Geotech - Rockmass Class
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Transcript of Geotech - Rockmass Class
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ROCK MASS CLASSIFICATIONS
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Rock Mass ClassificationRock Mass Classification
Why?
How does this help us in tunnel design?
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Rock Mass ClassificationRock Mass Classification
WHY?WHY?
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Ground interactionGround interaction
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Summary of rock mass characteristics, testingSummary of rock mass characteristics, testing
methods and theoretical considerationsmethods and theoretical considerations
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Engineering Rock Mass Classification SchemesEngineering Rock Mass Classification Schemes
Developed for estimation of tunnel support
Used at project feasibility and preliminary design stages
Simple check lists or detailed schemes Used to develop a picture of the rock mass and its
variability
Used to provide initial empirical estimates of tunnel
support requirements
Are practical engineering tools which force the user toexamine the properties of the rock mass
Do Not replace detailed design methods
Project specific
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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TerzaghisTerzaghis Rock Mass Classification (1946)Rock Mass Classification (1946)
Rock Mass Descriptions
Intact
Stratified
Moderately jointed
Blocky and Seamy
Crushed
Squeezing
Swelling
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Intact rock contains neither joints nor hair cracks. Hence, ifit breaks, it breaks across sound rock. On account of theinjury to the rock due to blasting, spalls may drop off theroof several hours or days after blasting. This is known as
a spalling condition. Hard, intact rock may also beencountered in the popping condition involving thespontaneous and violent detachment of rock slabs fromthe sides or roof.
Stratified rock consists of individual strata with little or noresistance against separation along the boundariesbetween the strata. The strata may or may not be
weakened by transverse joints. In such rock the spallingcondition is quite common.
Moderately jointed rock contains joints and hair cracks, butthe blocks between joints are locally grown together or so
intimately interlocked that vertical walls do not requirelateral support. In rocks of this type, both spalling and
TerzaghisTerzaghis Rock Mass Classification (1946)Rock Mass Classification (1946)
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
T hiT hi R k M Cl ifi i (1946)R k M Cl ifi ti (1946)
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Blocky and seamy rock consists of chemically intact or almost
intact rock fragments which are entirely separated from eachother and imperfectly interlocked. In such rock, vertical wallsmay require lateral support.
Crushed but chemically intact rock has the character of crusher
run. If most or all of the fragments are as small as fine sandgrains and no recementation has taken place, crushed rockbelow the water table exhibits the properties of a water-bearing
sand. Squeezing rock slowly advances into the tunnel without
perceptible volume increase. A prerequisite for squeeze is ahigh percentage of microscopic and sub-microscopic particles of
micaceous minerals or clay minerals with a low swellingcapacity.
Swelling rock advances into the tunnel chiefly on account of
expansion. The capacity to swell seems to be limited to thoserocks that contain clay minerals such as montmorillonite, with ahigh swelling capacity.
TerzaghisTerzaghis Rock Mass Classification (1946)Rock Mass Classification (1946)
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Rock Quality Designation Index (RQD)Rock Quality Designation Index (RQD)
(Deere et al. 1967)(Deere et al. 1967)
Aim : to provide a quantitative estimate of rock mass
quality from drill logs
Equal to the percentage of intact core pieces longer than
100mm in the total length of core
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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RQDRQD
Directionally dependant parameter
Intended to indicate rock mass quality in-situ
Adapted for surface exposures as Jv number of
discontinuities per unit volume
Used as a component in the RMR and Q systems
Palmstrom (1982)
Priesta i Hudsona (1976)
- number of joints per unit length
vJRQD 3.3115 =
( ) 1.01.01100 += eRQD
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Procedure for Measurement and Calculation of RQDProcedure for Measurement and Calculation of RQD
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Weathering of Basalt with depthWeathering of Basalt with depth
