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of this single index, recommendations for support measures denoted as “support
classes” and further specifications for the design are given.
Figure 12.2
Design based on
classification systems
(Sommer & Wittke 2011)
During construction documentation of the construction phases is carried out, and a moni-
toring program is established (Fig. 12.2) whereupon the latter is not always considered nec-
essary (Barton & Grimstad 2004). On the basis of the encountered rock mass conditions
the rock mass rating index is reviewed. If no agreement is obtained then the rock mass rat-
ing index needs to be re-evaluated, which may lead to a modification of the support classes.
The basis of each classification system is empirical. This means that the selection of the
influencing variables, their rating and the recommended support classes are based on the
experience of the developer, gained from practical cases. As a consequence, classification
systems generally have a subjective aspect. In order to overcome this shortcoming and
to detect misjudgements, the users of classification systems are recommended to apply
more than one system in parallel and to compare their results (Bieniawski 1988, Trunk &
Hönisch 1990, Alber 2001).
A comprehensive description of classification systems can be found in Bieniawski
(1989), Afrouz (1992) and Singh & Goel (1999). Also, Sommer (2009) provides an over-
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