Rock Mass Classification and also a brief description of Rock Mass Rating (RMR), Rock Structure Rating (RSR), Q valves and New Austrian Tunneling method(NATM)

3. Presentation
Topic:
Rock Mass Classification
Submitted To: Prof. Sohail Mustafa
Submitted By: Ahmed Younhais Tariq
7th Semester
Institute of Geology
THE UNIVERSITY OF AZAD JAMMU & KASHMIR
MUZAFFARABAD

4. Rock Mass
Classification:

5. Introduction to Rock Mass
Classification:

Rock mass classification schemes have been
developed to assist in (primarily) the collection of
rock into common or similar groups.
 The first truly organized system was proposed by
Dr. Karl Terzaghi (1946) and has been followed by
a number of schemes proposed by others.
 Terzaghi's system was mainly qualitative and
others are more quantitative in nature.
 The following subsections explain three systems
and show how they can be used to begin to
develop and apply numerical ratings to the
selection of rock tunnel support and lining.
 This section discusses various rock mass
classification systems mainly used for rock tunnel
design and construction projects.

6. Terzaghi's Classification:



Today rock tunnels are usually designed
considering the interaction between rock and
ground, i.e., the redistribution of stresses into
the rock by forming the rock arch.
However, the concept of loads still exists and
may be applied early in a design to "get a
handle" on the support requirement.
The concept is to provide support for a height
of rock (rock load) that tends to drop out of
the roof of the tunnel.

8. Rock Mass Rating
(RMR):

9. Rock Mass Rating (RMR):
The
Rock Mass Rating (RMR) system
is a geomechanical classification
system for rocks, developed by Z.T
Bieniawski between 1972 and 1973.

10. Introduction:
 During
the feasibility and preliminary design
stages of a project, when very little detailed
information is available on the rock mass
and its stress and hydrologic characteristics.
 The use of a rock mass classification
scheme can be of considerable benefit.
 This may involve using the classification
scheme as a check-list to ensure that all
relevant information has been considered.

11. At
the other end of the spectrum,
one or more rock mass classification
schemes can be used to build up a
picture of the composition and
characteristics of a rock mass to
provide initial estimates of support
requirements, and to provide
estimates of the strength and
deformation properties of the rock
mass.

12. Parameters of RMR:
Six parameters are used to classify a
rock mass using the RMR system:
Uniaxial compressive strength of rock
material
Rock Quality Designation (RQD)
Spacing of discontinuities
Condition of discontinuities
Groundwater conditions
Orientation of discontinuities

13. Each
of six parameters is assigned a
value corresponding to characteristic
of rock. These values are derived from
field surveys. The sum of the six
parameters is the "RMR value", which
lies between 0 and 100.
RMR =Ja1 + Ja2 + Ja3 + Ja4 + Ja5
+ Ja6

14. Classification table for the
RMR:
RMR
Rock quality
0 - 20
Very poor
21 - 40
Poor
41 - 60
Fair
61 - 80
Good
81 - 100
Very good

15. Applications Of Rock Mass
Rating:
 Rock
Mass Rating has found wide
application in various types of
engineering projects such as tunnels,
slopes, foundations, and mines.
 Rock
mass classification systems have
gained wide attention and are frequently
used in rock engineering and design.
However, all of these systems have
limitations, but applied appropriately and
with care they are valuable tools.

16.  Now
RMR system is applied to coal and
hard rock mining.
 The RMR system is also applicable to
slopes and to rock foundations. This is a
useful feature which can assist with the
design of slope near the tunnel portals as
well as allow estimates of deformability of
rock foundation for bridges and dams.
 Other special uses includes applications to
assess rock rippability, cuttability and
cavability.

17. RMR may be applied for
classification of the stability and
support estimates of tunnels and
rock caverns, preferably in jointed
rocks.
It may be used for planning
purposes.
It is less useful for prescription of
rock support during construction.
It is not likely that RMR is suitable to
express the effects of pre-grouting.


18. Using Rock Mass Classification
Systems:
The
two most widely used rock mass
classifications are Bieniawski's RMR
(1976, 1989) and Barton et al's Q
(1974).
Both methods incorporate geological,
geometric and design/engineering
parameters in arriving at a quantitative
value of their rock mass quality.


19. The
similarities between RMR and
Q system from the use of
identical, or very
similar, parameters in calculating
the final rock mass quality rating.

