## 5 Conclusions  
The following conclusions are obtained from this study:  
1. The two rock mass classification systems, \(RMR\) and \(Q\), are based on jointed rock mass data. They are developed for tunnel support design and updated empirically, either in the form of characterization or support, and extensively used for that purpose. Although there are clear guidelines for the rock mass characterization, generally discrete/lump approaches are used to obtain it because these latter methods are not difficult to use. However, they yield characterizations that are not as exact as those obtained through the use of continuous rating charts. To rate intact rock strength, \(RQD\), discontinuity spacing, and joint frequency correctly and without difficulty through the continuous function, equations that match well with available continuous rating charts are proposed.
2. Currently, in both systems, rock bolt spacing is the function of the rock mass quality only, whereas the shotcrete thickness is the function of the tunnel span along with the rock mass quality. However, their contribution to shotcrete thickness is not always the same. This principal of the support has been used for the development of the back analysis for rock mass quality determination.
3. The back calculation results from 462 tunnel sections show that significantly heavier supports than those estimated by \(RMR_{89}\) and \(RMR_{14}\) have been installed for the tunnel stability in highly stressed environments. The reason behind the difference in the actual and recommended supports is the absence of the stress parameter in the \(RMR\) structure. As the \(RMR_{89}\) system is based on shallow tunnel experiences, this parameter needs attention in the \(RMR_{89}\) structure to extend its application in such an environment.
4. The \(RMR_{14}\) system is explained for the purpose of correlating it with \(RMR_{89}\). It was found that a strong correlation exists between them. The explanation also reveals the importance of \(RMR_{89}\) in the structure of \(RMR_{14}\), which leads to the conclusion that \(RMR_{14}\) cannot be determined without \(RMR_{89}\).
5. The existing approaches for the correlation between \(RMR_{89}\) and \(Q\) were evaluated empirically. When using these systems for tunnel support design, correlating them is suggested. Results show that the rock mass fabric index approach yields comparatively better results than other approaches do. When using rock mass fabric index for correlating \(RMR\) and \(Q\), the limitation should be taken into account.  
[PERSON] supervised the research. [PERSON] has developed the proposed research concept. [PERSON] and [PERSON] helped in writing and re-checking the paper technically as well as grammatically.  
This study was supported by the Development of Design and Construction Technology for Double Deck Tunnel in Great Depth Underground Space (17 SCIP-B089409-04) from Construction Technology Research Program funded by Ministry of Land, Infrastructure and Transport of the Korean government. The authors ([PERSON] and [PERSON]) are extremely thankful to the Higher Education Commission (HEC) of Pakistan for HRDI-UESTPs scholarship.  
The authors declare no conflict of interest.