Guidelines for monitoring of rock movements using probe inclinometer

IS 14395: Scope & Key Specifications for Probe Inclinometer

• Purpose: Measures horizontal deviations and movements in boreholes by recording tilt angles of a probe inside a guide tube.

Key Specifications:

Measurement Principle:

• Tilt angle ( e ) between probe axis and vertical is recorded.
• Horizontal deviation ( d ) at depth ( z ) computed by integrating tilt measurements:

[ d = \int_0^z \tan(e) , dz ]

Rounding Off:

• Follow IS 2:1960 rules.
• Retain significant digits as per specified values.

flowchart LR
    A[Probe inclinometers] --> B[Probe with tilt sensor]
    B --> C[Guide tube with keyways]
    C --> D[Grouted borehole]
    B --> E[Electrical cable to readout]
    E --> F[Data acquisition & analysis]

This ensures precise monitoring of rock/borehole movements per IS 14395 guidelines.

IS 14395: Monitoring Systems for Rock Movements Using Probe Inclinometer

Key Components (Clause 2.1)

The monitoring system consists of:

• Probe: Detects angular displacement due to rock movement inside a borehole.
• Transmitting System: Transfers probe data to the surface; can be:
  • Rods (mechanical linkage)
  • Electrical cables (for electronic sensors)
  • Radiotelemetry (wireless transmission)
• Readout/Recording Unit: Converts transmitted data into usable form:
  • Dial gauges
  • Digital displays
  • Magnetic tape recorders or data loggers

Important Notes:

• The probe inclinometer measures relative angular displacement between successive points in the borehole.
• Data collected helps assess deformation profiles and movement rates.

Typical Formula for Angular Displacement (θ):

[ \theta = \frac{\Delta x}{L} ] Where:

• (\Delta x) = lateral displacement between two points
• (L) = length between measurement points

Summary Table for Monitoring System Components

flowchart LR
    Probe --> Transmission --> Readout
    subgraph Monitoring System
        Probe
        Transmission
        Readout
    end

This guideline ensures reliable, continuous monitoring of rock mass stability using probe inclinometers.

Principles of Operation of Probe Inclinometers (IS 14395)

• Probe Composition: Cylindrical housing with spring-loaded guide wheels (0.5m or 1m apart), containing a gravity-operated tilt sensor measuring angle e between probe axis and vertical.

• Guide Tube: Plastic or epoxy-coated aluminum with 4 orthogonal keyways; flexible to follow borehole curvature without buckling; grout-filled annulus with rigidity similar to surrounding rock.

• Measurement:

  • Probe lowered in stages inside guide tube.
  • Tilt angle e recorded at each depth.
  • Horizontal deviation ( \Delta x ) between depths calculated by:

  [ \Delta x = L \times \sin e ]

  where ( L ) = distance between successive readings.

• Accuracy & Sensitivity:

  • Reproducibility: ±0.01"
  • Cable graduation accuracy: better than 5 mm or 0.05% of depth.
  • Probe rotation limited to ≤1° per 3 m travel.

• Calibration: Adjustable inclinometer calibrator with independent angle measurement (accuracy <0.01°).

Key Formula for Horizontal Deviation

[ \boxed{ \Delta x = L \times \sin e } ]

flowchart LR
    A[Probe with Tilt Sensor] --> B[Lowered in Guide Tube]
    B --> C[Measure Tilt Angle \(e\)]
    C --> D[Calculate Horizontal Deviation \(\Delta x = L \sin e\)]
    D --> E[Monitor Ground Movement]

This method allows determination of borehole displacement by integrating successive horizontal deviations along the depth.

IS 14395 - Installation Key Points (Clause 4.2):

• Borehole Drilling: Drill boreholes to full depth; if steel casing is used, withdraw fully before guide tube installation.

• Ground Condition Logging: Inspect core/borehole; compile detailed geotechnical log focusing on movement zones.

• Guide Tube Installation:

  • Insert guide tube; record azimuth of keyways ±3".
  • Clamp guide tube; check for spiral using a spiral probe.

• Grouting:

  • Fill annular space between borehole and guide tube with grout.
  • Use tremie pipe for water-filled or deep holes to prevent grout-water mixing.
  • Flush and brush guide tube interior post-grouting.

• Protection:

  • Install lockable protective cap on guide tube end.
  • Record collar position and elevation ±5 mm for reference.

• Initial Readings:

  • Take multiple readings post-grout set; average for baseline.

• Measurement Procedure:

  • Lower probe with guide wheels in keyways; measure at intervals equal to or twice the wheel spacing.
  • Take two traverses per keyway, rotating probe 180° to check face error.
  • Optional: Repeat for second pair of keyways.

• Data Processing:

  • Average opposite face readings to correct face error.
  • Calculate incremental angle/displacement changes:

  [ \Delta d = L \sin \Delta \theta ]

  where,

  • (L) = distance between readings (mm),

  • (\Delta \theta) = incremental angle in radians (typically 80° between readings).

  • Sum increments from bottom to top to plot total displacement vs depth.

Summary Table: Installation Checklist

flowchart TD
    A[Borehole Drilling] --> B[Inspect Core & Log

IS 14395 – Data Processing Key Points

• Rounding Off: Final test values must be rounded as per IS 2:1960, retaining the same significant figures as the specified values.

• Data Scrutiny: Field data should be checked for obvious errors; corrections must be documented.

• Face Error Correction: Average pairs of opposite-face readings to correct face error.

• Incremental Changes:

  • Calculate incremental changes by subtracting corrected readings from initial readings at the same guide tube location.

  • Incremental angular changes (θ in degrees) can be converted to incremental displacement (Δ in mm) using:

    [ \Delta = L \times \sin \theta ]

    where L = distance between successive readings (mm), θ = incremental angle in degrees.

• Summation & Plotting: Sum incremental changes from bottom upwards to plot total displacement vs. depth and identify movement zones.

Summary Table for Data Processing

flowchart TD
    A[Initial Readings] --> B[Correct Face Error]
    B --> C[Calculate Incremental Changes]
    C --> D[Convert Angle to Displacement]
    D --> E[Sum Incremental Displacements]
    E --> F[Plot Displacement vs Depth]

This ensures precise monitoring of ground movement via inclinometer data per IS 14395.

IS 14395 - Committee Composition & Key Specifications

Committee Composition (Annex A)

The Technical Committee (Rock Mechanics Sectional Committee, CED 48) includes:

(Full list in Annex A of IS 14395)

Key Specifications for Installation & Data Processing (Clause 4.2 & 5)

• Borehole drilling: Full depth; casing withdrawn before guide tube installation.

• Guide tube: Azimuth accuracy ±3", annular space grouted using tremie pipe in water-filled holes.

• Protective cap: Lockable to prevent debris and vandalism.

• Reading intervals: Equal to probe guide wheel spacing; two opposite-face traverses for error checking.

• Data processing:

  • Correct face error by averaging opposite-face readings.

  • Incremental displacement (δ) from angle (θ) using:

    [ \delta = L \sin \theta ]

    where
    ( L ) = distance between readings (mm),
    ( \theta ) = incremental angle in radians (typically 80° in IS 14395).

• Plot total displacement vs. depth for movement zone identification.

flowchart TD
    A[Borehole Drilling] --> B