monitoring of rock movement using multi-point borehole extensometers-Guidelines

IS 13414: Scope & Key Specifications

• Scope:
  IS 13414 provides guidelines for monitoring rock movements using Multi-Point Borehole Extensometers (MPBX). It covers data collection, analysis, and interpretation to assess rock mass stability.

• Key Data Sheet (Annex A, Clause 5.2):
  Standard format for recording observations includes:

  Parameter	Description
  Project Name	Identification of project
  Date of Installation	When MPBX was installed
  Date of Excavation	Excavation start date
  Type of Rock Mass	Geological classification
  Angle of Borehole	Borehole inclination angle
  Depth of Anchors	Length of anchors in borehole
  Date & Time of Observations	Time-stamped displacement readings (mm) per anchor point

• Data Analysis (Clause 6.3):

  • Rate of Relative Displacement vs. Time plot (Fig. 5) is used to infer stability:
    • Curve 1 → Stability
    • Curves 2 & 3 → Instability

• Remarks for Observations:

  • Note joint/shear zones
  • Record repositioning of reference points or rod adjustments
  • Log blasting, excavation, or support installation times

• Rounding Off:
  Follow IS 2:1960 for numerical rounding rules.

Summary Table for Monitoring Data

graph LR
A[Rock Mass] --> B[Multi-Point Borehole Extensometer]
B --> C[Anchors at Various Depths]
C --> D[Displacement Measurements]
D --> E[Data Analysis]
E --> F{Stability Assessment}
F -->|Curve 1| G[Stable]
F -->|Curves 2 & 3| H[Unstable]

This standard ensures consistent,

IS 13414 - Key References, Formulas, and Tables

1. Data Analysis (Clause 6.3)

   • Stability inferred from plots of Rate of Relative Displacement vs Time:
     • Curve 1 → Stability
     • Curves 2 & 3 → Instability
   • Use these plots to monitor rock mass movement and structural behavior.

2. Annex A - Standard Data Sheet for Rock Movement Monitoring

   • Records include:
     • Project details, rock type, borehole angle, anchor depth.
     • Periodic observations of displacement (An1, An2, An3, An4) in mm.
     • Remarks on joints/shear zones, blasting, excavation, support installation.
   • Essential for systematic monitoring and analysis.

3. Rounding Off

   • Follow IS 2:1960 for rounding numerical values in reports.

4. Glossary

   • Refer IS 11358:1987 for terms and symbols related to rock mechanics.

Sample Data Sheet Format (Annex A)

Summary Diagram: Rock Movement Monitoring Workflow

flowchart TD
    A[Project Setup] --> B[Installation of Anchors]
    B --> C[Periodic Observations]
    C --> D[Data Recording (Annex A)]
    D --> E[Plot Rate of Relative Displacement]
    E --> F{Curve Analysis}
    F -->|Curve 1| G[Stable Structure]
    F -->|Curves 2 or 3| H[Instability Detected]
    H --> I[Take Corrective Action]

Note: For detailed formulas and stability criteria, refer to the full IS 13414 text and related rock mechanics standards.

IS 13414 Definitions - Key Points

• Reference Standard: Definitions follow IS 11358:1987 (Glossary of terms and symbols for rock mechanics).

• Data Analysis (Clause 6.3):

  • Stability inferred from rate of relative displacement curves (Fig. 5):
    • Curve 1 → Stability
    • Curves 2 & 3 → Instability

• Standard Data Sheet (Annex A, Clause 5.2):
  Used for rock movement monitoring with MPBX (Multipoint Borehole Extensometer). Key fields include:

  • Project details (name, installation, excavation dates)
  • Rock mass type, borehole angle, anchor depth
  • Observations table with displacement readings (An1 to An4) and remarks

• Rounding Off: Follow IS 2:1960 for numerical rounding rules.

Summary Table: Stability from Rate of Relative Displacement

Important Notes:

• Always consult IS 11358:1987 for precise terminology.
• Use the standard data sheet for systematic monitoring and reporting.
• Ensure rounding conforms to IS 2:1960 for consistency.

flowchart LR
    A[Rock Movement Monitoring] --> B[Data Collection]
    B --> C[Rate of Relative Displacement]
    C --> D{Curve Type}
    D -->|Curve 1| E[Stable]
    D -->|Curve 2 or 3| F[Instability]

This concise framework ensures clarity in definitions and monitoring per IS 13414.

