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Rock quality classification
Having tests that give an idea of
the quality of the rock mass isessential for engineering purposes
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What are we calling a rock?
Grade Description Lithology Excavation Foundations
VISoil Some organic content,
no original structure
May need to
save and re-use
Unsuitable
V Completelyweathered
Decomposed soil, someremnant structure
Scrape Assess by soiltesting
IV Highlyweathered Partly changed to soil,soil > rock Scrape NBcorestones Variable andunreliable
III Moderatelyweathered
Partly changes to soil,rock > soil
Rip Good for mostsmall structures
II Slightlyweathered
Increased fractures andmineral staining
Blast Good foranything exceptlarge dams
I Fresh rock Clean rock Blast Sound
Engineering classification of weathered rock
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Rock Mass Strength
Strength depends on the density, nature and
extent of the fractures within it
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Rock fractures and their
characterization
Typically carried out using 3 orthogonal scanlines
orientation
spacing length
roughness
aperture filling
block size
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Rock Quality Designation (RQD)
Quantitative estimate of rock mass quality
from drill core logs % intact core pieces >10cm in total length of core
Deere et al., 1967
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Rock Quality Designation (RQD)
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RQD
RQD
A. Very poor 0 25B. Poor 25 50C.Fair 50 75
D.Good 75 90E. Excellent 90 - 100
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RMR and Q Rock classification
systems
Primary use of RQD is as a parameter inmore widely used
RMR (Bieniawski, 1976) and Q Rock (Barton et al., 1974)
classification systems
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Rock Mass Rating (RMR),
Bieniawski (1976, 1989)
Classifies rock according to 6 parameters: UCS
RQD
Spacing of discontinuities
Condition of discontinuities
Groundwater conditions
Discontinuity orientation
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RMR or Geomechanics
Classification
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Rock Tunnelling Quality Index, Q
(or Norwegian Q system), Barton et al., 1974
=
SRF
Jw
Ja
Jr
Jn
RQDQ
RQD = Rock Quality Designation 100 - 10Jn = Joint set number 1 20Jr = Joint roughness factor 4 -1Ja = Joint alteration and clay fillings 1 20
Jw = Joint water inflow or pressure 1 0.1SRF = stress reduction factor 1 20
Typically: 0.01 < Q
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Q system
=
SRFJw
JaJr
JnRQDQ
(RQD/Jn) = crude measure of block size
(Jr/Ja) = roughness/friction of surfaces
(Jw/SRF) = ratio of two stress parameters (active stress)
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Guideline properties of Rock Mass
Classes
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Using Rock Mass Classification
Systems
RMR and Q most widely used
Both use similar parameters; difference in
weighting
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Using Rock Mass Classification
Systems
Good practice toassign a range ofvalues
Field example
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CN Tower, Toronto
Worlds tallest free-standingstructure
550m high, 110,000 tonnes
Foundations:
shale
UCS = 10 25 MPa
E = 3.7 GPa
RQD = 50 70 %
Mean load = 580 kPa
supported by slab foundation
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