f-rock mass classification
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ROCK MASS CLASSIFICATIONS
Numerous classifications proposed butTWO main ones in use :- Rock Mass Rating System RMR Rock Mass Rating System RMR
Q System (N.G.I.)Q System (N.G.I.)
Attempt to combine INDEX properties of INTACT rocks with the characteristics of field scale DISCONTINUITIES
Development of RockMass ClassificationsNeed for initial empirical design tool to assess
ground conditions and support requirements
Terzaghis Rock Load Classification (1946)
Rock Quality Designation RQD Index
Active Span and Stand-up time
RMR
Q System
ACTIVE SPAN
b. Support placed close to face
a. Support lagging behind face position
Support
S
S
RQD EXAMPLE (1)
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Core Logging
%100 x L x
RQD i
=
xi = Length of individual piecesof core => 100mmL = Total Length of core run
ENGINEERING LOGGINGOF ROCK CORE
R. Q. D
Used in support design Does not allow for discontinuity orientation
infill, weathering etc..
Very Good> 90Good75 - 90
Poor 50 - 75
Poor 25 - 50
Very Poor < 25Drill Core QualityRQD %
I. The Rock Mass Rating System(RMR)
Provides RMR of 0-100Based on 5 parameters INTACT ROCK STRENGTH RQD GROUNDWATER FRACTURE SPACING FRACTURE CONDITION
RATING ADJUSTMENT
BASED ON FRACTURE ORIENTATION
Other Adjustments
Blasting, In-situ stress, Major faults
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ROCK MASS RATING, RMRROCK MASS RATING SYSTEM
INFLUENCE
OF DIP
Drive with Dip
Drive against Dip
RMR and STAND-UP TIME
Immediatecollapse
No support required
10 4 10 5 10 610 310 210 -1 10 0 10 1Stand-up time in hours
20
30
40
50 6070 80
20
30
40
50
6070
80 901d 1wk 1mo 1yr 10yr
1
2
34
10
20
30
R o o f
S p a n
( m ) 8
65
R o c k M
a s s R a t i n
g
R o c k M
a s s R a t
i n g
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RMR SUPPORT GUIDELINES
THE NGI Q SYSTEM
RQD = Rock Quality DesignationJn = Joint Set No.Jr = Joint Roughness No.Ja = Joint alteration No.Jw = Joint water reduction No.SRF = Stress Reduction Factor
Q = (RQD/Jn)* (Jr/Ja) *(Jw/SRF)
Q varies from 0.001 to 1000
THE Q SYSTEMRQD/ J n represents structure of rock mass (block size)
Range 100/0.5 to 10/20
J r /J a represents roughness and frictional properties of joint wall and infill (interblock shear strength)
Rock wall contact
Rock wall contact before 10cm shearNo rock wall contact when sheared
J w/SRF represents the active stresses
loosening load where excavation through shear zonesand clay bearing rock
rock stress in competent rock squeezing loads in plastic rocks
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THE Q SYSTEM
Q SYSTEM
EXCAVATION SUPPORT RATIO
related to use of excavation and to extent of to which some instability is acceptable
roughly analogous to inverse of factor of
safety
Used in Support Design via
THE EQUIVALENT DIMENSION, De.
De = Excavation span, diameter or heightExcavation Support Ratio
EXCAVATION SUPPORT RATIO
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Geomechanics Rock Mass Rating, RMR
Tunneling Quality Index, Q
I n - s
i t u
M o d u l u s o f
D e f o r m a t
i o n .
G P a
E m = 2RMR-100
E m = 25log 10Q
E m = 10 (RMR-10)/40
0
90
60
30
100500 20 803010 9060 7040
0.040.01 1 4 10 40 100 400
Case HistoriesSerafim and PereiraBieniawski
ROCK MASS MODULUS OF DEFORMATION
SUPPORT
Use of UNWEDGE and stereographic techniques todesign openings in jointed rock Use of SWEDGE for design of rock slopes
TYPES OF SUPPORT TYPES OF SUPPORT
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TYPES OF SUPPORT TYPES OF SUPPORT
TYPES OF SUPPORT TYPES OF SUPPORT
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TYPES OF SUPPORT TYPES OF SUPPORT
TYPES OFSUPPORT
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TYPES OF SUPPORT
HIGHWALL AUGERING
HIGHWALL AUGERING
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