IS 13414 — Instrument/Equipment Key Points

1. Displacement Sensors (Clause 4.3.4)

• Types:
  • Mechanical: depth micrometer, dial gauge, vernier callipers.
  • Electrical: LVDT, rotary/linear potentiometers, vibrating wire, resistance strain gauges.
• Preferred: LVDT or vibrating wire sensors for stable long-term and computerized data acquisition.
• Cross-check: Use mechanical sensors periodically to verify electrical sensor reliability.

2. Installation Procedure for Multi-point Borehole Extensometer (Clause 5.2)

• Select borehole location, length, number of anchors based on site and instrumentation purpose.
• Drill borehole with diamond coring drill; clean before installation.
• Fix anchors by grouting; allow 24 hours for grout to harden.
• Use breather tube in upward boreholes to remove air during grouting.
• Use super invar rods for temperature stability if collar head is on surface or in slopes.
• Check LVDT and readout units before connecting.
• Record readings in standard data sheet (Annex A).

3. Standard Data Sheet (Annex A)

• Include joint/shear zone info, repositioning details, blast/excavation dates.

Summary Diagram: Sensor Selection & Installation Flow

flowchart TD
    A[Select Sensor Type] --> B{Mechanical or Electrical?}
    B -->|Mechanical| C[Use dial gauge/vernier]
    B -->|Electrical| D[LVDT or Vibrating Wire Preferred]
    D --> E[Cross-check with Mechanical Sensor]
    F[Installation Procedure] --> G[Drill Borehole]
    G --> H[Clean Borehole]
    H --> I[Fix Anchors by Grouting]
    I --> J[Allow 24 hrs for Grout Hardening]
    J --> K[Insert Breather Tube if Upward Borehole]
    K --> L[Connect Sensors & Check Calibration]
    L --> M[Record Data in Standard Sheet]

Note: Use super invar rods for temperature compensation when collar head is exposed

IS 13414: Classification & Specifications for Borehole Extensometers

1. Classification by Material & Usage (Clause 4.3.2.3)

• Wires:
  • Used for short-term (≤ 3 months)
  • Max depth: 10 m
  • Only in vertical boreholes
  • Require fixed tension at each observation
• Mild Steel Rods:
  • Suitable for observations up to 1 year
• Stainless Steel Rods:
  • Essential for observations > 1 year
  • Required for precise measurements

2. Dimensions & Tension (Clause 4.3.2.4)

• Wire Tension:
  • In-situ: Applied via coil or leaf spring (variable tension)
  • Other measurements: Constant tension via dead weight or spring balance

3. Components of Multi-Point Borehole Extensometer (Clause 4.3)

• Rods or wires
• Collar head
• Displacement sensors
• Anchorage (e.g., expansion shell, prongs)

4. Anchorage Types (Fig. 2)

• Prongs type
• Expansion shell with screw plug

flowchart TD
    A[Multi-Point Borehole Extensometer] --> B[Rods or Wires]
    A --> C[Collar Head]
    A --> D[Displacement Sensors]
    A --> E[Anchorage]
    E --> F[Prongs Type]
    E --> G[Expansion Shell]

Summary: Use rods for long-term and deep boreholes; wires for short-term and shallow vertical holes. Maintain recommended diameters and tension methods for reliable measurements.

IS 13414: Multi-point Borehole Extensometer (MPBX) Key Components & Specifications

Components (Clause 4.3)

• Rods or Wires:
  • Wires: For short-term (≤3 months), vertical boreholes, max depth 10 m, require fixed tension.
  • Mild Steel Rods: For observations up to 1 year.
  • Stainless Steel Rods: For >1 year and precise measurements.
• Collar Head: Provides reference and support at borehole mouth.
• Displacement Sensors: Measure relative movement between anchors and reference collar.
• Anchorage Types (Fig. 2):
  • Prongs Type
  • Expansion Shell with Screw Plug

Types of Extensometers (Clause 4.2.2)

• Single-point (SPBX): 1 anchor
• Double-point (DPBX): 2 anchors
• Multi-point (MPBX): >2 anchors

Installation Notes (Fig. 3)

• Anchors are grouted or expansion type.
• Outer protective shell for rods/wires.
• Electric readout unit for displacement measurement.