20. PARAMETERS:

21. Uniaxial compressive strength of
rock material:
The
strength of rock can be evaluated
using a laboratory compression test
on prepare core.
But
for rock classification purposes it
is satisfactory to determine
compressive strength approximately
using the point load test on intact
pieces of drill core.

22. Uniaxial compressive strength of
rock material:
UCS
of a material is verified by
applying compressive load until
failure occur due to fractures in core
sample.

23. When
stresses exceeds the bearing
limit it cracks the core sample. These
cracks are produce along the weaker
zones.
When
crack produced then we can
note the clock reading. That point
shows the maximum compressive
strength of rock.

24. Point load
Index
(MPa)
Unconfined
Rating
Compressive
Strength (MPa)
>200
15
100-200
12
2-4
50-100
7
1-2
25-50
4
Don’t use
10-25
2
Don’t use
3-10
1
Don’t use
<3
0
>8
4-8

25. Orientation of Discontinuities:
 Orientation
of the joints relative to the work
can have an influence on the behavior of
rock.
 Bieniawski recommended adjusting the
sum of first five rating numbers to account
for favorable or unfavorable orientation.
 No points are subtracted for very
favorable orientation of joints up to 12
points are deducted for unfavorable
orientation of joints in tunnels and up to 25
for unfavorable orientation in foundation.

26. The
orientation of joint sets cannot be
found from normal routine drilling of
rock masses but can be determined
from drill core with special tools or
procedures.
Logging
of the borehole using a
television or camera down hole will
reveal orientation of joints and
absolute orientation will also be
obtained from logging shafts and
adits.

27. Adjustment in RMR for joint
orientations:
Assessment of
influence of
orientation on the
work
Rating
increment for
tunnels
rating increment
for foundations
Very favorable
0
0
favorable
-2
-2
fair
-5
-7
unfavorable
-10
-15
Very unfavorable
-12
-25

28. Modifications to RMR for mining:
 Rock
Mass Rating (RMR) system was
originally based upon case histories drawn
from civil engineering.
 Laubscher
developed the Mining Rock
Mass Rating (MRMR) system by modifying
the Rock Mass Rating (RMR) system of
Bieniawski.

29.  In
the MRMR system the stability and
support are determined with the following
equations:
RMR = IRS + RQD + spacing + condition
In which:
RMR = Rock Mass Rating
IRS = Intact Rock Strength
RQD = Rock Quality Designation
Spacing = expression for the spacing
of discontinuities
Condition = condition
of discontinuities (parameter also dependent on
groundwater presence, pressure, or quantity of

30. Comparison of MRMR and
RMR:
MRMR = RMR x adjustment factors
In which:
Adjustment factors = factors to compensate for:
the method of excavation, orientation of
discontinuities and excavation, induced stresses,
and future weathering.
 The
adjustment factors depend on future
(susceptibility to) weathering, stress
environment and orientation.

31.  The
combination of values
of RMR and MRMR determines the socalled reinforcement potential.
 A rock
mass with a high RMR before the
adjustment factors are applied has a high
reinforcement potential, and can be
reinforced by, for example, rock bolts,
whatever the MRMR value might be after
excavation.

32. Parameters of MRMR:
 The
parameters to calculate the RMR value
are similar to those used in the RMR system.
This may be confusing, as some of the
parameters in the MRMR system are
modified, such as the condition parameter that
includes groundwater presence and pressure
in the MRMR system whereas groundwater is
a separate parameter in the RMR system.
 The
number of classes for the parameters and
the detail of the description of the parameters
are also more extensive than in the RMR
system.

33. Rock Structure
Rating (RSR):

34. Rock Structure Rating (RSR):
Rock
Structure Rating(RSR) is a
quantitative method for describing
quality of a rock mass and then
appropriate ground support.

35. Categories of RSR:
There
are considered two general
categories:
Geotechnical parameters:
Rock type; joint pattern; joint
orientations; type of discontinuities;
major faults; shear sand folds; rock
material properties; weathering or
alteration. and
Construction parameters:
Size of tunnel; direction of drive;
method of excavation.

36. Parameter A : Geology
General
appraisal of geological
structure on the basis of:
 Rock type origin (igneous, metamorphic,
sedimentary).
Rock hardness (hard, medium, soft,
decomposed).
Geologic structure (massive, slightly
faulted/folded, moderately faulted/folded,
intensely faulted/folded).

