## 2 A Hypothetical Example Application of the V-GSI Chart in a Tunnel
### Example Project Heading--Mapping Data and Photographs  
As an example, a single heading split heading map is presented below in Figure 4 for the left-hand-side excavation of the M120 tunnel excavated in the Hawkesbury Sandstone at a discrete tunnel chainage (exact location not provided to ensure confidentially of project information). At this location, the geology comprises the Hawkesbury Sandstone solely from the surface to below the tunnel invert. For clarity, this map is referred to hereafter as the left-hand-side M120 map (LHS M120 map). The map shown in Figure 4 only shows the trailing heading, but once fully excavated (both the left and right headings were excavated), the approximate tunnel excavation dimensions were as follows: width at shoulder--13 m, full height at centerline--8 m once the lower bench was removed (height at sidewalls excavations, and height includes the subsequent \"bench\" excavation).  
For the selected example LHS M120 map, the right-hand side heading was excavated prior to the left, as evidenced by the sidewall and void in the right-hand side of each photograph in Figure 5. Moreover, the adjacent M110 tunnel (eastbound) was excavated prior to the M120 in this location. While only one map is provided (Figure 4), the rock mass conditions for the right-hand side of the M120 were reviewed along with the information from the M110 in the same location.  
The rock mass for this mined heading and for this location in general (gleaned from adjacent maps as described above) comprised fresh (i.e., unweathered) sandstone, dry to damp, with a medium to high intact rock strength, and with a layered structure (bedding). Figure 4 above presents one of the output maps generated for this location, which includes (1) a geological map of the mined heading and crown and left hand sidewall, (2) discontinuity data for three observed bedding-parallel discontinuities including the calculated true spacing (and the other data as described in Section 3.3), (3) a V-GSI rating plotted on the embedded chart generated based on this true spacing data and discontinuity condition data, and (4) a stereonet of discontinuity orientation measurements (tunneling direction also shown on the stereonet-black line). The mean _VFC_ is estimated at 0.625 (1/1.6, i.e., 1/true mean spacing of bedding) with a rating of 54, the mean 1.5 \(\times\) Cond89 is around 29 and, as shown on the map, the calculated mean V-GSI rating is around 83 (54 + 29). Jr/Ja is around 0.75 and the calculated Q\({}^{\prime}\) rating is somewhere between 33.75 and 37.50. As can be seen on the scales on the horizontal axis, the lower range of 1.5 \(\times\) JCond89 is around 24, which correlates to 0.75 for the Jr/Ja assessment. This correlation on the lower scale provides a convenient method of cross-checking inputs for these two parameters. If they are not close, then inputs for both parameters should be checked.  
Figure 5 below shows two of the photographs attached to the trailing heading and the partially obstructed crown (bolt installation in the crown) LHS M120 map report. Note that the dark rock (minor laminated siltstone beds) in the crown and heading visible in the photographs are photos also shown in the geological map in Figure 5.  
The selected example map results indicate that the ground conditions were within the expected category (conditions predicted prior to construction), and therefore the pre-designed ground support class for these conditions was installed. In this location, the support class included arrays of 10 fully grouted and tensioned double-corrosion protected, end-anchored rock bolts in the crown, each 3.40 m in length, spaced on 1.5 m centers and at 1.5 m transverse spacing. In addition, a primary/initial layer of 80 mm thickness of SFRS was applied. In addition, for this specific heading, handlebar plates were installed within the laminite zone in the crown for better adherence and structural connectivity of the SFRS. Similar conditions were also encountered on the leading (right-hand-side) excavation heading.