The determination of rock mass properties for engineering design is considered from twoperspectives. These are in-situ measurement, including classification-based methods, and the limitations of the classification approach.

Several measurement methods are available which will give useful results, if used appropriately. The choice of different methods will depend on the nature of therock mass. The required accuracy should be considered realistically and, in many cases, high levels of accuracy are not, in fact, necessary. Examples are included, which show how the mass strengths of mine pillars were determined with acceptable accuracy using well known rock mass classification schemes, modified as necessary to accommodate local conditions.

Rock mass classification is a widely used, economical and extremely useful basis for determining properties, but there are dangers in uncritical application. The classification methodology is critically examined, and the use of multivariate statistics applied in a multi-dimensional space is considered to optimize the usefulness of the measured data.

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