37. Parameter A : Geology

38. Parameter B: Geometry
Effect
of discontinuity pattern with
respect to the direction of the tunnel
drive on the basis of:



Joint spacing.
Joint orientation (strike and dip)
Direction of tunnel drive.

39. Parameter B: Geometry

40. Parameter C:Effect of
Groundwater
Effect
of groundwater inflow and joint
condition on the basis of:
Overall rock mass quality on the basis
of A and B combined.
 Joint condition (good, fair, poor).
 Amount of water inflow (in gallons per
minute per 1000 feet of tunnel).


41. Parameter C:Effect of
Groundwater

42. Q- Values:

43. Introduction:
Barton
et al. (1974) at the Norvegian
Geotechnical Institute (NGI) proposed
the Rock Mass Quality (Q) System of
rock mass classification on the basis of
about 200 case histories of tunnels and
caverns.
It is a quantitative classification system,
and it is an engineering system
enabling the design of tunnel supports.

44. Factor Affecting:
 The
concept upon which the Q system is
based upon three fundamental
requirements:
a. Classification of the relevant rock mass
quality,
b. Choice of the optimum dimensions of
the excavation with consideration given
to its intended purpose and the required
factor of safety,
c. Estimation of the appropriate support
requirements for that excavation.

45. Q value:
The
Q-system for rock mass
classification is developed by Barton,
Lien and lunde. It expresses the quality
of rock mass, on which, the design and
support recommendations are based
for the underground excavations.
The Q- value is determined by the
following formula:
Q = RQD/Jn x Jr/ Ja x Jw/SRF

46. Where,
RQD = Rock Quality Designation
Jn = Joint Number
Jr = Joint Roughness
Ja = Joint Alteration
Jw = Joint Water Reduction Number
SRF = Stress Reduction Fraction

47. RQD
J
J
J
w
n
a
J
=Degree of Jointing(or block size)
r
SRF
=Joint Friction(inter-block shear strength)
=Active Stress

49. 
Q values can be determined in different
ways, by geological mapping in underground
excavation, on the surfaces , or alternatively
by core logging. The most correct values are
obtained from geological mapping
underground. Each of Six Parameters is
determined according to description found in
tables.

The Q values varies between 0.001 and
1000. Please note that it is possible to get
higher values and slightly lower values by
extreme combinations of parameters. In such
odd cases one can use 0.001 and 1000
respectively for determination of support.

50. RQD (Rock Quality Designation):
 “RQD
is the sum of length ( between natural
joints ) of all core pieces more than 10 cm
long as a percentage of the total core
length.”
 RQD
will therefore be a percentage
between 0 to 100. If 0 is used in the Q
formula it will give a Q value of 0 and
therefore all RQD values between 0 to 10
are increased to 10 when calculating the Q
value.

51. RQD (Rock Quality Designation):
 RQD
is used as a simple classification
system for the stability of rock masses.
Using the RQD values, 5 rock classes are
defined:
S. No
RQD
RQD Value
1
Very Poor (>27 joints per m3)
0 - 25
2
Poor (20 - 27 joints per m3)
25 - 50
3
Fair (13 - 19 joints per m3)
50 - 75
4
Good (8 - 12 joints per m3)
75 - 90
5
Excellent (0 - 7 joints per m3)
90 - 100

52. In the underground opening it is
usually possible to get a three
dimensional view of rock mass. A
three dimensional RQD may therefore
be used. That’s means that the RQD
m
values are estimated from the no of
joints per .
 The following formula may be used :
RQD = 115 - 3.3 Jv
m
J
Where is the number of joints per

3
3
v

54. Precautions:
RQD is intended to represent the rock
mass quality in situ. When using diamond
drill core, care must be taken to ensure
that fractures, which have been caused by
handling or the drilling process, are
identified and ignored when determining
the value of RQD.


55. Stress Reduction Factor:
It
describes the relation between
stress and rock strength around an
underground opening. The effect of
stresses can usually be observed in
an underground opening as spalling,
slabbing, deformation, squeezing,
dilatancy and block release. However,
sometime may pass before the stress
phenomena are visible.

58. Joint Roughness Number:
 It
depend on joint wall surfaces. If they are
undulating, planner, rough or smooth. Joint
description is based on roughness in two
scales:
The terms rough, smooth and slickenside
refer to small structures in a scale of cm and
mm. This can be evaluated by running a finger
along the joint wall; small scale roughness will
then be left.
2. Lange scale roughness is measured on a dm
to m scale and is measured by lying a one
meter long ruler on the joint surface to
determine the large scale roughness
1.

