## 5 Analysis and Results
### Construction Time with Mixed Geological Conditions  
In the actual tunnelling, the geological condition is not identical for the whole tunnel length; rather, the geological types vary from a soft rock or soil to a hard rock. Hence, based on the study on the effects of the five different tunnel supports varied with the Q-value on the construction time in Section 5.1, three cases (Table 7) representing mixed geological conditions are analysed. Figure 6 shows a typical example for the ratios given in Table 7. Case A, a good condition, consists of 20%, 30%, 30%, 10%, and 10% of the 3 km tunnel lengths for Types 1, 2, 3, 4, and 5, respectively, which are given in Table 2, where a favourable rock mass quality of over 60 in RMR forms 50% of the length, assuming that the tunnel excavation is carried out in the geological conditions presented in Figure 6. In Case B, the tunnel support types in medium geological conditions are made up of 10%, 25%, 30%, 25%, and 10%, respectively. In Case C, a bad geological condition, the distribution of the support types is 10%, 10%, 30%, 30%, and 20%, respectively, and a rock mass quality of below 40 in RMR forms 50% of the tunnel length. Figure 5: Correction for tunnel length and job training (Modified from [23]). Meanwhile, the terms used to define the geological condition of a tunnel in this study, i.e., good, medium or bad conditions, are only qualitative expressions, which leave ambiguity as to how good or bad these conditions are. Hence, a quantitative term, equivalent to the rock mass quality (ERQ), is suggested with Equation (1) to express the overall rock mass condition of a tunnel:  
\[\text{ERQ}=\frac{\sum_{i=1}^{n}\text{L}_{i}\cdot\text{RMR}_{i}}{\text{L}_{t}} \text{ or }\frac{\sum_{i=1}^{n}\text{L}_{i}\cdot\text{Q}_{i}}{\text{L}_{t}} \tag{1}\]  
where n is the number of total tunnel sections, L\({}_{i}\) is the length of each tunnel section (m), RMR\({}_{i}\) or Q\({}_{i}\) represents RMR or Q for each tunnel section, and L\({}_{t}\) is whole tunnel length (m). If ERQ is applied to this study, the overall rock mass quality of Cases A, B and C become 58, 50 and 42, respectively, based on RMR in Table 4 and the length of each tunnel section in Table 7.  
The analyses show that basic construction times for Cases A, B and C are 77, 85, and 97 weeks, respectively, and account for 36-38% of total construction time, as shown in Figure 7a. Additionally, the basic construction time of Case C in bad geological conditions increases by 26% compared to Case A under good conditions (Table 8), meaning that the time spent for basic operations (pure excavation), excluding tunnel supports, increases by 26% when the geology worsens from good to bad conditions. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Rock Mass Quality**} & **RMR** & **100–80** & **80–60** & **60–40** & **40–20** & **20–0** & \\ \cline{2-9}  & **Q-Value** & **\textgreater{}54** & **54–6** & **6–0.6** & **0.6–0.07** & **\textless{}0.07** & **\textless{}0.07** \\ \hline \hline \multirow{2}{*}{**Case**} & \multirow{2}{*}{**Unit**} & \multicolumn{6}{c}{**Tunnel Support Type**} \\ \cline{3-8}  & & **Type 1** & **Type 2** & **Type 3** & **Type 4** & **Type 5** & \\ \hline A & \% & 20\% & 30\% & 30\% & 10\% & 100\% & 100\% \\ \cline{2-9} (Good) & [m] & 600 & 900 & 900 & 300 & 300 & 3000 \\ \hline B & \% & 10\% & 25\% & 30\% & 25\% & 10\% & 100\% \\ \cline{2-9} (Medium) & [m] & 300 & 750 & 900 & 750 & 300 & 3000 \\ \hline C & \% & 10\% & 10\% & 30\% & 30\% & 20\% & 100\% \\ \cline{2-9} (Bad) & [m] & 300 & 300 & 900 & 900 & 600 & 3000 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Assumed ratio and tunnel length for each tunnel support type. Figure 6: Typical example of the ratios of tunnel support types for analysed cases. rate of a D&B for a bad rock mass quality tunnel decreases by 25% compared to those of a tunnel with a good rock mass quality, even though this ratio can be varied with given geological conditions, tunnel sizes and operation conditions.