## 1 Introduction
[1; 2; 13; 15]. Nevertheless, on the assumption that an unbiased RQD can be calculated, a theoretical correlation is provided with the _VFC_ parameter in the V-GSI chart (Figure 1), along with several other commonly used parameters. At the core of the V-GSI chart is the inclusion of a bias-free _VFC_ parameter (fractures/m\({}^{3}\)) on the vertical axis [1]. The _VFC_ parameter not only extends the use of the chart to more massive rock masses (_VFC_ \(<\) 3 where RQD is no longer sensitive--100%), but also more than adequately covers more blocky rock masses than the 2013 chart was intended for (RQD \(<\) 80%), but without the bias issues associated with RQD [1]. Validation of the VFC parameter in the V-GSI chart comes from its use to determine the degree of fracturing in the foundation rock mass on the Kates Arch Dam, Lesotho [1; 2], and subsequent prediction of the moduli of deformability of the foundation rock mass using the Hoek-Brown equations [3; 16; 20], and comparing the results to large scale deformability testing undertaken in adults and galleries below the foundation [1]. One of the other advantages of the _VFC_ parameter is that it does not require the running of advanced 3-D software to stochastically generate discrete fracture networks (DFNs) for rock masses to determine volumetric fracture counts. Field-collected apparent joint set spacing (_Sa_) data corrected to true spacing (_St_) data, using virtual measurement vectors on underground maps, outcrop maps and bench mapping, can be used to estimate reliable bias-free _VFCs_ and the vertical axis ratings on the V-GSI chart. This, in turn, can be used to quantify GSI ratings and Hoek-Brown strength and deformability parameters critical for rock mechanics analyses. The _VFC_ parameter is relatively easily quantified with field measurements or by scaling off _Sa_ data on maps that can be easily converted to St data per discontinuity set with the use of correction factors (_CFs_) obtained using dot product vector analysis [1; 2; 13; 15]. When properly calculated, the _VFC_ of a rock mass (within the same structural domain)is an intrinsic property that does not require the determination of block shapes and sizes to be valid and can include as many non-orthogonal joint sets as are present in the rock mass. A correlated scale is also provided with _VFC_ and P\({}_{32}\) (area of fractures/m\({}^{3}\)) in the V-GSI chart, since this parameter is frequently used in geo-mechanical modelling programs. An approximate correlation with both RQD and block volumes is also provided on the vertical axis of Figure 1, along with parameters used in the other two major rock mass classification systems, namely RQD and RQD/In [22; 23]. On the horizontal axis, the original surface descriptors used in the early chart [3; 6] are retained along with correlated scales for [PERSON]'s 1989 [22] Joint Condition rating (J(Cond89) chart) and Jr/Ja ([PERSON] et al., 1974) [23]. It should be noted that J(Cond89 has an applied correlation factor of 1.5, as used in [PERSON] et al., 2013 [12]. The _VFC_ parameter and associated rating scale used on the vertical axis has been shown to provide reliable strength and deformability estimates at all scales, but is particu  
Figure 1: V-GSI chart [1] with overlain results (red) from hypothetical tunnel rock mass assessment shown and discussed in Section 2. Mean V-GSI = 79, Upper Limit = 88 and Lower Limit = 67. Note: RQD/In is scaled for three joint sets only (Jn = 9). If more or less joint sets are present, then the scale should be adjusted accordingly [1]. larly useful in massive rock masses [1] (i.e., for rock masses where _VFC_ is <3 fractures/m\({}^{3}\) and where RQD tops out at 100% and is no longer sensitive; see Figure 1). As mentioned above, this confidence comes from the application of the V-GSI system to determine the deformation moduli of foundation rock mass at the Katese Arch Dam, Lesotho Highlands [1], and by comparing these data to moduli obtained with large scale deformability testing in foundation aids.