59. Jr
Rock wall contact , and
Rock wll contact before 10 cm of shear movement
A
Discontinuous Joints
4
B
Rough or irregular, Undulating
3
C
Smooth, Undulating
2
D
Slickenside, Undulating
1.5
E
Rough, Irregular, Planar
1.5
F
Smooth, Planer
1
G
Slickenside, Planar
0.5
 No rock wall contact when sheared
H
Zone containing clay minerals thick enough to prevent
rock wall contact when sheared
1

62. Joint Set Number:

Shape and size of the blocks in the rock mass
depends on the joints geometry.
 There will often be 2 to 4 joint sets at a certain
locations.
 Joints in it will be nearly parallel to one another
and will display a characteristic joint spacing.
 Joints that do not occur systematically or that
have a spacing of several meters are called
random joints.
 However, the effect of spacing strongly depend
upon the span or height of the underground
opening .
 If more than one joint belonging to a joint set
appears in a underground opening, it has an
effect on the stability and should be regarded

63. Table for determination of joint
set number:
Joint set Number:
Jn
A
Massive, no or few joints
0.5-1.0
B
One joint set
2
C
One joint set plus random joints
3
D
Two joint sets
4
E
Two joint sets plus random joints
6
F
Three joint sets
9
G
Three joint sets plus random joints
12
H
Four or more joint sets , randomly
heavily jointed “Sugar Cube “ etc
15
I
Crushed Rocks, earth like
20

65. RQD
J


=Degree of Jointing(or block size)
n
This fraction represents the relative
block size in the rock masses.
In addition to RQD and Jn. It is also
useful to make notes of the real size
and shape of the blocks, and the joint
frequency.

66. Joint Alternation Number:


In addition to the joint roughness the joint infill
is significant for joint friction. When
considering joint infill, two factors are
important; thickness and strength. These
factors depends on the mineral composition.
In the determination of joint alternation
number, the joint infill is divided into three
categories ; (a, b and c) based on thickness
and degree of rock wall contact when sheared
along the joint planes.

68. Joint water reduction Factor:


Joint water may soften or washout the
mineral in fills and there by reduce the
friction on the joint planes. Water
pressure may reduce the normal stress
on the joint wall and cause the blocks to
shear more easily.
A determination of joint water reduction
factor is based on inflow and water
pressure observed in a underground
opening. The lowest Jw values(Jw < 0.2)
represent large stability problems.

70. J
J
=Joint Friction(inter-block shear
strength)
r
a

71. New Austrian
Tunneling method
(NATM):

72. New Austrian Tunneling method
(NATM):
 The
term New Austrian Tunneling
Method Popularly Known as NATM got
its name from Salzburg (Austria).
 It was first used by Mr. Rabcewicz in
1962. It got world wise recognition
in1964.
 The first use of NATM in soft ground
tunnel in Frankfurt (Europe) metro in
1969.
 The basic aim of NATM is for getting

73. Definition of NATM:
“The
New Austrian Tunnelling Method is
a support method to stabilize the tunnel
perimeter by means of sprayed concrete
,anchors and other support and uses
monitoring too control stability”.

74. Principles of NATM:
Mobilization
of the strength of rock mass
Shotcrete protection
Measurements
Primary Lining
Rock mass classification
Dynamic Design

75. Summary of procedure in
NATM:
SHOTCRETING AT THE EXCAVATED
AREA(PRIMARY LINING)
PLACING OF THE WIREMESH ALONG THE
FACEOF THE TUNNEL
ERECTION OF THE LATTICE GIRDER
ALONG THE FACE OF THE TUNNEL
PERTICULAR TYPE OF ROCKBOLTING
SHOTCRETING THE WHOLE
ARRENGEMENT(SECONDARY LINING)

76. NATM Process on site:

77. POINTS TO CARRY OUT A
SUCCESSFUL NATM
PROCESS:
Consideration
of rock mechanics
Selection of a proper profile
Design of flexible support and slender lining (in
rock) Careful excavation
Maintenance of rock strength, avoidance of
loosening and over-breaks
Direct contact of rock/soil and support
Continuous control by geotechnical
measurements
 Installation of support without delay and in
correct sequence.

78. Thanks