June 2022 G-14642.71-006-R-Rev0_FINAL iii Recommendations We recommend that the following points be addressed as part of developing the design: Targeted subsurface investigations, such as boreholes at shaft locations, are recommended to supplement the currently available geotechnical information between Willows Road Farm and WUG. In addition, drilling ahead of the tunnel face will be important for predicting ground conditions ahead of the face for tunnel support and design of groundwater management, as well as geological exploratory information. Further investigation of in situ stress as part of detailed design of the WUG and access tunnels. Consideration should be given to the management of groundwater with potentially elevated temperatures if encountered during underground works. Hydrothermal alteration has widely affected the rock mass at the site, including placement of the WUG orebody. We are not aware of any evidence of on-going hydrothermal processes affecting the area; however, some inflows of hot groundwater are possible. Consideration should be given to the potential effect on design of the generally low strength rock mass, groundwater conditions and stress conditions. It is anticipated that squeezing ground may be present in areas of very weak ground. Measures should be developed to ensure that the portal remains serviceable for the duration of the project. Such measures should include management of surface water and shallow groundwater. Local support measures may be required, such as shotcrete and bolts or a mass gravity wall. Consideration should be given to the potential adverse effect of acidic water on ground support and underground infrastructure.
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