Civil Engineering April 2021 | Vol 29 No 3

32 April 2021 Civil Engineering afforded at the portal entrances and in areas of the platform below the highwall which would be utilised for mining activi- ties. A two-tiered approach was employed to achieve this. Firstly, a slope face protection system would be designed and implemented over the full extent of the face where failures could not be accommodated. This slope protection system was designed to stabilise and protect against small, shallow, and widespread instabilities caused by the unfavourable intersection of natural joints and blast-induced frac- turing. These instabilities are too small and frequent to receive localised or spe- cific treatment, and it is instead optimal to protect against these by installing a light system applied uniformly over areas of interest. A Hoek-Brown rock mass parameter set, representative of the material near the vertical face, was derived and various analyses were computed to assess mechanisms and derive appropriate slope protection measures. It was found that 20 mm diameter, 1.8 m long resin grouted Threadbar 500 rock bolts installed on a 2 m grid pattern over the portal face would be sufficient to stabilise the face. Figure 7 Comparison between (a) original mining slope and (b) completed design slope Figure 8 Development of portals and installation of shotcrete drainage and wire mesh. Note dyke and shear zone Dyke Shear-zone (a) (b)