Applications of rock muss cluss;f;cafion systems 1 99L I I I I I I
10-1 10" 10' 102 lo3 I o4 io5 I 06
Stand-up time, hrs
Figure 12.1 Excavation stand-up time for the RMR system.numbers in the classifications. For example, an RMR value of 62 is a 'good
rock: similarly, a Q-value of 20 indicates a 'good rock'. The RMR value
provides five such quality classes and the Q-system provides nine.
Both the classifications described were developed for estimating the
support necessary for tunnels excavated for civil engineering schemes. The
engineer should be careful when using classification schemes for other
projects. It is one thing to utilize the rock mass parameters in a taxonomic
system for classifying and describing the rock; it is quite another to
extrapolate the information to the general design of excavations and their
support. Bieniawski (1989) has noted "it is important that the RMR system
is used for the purpose for which it was developed and not as the answer
to all design problems".
0.00 I 0.01 0. I I IO 100 I'
Rock mass quality QFigure 12.2 Support requirements for the Q-system (for fuller details see
Bieniawski, 1989).