6/19/2019 Rock Mass Classification

Rock Mass Classification

1. 1. 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
2. 2. Rock Mass Classification:
3. 3. 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.
4. 4. 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.
5. 5. Rock Mass Rating (RMR):
6. 6. 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.
7. 7. 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.
8. 8. 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.
9. 9. 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
10. 10. 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
11. 11. 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
12. 12. 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.
13. 13. 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.
14. 14. 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.
15. 15. 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.
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16. 16. The similarities between RMR and Q system from the use of identical, or very similar,
parameters in calculating the final rock mass quality rating.
17. 17. PARAMETERS:
18. 18. 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.
19. 19. 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.
20. 20. 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.
21. 21. 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
22. 22. 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.
23. 23. 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.
24. 24. 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
25. 25. 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.
26. 26. 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
27. 27. 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.
28. 28. 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.
29. 29. 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.
30. 30. Rock Structure Rating (RSR):
31. 31. Rock Structure Rating (RSR): Rock Structure Rating(RSR) is a quantitative method for
describing quality of a rock mass and then appropriate ground support.
32. 32. 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.
33. 33. 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).
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34. 34. Parameter A : Geology

35. 35. 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.
36. 36. Parameter B: Geometry
37. 37. 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).
38. 38. Parameter C:Effect of Groundwater
39. 39. Q- Values:
40. 40. 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.
41. 41. 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.
42. 42. 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
43. 43. Where, RQD = Rock Quality Designation Jn = Joint Number Jr = Joint Roughness Ja = Joint
Alteration Jw = Joint Water Reduction Number SRF = Stress Reduction Fraction
44. 44. RQD J J J w n a J =Degree of Jointing(or block size) r SRF =Joint Friction(inter-block shear
strength) =Active Stress
45. 45. 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.
46. 46. 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.
47. 47. 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
48. 48. 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
49. 49. 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.
50. 50. 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.
51. 51. 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.
52. 52. 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
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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
53. 53. 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
54. 54. 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
55. 55. 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.
56. 56. 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.
57. 57. 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.
58. 58. J J =Joint Friction(inter-block shear strength) r a
59. 59. New Austrian Tunneling method (NATM):
60. 60. 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
61. 61. 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”.
62. 62. Principles of NATM: Mobilization of the strength of rock mass Shotcrete protection
Measurements Primary Lining Rock mass classification Dynamic Design
63. 63. 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)
64. 64. NATM Process on site:
65. 65. 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.
66. 66. Thanks

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