June 2022 G-14642.71-006-R-Rev0_FINAL 21 Test Test Zone (m BGL) Hydraulic conductivity (m/s) Packer 2 64.6 74.8 2.4 x 10-8 Packer 3 107.3 117.3 5.0 x 10-7 Packer 4 151.6 151.6 2.0 x 10-8 Packer 5 222.7 231.7 1.3 x 10-8 Table 6: Results from VW piezometers in WNDD007 (GWS 2020). VW Piezometer tip depth (m BGL) Depth to groundwater (m BGL) Groundwater elevation (m RL) 49.1 11.2 220.8 141.8 22.6 209.4 217.6 27.9 204.1 6.3.4 Key geotechnical issues Geotechnical issues that will affect construction of the ventilation shaft include: The generally weak to moderately strong volcanic rock, with strong rock below about 130 m BGL should be readily excavatable using standard construction techniques. High groundwater elevations are present at the site of Ventilation Shaft 1, though no high permeability zones were identified. This could indicate that inflows will be relatively low. The proposed collar site for Ventilation Shaft 1 is not affected by deep-seated slope instability, based on a review of aerial imagery and a site visit. Discontinuities interpreted from WNDD007 include a prominent sub-horizontal to gently east dipping set and three moderately inclined sets. Discontinuity spacing is variable, typically between 0.1 m to 5.0 m. The collapse in WNDD007 at about 204 m BGL may indicate relatively low rock mass strength at that depth compared to the in-situ stress field. It is anticipated that squeezing ground conditions could affect the construction and support requirements of Ventilation Shaft 1 in zones of very weak, soil-like material. Alimak raise is the proposed construction method. It is judged that the shaft will need to be fully lined to prevent collapse. The ground conditions are not suitable for construction by raise boring methods due to the high likelihood of collapse.
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