Rock Mass Rating system (RMR)

The Rock Mass Rating (RMR) system was developed by Bieniawski during 1972-1973. This system is used in wide engineering practice involving tunnels, chambers, mines, slopes, and foundations. Nevertheless, it is important that the RMR system is used for the purpose for which was it developed and not as answer to all design problems. The following six parameters are used to classify a rock mass using the RMR system

1. Unaxial compressive strength of rock material
2. Rock quality designation (RQD)
3. Spacing of discontinuities
4. Condition of discontinuities
5. Groundwater conditions
6. Orientation of discontinuities

To apply RMR, the rock mass is divided into a number of structural regions such that certain features are more or less uniform within each region. Although rock masses are discontinuous in nature, they may nevertheless be uniform in regions. In most cases, the boundaries of structural regions will coincide with major geological features. After the structural regions have been identified, the classification parameters for each structural region are determined from measurements in the field and entered onto input data sheets. On the data sheets there are parts of rating for: strength of intact rock, discontinuity density, discontinuity condition, and groundwater condition.

From those data sheets we can obtain parts of RMR rating. Sum of parts adjusted by discontinuity orientation gets basic RMR.

The Geomechanics Classification provides guidelines for the selection of rock reinforcement for tunnels. These guidelines depend on such factors as the depth bellow surface, tunnel size and shape, and the method of excavation.

Applications The Geomechanics Classification has found wide applications in various types of engineering projects such as tunnels, slopes, foundations, and mines. It is also adaptable for knowledge-based expert systems. Witch the introduction of fuzzy-set methodology the subjectiveness or fuzziness inherent in classification can be considered and incorporated into the expert system