Geoscience Reference
In-Depth Information
Rock mass classification systems
18.1 The rock mass rating systems
•
Rock Mass Rating systems are used to classify rock and subsequently use this
classification in the design of ground support systems. A few such ratings are
provided below.
Table 18.1
Rock mass rating systems.
Rock mass
Key features
Comments
Reference
rating system
Terzaghi's Rock
7 No. Classifications of in situ rock
One of the first rock
Terzaghi,
classification
for predicting tunnel support
mass classifications
1946
from Intact, stratified, moderately
jointed, blocky and seamy, crushed,
squeezing and swelling. Method
did not account for similar classes
could having different properties
Rock structure
Quantitative method that uses
Specifically related to
Wickham
Rating (RSR)
Parameter A - Geological structure
tunnels
et al., 1972
ParameterB-Joint pattern and
Direction of drive
ParameterC-Joint condition and
Groundwater
Rock mass
Quantitative method that uses
Based on the RMR
Bieniawski,
rating (RMR)
•
Strength of intact rock
classification one can
1973 and
or
Drill core quality (RQD)
determine: Average
1989
•
geomechanics
Spacing of discontinuities
stand up time,
•
classification
•
Condition of discontinuities
cohesion and friction
Groundwater
angle of the rock
•
•
Orientation of discontinuities
mass
Q System or
Quantitative method that uses
The log scale used
Barton
Norwegian
Rock quality designation
provides insensitivity
et al., 1974
•
Geotechnical
Joint set number
of the solutions to any
•
institute (NGI)
joint roughness number
individual parameter,
•
Method
•
Joint alteration number
and emphasizes the
Joint water factor
combined effects.
•
•
Stress reduction factor
Extensive correlations
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