Bieniawski (1976) published the details of a rock mass classification called the Geomechanics Classification or the Rock Mass Rating (RMR) system.
Over the years,this system has been successively refined as more case records have been examined andthe reader should be aware that Bieniawski has made significant changes in the rating sassigned to different parameters.
The discussion which follows is based upon the 1989version of the classification (Bieniawski, 1989). Both this version and the 1976 version deal with estimating the strength of rock masses. The following six parameters are used to classify a rock mass using the RMR system:
1. Uniaxial 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.
In applying this classification system, the rock mass is divided into a number of structural regions and each region is classified separately.
The boundaries of the structural region susually coincide with a major structural feature such as a fault or with a change in rocktype. In some cases, significant changes in discontinuity spacing or characteristics, with in the same rock type, may necessitate the division of the rock mass into a number of small structural regions
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