1. ROCK MASS CLASSIFICATIONS
ics
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

2. Rock Mass Classification
Why?
How does this help us in tunnel design?
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

3. Rock Mass Classification
WHY?
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

4. Ground interaction
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

5. Summary of rock mass characteristics, testing
methods and theoretical considerations
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

6. Types of failure which occur in rock masses
under low and high in-situ stress levels
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

7. Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

8. 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 Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

9. Terzaghi’s Rock Mass Classification (1946)
Rock Mass Descriptions
Intact
Stratified
Moderately jointed
Blocky and Seamy
Crushed
Squeezing
Swelling
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

10. Terzaghi’s 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 Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

11. Terzaghi’s 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 Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

12. 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 Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

13. Directionally dependant parameter
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 Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

14. Procedure for Measurement and Calculation of RQD
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

15. Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

16. Weathering of Basalt with depth
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

17. Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

18. 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 Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

19. 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 Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

20. Parameter A: General area geology
Rock Structure Rating
Parameter A: General area geology
Considers (a) rock type origin
(b) rock ‘hardness’
(c) geotechnical structure
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

21. Parameter B: Geometry : Effect of discontinuity pattern
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 Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

22. Parameter C: Groundwater, joint condition
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 Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

23. RSR support estimates for a 7.3m diameter
circular tunnel
Examples
RSR = 62
2” shotcrete 1”
5ft centres
RSR = 30
5” shotcrete
2.5ft centres
OR 8WF31 steel
3ft centres
(After Wickham et al. 1972)
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

24. 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 Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

25. 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 Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

26. Rock Mass Rating System
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

27. 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 Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

28. Development of Rock Mass Rating System
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

29. Rock Mass Rating System
(After Bieniawski 1989)
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

30. Rock Mass Rating System
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 Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

31. Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

32. Rock Mass Rating System
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

33. Guidelines for excavation and support of 10m
span rock tunnels in accordance with the RMR system
(After Bieniawski 1989)
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

34. Prediction of in-situ deformation modulus Em
from rock mass classifications
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

35. Rock Mass Rating System
Nicholson & Bieniawski (1990)
Bieniawski (1978) and Serafim & Pereira (1983)
Hoek i Brown (1997)
Verman (1993
H – depth, a = (decreases with rock strength)
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

36. Prediction of in-situ deformation modulus Em from rock mass classifications
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

37. Estimates of support capacity for tunnels
of different sizes
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

38. 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 Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

39. Rock Mass Rating System
Aydan & Kawamoto (2000)
Let’s assume:
Hoek:
Aydan:
Kalamaras & Bieniawski:
Aydan & Kawamoto (2000)
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

40. Rock Tunnelling Quality Index Q – Barton, Lien, Lunde
Based on case histories in Scandinavia
Numerical values on a log scale
Range to 1000
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

41. ‘Q’ Classification System
(After Barton et al. 1974)
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

42. ‘Q’ Classification System
represents the structure of the rockmass
crude measure of block or particle size
(After Barton et al. 1974)
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

43. ‘Q’ Classification System
represents roughness and frictional
characteristics of joint walls or infill material
(After Barton et al. 1974)
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

44. ‘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 Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

45. Classification of individual parameters used in
the Tunnelling Quality Index Q
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

46. Classification of individual parameters used in
the Tunnelling Quality Index Q (cont’d)
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

47. Classification of individual parameters used in
the Tunnelling Quality Index Q (cont’d)
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

48. ‘Q’ Classification System – SRF update
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

49. Q Classification Scheme
Resolves to three parameters
Block size ( RQD / Jn )
Interblock shear strength ( Jr / Ja )
Active stress ( Jw / SRF )
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

50. 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 Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

51. Equivalent Dimension De
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

52. Estimated support categories based on the tunnelling quality index Q
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

53. Q Classification Scheme
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

54. Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

55. Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

56. Q Classification Scheme
Roof pressure:
Length of the bolts: (roof) (walls)
Bhasin & Grimstad (1996):
Young’s modulus:
Seismic wave velocity:
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

57. RMR – Q - Correlations
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

58. 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 Cała – 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 Cała – 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 Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

61. Estimate of Geological Strength Index GSI
based on geological descriptions
Estimation of constants based upon rock
mass structure and discontinuity surface conditions
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

62. Geological Strength Index (GSI)
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

63. Geological Strength Index (GSI)
Estimate of Geological Strength Index GSI based on geological descriptions.
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

64. Plots of cohesive strength and friction angles
for different GSI and mi values
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics

65. Klasyfikacja KF
Marek Cała – Dept. of Geomechanics, Civil Engineering & Geotechnics