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Multi parameter Rock Mass ClassificationMulti parameter Rock Mass Classification
SchemesSchemes
Rock Mass Structure Rating (RSR)
Rock Mass Rating (RMR)
Rock Tunnelling Quality Index (Q)
Geological Strength Index (GSI)
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Rock Mass Structure Rating (RSR) (1972)Rock Mass Structure Rating (RSR) (1972)
Introduced the concept of rating components to arrive at
a numerical value
Demonstrates the logic in a quasi-quantitative rock mass
classification
Has limitations as based on small tunnels supported by
steel sets only
RSR = A + B + C
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Rock Structure RatingRock Structure RatingParameter A: General area geologyParameter A: General area geology
Considers (a) rock type origin
(b) rock hardness
(c) geotechnical structure
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Considers (a) joint spacing
(b) joint orientation (strike and dip)
(c) direction of tunnel drive
Rock Structure RatingRock Structure RatingParameter B: Geometry : Effect of discontinuity patternParameter B: Geometry : Effect of discontinuity pattern
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Considers (a) overall rock mass quality (on the basis of A + B)
(b) joint condition
(c) water inflow
Rock Structure RatingRock Structure RatingParameter C: Groundwater, joint conditionParameter C: Groundwater, joint condition
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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RSR support estimates for a 7.3m diameterRSR support estimates for a 7.3m diameter
circular tunnelcircular tunnel
(After Wickham et al. 1972)
Examples
RSR = 62
2 shotcrete
1 rockbolts @
5ft centres
RSR = 30
5 shotcrete
1 rockbolts @
2.5ft centres
OR 8WF31 steel
sets @ 3ft centres
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Geomechanics Classification orGeomechanics Classification or
Rock Mass Rating System (RMR) (Rock Mass Rating System (RMR) (BieniawskiBieniawski 1976)1976)
Based upon
uniaxial compressive strength of rock material rock quality designation (RQD)
spacing of discontinuities
condition of discontinuities
groundwater conditions
orientation of discontinuities
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Rock Mass Rating SystemRock Mass Rating System
Rock mass divided into structural regions
Each region is classified separately Boundaries can be rock type or structural, eg: fault
Can be sub divided based on significant changes, eg:
discontinuity spacing
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Rock Mass Rating SystemRock Mass Rating System
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Rock Mass Rating SystemRock Mass Rating System
BUT: 1976 to 1989 Bieniawski
System refined by greater data Ratings for parameters changed
Adapted by other workers for different situations
PROJECT SPECIFIC SYSTEMS
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Development of Rock Mass Rating SystemDevelopment of Rock Mass Rating System
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Rock Mass Rating SystemRock Mass Rating System
(After Bieniawski 1989)
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Rock Mass Rating SystemRock Mass Rating System
Rating Class Description
81-100 I Very Good Rock 61-80 II Good Rock
41-60 III Fair Rock
12-40 IV Poor Rock
Less than 20 V Very Poor Rock
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Rock Mass Rating SystemRock Mass Rating System
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Guidelines for excavation and support of 10mGuidelines for excavation and support of 10m
span rock tunnels in accordance with the RMR systemspan rock tunnels in accordance with the RMR system
(After Bieniawski 1989)
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Prediction of inPrediction of in--situ deformation modulus Esitu deformation modulus Emm
from rock mass classificationsfrom rock mass classifications
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Rock Mass Rating SystemRock Mass Rating System
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Nicholson & Bieniawski (1990)
Bieniawski (1978) and Serafim & Pereira (1983)
Hoek i Brown (1997)
Verman (1993
H depth, = 0.16-0.3 (decreases with rock strength)
)82.22/(2
9.00028.0RMR
s
rm
eRMRE
E
+=
)(501002 GPaRMRforRMREm >=
)(5010 40/)10( GPaRMRforE RMRm
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Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Estimates of support capacity for tunnelsEstimates of support capacity for tunnels
of different sizesof different sizes
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Rock Mass Rating SystemRock Mass Rating System
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Support pressure - Unal (1983)
s - tunnel width
sRMR
pv
= 100
100
Hoek (1994): m m ei
RMR
=100
28
s e
RMR
=100
9
mi - constant from 4 (weak shales) to 32 (granite).
