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 and Bieniawski has made significant changes in the ratings assigned to different parameters.
The following six parameters are used to classify a rock mass using the RMR system:
- Uniaxial compressive strength of rock material.
- Rock Quality Designation (RQD).
- Spacing of discontinuities.
- Condition of discontinuities.
- Groundwater conditions.
- Orientation of discontinuities.
Bieniawski (1989) published a set of guidelines for the selection of support in tunnels in rock for which value of RMR has been determined. These guidelines are shown on the table below:
Rock Mass Rating System (After Bieniawski 1989)
The table below shows the guidelines for excavation and support of 10m span rock tunnels in accordance with the RMR system (After Bieniawski 1989).
It should be noted that this table has not had a major revision since 1973. In many mining and civil engineering applications, steel fibre reinforced shotcrete may be considered in place of wire mesh and shotcrete.
Source: Rock mass classification.pdf
