Environmental Engineering Reference
In-Depth Information
(C.)
Rocks Mass Classes Determined from Total Ratings
Rating
100
← 81
80
←
61
60
←
41
40
←
21
21
Class number
I
II
III
IV
V
Description
Very good rock
Good rock
Fair rock
Poor rock
Very poor rock
(D.)
Meaning of Rock Classes
Class number
I
II
III
IV
V
Average stand-up time
20 years for 15 m span 1 year for 10 m span
1 week for 5 m span
10 h for 2.5 m span
30 min for 1m span
Cohesion of rock mass (kPa)
400
300-400
200-300
100-200
100
Friction angle of rock mass (deg)
45
35-45
25-35
15-25
15
(E.)
Guidelines for Classification of Discontinuity Conditions
Discontinuity length persistence
1m
1-3 m
3-10 m
10-20 m
20 m
Rating
6
4
2
1
0
Separation (aperture)
None
0.1 mm
0.1-1.0mm
1-5 mm
5 mm
Rating
6
5
4
1
0
Roughness
Very rough
Rough
Slightly rough
Smooth
Slickensided
Rating
6
5
3
1
0
Infilling (gouge)
None
Hard filling
5 mm
Hard filling
5 mm
Soft filling
5 mm
Soft filling
5 mm
Rating
6
4
2
2
0
Weathering
Unweathered
Slightly weathered
Moderately weathered
Highly weathered
Decomposed
Rating
6
6
3
1
0
(F.)
Effect of Discontinuity Strike and Dip Orientation in Tunnelling
b
Strike perpendicular to tunnel axis
Strike parallel to tunnel axis
Drive with dip—Dip 45
90
Drive with dip—Dip 20-45
Dip 45
90
Dip 20
45
Very favorable
Favorable
Very favorable
Fair
Drive against dip—Dip 45-90
Drive against dip—Dip 20-45
Dip 0-20
—Irrespective of strike
Fair
Unfavorable
Fair
a
Some conditions are mutually exclusive. For example, if infilling is present, the roughness of the surface will be overshadowed by the influence of the gouge. In such cases
use A.4 directly.
b
Modified after Wickham et al. (1972).
Note
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