## 4 Suggested Modifications of RQD
### Improved Rock Quality Designation (RQD\({}_{l}\))  
[PERSON] [22] highlighted the issues with piece length and discontinuity orientation, which have no bearing on the results, and proposed a new approach called RQD\({}_{l}\), which provides a more accurate and dependable estimate of rock quality. However, RQD\({}_{l}\) requires much more core logging work and time in order to obtain more precise results. An improved rock quality designation (RQDI) was proposed by [PERSON] [22] in order to lessen the drawbacks of the traditional approach. The expression for RQDI is as follows:  
\[\text{RQD}_{l}=100-\left[\frac{f_{l}+CW+Fr+Cr+K}{total\ core\ run\ length}x100\right] \tag{11}\]  
where  
- \(f_{i}\) is the rating factor obtained from Table 6;  
- \(CW\) is the length of the washed core segments;  
- \(Fr\) is the length of the fragmented segments, cm (with spacing of 15-50 mm);  
- \(Cr\) is the length of the crushed segments, cm (with spacing of \(<\)15 mm); and  
- \(K\) is the length of the karstic segments, cm. (i.e., karstic zone including vuggy; cavity, core lost, and other karstic phenomena).  
According to the suggestion of [PERSON] [22], the RQD\({}_{l}\) classification of rock masses is presented in Table 7.  
[PERSON] [22] outlined the benefits of the revised RQD\({}_{l}\) over the original RQD. First, in the case of two cores broken into segments longer than 10 cm, the original RQD assigns a value of 100% regardless of the segment length or joint orientation. In contrast, RQD\({}_{l}\) provides different values by considering factors such as segment length, joint orientation, washed core length, and karstic, broken, or crushed sections. A more fractured core is indicated by a lower RQDI. Second, RQDI separates cores depending on the previously indicated variables, whereas the original RQD would provide a value of 0% for cores divided into segments smaller than 10 cm.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Angle Interval** & \multicolumn{2}{c}{**Chosen Rating of Factor fi for RQD\({}_{l}\)**} \\ \multicolumn{1}{c}{**(Between Joint and Borehole) \(\delta\)**} & \multicolumn{1}{c}{**1/sin\(\delta\)**} & \multicolumn{1}{c}{**[20]**} \\ \hline \(>\)60\({}^{\circ}\) & \(<\)1.16 & 1.5 \\ \(30\)–60\({}^{\circ}\) & 1.16–1.99 & 3.5 \\ \(15\)–\(30^{\circ}\) & 2–3.86 & 5.5 \\ \(<\)15\({}^{\circ}\) & \(>\)3.86 & 7.5 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Angle intervals and ratings of the factor for each interval.  
\begin{table}
\begin{tabular}{c l l l l} \hline \hline
**RQD\({}_{l}\)** & **Rock Mass Description** & \multicolumn{1}{c}{**Rock Mass Quality**} & \multicolumn{1}{c}{**Class Number**} & \multicolumn{1}{c}{**Weak Segment**} \\ \multicolumn{1}{c}{**(\%)**} & & & & \\ \hline \(91\)–\(100\) & Massive rock mass & Excellent & I & 0–10 \\ \(76\)–\(90\) & Jointed rock mass & Very good & II & 11–25 \\ \(61\)–\(75\) & Very jointed rock mass & Good & III & 26–40 \\ \(46\)–\(60\) & Very jointed–fragmented rock mass & Medium & IV & 41–55 \\ \(31\)–\(45\) & Fragmented–crushed rock mass & Weak & V & 56–70 \\ \(\leq\)30 & Crushed rock mass & Very weak & VI & \(\geq\)71 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Classification of rock masses based on weak segment and RQD\({}_{l}\)[22].