 for rounding numerical values.
  • Maintain the same number of significant digits as specified.

Typical Quality Control Tests in IS 14448 Context:

Example: Pull-out Test Formula (IS 11309)

[ P = \frac{F}{A} ]

• P = Pull-out stress (MPa)
• F = Load at failure (N)
• A = Cross-sectional area of anchor bar (mm²)

flowchart LR
    A[Material Sampling] --> B[Physical Testing]
    B --> C{Test Type}
    C --> D[Cement Setting Time (IS 4031)]
    C --> E[Pull-out Test (IS 11309)]
    C --> F[Concrete Strength (IS 456)]
    D --> G[Report Results]
    E --> G
    F --> G
    G --> H[Apply Rounding (IS 2:1960)]
    H --> I[Quality Control Approval]

Summary: IS 14448 mandates testing per referenced IS codes, with proper rounding of results. Pull-out and setting time tests are key for quality assurance.

IS 14448: Design of Rock Reinforcement Systems - Key Points

1. Bond Strength for Redesign (Clause 8.4)

• Use bond strength (tf) between grout and rock or bond strength (Ta) between grout and steel anchor from pull-out tests for redesign.
• Pull-out test per IS 11309 (Clause 5.5.2) assesses anchor load capacity and verifies design assumptions.

2. When is Rock Reinforcement Needed? (Clause 10.4)

• Reinforcement required if:
  • Static Factor of Safety (FOS) < 1.2
  • Dynamic Factor of Safety < 1.0
• Even after complete drainage of water.

3. Design of Rock Anchors (Clause 9.2)

• Design anchors considering:
  • Bond strength from pull-out tests.
  • Load transfer mechanism between grout-rock and grout-steel.
  • Factor of safety on bond strength.
  • Anchor length and diameter based on required load capacity.

4. Typical Formula for Bond Capacity

[ P_b = \pi d L t_f ]

Where:

• (P_b) = bond capacity (N)
• (d) = diameter of anchor (m)
• (L) = bonded length of anchor (m)
• (t_f) = bond strength (N/m²) from pull-out test

5. Pull-out Test Reference (IS 11309)

• Determines bond strength and ultimate anchor load.
• Ensures design load (F_{design} \leq P_b / \text{Factor of Safety}).

flowchart TD
    A[Assess Rock Stability] --> B{FOS Static < 1.2 or Dynamic < 1.0?}
    B -- Yes --> C[Conduct Pull-out Test (IS 11309)]
    C --> D[Obtain Bond Strength (tf or Ta)]
    D --> E[Design Rock Anchor]
    E --> F[Calculate Bond Capacity: Pb = π d L tf]
    F --> G[Check Load <= Pb / FOS]
    G --> H[Implement Rock Reinforcement]
    B -- No --> I[No Reinforcement Needed]

IS 14448: Drainage System for Stabilized Slopes

Key Specifications & Formulas

• When to Provide Drainage (Clause 10.2):

  • If static factor of safety (F_s) > 1.2 and dynamic factor of safety (F_d) > 1.0 → Drainage system needed.
  • If F_s ≤ 1.2 or F_d ≤ 1.0 → Provide both rock anchors and drainage.

• Drain Hole Details (Clause 10.3):

  • Diameter (d) = 38 mm
  • Inclination = 10° dip towards valley
  • Spacing = 3 m x 3 m grid
  • Drain holes fitted with rolled wire net tubes for stability.

• Catch Drain (Clause 10.3.1):

  • Provide at toe of cut slope to collect and drain water.
  • Immediate drainage required if seepage occurs during normal seasons.

• Rock Anchor Length (Clause 9.3):

  • Minimum anchor length ( L_a \geq 0.2H ) (H = slope height)
  • Verify stability at extended plane beyond anchors.

Summary Table for Drain Holes

Conceptual Diagram of Drainage Layout

graph LR
    A[Slope Crest] --> B[Slope Face]
    B --> C[Drain Holes (38 mm dia, 10° dip)]
    C --> D[Catch Drain at Toe]
    D --> E[Valley / Outflow]

Note: Proper drainage reduces pore water pressure, increasing slope stability and safety factors.

IS 14448 - Computer Aided Design (Clause 11)

• Software Usage:

  • SASP: For general slope stability analysis.
  • WEDGE: Specialized for 3D wedge failure analysis in rock-reinforcement design.

• Key Points:

  • Computer programs complement manual design by handling complex geometries and failure modes.
  • Design principles remain consistent; software automates calculations and iterations.

• Related IS References:

  • IS 456: Concrete design.
  • IS 11309: Pull-out test methods for anchors.
  • Bond strength values from pull-out tests (Clause 8.4) are essential input parameters for software.

Typical Parameters for Rock-Anchor Design (from IS 14448 & related standards):

Conceptual Workflow for Computer-Aided Rock Slope Design

flowchart TD
    A[Input Geological & Geotechnical Data] --> B[Define Geometry & Load Conditions]
    B --> C[Select Design Software (SASP/WEDGE)]
    C --> D[Input Parameters: Bond Strength, Anchor Length, Spacing]
    D --> E[Run Stability Analysis & Failure Mode Identification]
    E --> F[Evaluate Results & Optimize Design]
    F --> G[Generate Design Reports & Drawings]

Summary: IS 14448 endorses use of specialized software (SASP, WEDGE) for rock slope and reinforcement design, using bond strength data from pull-out tests (IS 11309) as critical input. Manual design principles apply; software enhances precision and efficiency.

IS 14448: Committee Composition Summary

Committee: Rock Mechanics Sectional Committee, CED 48
Purpose: Formulation and review of standards related to rock mechanics and rock slope engineering.

Key Points on Committee Composition (Annex A):

• Chairman: Prof. Bhawani Singh, University of Roorkee
• Member Secretary: Central Board of Irrigation and Power, New Delhi
• Members: Experts from diverse organizations including:
  • Universities (Roorkee, IIT Delhi, IIT Kanpur)
  • Government departments (Irrigation, Geological Survey, Central Water & Power Research)
  • Research Institutes (CSIR labs, National Geophysical Research Institute)
  • Industry representatives (Asia Foundations, Hindustan Construction Co., Naptha Jhakri Power)
  • Personal capacities (experienced professionals)
• Subcommittee on Rock Slope Engineering and Foundation on Rock:
  • Convener: Dr. P. K. Jain (University of Roorkee)
  • Members represent research, academia, government, and industry.

Specifications:

• The committee includes multi-disciplinary experts ensuring comprehensive standard development.
• Members have alternate representatives for continuity.
• The committee structure supports collaborative and peer-reviewed standard formulation.

Visual Summary (Mermaid Diagram):

graph TD
    A[Rock Mechanics Sectional Committee, CED 48]
    A --> B[Chairman: Prof. Bhawani Singh]
    A --> C[Member Secretary: Central Board of Irrigation and Power]
    A --> D[Members]
    D --> D1[Academia (IITs, Universities)]
    D --> D2[Government Departments]
    D --> D3[Research Institutes (CSIR, NGRI)]
    D --> D4[Industry Representatives]
    A --> E[Subcommittee: Rock Slope Engineering]
    E --> E1[Convener: Dr. P.K. Jain]
    E --> E2[Members from research, govt, industry]

This composition ensures expertise across academia, research, government, and industry, critical for robust and practical standards in rock mechanics and slope engineering.