Rock mass classification
Introduction
During the feasibility and preliminary design stages of a project, when very little detailed
information is available on the rock mass and its stress and hydrologic characteristics, the
use of a rock mass classification scheme can be of considerable benefit. At its simplest,
this may involve using the classification scheme as a check-list to ensure that all relevant
information has been considered. At the other end of the spectrum, one or more rock
mass classification schemes can be used to build up a picture of the composition and
characteristics of a rock mass to provide initial estimates of support requirements, and to
provide estimates of the strength and deformation properties of the rock mass.
It is important to understand the limitations of rock mass classification schemes
(Palmstrom and Broch, 2006) and that their use does not (and cannot) replace some of the
more elaborate design procedures. However, the use of these design procedures requires
access to relatively detailed information on in situ stresses, rock mass properties and
planned excavation sequence, none of which may be available at an early stage in the
project. As this information becomes available, the use of the rock mass classification
schemes should be updated and used in conjunction with site specific analyses.
Engineering rock mass classification
Rock mass classification schemes have been developing for over 100 years since Ritter
(1879) attempted to formalise an empirical approach to tunnel design, in particular for
determining support requirements. While the classification schemes are appropriate for
their original application, especially if used within the bounds of the case histories from
which they were developed, considerable caution must be exercised in applying rock
mass classifications to other rock engineering problems.
Summaries of some important classification systems are presented in this chapter, and
although every attempt has been made to present all of the pertinent data from the
original texts, there are numerous notes and comments which cannot be included. The
interested reader should make every effort to read the cited references for a full
appreciation of the use, applicability and limitations of each system.
Most of the multi-parameter classification schemes (Wickham et al (1972) Bieniawski
(1973, 1989) and Barton et al (1974)) were developed from civil engineering case
histories in which all of the components of the engineering geological character of the
rock mass were included. In underground hard rock mining, however, especially at deep
levels, rock mass weathering and the influence of water usually are not significant and
may be ignored. Different classification systems place different emphases on the various