Page 566 - Rock Mechanics For Underground Mining

MONITORING ROCK MASS PERFORMANCE

Table 18.1 Displacement monitoring methods (after Windsor, 1993).

Deformation Measurement Measurement Measurement Measurement Sensitivity
Technique Access Method
OBSERVATIONAL TECHNIQUES
GPS E M M
Terrestrial Surveying E M M
EDM & Automatic Surveillance E A M
INSTRUMENT TECHNIQUES
Movement Indicators
Axial B/F O L
Shear B/F O L
Convergence Indicators
Wire/Tape F M M
Rod F M/A M
Strain Meter
Resistance Strain Gauges B A H
Vibrating Wire Strain Gauges B A H
Joint Meters
Glass Plates F M M
Pin Arrays F M/A M
Strain Gauges B A H
Proximity Transducer F A H
Fibre Optic B A H
Potentiometers B/F A H
Extensometers
Fixed Extensometer
Wire/Rod B M/A H
Reference Point Sensing B M/A H
Strain Sensing B M H
Portable Extensometer
Magnetic Anchor B M H
Magneto-strictive B M H
Sliding Micrometer B M H
Inclinometers
Fixed Inclinometer B A H
Portable Inclinometer B M H
Deflectometers B A H
Extensometer-Inclinometer B M H
Extensometer-Deflectometer B M H
F = Rock Face, B = Borehole, E = Exposure, M = Manual, A = Automatic, O = Observations, L = Low,
M = Medium, H = High

78.5 kN to a 1.0 mm diameter invar wire stretched between an anchoring point and the
instrument which is itself attached to the second anchoring point at the rock surface.
The tensioning device moves the end of the wire towards the displacement gauge with
a precision thread. The applied tension is read on the dynamometer. The displacement
gauge has a readability of 0.01 mm and a range of 100 mm. The overall accuracy of the
convergence measurements is ± 0.02 mm. Normally, these levels of readability and
accuracy are not required for routine convergence monitoring in underground mining.
When interpreting convergence measurement results, it is important to consider
the time rates of convergence and any changes in those rates, as well as the total
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