## 7 Extension of Empirical Classification Systems for Tunnel Support Design  
### General  
The previous experience from tunneling is the basis for the development of empirical classification systems and it is now used worldwide in the design and construction of underground excavation systems, particularly for their support recommendation. In these systems, the descriptive methods that are followed by numerical characterization is used for the design parameters [64,65]. In the case of complex rock mass, this characterization process is not appropriate for rock mass classification in existing systems; therefore, modification is required in existing systems for appropriate utilization [66]. The rock mass assessment in a precise way is important for a suitable excavation approach as well as for construction schedule development and proper support selection. This assessment of rock mass and its further use in tunnel design and construction through empirical classification are undeniably the best evaluation methods [67]. From the middle of the 20 th century, approximately a dozen classification systems for rock masses have been offered with consideration of different purposes in rock engineering. Of these, only a few have gained international recognition, including rock mass rating (RMR) [6,68,69] and tunneling quality index (Q), in the tunnel support design field. The different characterization parameters combine in a unique way in their different versions (as shown in Equations (8)-(12)) [8]. \[RMR_{89}=R_{1}+R_{2}+R_{3}+R_{4}+R_{5}+R_{6} \tag{8}\]  
\[RMR_{13}=R_{1}+R_{2-3}+R_{4}+R_{5}+R_{6} \tag{9}\]  
\[RMR_{14}=(RMR_{b}+F_{0})\times F_{s}\times F_{e} \tag{10}\]  
\[Q=\frac{RQD}{J_{n}}\times\frac{I_{r}}{J_{a}}\times\frac{J_{w}}{SRF} \tag{11}\]  
\[Q_{c}=\frac{RQD}{J_{n}}\times\frac{I_{r}}{J_{a}}\times\frac{J_{w}}{SRF}\times \frac{\sigma_{c}}{100} \tag{12}\]  
\(RMR_{89}\), \(RMR_{13}\), and \(RMR_{14}\) are the RMR versions of 1989, 2013, and 2014, respectively, while \(Q\) and \(Q_{c}\) are the original and modified versions of \(Q\) classification systems, respectively. Because these systems are based on a conventional shallow tunneling database, \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Test No.** & \(\sigma_{3}^{0}\) **(MPa)** & \(v\) & **E (GPa)** & **Peak Deviatoric Stress (MPa)** & \(\mathbf{U^{e\text{-}max}}\) \\ \hline \(1\) & & 0.26 & 40.2 & 250 & 820 \\ \hline \(2\) & \(35\) & 0.22 & 35.9 & 245 & 866.5 \\ \hline \(3\) & & 0.24 & 38.3 & 246 & 833.4 \\ \hline \(4\) & & 0.23 & 34.2 & 269 & 1114.3 \\ \hline \(5\) & \(45\) & 0.24 & 40.3 & 282 & 1053.1 \\ \hline \(6\) & & 0.27 & 51.7 & 283 & 898 \\ \hline \(7\) & & 0.22 & 32.1 & 267 & 1363.9 \\ \hline \(8\) & \(55\) & 0.24 & 32.8 & 286 & 1445.8 \\ \hline \(9\) & & 0.23 & 32.7 & 285 & 1434 \\ \hline \(10\) & & 0.28 & 52.4 & 336 & 1667.5 \\ \hline \(11\) & \(65\) & 0.21 & 29.1 & 329 & 1909.8 \\ \hline \(12\) & & 0.24 & 30.8 & 301 & 1788.8 \\ \hline \(13\) & & 0.23 & 28.0 & 338 & 2233.2 \\ \hline \(14\) & \(75\) & 0.25 & 35.0 & 357 & 2097.9 \\ \hline \(15\) & & 0.25 & 38.3 & 353 & 1801.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Unloading confining stress results for sandstone in the Neelum–Jhelum Hydroelectric Project. excavated in jointed rock mass, their application as a design tool is acceptable for similar tunneling. In the case of deep tunneling under high stresses, the \(Q\) system has an \(SRF\) for massive rock conditions, but both of the systems have limitations in a highly stressed jointed rock mass environment [32]. Based on the data of NJHEP and other projects in the area, where conventional excavation progressed through jointed rock mass under high overburden, the aforementioned systems were empirically extended through a back-calculation approach [70]. In this approach, the thickness of shotcrete and spacing of the rock bolt were applied with the tunnel span in the support chart for the RMR and Q systems.