An assessment of roof support design requirements in hard rock mining based on the MBR (modified basic rock mass rating)

This dissertation describes an investigation carried out at Baluba Mine to assess the quality of rock mass and support
requirements in haulage drives developed in the -footwall quartzite -Formations. The rock mass o-F the -Footwall Formation is geotechnicallv quantified using the Modi-Fied Basic Rock mass rating system (MBR) and the Norwegian Geotechnical Institute index (NGI) or "Q**-svstem. Both
classification systems are described and applied to three haulage drives, namely, the 245m, 300m and 480m levels. The purpose o-F this study was to determine whether the MBR was suitable and applicable to local conditions at Baluba Mine. A comparison o-F the results between the MBR and NGI showed
that both systems use similar parameters except that they are expressed and used in different ways to quantify rock mass.
The ma/for difference is that MBR goes further to take into account production effects on haulage stability. The
conclusions drawn from the field study data are that the four initial input geotechnical parameters used in the MBR are easily measurable and of the three first adjustment
parameters used, blasting damage proved difficult to assess and to quantify. The main conclusion, however, is that
despite limitations in quantifying blasting damage and determining Rock Quality Designation (RQD) on haulage sidewalls, the MBR is suitable and applicable to the mining
environment at Baluba Mine as long as the following recommendation is considered; blasting damage adjustment should be replaced bv a Modified Fracture Frequency (MFF) which will take into account natural and artificial fractures. It is further recommended that in order to enhance the data base generated by the MBR, a complete hazard analysis of the drives be part of routine rock mass quality assessment.
In Appendix A, individual parameter rating tables and figures and support recommendation tables for both MBR and NGI are given. All field data are given in Appendix B.