Geoscience Reference
In-Depth Information
18.7 RMR - application
The classes and its meaning are provided in the table below.
Table 18.7 Meaning of rock mass classes (Bieniawski, 1989).
RMR class no.
Average stand up time
Rock mass strength
Cohesion of rock mass, kPa
Friction angle (deg)
I
20 yr for 15 m span
400
45
>
>
II
1 yr for 10 m span
300-400
35-45
III
1 wk for 5 m span
200-300
25-35
IV
10 h for 2.5 m span
100-200
15-25
V
30 min for 1 m span
<
100
<
15
Figure 18.1 Support function (Kaiser et al., 2000).
18.8 RMR - excavation and support of tunnels
The classes and its application to tunnel design are provided in the table
below.
-
20mm diameter fully grouted rock bolts assumed.
 
 
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