## 2 _RMR_ and \(Q\) System Establishment
### Development of the \(Q\) System  
This classification system was established in 1974 after the _RMR_ system based on 212 tunnel cases. The development of this system was the result of the Seminar on Large Permanent Underground Openings held in Oslo in 1969. Two main breaches pointed out in the symposium were: (i) the acquisition of mechanical data and whether an excavation should be lined, or rock bolted, or unlined [47]; and (ii) the dilatant property of the rock had been unnoticed when designing rock-bolt spacing [48]. This system was independent from the _RMR_ system but there are some parameters in  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multirow{2}{*}{**1973 [8]**} & \multirow{2}{*}{**1974 [42]**} & \multicolumn{6}{c}{**RMR**} \\  & & & & **1975** [43] & **1979 [44]** & **1989** [22] & **2011 [45]** & **2013 [46]** & **2014 [23]** \\ \hline \hline \multicolumn{1}{c}{Intact rock strength} & & & & & & & & \\ (MPa) & 10–0 & 10–0 & 15–0 & 15–0 & 15–0 & 15–0 & 15–0 & 15–0 \\ _RQD_ (\%) & 16-3 & 20–3 & 20–3 & 20–3 & 20–3 & 20–0 & - & - \\ Joint spacing (mm) & 30–5 & 30–5 & 30–5 & 20–5 & 20–5 & 20–0 & - & - \\ Discontinuity density & & & & & & & & \\ (joints per meter) & - & - & - & - & - & - & 40–0 & 40–0 \\ Separation of joints (mm) & 5–1 & - & - & - & - & - & - & - \\ Continuity of joints (mm) & 5–0 & - & - & - & - & - & - & - \\ Weathering & 9–1 & - & - & - & - & - & - & - \\ Condition of joints & - & 15–0 & 25–0 & 30–0 & 30–0 & 30–0 & 30–0 & 20–0 \\ Groundwater & 10–2 & 10–2 & 10–0 & 15–0 & 15–0 & 15–0 & 15–0 & 15–0 \\ Alterability (\%) & - & - & - & - & - & - & - & 10–0 \\ \(F_{0}\) & 15–3 & 15–3 & 0–(\(-12\)) & 0–(\(-12\)) & 0–(\(-12\)) & 0–(\(-12\)) & 0–(\(-12\)) & 0–(\(-12\)) \\ Adjustment & \(F_{e}\) & - & - & - & - & - & - & - & 1.32–1 \\ \(F_{s}\) & - & - & - & - & - & - & - & 1.3–1 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Characterization criteria in different versions of the rock-mass rating (RMR) system.  
common, that is, rock-quality designation (_RQD_) and groundwater. The system also included joint roughness, infilling of the joints and rock load, which were missed in the _RMR_ system. The plot between _RQD_ and the tunnel span for the tunnel case records [49] was the start of the development of support plot for the \(Q\) system [9]. The correlation was improved between _RQD_ and the unsupported span by including the joint set number as an additional parameter. This modified _RQD_ was further improved by including the joint roughness, joint alteration, water pressure and rock load. Afterward, an evaluation was done for case records in the literature, a clear picture was obtained between the rock-mass quality and excavation span. This trial-and-error and empiricism using more than 200 case records finally enabled an answer to the challenging question asked by the Norwegian State Power Board (Statkraft) from _NGI_ in 1973: \"Why are Norwegian powerhouses showing such a wide range of deformations?\" [50; 51]. This evaluation includes the tunnel span and purpose of excavation as additional parameters for the type and amount of rock support; however, they are not involved in the calculation of rock-mass quality as proposed for rock-mass classification [52]. The six parameters are united in the following manner to compute the rock-mass quality:  
\[Q=\left(\frac{RQD}{J_{n}}\right)\times\left(\frac{J_{r}}{J_{n}}\right)\times \left(\frac{J_{w}}{SRF}\right) \tag{1}\]  
where _RQD_ is with a minimum score of 10, \(J_{n}\) symbolizes the score of the joint sets number, \(J_{r}\) is the score for the roughness of joint surface, \(J_{a}\) symbolizes the score for the clay filling or alteration degree, \(J_{w}\) symbolizes the groundwater pressure effects scores and the stress reduction factor (_SRF_) is the score for faulting, strength and stress ratios in hard rocks and squeezing or swelling. The system categorizes rock masses into nine classes.