Summary Table: Rod/Wire Usage

flowchart LR
    A[Multi-point Borehole Extensometer] --> B[Rods or Wires]
    A --> C[Collar Head]
    A --> D[Displacement Sensors]
    B --> E[Wire (Short-term, ≤10m)]
    B --> F[Mild Steel Rod (Up to 1 year)]
    B --> G[Stainless Steel Rod (>1 year)]
    C --> H[Reference Collar]
    D --> I[Electric Readout Unit]

This structure ensures reliable rock movement monitoring per IS 13414 guidelines.

IS 13414: Anchorage Types & Movement Transferring Elements

Anchorage Types (Clause 4.2.4)

• Mechanical Anchors:

  • Expansion shell type
  • Prong type
    (See Fig. 2 in IS 13414)

• Grouted Anchors:

  • Anchors grouted into borehole
  • Movement transferring elements kept free inside rigid PVC pipes

Movement Transferring Elements (Clause 4.2.1 & 4.3.2.1)

• Wire type: Wire connects anchors to borehole collar (Fig. 1A)

• Rod type: Rod connects anchors to borehole collar

• Probe type: No direct connection; probe measures displacement

• Rods/wires are placed inside rigid PVC pipes for free movement.

• Use spacers to align and position PVC pipes.

• Rods should be threaded at both ends for joining.

Key Specifications

Important Notes

• Movement elements must allow free displacement inside PVC pipes.
• Proper alignment with spacers prevents jamming.
• Threaded rods enable modular length adjustment.

Illustration of Movement Transferring Element Setup

graph LR
A[Anchor] -->|Rod/Wire| B(PVC Pipe)
B --> C[Borehole Collar]
subgraph Borehole
B
end

This setup allows accurate displacement measurement while isolating anchors from collar movement.

For detailed data recording, refer to Annex A standard data sheet for rock movement monitoring.

Summary:
Use mechanical or grouted anchors with rods or wires as movement elements inside PVC pipes. Ensure free movement and alignment for reliable displacement monitoring as per IS 13414.

IS 13414 - Displacement Sensors: Key Points & Formulas

Types of Displacement Sensors (Clause 4.3.4)

• Mechanical: Depth micrometer, dial gauge, vernier calipers.
• Electrical:
  • LVDT (Linear Variable Differential Transformer) — preferred for stable, long-term measurements.
  • Rotary/linear potentiometers.
  • Vibrating wire or resistance strain gauges (also stable for long-term use).

Recommendation: Use electrical sensors with mechanical backups for cross-checking reliability.

Measurement & Data Correction (Clause 6.1)

• Mechanical sensors: Direct reading = displacement.
• Electrical sensors: Reading must be corrected using calibration charts.
• Permissible error: ±0.002 mm.

Multi-point Borehole Extensometer Components (Clause 4.3)

• Rods/wires
• Collar head
• Displacement sensors

Data Analysis (Clause 6.3)

• Plot relative displacement vs. time.
• Stability indicated by curve trends (see Fig. 5 in IS 13414).

Calibration & Data Sheet (Annex A)

• Record date/time, anchor depths, rock type, borehole angle.
• Note joint/shear zones and events like blasts or support installation.
• Use standardized data sheets for consistency.

Summary Table: Displacement Sensor Selection

flowchart TD
    A[Displacement Sensors] --> B[Mechanical]
    A --> C[Electrical]
    B --> D[Dial Gauge]
    B --> E[Micrometer]
    C --> F[LVDT]
    C --> G[Vibrating Wire]
    C --> H[Potentiometer]

Use IS 13414 guidelines for sensor selection, installation, calibration, and data analysis to ensure precise rock movement monitoring.

IS 13414: Installation Procedure for Multi-point Bore Extensometer (MPBX)

Key Steps (Clause 5.2)

1. Site Selection & Preparation

   • Decide borehole location, orientation, length, and number of anchors based on site and instrumentation purpose.
   • Keep collar head inside underground opening to avoid temperature effects.
   • Use Super Invar rods for boreholes on ground surface or slopes.