R sRcrm c= ( )RR
m m srrmc
= +2 42
Aydan & Kawamoto (2000)5.20016.0 RMRRcrm =
Kalamaras & Bieniawski (1995)85
15
2
=
RMRRR ccrm
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Rock Mass Rating SystemRock Mass Rating System
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Aydan & Kawamoto (2000)
( )RMRRMRRMR
RR ccrm +=
1006
Lets assume: 60=RMR MPaRc 80=
Hoek:
Aydan:
Kalamaras & Bieniawski:
MPaRc 67.8=
MPaRc 62.44=
MPaRc 18.21=
Aydan & Kawamoto (2000) RMRrm 05.022 +=
rm
rmcrm
rm
R
c
cos
sin1
2
=Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
k lli Q li d Q i d
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Rock Tunnelling Quality Index QRock Tunnelling Quality Index QBartonBarton,, LienLien,, LundeLunde
Based on case histories in Scandinavia
Numerical values on a log scale
Range 0.001 to 1000
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Q Cl ifi i SQ Cl ifi i S
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Q Classification SystemQ Classification System
(After Barton et al. 1974)
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Q Cl ifi ti S tQ Cl ifi ti S t
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Q Classification SystemQ Classification System
(After Barton et al. 1974)
represents the structure of the rockmass crude measure of block or particle size
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Q Cl ifi ti S tQ Cl ifi ti S t
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Q Classification SystemQ Classification System
(After Barton et al. 1974)
represents roughness and frictionalcharacteristics of joint walls or infill material
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Q Cl ifi ti S tQ Classification System
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Q Classification SystemQ Classification System
(After Barton et al. 1974)
consists of two stress parameters SRF can be regarded as a total stress parameter
measure of
loosening load as excavated through shear zones
rock stress in competent rock
squeezing loads in plastic incompetent rock
JW is a measure of water pressure
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Classification of individual parameters used inClassification of individual parameters used in
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Classification of individual parameters used inClassification of individual parameters used in
the Tunnelling Quality Index Qthe Tunnelling Quality Index Q
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Classification of individual parameters used inClassification of individual parameters used in
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Classification of individual parameters used inClassification of individual parameters used in
the Tunnelling Quality Index Qthe Tunnelling Quality Index Q (contd)
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Classification of individual parameters used inClassification of individual parameters used in
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Classification of individual parameters used inClassification of individual parameters used in
the Tunnelling Quality Index Qthe Tunnelling Quality Index Q (contd)
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Q Classification SystemQ Classification SystemSRFSRF updateupdate
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Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Q Classification SchemeQ Classification Scheme
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Q Classification SchemeQ Classification Scheme
Resolves to three parameters
Block size ( RQD / Jn
)
Interblock shear strength ( Jr/ Ja )
Active stress ( Jw / SRF )
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Q Classification SchemeQ Classification Scheme
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Q Classification SchemeQ Classification Scheme
Resolves to three parameters
Block size ( RQD / Jn
)
Interblock shear strength ( Jr/ Ja )
Active stress ( Jw / SRF )
Does NOT include joint orientation
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Equivalent Dimension DEquivalent Dimension Dee
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Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Estimated support categories based on theEstimated support categories based on the
t lli lit i d Qtunnelling quality index Q
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tunnelling quality index Qtunnelling quality index Q
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Q Classification SchemeQ Classification Scheme
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Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
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Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Q Classification SchemeQ Classification Scheme
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Roof pressure:31
= Q
JJp
r
nroof
Length of the bolts: (roof) (walls)ESR
sL
15.02 +=
31
32.0
= QJ
Jpr
n
roof
Bhasin & Grimstad (1996): 3140
= Q
J
sp
r
roof
Youngs modulus:
Seismic wave velocity: ]/[100
log5.3 skmR
QV cp +=
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
LH
ESR=+2 0 15.
[ ]MPaR
QE c33
310=
RMRRMRQQ -- CorrelationsCorrelations
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Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Rock Mass Classification SystemRock Mass Classification System
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RMR and Q system or variants are the most widely used
both incorporate geological, geometric and
design/engineering parameters to obtain a value of
rock mass quality
empirical and require subjective assessment
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Rock Mass Classification SystemRock Mass Classification System
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Approach:
accurately characterise the rockmass ie: full and
complete description of the rockmass
assign parameters for classification later
always use two systems for comparison
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Geological Strength Index (GSI)Geological Strength Index (GSI)
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Method to link the constants m and s of Hoek-Brown
failure criterion to observations in the field
ie: a possible solution to the problem of estimating
strength of jointed rockmass
A system for estimating the reduction in rockmassstrength for different geological conditions
Overcomes deficiencies of RMR for poor quality rock
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Estimate of Geological StrengthEstimate of Geological Strength
Index GSIIndex GSI
b d l i l d i i
Estimation of constants based upon rockEstimation of constants based upon rock
mass structure and discontinuity surfacemass structure and discontinuity surface
di i
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based on geological descriptionsbased on geological descriptions conditionsconditions
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Geological Strength Index (GSI)Geological Strength Index (GSI)
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Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Geological Strength IndexGeological Strength Index
(GSI)(GSI)
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(GSI)(GSI)
Estimate of Geological
Strength Index GSI
based on geologicaldescriptions.
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Plots of cohesive strength and friction anglesPlots of cohesive strength and friction angles
f diff t GSI df diff t GSI d ll
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for different GSI andfor different GSI andmmii valuesvalues
Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics
Klasyfikacja KF
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Marek Caa Dept. of Geomechanics, Civil Engineering & Geotechnics