The role of classification in rock engineering and design is discussed. It is important to distinguish between characterization, classification and empirical design method. The classification systems used today should, strictly speaking, either be described as rock mass characterization systems or empirical design methods, as long as the outcome is not organised into classes.
The main requirements for a true classification system capable of solving rock engineering problems are as follows. 1) The reliability of the classes to assess the given rock engineering problem must be estimated. 2) The classes must be exhaustive (every object belongs to a class) and mutually exclusive, (no object belongs to more than one class). 3) The principles of division (rules) governing assignment into the classes must be based on suitable indicators (ground parameters etc.) and must include the possibility of being updated during construction using the experience gained. 4) These rules must also be so flexible that additional indicators can be incorporated. 5) The uncertainties, or the quality, of the indicators must be established so that the probability of mis-classification can be estimated. 6) The useful system should be practical and robust, and give an economic and safe design.
In the author's opinion, none of the main classification systems in use today fulfils these requirements. They may, however, serve as supervised systems as a basis in the development of local systems adapted to the actual site conditions.