June 2022 G-01483.84-017-R-Rev0 Because the 27 6.11 WRS Staging and Construction Methodology 6.11.1 Construction Methodology The WRS is situated in a relatively steep gully to the north of the SFA. While we believe it is feasible to build a facility in this location, there will be challenges due to the steep slopes. Bottom-up construction techniques will be used to place material in compacted layers allowing for stripping of topsoil and weaker materials within the footprint, and establishment of drainage control from a flat bench surface as each layer is placed. Based on the test pit data, topsoil depth varies over the WRS 5 ha footprint, but is assumed for the purpose of construction volume estimation at this study level to average 0.3 m. On the northern side of the WRS, where the natural slope angle is adverse to stability, weak materials (stiff clay/weathered volcanic ash) require removal to an estimated depth of 1.0 m prior to fill material placement (refer to sections C, Appendix C). The development plan is to access and place the first WRS layers from the lower access road, formed along the existing farm track, using smaller 30 tonne class trucks until enough bench width is developed. The track requires upgrading during the initial development phase to a width of 5.5 m, including a lined side drainage channel and engineered bunded edge. Once material is placed up to approximately the 205 mRL, the remaining lifts are placed from the main portal access ramp. A dual lane haul road, formed in the WRS at a gradient of 1v:7h to access upper benches, is advanced with each rock layer placed up to the final planned bench height at 265 mRL. The access road to the portal is proposed as a single lane access for maintenance only and entirely to be in cut due to the steep terrain. The access road starts at approximately 162 mRL ramping up gradually (average 1:12 for lower section) up to 1v:7h gradient to the 205 mRL level to establish the tunnel portal (Figure 13). The access road connects through to access the WRS at the 210 mRL. 6.11.2 Materials Movement Schedule The WRS staged development is based on the OGNZL underground development rock movement schedule1 for the project (Appendix D). Table 12 provides a summary of material movement to the WRS for startup development in Year 1, then annually up to when the total design capacity of 876,000 lcm is reached in approximately first quarter of Year 5 (end of Quarter 17 [Q17]). The WCP, WUG portal access road and WRS toe seepage pond are planned to be developed at project commencement (Year 1, Quarter 1 [Q1]). Excess materials not used for infrastructure construction or site bunding will form the bottom lifts of the WRS. Weak materials may have to be selectively placed or stockpiled within the WRS footprint and blended with spoil rock in later lifts to avoid formation of weak planes or zones in the WRS toe. Material properties are to be confirmed at the detail design level. Founding material are to be confirmed by geotechnical practitioner. Site monitoring during placement of the first layers is recommended. Tunnel development spoil is placed in the WRS up to approximately the first quarter of Year 5, Q17. WRS spoil reclaim as backfill material for the underground is planned to start in approximately Year 6 with compete removal of the WRS by year 10. The development of the WRS including bench elevations, disturbance area and water management elements for each period are presented in a series of stage plans. Individual plans were generated for period Year 1, Q1 and then every second quarter to Q17 (Plans number C001-C010, Appendix C). 1 Rock to Willows Stacks based on WAI-985-000-SCH-MI-0001.0.IFU.xlsx, supplied by OGC 29 07 2021.
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