2. Drilling & Cleaning

   • Drill borehole to required depth with diamond coring drill.
   • Clean borehole thoroughly before installation.

3. Anchor Placement

   • Fix anchors at designated depths considering stability and geological discontinuities.
   • Use grouting for anchorage; allow minimum 24 hours for grout to set before sensor installation.
   • Insert a PVC breather tube for upward holes to vent air during grouting.

4. Sensor Installation & Testing

   • Check LVDT or other sensors before connecting.
   • Protect collar head with a suitable cover.

5. Data Recording

   • Use the Standard Data Sheet (Annex A) for recording observations.
   • Include remarks on geological features, excavation events, or sensor adjustments.

Standard Data Sheet Format (Annex A)

Notes on Sensors (Clause 4.3.4)

• Prefer LVDT or vibrating wire sensors for stable, long-term measurements.
• Use mechanical sensors for cross-checking if electrical sensor reliability is uncertain.

flowchart TD
    A[Site Selection & Orientation] --> B[Drilling Borehole]
    B --> C[Cleaning Borehole]
    C --> D[Anchor Placement & Grouting]
    D --> E[Sensor Installation & Testing]
    E --> F[Data Recording & Monitoring]

Summary: Follow a systematic approach involving site assessment, precise drilling, anchor grouting, sensor installation, and meticulous data logging to ensure reliable rock movement monitoring using MPBX per IS 13414.

IS 13414 - Data Analysis Key Points (Clause 6.3 & Annex A)

1. Calculation of Relative Displacement (Clause 6.1)

• For mechanical sensors:
  [ \Delta d = \text{Change in reading} ]
• For electrical sensors:
  [ \Delta d = \text{Corrected reading using calibration chart} ]
• Permissible error: ±0.002 mm

2. Interpretation of Rate of Relative Displacement (Clause 6.3)

• Plot rate of relative displacement vs. time (Fig. 5).
• Curve interpretations:
  • Curve 1: Indicates stability.
  • Curves 2 & 3: Indicate instability.

3. Standard Data Sheet for Monitoring (Annex A)

• Record joint/shear zone info in remarks.
• Note repositioning or rod length adjustments.
• Include blast/excavation/support installation dates for analysis.

Summary Diagram: Data Analysis Flow

flowchart TD
    A[Sensor Reading] --> B{Sensor Type}
    B -->|Mechanical| C[Direct displacement change]
    B -->|Electrical| D[Apply calibration correction]
    C --> E[Calculate relative displacement]
    D --> E
    E --> F[Plot displacement rate vs. time]
    F --> G{Curve Type}
    G -->|Curve 1| H[Structure Stable]
    G -->|Curve 2 or 3| I[Structure Unstable]

Use this process to monitor rock mass movement and assess stability effectively as per IS 13414.

IS 13414: Standard Data Sheet & Key Specifications for Rock Movement Monitoring

1. Standard Data Sheet (Annex A, Clause 5.2)

Observation Table Format:

Remarks:

• Note joint/shear zones.
• Record repositioning or rod readjustment times.
• Include blast/excavation/support installation dates for analysis.

2. Key Concepts (Clause 3.1 & 6.3)

• Rock Movement: Relative displacement between anchor points and collar.
• Causes: loosening, swelling, creeping, destressing, etc.
• Rate of Relative Displacement: Stability indicated by displacement rate plots (Fig. 5):
  • Curve 1 → Stable
  • Curves 2 & 3 → Instability

3. Multi-Point Borehole Extensometer Components (Clause 4.3)

• Anchorages (prongs, expansion shells)
• Rods or wires
• Collar head
• Displacement sensors

4. Formula for Rate of Relative Displacement

[ \text{Rate} = \frac{\Delta d}{\Delta t} ]

• ( \Delta d ) = Change in displacement (mm)
• ( \Delta t ) = Time interval (days/hours)

5. Illustration of Data Flow

flowchart TD
    A[Installation] --> B[Observation Recording]
    B --> C[Data Analysis]
    C --> D{Displacement Rate}
    D -->|Stable