ROCK%20MASS%20CLASSIFICATIONS

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ROCK MASS CLASSIFICATIONS
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Rock Mass Classification

• Why?
• How does this help us in tunnel design?

Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Rock Mass Classification WHY?
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Ground interaction
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Summary of rock mass characteristics,
testing methods and theoretical considerations
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Types of failure which occur in rock masses under
low and high in-situ stress levels
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Engineering 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 to
• examine the properties of the rock mass
• Do Not replace detailed design methods
• Project specific

Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Terzaghis Rock Mass Classification (1946)

• Rock Mass Descriptions
• Intact
• Stratified
• Moderately jointed
• Blocky and Seamy
• Crushed
• Squeezing
• Swelling

Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Terzaghis Rock Mass Classification (1946)

• Intact rock contains neither joints nor hair
  cracks. Hence, if it breaks, it breaks across
  sound rock. On account of the injury to the rock
  due to blasting, spalls may drop off the roof
  several hours or days after blasting. This is
  known as a spalling condition. Hard, intact rock
  may also be encountered in the popping condition
  involving the spontaneous and violent detachment
  of rock slabs from the sides or roof.
• Stratified rock consists of individual strata
  with little or no resistance against separation
  along the boundaries between the strata. The
  strata may or may not be weakened by transverse
  joints. In such rock the spalling condition is
  quite common.
• Moderately jointed rock contains joints and hair
  cracks, but the blocks between joints are locally
  grown together or so intimately interlocked that
  vertical walls do not require lateral support.
  In rocks of this type, both spalling and popping
  conditions may be encountered.

Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Terzaghis Rock Mass Classification (1946)

• Blocky and seamy rock consists of chemically
  intact or almost intact rock fragments which are
  entirely separated from each other and
  imperfectly interlocked. In such rock, vertical
  walls may 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 sand grains and no
  recementation has taken place, crushed rock below
  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 a high percentage of
  microscopic and sub-microscopic particles of
  micaceous minerals or clay minerals with a low
  swelling capacity.
• Swelling rock advances into the tunnel chiefly on
  account of expansion. The capacity to swell seems
  to be limited to those rocks that contain clay
  minerals such as montmorillonite, with a high
  swelling capacity.

Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Rock Quality Designation Index (RQD) (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 Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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RQD

• 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)
• l - number of joints per unit length

Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Procedure for Measurement and Calculation of RQD
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Weathering of Basalt with depth
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Multi parameter Rock Mass Classification Schemes

• Rock Mass Structure Rating (RSR)
• Rock Mass Rating (RMR)
• Rock Tunnelling Quality Index (Q)
• Geological Strength Index (GSI)

Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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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 Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Rock Structure Rating Parameter A General area
geology
Considers (a) rock type origin (b) rock
hardness (c) geotechnical structure
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Rock Structure Rating Parameter B Geometry
Effect of discontinuity pattern
Considers (a) joint spacing (b) joint
orientation (strike and dip) (c) direction of
tunnel drive
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Rock Structure Rating Parameter C Groundwater,
joint condition
Considers (a) overall rock mass quality (on the
basis of A B) (b) joint condition (c) water
inflow
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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RSR support estimates for a 7.3m
diameter circular tunnel
Examples RSR 62 2 shotcrete 1 rockbolts _at_
5ft centres RSR 30 5 shotcrete 1 rockbolts
_at_ 2.5ft centres OR 8WF31 steel sets _at_ 3ft centres
(After Wickham et al. 1972)
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Geomechanics Classification or Rock Mass Rating
System (RMR) (Bieniawski 1976)

• Based upon
• uniaxial compressive strength of rock material
• rock quality designation (RQD)
• spacing of discontinuities
• condition of discontinuities
• groundwater conditions
• orientation of discontinuities

Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Rock 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 Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Rock Mass Rating System
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Rock 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 Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Development of Rock Mass Rating System
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Rock Mass Rating System
(After Bieniawski 1989)
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Rock 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
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Rock Mass Rating System
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Guidelines for excavation and support of 10m span
rock tunnels in accordance with the RMR system
(After Bieniawski 1989)
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Prediction of in-situ deformation modulus Em from
rock mass classifications
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Rock Mass Rating System

• Nicholson Bieniawski (1990)
• Bieniawski (1978) and Serafim Pereira (1983)
• Hoek i Brown (1997)
• Verman (1993
• H depth, a 0.16-0.3 (decreases with rock
  strength)

Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Prediction of in-situ deformation modulus Em from
rock mass classifications
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Estimates of support capacity for tunnels of
different sizes
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Rock Mass Rating System
Support pressure - Unal (1983) s - tunnel
width
Hoek (1994)
mi - constant from 4 (weak shales) to 32
(granite).
Aydan Kawamoto (2000)
Kalamaras Bieniawski (1995)
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Rock Mass Rating System
Aydan Kawamoto (2000)
Lets assume
Hoek Aydan Kalamaras Bieniawski
Aydan Kawamoto (2000)
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Rock Tunnelling Quality Index Q Barton, Lien,
Lunde

• Based on case histories in Scandinavia
• Numerical values on a log scale
• Range 0.001 to 1000

Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Q Classification System
(After Barton et al. 1974)
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Q Classification System

• represents the structure of the rockmass
• crude measure of block or particle size

(After Barton et al. 1974)
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Q Classification System

• represents roughness and frictional
• characteristics of joint walls or infill
  material

(After Barton et al. 1974)
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Q Classification System

• 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

(After Barton et al. 1974)
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Classification of individual parameters used in
the Tunnelling Quality Index Q
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Classification of individual parameters used in
the Tunnelling Quality Index Q (contd)
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Classification of individual parameters used in
the Tunnelling Quality Index Q (contd)
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Q Classification System SRF update
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Q Classification Scheme

• Resolves to three parameters
• Block size ( RQD / Jn )
• Interblock shear strength ( Jr / Ja )
• Active stress ( Jw / SRF )

Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Q 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 Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Equivalent Dimension De
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Estimated support categories based on the
tunnelling quality index Q
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Q Classification Scheme
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Q Classification Scheme
Roof pressure
Length of the bolts (roof)
(walls)
Bhasin Grimstad (1996)
Youngs modulus
Seismic wave velocity
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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RMR Q - Correlations
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Rock Mass Classification System

• 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 Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
59
Rock Mass Classification System

• 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 Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
60
Geological Strength Index (GSI)

• 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
  rockmass
• strength for different geological conditions
• Overcomes deficiencies of RMR for poor quality
  rock

Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Estimate of Geological Strength Index GSI based
on geological descriptions
Estimation of constants based upon rock mass
structure and discontinuity surface conditions
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Geological Strength Index (GSI)
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Geological Strength Index (GSI)
Estimate of Geological Strength Index GSI based
on geological descriptions.
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Plots of cohesive strength and friction angles
for different GSI and mi values
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics
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Klasyfikacja KF
Marek Cala Dept. of Geomechanics, Civil
Engineering Geotechnics