Environmental Engineering Reference
In-Depth Information
TABLE 5.25
The Rock-Mass Rating System
(A.)
Classification parameters and their ratings
Parameter
Range of values
1
Strength of Intact Rock Material
Point-load strength index
10 MPa
4-10 MPa
2-4 MPa
1-2 MPa
For this low range-uniaxial
compressive test is
preferred
Uniaxial comp. strength
250 MPa
100-250 MPa
50-100 MPa
25-50 MPa
5-25 MPa 1-5 MPa
1 MPa
Rating
15
12
7
4
2
1
0
2
Drill core quality
RQD
90-100%
75-90%
50-75%
25-50%
25%
Rating
20
17
13
8
3
3
Spacing of discontinuities
2m
0.6-2m
200-600mm
60-200 mm
60 mm
Rating
20
15
10
8
5
4
Condition of discontinuities
Very rough surfaces
Slightly rough
Slightly rough
Slickensided surfaces
Soft gouge
5 mm
(see E)
Not continuous
surfaces
surfaces
or Gouge
thick or
No Separation
Separation
Separation
5 mm thick or
Separation
5 mm
Unweathered wall
1 mm Slightly
1 mm Highly
Separation 1-5 mm
Continuous
rock
weathered walls
weathered walls
Continuous
Rating
30
25
20
10
0
5
Ground water
Inflow per 10 m
None
10
10-25
25-125
125
Tunnel length (1/m)
(Joint water press)/
0
0.1
0.1, 0.2
0.2, 0.5
0.5
(Major principal
)
General conditions
σ
Completely dry
Damp
Wet
Dripping
Flowing
Rating
15
10
7
4
0
(B.)
Rating Adjustment for Discontinutiy Orientations (See F)
Strike and dip orientations
Very favorable
Favorable
Fair
Unfavorable
Very unfavorable
Rating
